Luminous Landscape Forum

Equipment & Techniques => Cameras, Lenses and Shooting gear => Topic started by: Guillermo Luijk on September 02, 2013, 06:55:45 PM

Title: DxOMark's new resolution magnitude: P-Mpix
Post by: Guillermo Luijk on September 02, 2013, 06:55:45 PM
DxOMark has defined a composite magnitude called Perceptual Mpix (or P-Mpix) to represent the output resolution/sharpness one can expect from a given combo: lens + sensor. According to DxOMark's definition:

"P-Mpix is the unit of a sharpness measurement. The number of P-Mpix of a camera/lens combination is equal to the pixel count of a sensor that would give the same sharpness if tested with a perfect theoretical optics, as the camera/lens combination under test."

Looking for new photo gear? DxOMark's Perceptual Megapixel can help you! (http://www.dxomark.com/index.php/Reviews/Looking-for-new-photo-gear-DxOMark-s-Perceptual-Megapixel-can-help-you)

(http://img822.imageshack.us/img822/6422/m8f8.png)

I wonder at what aperture is this magnitude defined. The one that provides max resolution for each lens? any thoughts?. I think it's a very interesting benchmark to quantify the effective resolution of a particular camera and/or lens, but the definition is still a bit vague.

Regards
Title: Re: DxOMark's new resolution magnitude: P-Mpix
Post by: RFPhotography on September 02, 2013, 07:35:15 PM
They've had that rating for a while.  Since they don't really provide any information as to how the number is derived, it would seem to be a bit of folly to put much stock in it.  They don't, as far as I recall, provide any information as to how they define or create the theoretical 'perfect' optics.  Seems more a marketing ploy than a reliable value.  Not unlike their tests which present camera performance in terms of a common number (8 MP, if I recall) as the headline number.
Title: Re: DxOMark's new resolution magnitude: P-Mpix
Post by: jrsforums on September 02, 2013, 08:18:24 PM
In addition, they only test one lens.  Makes it very difficult to tell if the results are from a typical lens or from an outlier, either very good or bad.
Title: Re: DxOMark's new resolution magnitude: P-Mpix
Post by: Guillermo Luijk on September 02, 2013, 08:20:26 PM
Seems more a marketing ploy than a reliable value.
If their figures are based in measures there is no marketing here. Another story is that they are not explaining for which precise situation the figures are calculated.
Title: Re: DxOMark's new resolution magnitude: P-Mpix
Post by: BJL on September 02, 2013, 08:27:43 PM
It would be nice if they:
- stated the aperture used [my guess: they try several and report the maximum],
and
- if/how they weight between center and edges [my guess; if their MTF graphs were center only, this is too, because they are reprocessing their MTF data into a single number.]

It would also be fun if they reported values for a sequence of aperture values: then it would help to show that increasing the pixel count does not make resolution worse at small apertures in any relevant sense, or "prevent" use of small apertures when abundant DOF is desired!
Title: Re: DxOMark's new resolution magnitude: P-Mpix
Post by: NancyP on September 02, 2013, 09:14:27 PM
I tend to pay attention to Roger Cicala, because as owner of a lens rental business, he can test 10 or 15 copies of a lens to get an idea of consistency of performance. Most reviewers have a sample size of n = 1.
Title: Re: DxOMark's new resolution magnitude: P-Mpix
Post by: Fine_Art on September 03, 2013, 01:05:50 AM
Their number troubled me a bit too when I first started using it. It is very useful for sorting lenses you would consider buying. I trust it to give better lenses a higher number, that is about as much credence as I give it. I am not sure what the absolute number means relative to the sensor megapixels. I have lenses that it rates relatively poorly (Minolta primes) that give good detail at the pixel level much higher that their number states. I did use it to buy a nikon 85 1.8G with good results.

If you really want to see how your lens operates at various apertures use the SLRGear Imatest diagrams. If you click on the graph it opens up into a window where you can move sliders around for various apertures or zooms.

http://www.slrgear.com/reviews/index.php (http://www.slrgear.com/reviews/index.php)

The downside of this is you mentally file away f4 to f8 for most lenses based on the large purple center (extreme sharpness) making you focus stack pictures for future processing that you never do. I have many landscapes like that. ;) I also have f8 to f16s that I end up using while part of me grumps about the lost resolution.
Title: Re: DxOMark's new resolution magnitude: P-Mpix
Post by: BartvanderWolf on September 03, 2013, 04:12:46 AM
If their figures are based in measures there is no marketing here. Another story is that they are not explaining for which precise situation the figures are calculated.

Hi Guillermo,

They indeed leave a number of questions unanswered, but they do give a rough indication (http://www.dxomark.com/index.php/Reviews/Looking-for-new-photo-gear-DxOMark-s-Perceptual-Megapixel-can-help-you) as to which parameters play a role in their score.

Quote from: DxOmark.com
A great metric backed up by science and the industry
DxOMark’s new Perceptual MPix measurements are based on acutance and human contrast sensitivity function (CSF) published in recently-released image quality standards from the International Standards Organization (ISO) and the International Imaging Industry Association (I3A). A member of the working groups involved in image quality, DxO Labs has been working diligently with giants in the digital imaging industry such as AMD, Nokia, Kodak, Nvidia, Fujifilm, HP, RIM, Intel, Microsoft, Google, and others.

DxOMark has also relied on the very recent scientific research of CNES (the French space agency) with respect to the optimization of digital acquisition systems, notably those for satellite imagery.

Human perception (visual acuity and contrast sensitivity) play a role, MTFs play a role, the sensor's sampling density and AA-filter play a role, and since it's a relative score versus a theoretically optimal lens, it can be used to compare combinations of camera and lens.

However, as always when a single number metric is used, it doesn't tell the whole story, such as how consistent the score is across the image (center versus edges/corners). It also doesn't tell anything about the viewing distance/image magnification, bokeh rendering,  vignetting, etc., etc.

Cheers,
Bart
Title: Re: DxOMark's new resolution magnitude: P-Mpix
Post by: hjulenissen on September 03, 2013, 05:18:18 AM
Is the theoretically perfect reference lens still affected by diffraction, or are they idealizing away that as well?

-h
Title: Re: DxOMark's new resolution magnitude: P-Mpix
Post by: BartvanderWolf on September 03, 2013, 05:51:50 AM
Is the theoretically perfect reference lens still affected by diffraction, or are they idealizing away that as well?

Hi,

I think we can assume so, but we do not know its weighting in the total metric. Diffraction is the same if the aperture is the same, regardless of lens (give or take some iris shape influences), so one can still compare lenses when this parameter stays constant. Of course, a different sensor may be able to sample the diffraction pattern at a different density, which would affect the MTF. The MTF will include lens distortions and diffraction effects.

Therefore, if MTF is used as part of the equation (which is likely, because of the need to relate that to the Contrast Sensitivity curve of the human eye), diffraction effects will be in there as well.

Cheers,
Bart
Title: Re: DxOMark's new resolution magnitude: P-Mpix
Post by: Ray on September 04, 2013, 04:29:57 AM
I wonder at what aperture is this magnitude defined. The one that provides max resolution for each lens? any thoughts?. I think it's a very interesting benchmark to quantify the effective resolution of a particular camera and/or lens, but the definition is still a bit vague.

Regards


Good question, Guillermo. My guess is the P-Mpix would have to refer to the performance of the lens at it's sharpest aperture, otherwise such ratings would not make sense.

The purpose of the rating is to evaluate the perceived sharpness of a lens in conjunction with a particular camera or sensor. At small apertures (big f/stop numbers), all lenses are equal. It would serve little purpose to create an average performance of a lens, from its maximum aperture to F22 for example, in order to assess the differences between a first  rate prime used with a low resolution sensor, and a medium quality zoom used with a high resolution sensor.

What I find a bit puzzling is the 'Best at' scores at the top, as in my attached image, showing the DXO comparison between the Nikkor 24-120mm on the D800, and two high quality primes on the 12mp D3.

These scores describe the Nikkor 24-120 as being best at 35mm and F4. Now, according to Photozone, this lens actually is sharpest at 35mm and F4, but only in the centre. At the borders, the lens is much better at 24mm. Can one conclude that 'best at' refers to centre sharpness?
Not if one considers the Photozone results for the Nikkor 85mm and Sigma Art 35mm. These lenses are definitely not sharpest at maximum aperture, whether at the centre or the borders.

Clicking on the question mark next to the DXO 'Best at' scores, I get the following notice:

Quote
DxOMark Score
The DxOMark Score reports average lens-camera performances over the whole focal length and aperture ranges.
The DxOMark Score is reported using a gauge that shows the score itself as well as the range of scores over the focal range. With this gauge, photographers can view the homogeneity of the lenses image quality over their focal range.
The DxOMark Score is measured for defined exposure conditions corresponding to low-light scene with 150 lux illumination and an exposure time of 1/60s. These conditions were chosen as we believe low-light performances are very important for today’s photography and it is also important for photographers to know how well lenses perform at the widest aperture.

There's some serious confusion here.
Title: Re: DxOMark's new resolution magnitude: P-Mpix
Post by: RFPhotography on September 04, 2013, 07:23:35 AM
If their figures are based in measures there is no marketing here. Another story is that they are not explaining for which precise situation the figures are calculated.

Not at all.  Companies use measurements in marketing all the time.  It's a matter of what's being measured.  Don't know about Europe  but here in Canada cell phone companies engage in marketing based on measurements all the time.  They will all claim, for example, the fastest 4G speeds.  It's not possible that they can all be the fastest.  But they all do the measurements differently or measure different things so as to be able to make the claim.  Without the information needed to know how DxO does its lens testing,  without knowing what and how it's measuring, it's difficult to know the validity of the results.  Another member asked much the same question I did about the 'theoretically perfect optics' when he asked if they theorise away diffraction.
Title: Re: Re: DxOMark's new resolution magnitude: P-Mpix
Post by: Guillermo Luijk on September 04, 2013, 08:40:19 AM
The point is they are not selling anything.
Title: Re: Re: DxOMark's new resolution magnitude: P-Mpix
Post by: RFPhotography on September 04, 2013, 09:36:40 AM
The point is they are not selling anything.

No?  They don't sell software?  Being known as the top review site wouldn't have any impact on their software sales?  What about planning for the future?  Things we don't know about yet.  They don't have a design service?  That wouldn't benefit from have a very strong reputation as a review site and the number of people who read and (maybe) rely on their tests? 
Title: Re: Re: DxOMark's new resolution magnitude: P-Mpix
Post by: Guillermo Luijk on September 04, 2013, 12:45:29 PM
No?  They don't sell software?  Being known as the top review site wouldn't have any impact on their software sales?  What about planning for the future?  Things we don't know about yet.  They don't have a design service?  That wouldn't benefit from have a very strong reputation as a review site and the number of people who read and (maybe) rely on their tests?
Come on Bob, they are not selling any of the stuff (cameras and lenses) they are qualifying through their measurements. Is that clear now?. So there is no reason why this new benchmark should be just marketing without a real technological justification.

I think lately they have become a bit more obscure in the explanation of where they figures come from, and IMO that is not the best approach to gain reputation. For example they used to provide the SNR curves but don’t do it anymore:

(http://www.guillermoluijk.com/article/digitalp02/snr_d200.gif)

At this moment I find the information about how the P-Mpix are calculated insufficient to rely on it in choosing a particular camera and/or lens.
Title: Re: DxOMark's new resolution magnitude: P-Mpix
Post by: Guillermo Luijk on September 04, 2013, 12:48:48 PM
Good question, Guillermo. My guess is the P-Mpix would have to refer to the performance of the lens at it's sharpest aperture, otherwise such ratings would not make sense

I agree, but I wonder if P-Mpix models the behaviour of the lens across the entire sensor surface (which would make sense since they are comparing camera + lens, and that includes the format), or only at the centre (where sharpness reaches its max).
Title: Re: Re: DxOMark's new resolution magnitude: P-Mpix
Post by: RFPhotography on September 04, 2013, 03:52:29 PM
Come on Bob, they are not selling any of the stuff (cameras and lenses) they are qualifying through their measurements. Is that clear now?. So there is no reason why this new benchmark should be just marketing without a real technological justification.

No, they never were.  Of course that's clear.  It was never in question.  But they are selling their technology to other commercial users.  So in that regard, being regarded as the 'best' at what they do is beneficial.  It's a big picture view.  I don't expect many on here to understand it.

Quote
I think lately they have become a bit more obscure in the explanation of where they figures come from, and IMO that is not the best approach to gain reputation. For example they used to provide the SNR curves but don’t do it anymore:

(http://www.guillermoluijk.com/article/digitalp02/snr_d200.gif)

At this moment I find the information about how the P-Mpix are calculated insufficient to rely on it in choosing a particular camera and/or lens.


Agreed.  I think that was clear from the outset. 
Title: Re: DxOMark's new resolution magnitude: P-Mpix
Post by: Dale_Cotton2 on September 04, 2013, 04:34:51 PM
Probably I'm missing something here, but I don't even bother with the P-Mpix score. I go into the measurement tab's data displays, and look at the field maps (particularly the one for sharpness). Here I can see how each parameter varies over the sensor area for each focal and aperture. Presumably, the same data they use to generate their raw converter lens profiles, so likely pretty good.

Sure, it would be nice to have a valid, relative ranking for each tested lens to help with decision making. But how can you know how closely their criteria resemble your criteria? For one thing: they make their measurements at 50 Lux, or some such low light level. Does this matter? Would the numbers be different if done at the light levels typical for daylight work? I have no idea. Even the second-level Lens Metric Scores seem too simplistic. If I shoot landscapes at f/8 or f/11 nearly all the time, do I care what the mean value for all measured apertures and focal lengths happens to be? How many zooms aren't soft in the corners at wide angles or sacrifice sharpness at one end of their range versus another?

But even sticking to the actual measurement displays you have to be careful. Nearly didn't buy the RX100M2, given the DxO data. What wasn't at all obvious to me is that they are reporting the results without the metadata distortion corrections applied. You can't even view the uncorrected output in Lightroom and certainly not from the OOC JPEGs. That's like holding a paralympics but refusing the use of prosthetic devices. Surely distortion correction is essential to small camera zoom lens design? At the very least make it very clear that the numbers only apply to the uncorrected output of the lens. Put a red warning note on each screen in such cases.
Title: Re: DxOMark's new resolution magnitude: P-Mpix
Post by: Ray on September 04, 2013, 11:32:02 PM
Sure, it would be nice to have a valid, relative ranking for each tested lens to help with decision making. But how can you know how closely their criteria resemble your criteria?

Hi Dale,
If you have the time and own some of the cameras and lenses that DXO have used for their tests, you could verify the results for yourself, making allowances for minor variations in lens quality control.

For example, I own a D800E, D700 and the 3 lenses shown in the DXO test results above, in my reply #10.

What I find fascinating is that the P-Mpix of the medium quality Nikkor 24-120/F4 zoom, when used on the 36mp D800, is about the same as the P-Mpix ratings for the excellent 85mm and 35mm primes when those lenses are used on a 12mp full-frame camera.

Now I don't have my D700 with me at present, just the D800E and the D7100, so I'm unable to carry out such tests for myself. However, what I would expect to find is that the zoom set at 35mm and 85mm, used on the D800E, would provide a very similar image quality to those primes used on the 12mp D700, when such lenses are used at their sharpest apertures, and the D800 images are downsampled to 12mp.

If this were to be correct, it would be useful information for those who may already be satisfied with the pixel count of their camera but who would like to upgrade their lenses. Instead of buying a few expensive primes to use with one's D700, one could just buy a D800 and continue using the 24-120 zoom on the new camera. If one doesn't need 36mp, no problem, just downsample the images to 12mp and get the image quality of a first rate prime used on the old camera.

The primes may always have the advantage of a wider aperture, but the zoom has, in many circumstances, the more significant advantages of flexibility of focal length range and image stabilization.
Title: Re: DxOMark's new resolution magnitude: P-Mpix
Post by: Dale_Cotton2 on September 05, 2013, 12:32:54 PM
Ray: I have the time but not the lenses. The only camera+lens combo I have that DxO has tested is the RX100M2 with its built-in zoom that I ranted about above.

Whatever the P-Mpix is, it isn't simply a report on sharpness/res/acutance. If you go to the Measurements tab for a given lens, then look at the DxOMark Score Map chart, then look at the Sharpness chart for that same lens, you'll see a different pattern of colours. The lens I'm looking at right now is the Nikon AF-S DX Nikkor 18-55mm f/3.5-5.6G VR mounted on the D7000. The score map only shows even hints of green at the bottom left, which is wide open and wide angle. But the sharpness chart shows no green at all and seems to indicate max sharpness is yellow at f/8 in the wide angle range. Nor can I find any pattern of transmission, distortion, vignetting, or CA that seems to concentrate at the bottom left.

Colour me totally mystified.
Title: Re: DxOMark's new resolution magnitude: P-Mpix
Post by: Ray on September 06, 2013, 01:39:57 AM
Whatever the P-Mpix is, it isn't simply a report on sharpness/res/acutance.

Dale,
As I understand, sharpness and acutance as it relates to perceived detail is always a combination of lens resolution and sensor resolution, assuming adequate lighting and shutter speed.

The P-Mpix ratings from DXO appear to basically combine these two variables, lens resolution and sensor resolution, to provide an overall score for general, perceived sharpness, which I assume would apply at any print size (always comparing equal size prints of course).

I don't often bother using prime lenses because of the inconvenience of a fixed focal length, but I was seduced by the glowing reports of the exceptional quality of the Sigma Art 35/1.4, so I decided to get one.

Now, what I find interesting about the P-Mpix ratings for the Sigma 35/1.4, and my most used Nikkor lens, the 24-120/F4, is that a tripling of pixel count (from the 12mp of the D3 to the 36mp of the D800) more than offsets the lower resolution of the 24-120 zoom, compared with the Sigma prime. The rating for the zoom used with the D800 is 12 P-Mpix, and that for the Sigma Art used with the D3, is slightly less at 11 P-Mpix.

What's also interesting is that the rating for the Sigma 35mm when used with the 16mp D7000 is the same as that for the 12mp D3, ie, 11 P-Mpix.
Since I've hardly used my Sigma 35mm so far, this would seem to be an appropriate time to do a bit of testing in preparation for future decision-making as I take photos on my travels. So I took the following shots from the balcony of my hotel room, using the 24-120 zoom with my D800E and the Sigma Art 35/1.4 on the D7100.

Now, DXO haven't tested either of these lenses on the D7100. I'm making a reasonable assumption that the P-Mpix would jump from 11 to around 13 or 14 as a result of the 50% increase in pixel count. I would therefore expect to see a slight, but perhaps barely noticeable improvement from the Sigma on the D7100, compared with the 24-120 zoom on the D800.
The equivalent focal length on the full-frame format is around 50mm, and to achieve an equivalent DoF as well as FoV I used F5.6 at 50mm, and F4 with the Sigma 35mm.

It so happens that Photozone rate these lenses on the Nikon D3X as being sharpest at F4, in the case of the Sigma, and sharpest at F5.6 in the case of the Nikkor zoom at 50mm. This fact, if it applies to my particular lenses, which might be different due to quality control issues, should make my test more legitimate.

I have to say that I'm very surprised at the results, shown in attached 100% crops. Exactly the same sharpening, clarity and vibrance has been applied to both images in ACR, yet I cannot discern any significant or meaningful difference in resolution and detail in any part of the images.

I would have expected the Sigma to at least be sharper at the edges of the cropped frame, yet it isn't. In fact, the zoom at 50mm appears very slightly sharper in the bottom left corner. Perhaps my copy of the Sigma is below standard, or perhaps my copy of the Nikkor 24-120/F4 is above standard. Looks like I'll need to do more testing.

If the color or contrast of these test images doesn't look quite right, it's because the images have been processed on an uncalibrated laptop.

Any explanations as to what's going on here would be welcome.
Title: Re: DxOMark's new resolution magnitude: P-Mpix
Post by: Dale_Cotton2 on September 06, 2013, 08:45:49 AM
Ray: might be better to take this off-line then report back if anything we come up with relates to the P-Mpix theme of this thread. You can reach me via the e-mail link on my website.
Title: Re: DxOMark's new resolution magnitude: P-Mpix
Post by: Hans Kruse on November 22, 2013, 07:52:19 AM
Dale,
As I understand, sharpness and acutance as it relates to perceived detail is always a combination of lens resolution and sensor resolution, assuming adequate lighting and shutter speed.

The P-Mpix ratings from DXO appear to basically combine these two variables, lens resolution and sensor resolution, to provide an overall score for general, perceived sharpness, which I assume would apply at any print size (always comparing equal size prints of course).

I don't often bother using prime lenses because of the inconvenience of a fixed focal length, but I was seduced by the glowing reports of the exceptional quality of the Sigma Art 35/1.4, so I decided to get one.

Now, what I find interesting about the P-Mpix ratings for the Sigma 35/1.4, and my most used Nikkor lens, the 24-120/F4, is that a tripling of pixel count (from the 12mp of the D3 to the 36mp of the D800) more than offsets the lower resolution of the 24-120 zoom, compared with the Sigma prime. The rating for the zoom used with the D800 is 12 P-Mpix, and that for the Sigma Art used with the D3, is slightly less at 11 P-Mpix.

What's also interesting is that the rating for the Sigma 35mm when used with the 16mp D7000 is the same as that for the 12mp D3, ie, 11 P-Mpix.
Since I've hardly used my Sigma 35mm so far, this would seem to be an appropriate time to do a bit of testing in preparation for future decision-making as I take photos on my travels. So I took the following shots from the balcony of my hotel room, using the 24-120 zoom with my D800E and the Sigma Art 35/1.4 on the D7100.

Now, DXO haven't tested either of these lenses on the D7100. I'm making a reasonable assumption that the P-Mpix would jump from 11 to around 13 or 14 as a result of the 50% increase in pixel count. I would therefore expect to see a slight, but perhaps barely noticeable improvement from the Sigma on the D7100, compared with the 24-120 zoom on the D800.
The equivalent focal length on the full-frame format is around 50mm, and to achieve an equivalent DoF as well as FoV I used F5.6 at 50mm, and F4 with the Sigma 35mm.

It so happens that Photozone rate these lenses on the Nikon D3X as being sharpest at F4, in the case of the Sigma, and sharpest at F5.6 in the case of the Nikkor zoom at 50mm. This fact, if it applies to my particular lenses, which might be different due to quality control issues, should make my test more legitimate.

I have to say that I'm very surprised at the results, shown in attached 100% crops. Exactly the same sharpening, clarity and vibrance has been applied to both images in ACR, yet I cannot discern any significant or meaningful difference in resolution and detail in any part of the images.

I would have expected the Sigma to at least be sharper at the edges of the cropped frame, yet it isn't. In fact, the zoom at 50mm appears very slightly sharper in the bottom left corner. Perhaps my copy of the Sigma is below standard, or perhaps my copy of the Nikkor 24-120/F4 is above standard. Looks like I'll need to do more testing.

If the color or contrast of these test images doesn't look quite right, it's because the images have been processed on an uncalibrated laptop.

Any explanations as to what's going on here would be welcome.

I looked at your examples and I see a clear difference in the crops. The D7100 with the Sigma 35 is not quite sharp in corners compared to the D800 with the 24-120. 

Now the D7100 has been tested with the Sigma 35 f/1.4 and the MPix rating is 16Mpix compared to the 12Mpix of the 24-120 on the D800. And field map attached.
Title: DxOMark's new resolution magnitude, P-Mpix: uses best aperture
Post by: BJL on November 22, 2013, 10:47:57 AM
DxOMark has defined a composite magnitude called Perceptual Mpix (or P-Mpix) to represent the output resolution/sharpness one can expect from a given combo: lens + sensor. ...

I wonder at what aperture is this magnitude defined. The one that provides max resolution for each lens?

Some details from http://www.dxomark.com/About/Lens-scores/Metric-Scores
Quote
The resolution score is computed as follows:
For each focal length and each f-number, we first compute sharpness and then weight it throughout the field, tolerating less sharpness in the corners than in the center. This gives one number for each focal and aperture combination.
Then, for each focal length, we select the maximal value of sharpness over the range of available apertures. We average this value over the whole range of focal length to obtain the DxOMark resolution score that we report (in P-MPix).
So yes, for each focal length, the results for best aperture are used … but there is averaging over the field (center to edge) and for zooms, averaging over focal lengths.

Ironically, DPReview published more detailed data derived from DXOMark testing, or at least makes it easier to find than at the DXO site, allowing one to examine values at any tested aperture ratio. For example, here is the new Zeiss 55/1.4: http://www.dpreview.com/reviews/lens-widget-fullscreen?compare=false&lensId=zeiss_otus_55_1p4&cameraId=nikon_d7100&version=0&fl=55&av=1.4&view=mtf-ca
Title: Re: DxOMark's new resolution magnitude: P-Mpix
Post by: NancyP on November 22, 2013, 11:27:21 AM
The one thing DXO doesn't have is a p value! How many lenses are tested for lens scores? How many bodies are tested for sensor scores? The singular of data is "anecdote".
Title: Re: DxOMark's new resolution magnitude: P-Mpix
Post by: Hans Kruse on November 23, 2013, 12:19:27 PM
I looked at your examples and I see a clear difference in the crops. The D7100 with the Sigma 35 is not quite sharp in corners compared to the D800 with the 24-120. 

Now the D7100 has been tested with the Sigma 35 f/1.4 and the MPix rating is 16Mpix compared to the 12Mpix of the 24-120 on the D800. And field map attached.


Shot Nikon (and Sony) decide to make a full frame sensor with the same pixel pitch as the D7100 it would be 54MP and if scaled up the Sigma resolution would be 36MP. Maybe not quite but it indicates that with such a sensor a 35mm camera could finally rival the lower rez MF cameras as the Leica S and Pentax 645D.
Title: Re: DxOMark's new resolution magnitude: P-Mpix
Post by: Ray on November 23, 2013, 10:33:53 PM
Shot Nikon (and Sony) decide to make a full frame sensor with the same pixel pitch as the D7100 it would be 54MP and if scaled up the Sigma resolution would be 36MP. Maybe not quite but it indicates that with such a sensor a 35mm camera could finally rival the lower rez MF cameras as the Leica S and Pentax 645D.

If Nikon were to offer a 54 mp upgrade to the D800, I certainly hope they would address the banding problems that are the main disappointment with the D7100.

I was very pleased with the D7000's extremely wide DR and ISO-less nature. When shooting at shutter speeds and apertures that require an increase in the ISO setting for a good ETTR, one could simply underexpose at base ISO. After processing the underexposed image in Photoshop, the result would be virtually as good as the same shot taken at a higher ISO, but with the advantage of no risk of blown highlights.

The sensor in the D7100 appears to be from a manufacturer other than Sony. I've see reports that Toshiba are the manufacturer.
Now, according to DXOMark, the D7100 has similar noise and DR characteristics to the D7000, except at its base ISO of 100. The DR difference between ISO 100 and 200 on the D7000, is virtually a full stop, or to be precise, 0.96 EV. However, on the D7100 that DR difference between ISO 100 and 200 is only 1/3rd of a stop.

For this reason, I would prefer to underexpose, say 3 stops at ISO 200 than 4 stops at ISO 100, when using the D7100. To put it another way, if one underexposes 3 stops at ISO 200, instead of using ISO 1600 for an ETTR, one loses only 1/3rd of a stop of DR, which is not significant in my books. The freedom from the risk and concerns about blown highlights, and the wasted time in trying to get it right, makes that trade-off worth it, in my view.

However, if one underexposes 4 stops at ISO 100, one gets a full stop of worse DR compared with ISO 1600. A full stop, or a 1 EV difference, can be very significant if one wants detail in those shadows. So for this reason I use ISO 200 as a base ISO when shooting at relatively fast shutter speeds that would require a higher ISO for an ETTR exposure.

Alas! As I process the D7100 images I took recently on a photographic trip to Nepal, I'm finding lots of banding in the deep shadows, which I never noticed in any of my D7000 images. If the subject is static, no problem. One can bracket exposure for HDR purposes. However, if one is trying to 'capture the moment', one gets only one shot.

The following image was underexposed by about 3 stops at ISO 200. I can't help wondering if that very noticeable banding in the shadows would have been significantly less if I'd used ISO 1600. I guess I'll have to do some testing to find out.
Title: Re: DxOMark's new resolution magnitude: P-Mpix
Post by: Hans Kruse on November 24, 2013, 12:20:03 PM
It seems to me that you are exposing to the left  ;) I would argue that would get much better results on casual shooting where you need to catch the moment in rapidly changing light by using auto ISO on manual and set the aperture and shutter speed you need and exposure compensation to -1 on matrix metering. Using Lightroom or ACR with the automatic highlight recovery I would expect that only would get blown out highlights seldomly and you could lift the exposure in pp without the banding you are seeing now. Of course keep en eye on the ISO chosen by the camera from time to time and compensate by shutter speed needed and aperture needed.
Title: Re: DxOMark's new resolution magnitude: P-Mpix
Post by: BJL on November 24, 2013, 12:46:58 PM
... I would argue that would get much better results on casual shooting ... by using auto ISO ... set[ting] the aperture and shutter speed you need and ... using ... exposure compensation to -1 on matrix metering.
Agreed! With sensors that suffer very little from read noise, and so approach the ideal of being "ISO-less" we can probably avoid a lot of agonizing by just choosing the aperture and shutter speed we want (unless this blows highlights in the photosites themselves) and letting the camera count the resulting photons, with the only care needed being not to amplify the signals from some photosites into clipping by the analog amplifier of ADC. For the latter, a modest "under-amplification" like your suggested -1 will usually be enough to avoid clipping problems. JPEG/print/screen display levels can then be handled later; often with simple auto-levels in PP, at least as a starting point.

Of course Ray is doing this "highlight protection", but his example takes it to the extreme of three stops of protection, and in running as dar away as possible from one problem, he runs into others, like banding.

By the way, increasing ISO speed setting without increasing exposure time or aperture size is not "exposing to the right", because the sensor gets no more exposure; I call it "amplify to the right", or ATTR: pushing the numerical  raw level histogram to the right.  With good modern almost ISO-less sensors that do column-parallel ADC, this ATTR does not seem very useful.


There are other options for highlight protection, such as:
- the Hasselblad/Kodak sensor approach of just counting photons with a good enough ADC that no analog amplification is needed, with all display levels adjustments handled later, in the digital domain,
and
- the approach of some cameras from Olympus and others of systematically using less analog gain and so placing mid-tones a stop or so lower relative to the maximum raw level, and then balancing this with more digital gain in default raw conversion. This is sort of like "-1 comp in exposure , +1 push in digital processing".
Title: Re: DxOMark's new resolution magnitude: P-Mpix
Post by: Ray on November 24, 2013, 07:22:04 PM
It seems to me that you are exposing to the left  ;) I would argue that would get much better results on casual shooting where you need to catch the moment in rapidly changing light by using auto ISO on manual and set the aperture and shutter speed you need and exposure compensation to -1 on matrix metering.

You certainly would with a Canon camera, Hans. However, if the camera is truly ISO-less, or as close as matters, as the D7000 is, then why make matters more complicated than they need be. When one is trying to catch a scene or event which is not only unexpected and rapidly changing, but which also appears in continually varying  lighting  conditions as one walks along the path, one might not even have time to set the the most appropriate shutter speed.

As you can see from the above images, that shutter speed of 1/200th is not ideal for a moving subject like a mule carrying a cage of squabbling chickens whilst lurching from side to side as it walks. I would have preferred a 400th. In such circumstances one also has to be very careful that the mule does not knock one off the path.  ;)
Title: Re: DxOMark's new resolution magnitude: P-Mpix
Post by: Ray on November 24, 2013, 07:36:14 PM
Of course Ray is doing this "highlight protection", but his example takes it to the extreme of three stops of protection, and in running as dar away as possible from one problem, he runs into others, like banding.

BJL,
As I'm sure you realize, the 3 stops underexposure is not for the purpose of highlight protection. The underexposure is an unavoidable consequence of a particular combination of aperture and shutter speed in the particular lighting conditions. It is the method I've used to achieve this which also happens to give maximum highlight protection as a bonus. The main purpose of this method or approach is to achieve maximum image quality on the spur of the moment without wasting time making more than the simplest of camera adjustments.

Of course, you are right that I've inadvertently run into the problem of banding as a result of this approach, hence the purpose of my post, to bring this to the attention of others. But to be logical again, such banding is a property of the Toshiba sensor in the D7100. There was no such banding in the D7000 images. It seems that Nikon, with the D7100, have taken one step forward in relation to sensor resolution, and one step backward in relation to deep-shadow noise. As I've mentioned, I sure hope that Nikon fix this problem if they ever offer  us  a 54 mp full-frame.

The question that now needs to be resolved is whether or not such banding issues remain when one exposes to the right of the histogram, as opposed the the left of the histogram, using the same exposure on the D7100. My only other experience of annoying banding was with the Canon 5D many years ago, but this was the sort of camera that produced a very significant improvement when exposing to the right of the histogram at any ISO above base, compared with underexposing at base using the same exposure.

Quote
By the way, increasing ISO speed setting without increasing exposure time or aperture size is not "exposing to the right", because the sensor gets no more exposure; I call it "amplify to the right", or ATTR: pushing the numerical  raw level histogram to the right.  With good modern almost ISO-less sensors that do column-parallel ADC, this ATTR does not seem very useful.

I think we're into semantics here. ETTR means exposing to the right of the histogram. The only histogram that's available to view on a DSLR is the one that is displayed in relation to the ISO setting one has made, whatever that setting may be. As Hans has mentioned, with a wink, I've exposed to the left in my example above. If I'd used ISO 1600 instead ISO 200, the exposure would have been to the right of the histogram. As you should note, I'm a fairly logical sort of person.  ;)
Title: Re: DxOMark's new resolution magnitude: P-Mpix
Post by: Fine_Art on November 24, 2013, 09:03:16 PM
Ray,

Topaz denoise has a decent de-banding filter, in case you have not seen it already.
Title: Re: DxOMark's new resolution magnitude: P-Mpix
Post by: Ray on November 24, 2013, 09:44:49 PM
Ray,

Topaz denoise has a decent de-banding filter, in case you have not seen it already.

Thanks! I'll check that out. I recall using Topaz many years ago, but now that both ACR and Photoshop have noise-reduction filters, I rely upon them almost exclusively. One gets used to the convenience of familiarity. I'm a bit reluctant to go to the expense and trouble of using new software if it provides only a very marginal improvement, or if it's likely I would use it very rarely.

I'd much prefer it if Nikon would get its act together.  ;)
Title: Re: DxOMark's new resolution magnitude: P-Mpix
Post by: Fine_Art on November 24, 2013, 09:46:57 PM
I thought I would give that banding a try with IP. It is more difficult to use than the commercial, one click NR packages. The detail kept can be good if you are ok with a grain look left in.

Title: Exposure settings with almost "ISO-less" cameras
Post by: BJL on November 24, 2013, 09:47:27 PM
Ray, can you expain what lead to this "histogram three stops too far to the left" problem?

I agree that one cannot alway use manual setting of shutter speed and aperture, so I suppose you were in a mode like aperture or shutter priority, but then how did you end up with those very low raw levels? Was it shutter priority plus ISO 200 leading to hitting the maximum aperture available? Anyway, you surely realize that we are not yet dealing with completely "ISO-less" cameras, and with recent Nikons, there is something to be gained by extra amplification up to about ISO speed 400 or 800, so long as highlight clipping is avoided. So wouldn't something like S mode combined with auto ISO limited to about 400 or 800 be safer and still simple enough?
Title: Re: DxOMark's new resolution magnitude: P-Mpix
Post by: Fine_Art on November 24, 2013, 09:49:41 PM
Thanks! I'll check that out. I recall using Topaz many years ago, but now that both ACR and Photoshop have noise-reduction filters, I rely upon them almost exclusively. One gets used to the convenience of familiarity. I'm a bit reluctant to go to the expense and trouble of using new software if it provides only a very marginal improvement, or if it's likely I would use it very rarely.

I'd much prefer it if Nikon would get its act together.  ;)

Understood. It's not as if many of your shots would be lost to that kind of problem to begin with.

Yes, the toshiba chip seemed good at detail at the expense of noise.
Title: Pushing the wrong histogram right is useless for shot noise or ISO-less sensors
Post by: BJL on November 24, 2013, 10:05:20 PM
I think we're into semantics here. ETTR means exposing to the right of the histogram.
Semantics indeed: you are confusing the meaning and underlying goal of exposing to the right with one method of measuring that exposure, the raw histogram. The original goal, let me remind you yet again, is maximizing S/N ratios by maximizing the light gathered at each photosite, within the constraint of not overfilling any photosite. The relevant histogram to be pushed to the right is of photosite occupancy levels, which is roughly the one seen at base ISO-speed setting.

Taking an exposure situation where you are stuck with substantially underfilled photosites even in the highlights (as in your light-constrained Nepalese examples) and moving the ADC output histogram to the right by using a higher analog gain (higher ISO setting) does nothing of the kind, and does nothing with respect to photon shot noise effects. At best, it can help to overcome the weaknesses of some cameras (particularly Canon DSLRs) with respect to read noise at low gain settings, but is useless in a truly ISO-less sensor, and is useless beyond about ISO 400 with most recent "non-Canon" sensors.
Title: Re: DxOMark's new resolution magnitude: P-Mpix
Post by: Hans Kruse on November 25, 2013, 05:24:28 AM
You certainly would with a Canon camera, Hans. However, if the camera is truly ISO-less, or as close as matters, as the D7000 is, then why make matters more complicated than they need be. When one is trying to catch a scene or event which is not only unexpected and rapidly changing, but which also appears in continually varying  lighting  conditions as one walks along the path, one might not even have time to set the the most appropriate shutter speed.

As you can see from the above images, that shutter speed of 1/200th is not ideal for a moving subject like a mule carrying a cage of squabbling chickens whilst lurching from side to side as it walks. I would have preferred a 400th. In such circumstances one also has to be very careful that the mule does not knock one off the path.  ;)


My recommendation stands nevertheless and I'm sure you will get better results that way, try it :) Maybe an unfair comment, but your comment on being logical got me thinking that you should have tested your approach on the D7100 before using it on a trip where you can't go and retake the pictures.

Another reason my suggestion is a much better approach is that using that you can even see and review your pictures on your camera whereas heavily underexposed pictures will just be black. So although the ISO-less cameras when truly so does allow for the technique you used, it's actually not very practical IMHO.

Title: Re: Exposure settings with almost "ISO-less" cameras
Post by: Hans Kruse on November 25, 2013, 06:16:42 AM
Ray, can you expain what lead to this "histogram three stops too far to the left" problem?

I agree that one cannot alway use manual setting of shutter speed and aperture, so I suppose you were in a mode like aperture or shutter priority, but then how did you end up with those very low raw levels? Was it shutter priority plus ISO 200 leading to hitting the maximum aperture available? Anyway, you surely realize that we are not yet dealing with completely "ISO-less" cameras, and with recent Nikons, there is something to be gained by extra amplification up to about ISO speed 400 or 800, so long as highlight clipping is avoided. So wouldn't something like S mode combined with auto ISO limited to about 400 or 800 be safer and still simple enough?

Are you suggesting that digital amplification is better than analog amplification since you suggest limit the ISO to 400 or 800? (assuming no highlight clipping).
Title: Re: Exposure settings with almost "ISO-less" cameras
Post by: hjulenissen on November 25, 2013, 08:02:05 AM
Are you suggesting that digital amplification is better than analog amplification since you suggest limit the ISO to 400 or 800?
I would suggest that if in-camera ISO adjustment is done by a perfect multiplication (followed by quantisation and clipping to 14 bits), or at least appears to work like this analysed as a black-box, then you would (from a purely image-quality-perspective) be better off by doing this operation in your raw converterter, where you can tailor the degree of amplification, preserve the colour of highlights when wilfully clipping, have a floating-point pipeline, do non-linear/signal-dependant amplification etc. The Nikon D7000 seems to be close to this ideal, other cameras seems to be reasonably close above some ISO value.

Of course, this comes at the cost of operating the camera in a way that it probably was not designed for, including overriding light metering and unusable LCD preview/histogram.
(assuming no highlight clipping).
I believe that highlight-clipping headroom is the main reason to limit ISO. If you are certain that there are no highlights, then there may be no strong IQ arguments for it, but I would say that having more headroom is always a good thing.

-h
Title: Re: Exposure settings with almost "ISO-less" cameras
Post by: Ray on November 25, 2013, 08:43:54 AM
Ray, can you expain what lead to this "histogram three stops too far to the left" problem?

I agree that one cannot alway use manual setting of shutter speed and aperture, so I suppose you were in a mode like aperture or shutter priority, but then how did you end up with those very low raw levels? Was it shutter priority plus ISO 200 leading to hitting the maximum aperture available?

BJL,
I was in full manual mode regarding aperture and shutter speed. I had adopted the principle of 'F8 and be there', because I was there. The shutter speed happened to be set at 1/200th because my earlier recent shots, with 24-120/F4 zoom attached, had been taken with the lens fully extended at 120 mm, which is 180 mm in 35 mm terms. From experience I've found that a shutter speed of at least 1/FL(35mm), in combination with Image Stabilization, is necessary to get good sharpness from very high-resolution sensors such as the D800 and D7100, when the cameras are hand-held. Some folks might disagree with this. I suppose it depends on how steadily one can hold the camera. I have no signs of Parkinson's yet.

Whilst I can't remember my precise thoughts when I took this particular shot (one of thousands taken during a period of a few weeks), I always pay particular attention to the exposure indicator stretched along the bottom of the viewfinder, whenever I shoot in manual mode. I would have noticed that a 200th at F8 was resulting in significant underexposure. I would have been reluctant to reduce exposure even further by using a shutter speed of 1/400th, and reluctant to reduce DoF by adjusting the aperture to F5.6.

Quote
Anyway, you surely realize that we are not yet dealing with completely "ISO-less" cameras, and with recent Nikons, there is something to be gained by extra amplification up to about ISO speed 400 or 800.

I can't agree that none of the recent Nikon DSLRs are completely ISO-less in practical terms. If you check out the results for the D7000 at DXOMark and compare noise levels at ISO 100 and ISO 3200, which represents a 5 stop difference, you'll find that the differences in DR measurements between ISO 100 and ISO 3200 is exactly 5 EV, or 5 stops. If I've interpreted this correctly, it means that a shot with an underexposure of 5 stops at ISO 100 will have exactly the same degree of shadow noise as that same exposure used at ISO 3200.

As regards SNR at 18% grey, the results are very close. At ISO 100 we have 41.1 dB. At ISO 3200, 26.7 dB. That's a difference of 14.4 dB. On the basis that 3 dB is equivalent to a difference of 1 EV or 1 stop, an underexposure of 5 stops at ISO 100 should result in a fall of 15 dB in SNR. One gains a mere 0.6 dB in SNR at 18% by using ISO 3200. Wow!  I bet you that difference would be invisible on any size print, even on the creamiest skin of the most beautiful model.  ;)

The DXO results for the Nikon D800E are similar, with the exception of DR between ISO 100 and 200. It's less than it should be for an ISO-less camera. However, SNR at 18% is exactly 8 stops down at ISO 25,600, or 24 dB down, which is what 8 stops of underexposure at ISO 100 should produce. The D800E can be described as a  true ISO-less camera from ISO 200 to ISO 25,600. The loss in DR in those 7 stops of underexposure is a mere 1/3rd of a stop, and there's no loss at all in SNR at 18%. That's not bad.

If we compare the DXO measurements for the D7100, we find that the ISO-less nature is not quite as good as that of the D7000 and is best within a narrower range of ISOs, specifically from ISO 200 to ISO 1600, which represents the 3 stops underexposure that I used in my above shot of the mule.

According to DXOmark, I've sacrificed 1/3rd of a stop of DR, and 0.3 dB of SNR at 18%, by underexposing 3 stops at ISO 200 instead of raising ISO to 1600. DXOMark in their articles on such matters claim that a difference of 0.5 EV in DR should be noticeable, implying that any differences less than 0.5 EV might not be noticeable, or not significant.

In summary, the D7000 is very close to the true ISO-less camera, closely followed by the D800E. The D7100 is clearly a backward step in this regard, particularly in view of the banding which is not apparent in either the D7000 or D800E.
Title: Re: Exposure settings with almost "ISO-less" cameras
Post by: BJL on November 25, 2013, 10:44:25 AM
Are you suggesting that digital amplification is better than analog amplification since you suggest limit the ISO to 400 or 800? (assuming no highlight clipping).
Not universally, but in one somewhat common situation: once the analog gain is enough to raise all noise in its input comfortably above any noise that comes later (like ADC quantization noise), further analog gain has no further benefit in S/N ratios, and instead using perfectly noise-less digital "bit shifting" for any further level/brightness adjustments has several potential advantages over the inherent imperfections and noise sources of additional analog gain:

1. avoiding clipping of highlights by the amplifier or ADC from over-amplifying the signal from a "bright" but not overfull photosite.

2. simplifying the amplifier and/or chip design. The extreme case is if an ADC is good enough that a "base-ISO speed" amplification that sends full wells to a voltage just within the ADC's range then has the ADC quantization noise floor well below the noise floor of this input signal: then it is probably best to used a fixed gain circuit design rather than adding the imperfections of a variable gain amplifier. Hasselblad seems to do this in some backs with their combination of 12-13 stop DR sensors and good 16-bit off-board ADCs.
Another example is a method of applying analog gain in CMOS sensors described in a Canon research paper: using multiple sense capacitors at the edge of the sensor, and reading to a larger or smaller one in order to apply more or less charge gain. Here needing fewer gain levels and thus fewer sense capacitors and less switching circuitry probably has some design advantages.


The limits of 400 and 800 I mention are roughly what I see with recent Nikon and Olympus system cameras, where analog gain beyond those levels raises total noise levels almost exactly in proportion to signal levels, so offering no gain in SNR or DR or any other IQ metric I can think of; only a potential loss in DR through highlight clipping.
Title: Re: DxOMark's new resolution magnitude: P-Mpix
Post by: BJL on November 25, 2013, 10:52:06 AM
Ray,
    I see only two possibilities:

1. The banding can be completely fixed with appropriate post-processing, so choosing a higher ISO speed setting would only have been a matter of convenience, not IQ.

2. Despite the ISO-independence of the DR and SNR measurements you cite, there are other issues such as pattern noise which sometimes lead to problems like the banding you have seen when the signal from the far less than fully exposed sensor is amplified too little. That is, there can be more to the ISO-less ideal that "the ISO setting is irrelevant to IQ except to avoid amplifier clipping" than revealed by DR and SNR specs alone.
Title: Re: Exposure settings with almost "ISO-less" cameras
Post by: Hans Kruse on November 25, 2013, 12:18:51 PM
Not universally, but in one somewhat common situation: once the analog gain is enough to raise all noise in its input comfortably above any noise that comes later (like ADC quantization noise), further analog gain has no further benefit in S/N ratios, and instead using perfectly noise-less digital "bit shifting" for any further level/brightness adjustments has several potential advantages over the inherent imperfections and noise sources of additional analog gain:

1. avoiding clipping of highlights by the amplifier or ADC from over-amplifying the signal from a "bright" but not overfull photosite.

2. simplifying the amplifier and/or chip design. The extreme case is if an ADC is good enough that a "base-ISO speed" amplification that sends full wells to a voltage just within the ADC's range then has the ADC quantization noise floor well below the noise floor of this input signal: then it is probably best to used a fixed gain circuit design rather than adding the imperfections of a variable gain amplifier. Hasselblad seems to do this in some backs with their combination of 12-13 stop DR sensors and good 16-bit off-board ADCs.
Another example is a method of applying analog gain in CMOS sensors described in a Canon research paper: using multiple sense capacitors at the edge of the sensor, and reading to a larger or smaller one in order to apply more or less charge gain. Here needing fewer gain levels and thus fewer sense capacitors and less switching circuitry probably has some design advantages.


The limits of 400 and 800 I mention are roughly what I see with recent Nikon and Olympus system cameras, where analog gain beyond those levels raises total noise levels almost exactly in proportion to signal levels, so offering no gain in SNR or DR or any other IQ metric I can think of; only a potential loss in DR through highlight clipping.

So you are basically saying that there is no advantage in underexposing in capture and raise exposure in pp relative to raising ISO in the camera (still assuming no highlight clipping).

Given that I simply don't understand why anybody would underexposure many stops and make it impossible to use the LCD to review or even see pictures and also have to adjust exposure in e.g. Lightroom to even review the pictures initially.

I see no practical purpose in that method and also it as unncessary. However it is a benefit to use a technique whereby it is not neccessary to constantly review histograms and adjust exposure compensation. I would much prefer to have an ETTR setting on my camera so that the camera automatically would exposure to the right without having to work against the metering. This would be really beneficial on both Canons and Nikons etc. for low ISO work as well as higher ISO work. For Canons one would still need to bracket more than Nikons, but still for Nikons (or similar behavior) bracketing is needed for optimum IQ. I shot both cameras and on the Nikon D800E I see noise coming in lifting exposure by two stops where optimal exposure mostly leaves a smooth noise free tone in e.g. clouds shooting at ISO 100. Raising more than a few stops ruins IQ in the details. What my experience tells me is that at ISO 100 optimum IQ also needs optimum exposure.
Title: Re: Exposure settings with almost "ISO-less" cameras
Post by: Hans Kruse on November 25, 2013, 12:20:01 PM
BJL,
I was in full manual mode regarding aperture and shutter speed. I had adopted the principle of 'F8 and be there', because I was there. The shutter speed happened to be set at 1/200th because my earlier recent shots, with 24-120/F4 zoom attached, had been taken with the lens fully extended at 120 mm, which is 180 mm in 35 mm terms. From experience I've found that a shutter speed of at least 1/FL(35mm), in combination with Image Stabilization, is necessary to get good sharpness from very high-resolution sensors such as the D800 and D7100, when the cameras are hand-held. Some folks might disagree with this. I suppose it depends on how steadily one can hold the camera. I have no signs of Parkinson's yet.

Whilst I can't remember my precise thoughts when I took this particular shot (one of thousands taken during a period of a few weeks), I always pay particular attention to the exposure indicator stretched along the bottom of the viewfinder, whenever I shoot in manual mode. I would have noticed that a 200th at F8 was resulting in significant underexposure. I would have been reluctant to reduce exposure even further by using a shutter speed of 1/400th, and reluctant to reduce DoF by adjusting the aperture to F5.6.

I can't agree that none of the recent Nikon DSLRs are completely ISO-less in practical terms. If you check out the results for the D7000 at DXOMark and compare noise levels at ISO 100 and ISO 3200, which represents a 5 stop difference, you'll find that the differences in DR measurements between ISO 100 and ISO 3200 is exactly 5 EV, or 5 stops. If I've interpreted this correctly, it means that a shot with an underexposure of 5 stops at ISO 100 will have exactly the same degree of shadow noise as that same exposure used at ISO 3200.

As regards SNR at 18% grey, the results are very close. At ISO 100 we have 41.1 dB. At ISO 3200, 26.7 dB. That's a difference of 14.4 dB. On the basis that 3 dB is equivalent to a difference of 1 EV or 1 stop, an underexposure of 5 stops at ISO 100 should result in a fall of 15 dB in SNR. One gains a mere 0.6 dB in SNR at 18% by using ISO 3200. Wow!  I bet you that difference would be invisible on any size print, even on the creamiest skin of the most beautiful model.  ;)

The DXO results for the Nikon D800E are similar, with the exception of DR between ISO 100 and 200. It's less than it should be for an ISO-less camera. However, SNR at 18% is exactly 8 stops down at ISO 25,600, or 24 dB down, which is what 8 stops of underexposure at ISO 100 should produce. The D800E can be described as a  true ISO-less camera from ISO 200 to ISO 25,600. The loss in DR in those 7 stops of underexposure is a mere 1/3rd of a stop, and there's no loss at all in SNR at 18%. That's not bad.

If we compare the DXO measurements for the D7100, we find that the ISO-less nature is not quite as good as that of the D7000 and is best within a narrower range of ISOs, specifically from ISO 200 to ISO 1600, which represents the 3 stops underexposure that I used in my above shot of the mule.

According to DXOmark, I've sacrificed 1/3rd of a stop of DR, and 0.3 dB of SNR at 18%, by underexposing 3 stops at ISO 200 instead of raising ISO to 1600. DXOMark in their articles on such matters claim that a difference of 0.5 EV in DR should be noticeable, implying that any differences less than 0.5 EV might not be noticeable, or not significant.

In summary, the D7000 is very close to the true ISO-less camera, closely followed by the D800E. The D7100 is clearly a backward step in this regard, particularly in view of the banding which is not apparent in either the D7000 or D800E.


This can all be true but I do not understand why you choose this technique as there are so many disadvantages with it.
Title: Re: Exposure settings with almost "ISO-less" cameras
Post by: ErikKaffehr on November 25, 2013, 06:03:52 PM
Hi,

That seems to me like the optimum recipe for perfection.

The impression I have is that it is beneficial to raise ISO on Canons, perhaps up to 1000 ISO instead of just reducing exposure as higher ISO will reduce shadow noise.

Pushing up ISO will tell camera firmware and raw processor that it is a high ISO image. So raw processor can increase noise reduction.

Best regards
Erik

What my experience tells me is that at ISO 100 optimum IQ also needs optimum exposure.
Title: Re: Exposure settings with almost "ISO-less" cameras
Post by: Hans Kruse on November 25, 2013, 06:51:04 PM
Hi,

That seems to me like the optimum recipe for perfection.

The impression I have is that it is beneficial to raise ISO on Canons, perhaps up to 1000 ISO instead of just reducing exposure as higher ISO will reduce shadow noise.

Pushing up ISO will tell camera firmware and raw processor that it is a high ISO image. So raw processor can increase noise reduction.

Best regards
Erik


At ISO 100 for both Canon and Nikon you will get the best IQ with the longest exposure without burning out essential detail (=highlights) and judged in Lightroom.

Title: Re: Exposure settings with almost "ISO-less" cameras
Post by: BJL on November 25, 2013, 08:13:14 PM
So you are basically saying that there is no advantage in underexposing in capture and raise exposure in pp relative to raising ISO in the camera (still assuming no highlight clipping).

Firstly, I am talking about "limited light" situations where using base ISO speed, say 100, would be significant underexposure, and in this case, your talk of using ISO 100 and optimum exposure is irrelevant. For example, in Ray's Nepalese photo, using ISO 100 and "properly exposure" would have given images been blurred due to excessively long exposure times.

Secondly, I am not talking about reducing _exposure_, in the sense of increasing either shutter speed or aperture ratio; I am talking solely about what ISO setting to use when one is already using the lowest acceptable shutter speed and the largest acceptable aperture, and so the sensor is already getting as much light as is possible from the scene, and this is still leaving all the photosites well short of full. (That is, "exposing to the right" in the original sense is not an option.)

With that clarified, what I am saying is that sometimes, when things are happening too quickly to allow careful metering decisions, it can be wise to be conservative in ISO setting (meaning maybe 200 to 800) and thus use a lowish level of analog gain, in order to avoid clipping of highlights --- meaning highlights where the photosite was short of full, so they are not blown in the photosite, but where a too high analog gain can push the value beyond the maximum of the amplifier and ADC.

However, I only suggest this as a last resort, when simpler options like bracketing are ruled out, for example because the scene is changing too quickly to allow more than one frame.

And only with "near ISO-less" sensors! Ray has in years past posted evidence of the IQ problems that this underamplification caused with some Canon DSLRs.

P. S. Another clarification: I am not suggesting that one always limit the ISO setting to 400 or 800 or whatever on cameras like the Nikon 7000 or 7100; when the metering is clear cut, using a higher ISO setting to get suitable levels in standard JPEG conversions seems simpler and safe. (But with some cameras, the effects of a setting like ISO 1600 might best be implemented with the same analog gain as ISO 100, plus a flag in the raw file for 16x digital shift.)
Title: Re: Exposure settings with almost "ISO-less" cameras
Post by: ErikKaffehr on November 25, 2013, 08:49:50 PM
Hans,

I have a small issue with 'judged in Lightroom'. Lightroom with PV2012 does some highlight recovery and often shows a nice histogram even with clipped highlights. I often use RawDigger to look at 'real' histogram in the raw file.

Best regards
Erik


At ISO 100 for both Canon and Nikon you will get the best IQ with the longest exposure without burning out essential detail (=highlights) and judged in Lightroom.


Title: Re: Exposure settings with almost "ISO-less" cameras
Post by: Ray on November 25, 2013, 09:02:11 PM
This can all be true but I do not understand why you choose this technique as there are so many disadvantages with it.

Hans,
I'm simply not aware of the many disadvantages you refer to. The main disadvantage that I've experienced is that one cannot show off to another person the interesting shot one has just taken, because it appears so underexposed on the camera's LCD screen.

As regards reviewing the image for the purpose of retaking the shot if it doesn't look satisfactory, that should not be a concern in the circumstances. If the shot is not satisfactory, the moment will likely have passed by the time one has enlarged the review to inspect the image.

The advantage of shooting in full manual mode at base ISO in circumstance where one knows that underexposure in relation to full-well capacity is unavoidable, is that one has the greatest certainty that  the ISO setting,  and any possible overexposure in terms of blown highlights, will not be an issue.

Have you never taken a shot with a 'minus-1-stop' exposure compensation, that has turned out to have blown highlights? I have. Shoot (in a hurry) some interesting activity that's taking place in the shadows in, say, the lower right corner of the frame, against a background of an interesting, brightly lit sky in the upper left corner, and you might find that a 'minus one stop EC' is not sufficient to bring out the detail in the sky in the top left corner of the frame.

Your approach of using auto ISO with a minus one stop exposure compensation might work just as well most of the time, but would seem to me to provide less certainty for all situations that one might encounter. Perhaps you would then recommend a minus-2-stop EC.

I'll give you an example of what would appear to me to be an unsatisfactory outcome that could result from your method of using auto-ISO in conjunction with exposure compensation. But I'm no expert with this method. There might be settings in the menu of the D7100 I am unfamiliar with.

Let's consider the situation of using a 'minus 2 stop' exposure compensation in auto-ISO mode. In the circumstances of continuously changing lighting conditions that occur when walking along a mountain track, you might inadvertently underexposed at ISO 100. The best choice might have been, for example, ISO 200, which is the setting that I would use with the D7100.  As a result of the 'minus-2 stops' exposure compensation in conjunction with auto-ISO, the camera has lowered ISO to 100 and underexposed a further stop.

In such circumstances, using the D7100, your shot would have more than a full stop worse noise and DR than mine. Is this not the case? If not, please advise what settings you would use on the D7100 to avoid this situation.

In fact, having just now experimented with your recommended method on the D7100 as I write this, I'm rather puzzled that I get no indication of underexposure on the indicator at the foot of the viewfinder. It's either zero or in the overexposed region, yet I can take shots that look underexposed on the LCD review. What's going on here?
Title: Re: Exposure settings with almost "ISO-less" cameras
Post by: Hans Kruse on November 26, 2013, 04:49:20 AM
Firstly, I am talking about "limited light" situations where using base ISO speed, say 100, would be significant underexposure, and in this case, your talk of using ISO 100 and optimum exposure is irrelevant. For example, in Ray's Nepalese photo, using ISO 100 and "properly exposure" would have given images been blurred due to excessively long exposure times.

Secondly, I am not talking about reducing _exposure_, in the sense of increasing either shutter speed or aperture ratio; I am talking solely about what ISO setting to use when one is already using the lowest acceptable shutter speed and the largest acceptable aperture, and so the sensor is already getting as much light as is possible from the scene, and this is still leaving all the photosites well short of full. (That is, "exposing to the right" in the original sense is not an option.)

With that clarified, what I am saying is that sometimes, when things are happening too quickly to allow careful metering decisions, it can be wise to be conservative in ISO setting (meaning maybe 200 to 800) and thus use a lowish level of analog gain, in order to avoid clipping of highlights --- meaning highlights where the photosite was short of full, so they are not blown in the photosite, but where a too high analog gain can push the value beyond the maximum of the amplifier and ADC.

However, I only suggest this as a last resort, when simpler options like bracketing are ruled out, for example because the scene is changing too quickly to allow more than one frame.

And only with "near ISO-less" sensors! Ray has in years past posted evidence of the IQ problems that this underamplification caused with some Canon DSLRs.

P. S. Another clarification: I am not suggesting that one always limit the ISO setting to 400 or 800 or whatever on cameras like the Nikon 7000 or 7100; when the metering is clear cut, using a higher ISO setting to get suitable levels in standard JPEG conversions seems simpler and safe. (But with some cameras, the effects of a setting like ISO 1600 might best be implemented with the same analog gain as ISO 100, plus a flag in the raw file for 16x digital shift.)

Probably I didn't say that clearly enough, but my question to you was rather specific and not about Ray's situation. It was simply: Is there a difference in IQ of the resulting image between the two situations where you shoot 1) one picture at ISO 100 and underexposed by zero to e.g. 6 stops and 2) the same picture shot at ISO settings 100, 200, 400 and 6400? Again assuming no highlight clipping.

I assume the amplification in the camera for lifting ISO is done in the analogue domain and not in the digital domain in cameras like the Nikon D7100, D800 etc. If the sensor is truly ISO-less the two situations above should be the same except for the resolution, i.e. the number of bits representing the tones where the analogue amplification and then digitizing will represent the picture with a full 14bit resolution where digital amplification is simply shifting the bits x-number of positions (where is the number of stops). The other difference could be the noise characteristics with a noise floor that gets amplified with digital amplification but not with analogue (noise floor in the ADC). With a truly ISO-less camera the noise floor of the ADC should be zero. Are there other factors?

Btw. the 16x shift, I assume you mean 4x shift (shifting bits 4 positions) going from ISO 100 to ISO 1600.
Title: Re: Exposure settings with almost "ISO-less" cameras
Post by: Hans Kruse on November 26, 2013, 05:27:50 AM

P. S. Another clarification: I am not suggesting that one always limit the ISO setting to 400 or 800 or whatever on cameras like the Nikon 7000 or 7100; when the metering is clear cut, using a higher ISO setting to get suitable levels in standard JPEG conversions seems simpler and safe. (But with some cameras, the effects of a setting like ISO 1600 might best be implemented with the same analog gain as ISO 100, plus a flag in the raw file for 16x digital shift.)

I did a small test with my D800E at ISO 6400 compared with ISO 100. For the ISO 100 I lifted the exposure in Lightroom.

Here is a 1:1 crop from the two pictures as shown in Lightroom. I would say a huge difference where the ISO6400 looks rather good and the ISO 100 lifted is really poor. The histogram for the ISO 100 has a lot posterization where the ISO 6400 looks smooth.



Title: Re: Exposure settings with almost "ISO-less" cameras
Post by: Hans Kruse on November 26, 2013, 05:43:08 AM
Hans,
I'm simply not aware of the many disadvantages you refer to. The main disadvantage that I've experienced is that one cannot show off to another person the interesting shot one has just taken, because it appears so underexposed on the camera's LCD screen.

As regards reviewing the image for the purpose of retaking the shot if it doesn't look satisfactory, that should not be a concern in the circumstances. If the shot is not satisfactory, the moment will likely have passed by the time one has enlarged the review to inspect the image.

The advantage of shooting in full manual mode at base ISO in circumstance where one knows that underexposure in relation to full-well capacity is unavoidable, is that one has the greatest certainty that  the ISO setting,  and any possible overexposure in terms of blown highlights, will not be an issue.

Have you never taken a shot with a 'minus-1-stop' exposure compensation, that has turned out to have blown highlights? I have. Shoot (in a hurry) some interesting activity that's taking place in the shadows in, say, the lower right corner of the frame, against a background of an interesting, brightly lit sky in the upper left corner, and you might find that a 'minus one stop EC' is not sufficient to bring out the detail in the sky in the top left corner of the frame.

Your approach of using auto ISO with a minus one stop exposure compensation might work just as well most of the time, but would seem to me to provide less certainty for all situations that one might encounter. Perhaps you would then recommend a minus-2-stop EC.

I'll give you an example of what would appear to me to be an unsatisfactory outcome that could result from your method of using auto-ISO in conjunction with exposure compensation. But I'm no expert with this method. There might be settings in the menu of the D7100 I am unfamiliar with.

Let's consider the situation of using a 'minus 2 stop' exposure compensation in auto-ISO mode. In the circumstances of continuously changing lighting conditions that occur when walking along a mountain track, you might inadvertently underexposed at ISO 100. The best choice might have been, for example, ISO 200, which is the setting that I would use with the D7100.  As a result of the 'minus-2 stops' exposure compensation in conjunction with auto-ISO, the camera has lowered ISO to 100 and underexposed a further stop.

In such circumstances, using the D7100, your shot would have more than a full stop worse noise and DR than mine. Is this not the case? If not, please advise what settings you would use on the D7100 to avoid this situation.

In fact, having just now experimented with your recommended method on the D7100 as I write this, I'm rather puzzled that I get no indication of underexposure on the indicator at the foot of the viewfinder. It's either zero or in the overexposed region, yet I can take shots that look underexposed on the LCD review. What's going on here?


There are at least two major disadvantages to the method of shooting at ISO 100 and allow underexposure 1) You can't even see the pictures on the LCD, you can't review focus or show it to anyone 2) you have to adjust exposure when importing into Lightroom or any other RAW converter before you can review the pictures for selection or rejection.

Check the examples of my ISO 6400 test I have just posted. Try it with your D7100 and it will likely be much worse.

I'm not saying you would never get clipped highlights by exposure compensation -1 on matrix metering, but what I say is that it is relatively rare and rare enough as a good general setting.

My experience from shooting landscapes, where I need at adjust the lighting over the image area, is that even with the D800 lifting exposure more than 2-3 stops starts to make colors look less good and noise comes and washes out details. Surely the Canon 5D III which I also shoot is not as good. In both cases I always bracket and make sure that there is always one overexposed and one underexposed in the bracket sequence and then I choose the most exposed without clipping in Lightroom. Lightroom has since version 4 an automatic highlight recovery which recovers from clipping one or two channels and does it in 99% of the time without visual defects. I do miss a true RAW clipping indicator in Lightroom to allow me to see where the clipping occurs. The clipping can be checked in a RAW analyzer like RAW digger which I use in rare cases. This is mostly needed with the Canon but the Nikon also gets better IQ in the difficult shots by this method. I never need to look at histograms, I can just check the blinking indicators for the bracket sequence if I'm in doubt and this is quick to do and does not interrupt the flow of shooting.

Now with casual shooting like what you refer to here I use auto ISO on either manual or aperture priority and on the Canon 5D III I bracket always with the same rule as above. With the Nikon I usually also bracket but could also use the exposure compensation -1 (or -2) to get nearly as good results without the bracketing overhead. Yes, there may still be exceptions in rare cases but usually these are the cases where I can reshoot.

I do follow your wish to have a no worry shooting setup so you can concentrate 100% on capturing the moment :) The reason for my landscape and casual shooting technique is the same. I almost always come back with good technical quality shots using this method on both the Canon and the Nikon.
Title: Re: Exposure settings with almost "ISO-less" cameras
Post by: Hans Kruse on November 26, 2013, 05:59:54 AM
I have a small issue with 'judged in Lightroom'. Lightroom with PV2012 does some highlight recovery and often shows a nice histogram even with clipped highlights. I often use RawDigger to look at 'real' histogram in the raw file.

I agree to some degree on this and I use bracketing always for my landscape work not only to recover from the rare occassion where Lightroom shows no clipping for a clipped RAW file, but also to achieve to highest possible exposure to have the maximum data to work with which gives the minimum noise and the maximum flexibility to adjust. Sometimes my adjustments are huge and the quality of the RAW file is crucial to get the best result. Still HDR merging is in my opinion a plan B solution. I also use RawDigger to check when I suspect there is an issue in e.g. clouds. I wish Adobe would include an optional RAW clipping overlay on the image to see where the RAW file has any clipping to make it easier to see if the is an issue. In my experience it is very rare that there is an issue if Lightroom does not show any clipping on a default conversion and AWB from the camera. Even a wrong WB could cause clipping to occur even if the there is no clipping in the RAW file.... Rather than checking with RawDigger what I usually do is that I synchronize the editing of a picture to one that is exposed one stop less and adjust the exposure in Lightroom +1 and then check 1:1 in areas where I have a doubt if certain structures in e.g. clouds is caused by clipping or not. Sometimes a strongly lit cloud by the sun can show an area with no detail where there is still no detail when using an image with no clipping at all as shown in RawDigger. So all in all I'm happy with the results of the automatic highlight recovery in Lightroom and very seldomly I see artifacts created by this.
Title: Re: Exposure settings with almost "ISO-less" cameras
Post by: BartvanderWolf on November 26, 2013, 06:26:21 AM
So all in all I'm happy with the results of the automatic highlight recovery in Lightroom and very seldomly I see artifacts created by this.

Hi Hans,

But it (PV2012) also causes major highlight compression at Default settings, which tends to take a lot of life out of images with important light tones. This is something many users don't realize because it is not made clear by the default settings, but a significantly reduced Highlights slider control is required to get IMHO more natural looking images.

Cheers,
Bart
Title: Re: Exposure settings with almost "ISO-less" cameras
Post by: Hans Kruse on November 26, 2013, 06:53:21 AM
Hi Hans,

But it (PV2012) also causes major highlight compression at Default settings, which tends to take a lot of life out of images with important light tones. This is something many users don't realize because it is not made clear by the default settings, but a significantly reduced Highlights slider control is required to get IMHO more natural looking images.

Cheers,
Bart

Hi Bart,

I agree and I almost always use the highlight slider to bring out detail in the highlights, no matter the exposure. Same with the shadows slider. Both sliders are used in combination with the whites and blacks sliders (of course) and contrast/tone curve.

Update: However if you compare the histogram of an exposure with the compressed highlights taken down by one stop and compare with another exposure without the compression you will see an almost identical histogram in the highlights. So adding to the above I very often take the exposure down in Lightroom even when there is no compression visible of highlights and then use the highlights and shadows sliders as mentioned.

Attached histograms that shows this. The EV+1 is a EV+1 from a bracket sequence. This one is taken down by one stop in Lightroom and the resulting histogram is shown and can be compared with a EV0 histogram.
Title: Re: Exposure settings with almost "ISO-less" cameras
Post by: BJL on November 26, 2013, 09:02:03 AM
There are at least two major disadvantages to the method of shooting at ISO 100 and allow underexposure 1) You can't even see the pictures on the LCD, you can't review focus or show it to anyone 2) you have to adjust exposure when importing into Lightroom or any other RAW converter before you can review the pictures for selection or rejection.
I quite agree, and this is part of the reason that I would rather not have to use this technique ... but they do not directly affect Ray's energetic pursuit of maximum IQ, so I suppose that it why he puts up with those inconveniences.

But the bigger part of why I have not felt much need for this practice is that the problems that Ray faces can be mitigated or avoided by different firmware than what Nikon offers, and my EM5 offers what is for me an adequate approximation.

Plan A: an ISO speed selection system that uses one ISO speed value for JPEG conversion (including the on-camera review, in-camera JPEG, and default raw->JPEG conversion) but a fixed analog gain, so that raw files are always at the numerical levels of base ISO speeds, and there is never any amplifier clipping. The difference between the gain used to produce raw and the "JPEG intent" is flagged in raw file metadata.

Plan B: same as above as far as JPEG, and again with metadata flagging, but with the gain used in producing raw files intermediate, say one or two stops less than the "JPEG intent". This could be useful when the sensor/ADC combination is not perfectly "ISO-free", so that analog gain up to about 400 or 800 helps to mitigate effects like quantization noise.

Neither strategy uses the one stop underexposure (-1 compensation) that you mention, let alone the two stop underexposure that Ray worries about in his response; they are solely choices of when and how to amplify the signal after the sensor exposure level is set.

Ironically, these strategies are similar to ones used by some camera makers (Hasselblad, Phase One, Olympus)  that Ray and others have described somewhat disparagingly with words like "over-stating the ISO speed" and "underexposure", partly because of widespread confusion (excacerbated by some confusing description of measurements by DXO) between "less exposure" and "less analog amplification of the results of an exposure".
Title: Re: Exposure settings with almost "ISO-less" cameras
Post by: Fine_Art on November 26, 2013, 10:07:54 AM
I did a small test with my D800E at ISO 6400 compared with ISO 100. For the ISO 100 I lifted the exposure in Lightroom.

Here is a 1:1 crop from the two pictures as shown in Lightroom. I would say a huge difference where the ISO6400 looks rather good and the ISO 100 lifted is really poor. The histogram for the ISO 100 has a lot posterization where the ISO 6400 looks smooth.





That is a limitation of lightroom. At least for now. If you use other software that does it's calculation in floating point, the resultant histogram will be smooth. RAW Therapee is now 64 bit floating point for example. So is Images Plus.
Title: Re: Exposure settings with almost "ISO-less" cameras
Post by: Hans Kruse on November 26, 2013, 10:39:00 AM
That is a limitation of lightroom. At least for now. If you use other software that does it's calculation in floating point, the resultant histogram will be smooth. RAW Therapee is now 64 bit floating point for example. So is Images Plus.

I thought I would check this, but Raw Therapee will not run on my Mavericks MBP. Anyway this is only of theoretical interest for me as I don't see why I should shoot like this anyway ;)

Update: I checked Capture One 7 and lifting exposure and brightness to the same levels as Lightroom does not create the jagged histogram. I checked some of the other exposures as it appears that +4EV on exposure is the maximum in Lightroom without creating the posterization. Histograms attached.

So it's clear that using Lightroom or ACR lifting exposure more than 4 stops is not good.
Title: Re: Exposure settings with almost "ISO-less" cameras
Post by: Hans Kruse on November 26, 2013, 10:40:52 AM
I quite agree, and this is part of the reason that I would rather not have to use this technique ... but they do not directly affect Ray's energetic pursuit of maximum IQ, so I suppose that it why he puts up with those inconveniences.

But the bigger part of why I have not felt much need for this practice is that the problems that Ray faces can be mitigated or avoided by different firmware than what Nikon offers, and my EM5 offers what is for me an adequate approximation.

Plan A: an ISO speed selection system that uses one ISO speed value for JPEG conversion (including the on-camera review, in-camera JPEG, and default raw->JPEG conversion) but a fixed analog gain, so that raw files are always at the numerical levels of base ISO speeds, and there is never any amplifier clipping. The difference between the gain used to produce raw and the "JPEG intent" is flagged in raw file metadata.

Plan B: same as above as far as JPEG, and again with metadata flagging, but with the gain used in producing raw files intermediate, say one or two stops less than the "JPEG intent". This could be useful when the sensor/ADC combination is not perfectly "ISO-free", so that analog gain up to about 400 or 800 helps to mitigate effects like quantization noise.

Neither strategy uses the one stop underexposure (-1 compensation) that you mention, let alone the two stop underexposure that Ray worries about in his response; they are solely choices of when and how to amplify the signal after the sensor exposure level is set.

Ironically, these strategies are similar to ones used by some camera makers (Hasselblad, Phase One, Olympus)  that Ray and others have described somewhat disparagingly with words like "over-stating the ISO speed" and "underexposure", partly because of widespread confusion (excacerbated by some confusing description of measurements by DXO) between "less exposure" and "less analog amplification of the results of an exposure".

Interesting thoughts, but more for a camera engineer than a photographer :) I really believe Ray is wrong about his pursuit about optimum IQ....
Title: Re: Exposure settings with almost "ISO-less" cameras
Post by: BJL on November 26, 2013, 11:01:29 AM
Probably I didn't say that clearly enough, but my question to you was rather specific and not about Ray's situation. It was simply: Is there a difference in IQ of the resulting image between the two situations where you shoot 1) one picture at ISO 100 and underexposed by zero to e.g. 6 stops and 2) the same picture shot at ISO settings 100, 200, 400 and 6400? Again assuming no highlight clipping.
I think we are essentially in agreement, but just to clarify ...

Last point first; the only potential benefit that I am claiming for this procedure of using less analog gain is to avoid highlight clipping, so that last assumption is a bit weird!

But indeed, I find it hard to imagine a situation where four stops of under-amplification (100 vs 1600) would be needed to avoid amplifier clipping of highlights, which is why I prefer a middle ground of placing the raw levels one or two stops below "normal" and flagging that placement in the metadata. But perhaps Ray can find an example where his light metering or exposure settings were off by a full four stops and clipped some highlights!

Also, I have repeatedly talked about under amplifying to about ISO 400 with cameras like Nikons, not all the way down to ISO 100, because from what I have read, there could be some benefit in reduced quantization noise and thus reduced posterization in raising the gain that far. So your 100 vs 1600 experiment is not relevant to my comments, but might be relevant to the more extreme "minimal amplification" approach described by Ray. (The one situation I know of where it might be good to always use the same "base ISO" amplifier gain is with some combinations of Kodak CCDs and good 16-bit off-board ADCs, where that gain already puts sensor/read noise well above the ADC's quantization noise level.)

Btw. the 16x shift, I assume you mean 4x shift (shifting bits 4 positions) going from ISO 100 to ISO 1600.
Yes, 16x means shifting the values by multiplying by a factor of 16, so shifting four bits to the left.
Title: Re: Exposure settings with almost "ISO-less" cameras
Post by: Ray on November 26, 2013, 06:43:39 PM
There are at least two major disadvantages to the method of shooting at ISO 100 and allow underexposure 1) You can't even see the pictures on the LCD, you can't review focus or show it to anyone 2) you have to adjust exposure when importing into Lightroom or any other RAW converter before you can review the pictures for selection or rejection.

Hans,

First let me congratulate you on your spectacular landscape images on your linked site.
Now to business. ;D

I've already agreed there is a disadvantage in not being able to share the images with anyone on the camera's LCD screen. However, if one was attempting to capture the moment, the ability to review the image for focus and other issues is not likely to serve much purpose. Would Cartier-Bresson have found the ability to review his shots useful? Refer attached image. ;)

The extra work of adjusting exposure in the RAW converter before determining whether or not to delete an image is trivial for me. By far the greater proportion of my rejects over the years have been those taken in Aperture Priority mode when the automatic selection of shutter speed has been too slow to freeze movement or too slow to avoid blown highlights in parts of the scene that I considered important.

It is this very preponderance of such rejects that has led me to this approach of using the camera as though it were ISO-less. Nevertheless, I accept there are small, incremental losses in image quality, compared with using a 'correct' ISO in relation to an ETTR, which might be noticeable if the underexposure is taken to extremes.

For me it's really a trade-off between the two concerns of (1) getting the shot with a confidence that there will be nothing seriously wrong that will cause it to be a reject, and (2) missing  the moment entirely as a result of spending too much time making camera adjustments to ensure maximum image quality.

Your approach of using auto-ISO should be better when using extreme underexposure. I'll give it a try. My main concern is that there appears to be no indication in the D7100 viewfinder of underexposure when a minus value of EC is enabled.

Quote
Check the examples of my ISO 6400 test I have just posted. Try it with your D7100 and it will likely be much worse.

Now, Hans, you are getting a bit tricky. ;D  I mentioned specifically that Nikon is going backwards with regard to the ISO-less nature of their most recent models, including the D800 and the D7100. A consequence of this is that one should try to avoid using ISO 100 when underexposing. You've not only used ISO 100, but given 6 stops of underexposure as well.This is what I wrote earlier, in reply to BJL:

Quote
If we compare the DXO measurements for the D7100, we find that the ISO-less nature is not quite as good as that of the D7000 and is best within a narrower range of ISOs, specifically from ISO 200 to ISO 1600, which represents the 3 stops underexposure that I used in my above shot of the mule.

Just to confirm that I am correct in this view that there should be no significant problem in underexposing by 3 stops at ISO 200 with the D7100 (apart from possible banding), I took the following shots just after sunrise this morning, Australian time.

Perhaps I should not have labelled these shots, and should have asked you to guess which was taken at ISO 200. I simply cannot discern any differences at 100% view that would indicate that one of the shots was an underexposure in relation to its ISO setting. Can you?

I should also point out that I have made no adjustments to either of these images apart from raising the exposure of the underexposed shot to +3 in ACR, and apart from letting the default sharpening of 25 apply to both images. The conversions are from the settings that appear in the attached screen capture of the ACR window, with no further adjustment in Photoshop.

Title: Re: Exposure settings with almost "ISO-less" cameras
Post by: Torbjörn Tapani on November 26, 2013, 07:17:30 PM
Hans,

First let me congratulate you on your spectacular landscape images on your linked site.

Ray, I would like to thank you for pointing this out. And Hans, what a fantastic set of images you got there!
Title: Time to look at photos instead
Post by: BJL on November 26, 2013, 09:41:55 PM
Ray, I would like to thank you for pointing this out. And Hans, what a fantastic set of images you got there!
Indeed! I was almost tempted to comment on this debate yet again, but then decided it is far better to sit back and look at those beautiful photographs. It is edifying, though a bit humiliating, to see photographs of scenes that I have also visited (some of those sites in the Dolomites) that are so much better than anything I achieved there.
Title: Re: Exposure settings with almost "ISO-less" cameras
Post by: Hans Kruse on November 27, 2013, 01:28:34 PM
Hans,

First let me congratulate you on your spectacular landscape images on your linked site.
Now to business. ;D


Thanks very much :)

Quote

I've already agreed there is a disadvantage in not being able to share the images with anyone on the camera's LCD screen. However, if one was attempting to capture the moment, the ability to review the image for focus and other issues is not likely to serve much purpose. Would Cartier-Bresson have found the ability to review his shots useful? Refer attached image. ;)


He didn't need that for sure for this shot. For me it would be a major disadvantage if I could look at my shots, but if that does not really mean anything to then this item is out.

Quote


The extra work of adjusting exposure in the RAW converter before determining whether or not to delete an image is trivial for me. By far the greater proportion of my rejects over the years have been those taken in Aperture Priority mode when the automatic selection of shutter speed has been too slow to freeze movement or too slow to avoid blown highlights in parts of the scene that I considered important.


When using aperture priority and auto ISO, I always make sure to have set a minimum shutter speed. That's on my Canon since I can't use exposure compensation in manual mode on the Canon.

Quote

It is this very preponderance of such rejects that has led me to this approach of using the camera as though it were ISO-less. Nevertheless, I accept there are small, incremental losses in image quality, compared with using a 'correct' ISO in relation to an ETTR, which might be noticeable if the underexposure is taken to extremes.

For me it's really a trade-off between the two concerns of (1) getting the shot with a confidence that there will be nothing seriously wrong that will cause it to be a reject, and (2) missing  the moment entirely as a result of spending too much time making camera adjustments to ensure maximum image quality.

Your approach of using auto-ISO should be better when using extreme underexposure. I'll give it a try. My main concern is that there appears to be no indication in the D7100 viewfinder of underexposure when a minus value of EC is enabled.


If you are unsure you only need to push the EC button. Alternatively you could set bracketing to two exposures one stop apart which would result in a -1 and a -2 and set the camera to continous shooting so when you hold down the shutter button it will fire off 2 shots immediately. On my Canon 5D III I use bracket one stop apart and 3 and set to continous shooting it will fire off 3 shots rapidly and I can always shoot again. I can set exposure compensation to -1 which results in -2, -1 and 0 EC and I very seldomly will have blown out essential parts of my photos. I will notice the ISO's chosen form time to time when lighting changes a lot like indoor and I will change aperture to the minimum required for DOF. I usually with my 24-70 set the minimum shutter speed to 1/125 but sometimes to 1/60. I get sharp focused results and good IQ (even from a Canon :)) and I don't have to check histograms and can fire away and I can see my shots on the LCD. I don't really loose any shots this way except where I should use a tripod, but then this is casual shooting and I don't bring a tripod in this case.

Quote


Now, Hans, you are getting a bit tricky. ;D  I mentioned specifically that Nikon is going backwards with regard to the ISO-less nature of their most recent models, including the D800 and the D7100. A consequence of this is that one should try to avoid using ISO 100 when underexposing. You've not only used ISO 100, but given 6 stops of underexposure as well.This is what I wrote earlier, in reply to BJL:


I thought you were referring mainly to the D7100 as the D800 is not that recent :) But anyway look at the attached DxO chart of the D800, D610 and D7100 and notice that the recent D610 is as good and even better than the D800 at the pixel level for DR. And yes there is a little drop from linearity between ISO 100 and 200. Notice also my other posts on Lightoom processing of less than 6 stops and that there is an issue with Lightroom and ACR lifting more than 4 stops in exposure.

Quote


Just to confirm that I am correct in this view that there should be no significant problem in underexposing by 3 stops at ISO 200 with the D7100 (apart from possible banding), I took the following shots just after sunrise this morning, Australian time.

Perhaps I should not have labelled these shots, and should have asked you to guess which was taken at ISO 200. I simply cannot discern any differences at 100% view that would indicate that one of the shots was an underexposure in relation to its ISO setting. Can you?


No, they look pretty much the same to me.

Quote


I should also point out that I have made no adjustments to either of these images apart from raising the exposure of the underexposed shot to +3 in ACR, and apart from letting the default sharpening of 25 apply to both images. The conversions are from the settings that appear in the attached screen capture of the ACR window, with no further adjustment in Photoshop.


Title: Re: Time to look at photos instead
Post by: Hans Kruse on November 27, 2013, 01:31:12 PM
Indeed! I was almost tempted to comment on this debate yet again, but then decided it is far better to sit back and look at those beautiful photographs. It is edifying, though a bit humiliating, to see photographs of scenes that I have also visited (some of those sites in the Dolomites) that are so much better than anything I achieved there.

Thanks very much. But don't forget that I have been visiting the Dolomites two to four times a year since 2009 :) It has been a lot of time and hard work. Now I do 4 workshops per year in the Dolomites which gives me a lot of time to shoot.
Title: Re: Exposure settings with almost "ISO-less" cameras
Post by: Hans Kruse on November 27, 2013, 01:32:34 PM
Ray, I would like to thank you for pointing this out. And Hans, what a fantastic set of images you got there!

Thanks very much!