Digital Camera's Native ISO

[JonathanRimmel]

I have been surfing the web checking out various photography related articles and videos and have come across a few which indicated the ISO's I thought were native to my camera may not be. Perhaps there is already some info pertaining to this on LuLa, if so please point me in the right direction. What my real question is what ISO's are best to use? Should I use 200, 400, 800, 1600, ect or the intermediate ISO's such as 160, 320, 640, 1250, ect. Are there ISO's that give better overall performance and translate to better image quality that others? (obviously higher ISO's usually translate to more noise) Is there perhaps something I am missing here? I am very much interested in this topic as I have to use high ISO's frequently for my work and I would like to get a higher level of image quality than what I am.

[Guillermo Luijk]

There is not a clear response.

To obtain the maximum quality in terms of noise, expose as much as possible your RAW file without clipping the highlights (ETTR), using the lowest real ISO that allows you to achieve that. Only real ISOs are worth using, so intermediate ISOs should be avoided. On the other hand ISOs over ISO1600 don't improve noise on any camera, so they can also be avoided (in fact in Sony sensors, it's hardly worth to go beyond base ISO100). I.e. if you still cannot ETTR at ISO1600, it is not worth pushing ISO any more, just stay at ISO1600 underexposed and push exposure in the RAW developer (that will save highlights at no cost).

When shooting JPEG, ETTR is nonsense, and the only rule is expose correctly your JPEG at the lowest possible ISO. So here ALL ISOs are available (intermediate ISOs or any ultra-high ISO value)

But all that story is about image quality in terms of noise. Imagine that to achieve ETTR in the RAW file (or to expose correctly your JPEG) using the lowest possible ISO, you set such a large aperture that produces insufficient DOF, or such a low shutter speed that you loose sharpness because of motion blur. In those situations you are making your final image worse just because of insisting in reducing noise. Lack of sharpness is worse to an image than some additional noise.

Regards

[jonathanlung]

What Guillermo said. But to add something: I don't think you need to worry about 160 vs. 200 (on the basis of being an "intermediate" ISO value) except in the case of (some?) Canon SLRs that simulate 200, 400, etc. Instead of amplifying the signal, the camera instead applies an adjustment to the meter, so you're not actually shooting at 200, 400, etc. Instead, if you've got one of those cameras, stick to, as Guillermo said, one of the real ISOs (160, 320, etc.) on your camera.

A reference re: simulated intermediate ISOs: http://www.fredmiranda.com/forum/topic/682945/0

[allegretto]

Great info gentlemen

Are all cameras "true" ISO's the multiples of 100 or are some multiples of 160?

[luxborealis]

The other aspect of "correct ISO" to consider is dynamic range - the ISO you choose should also provide the greatest dynamic range. For most cameras, the native ISO does this, and is often 200, but that might be something worth testing or at least checking on a reputable camera testing site.

[Schewe]

Are all cameras "true" ISO's the multiples of 100 or are some multiples of 160?

It all depends on the sensor...Nikon is usually 200, Canon 100. The new Phase One IQ180 backs have an ISO base of 35. So, it all depends...

[jonathanlung]

To the best of my knowledge, Canon is the only company for which (some of) their cameras have settable ISOs that are not "real" (w.r.t changing sensor gain), excluding push/pull ISOs at the extrema.

[ejmartin]

Here is a good discussion:

http://www.naturescapes.net/phpBB3/viewtopic.php?f=2&t=139621

Most of the posts (apart from mine, of course ) in the FM thread linked to above are misinformed.  What Guillermo wrote above is correct, but only for Canon cameras.  Bottom line is that the optimal choice of ISO for a given situation very much depends on the camera model you are using.  The point of the ISO adjustment in raw capture is to optimize the DR of the capture device relative to the scene DR.  One needs to know the DR characteristics of the camera (which can be obtained eg from DxO measurements available at their website DxOmark.com) and apply that to a given shooting situation.

[NikoJorj]

Are all cameras "true" ISO's the multiples of 100 or are some multiples of 160?

I'd say that true ISOs are indicated in the dxomark plots - their way of measuring sensibility according to ISO12232 (and saturation) should effectively defeats the intermediate ISO trick (actually 1/3 over-or underexposing and compensating).

There, you can also see if lowest ISO is actually base ("native") ISO, or overexposed next stop. And you can even see if it's worth to increase ISO (does the DR falls less than 1 EV with 1 stop more ISO?).

[ejmartin]

I'd say that true ISOs are indicated in the dxomark plots - their way of measuring sensibility according to ISO12232 (and saturation) should effectively defeats the intermediate ISO trick (actually 1/3 over-or underexposing and compensating).

DxO misuses the term ISO, which refers to what particular light intensity input yields a particular output brightness.  Since raw data is unrendered, ISO does not apply.  Their measurement determines what particular light intensity input yields a particular raw level in the raw data, which is something different.

[ErikKaffehr]

Hi,

For best image quality you would use the lowest ISO on the camera and expose to the right, avoiding clipping any important highlights.

Reason: you want to collect as many photons as possible.

A photon is a "particle" or "quantum package" of light.

Best regards
Erik

Here is a good discussion:

http://www.naturescapes.net/phpBB3/viewtopic.php?f=2&t=139621

Most of the posts (apart from mine, of course ) in the FM thread linked to above are misinformed.  What Guillermo wrote above is correct, but only for Canon cameras.  Bottom line is that the optimal choice of ISO for a given situation very much depends on the camera model you are using.  The point of the ISO adjustment in raw capture is to optimize the DR of the capture device relative to the scene DR.  One needs to know the DR characteristics of the camera (which can be obtained eg from DxO measurements available at their website DxOmark.com) and apply that to a given shooting situation.

[NikoJorj]

DxO misuses the term ISO, which refers to what particular light intensity input yields a particular output brightness.

From what I understood, DxO adapted the saturation-based technique, which would be described for rendered jpegs in the ISO norm, to the raw output, which is definitely what interest us raw shooters isn't it?

It would seem to me that this misuse (if we conform to the lettre of the norm) is indeed more faithful to the goal of the norm, which is (or at least should be?) to give photographers an indication of sensitivity with the greatest repeatability (hence, no rendered converter-dependant jpeg output shall be used but raw output only) and practical interest (hence the reference point taken on raw saturation, which should primarily base the exposure, rather than an arbitrary gray level).

But yes, I fully agree that all the above is subjective speculation rather than strict ISO norm.


Edit : Sorry I didn't open your naturescape link before, and so have to reckon that my precedent assumption is wrong : Nikon's sensors should have measurement points at intermediate ISO in their DxOMark graphs, and it seems that DxOMark just doesn't care about it.

[Guillermo Luijk]

From what I understood, DxO adapted the saturation-based technique, which would be described for rendered jpegs in the ISO norm, to the raw output, which is definitely what interest us raw shooters isn't it?

Not exactly. Let's differentiate:

• Real ISO: ISO based on an analogue amplification into the camera. They are the only ISOs useful to improve SNR, but just up to a certain value (ISO1600 on most cameras, ISO100 in the recent Sony sensors)
• Effective ISO: ISO based on levels encoded in the RAW file (i.e. the saturation criteria you mention)

DxO measures effective ISOs (the only ones that can be measured from RAW data), not real ISOs (the ones that need to be analysed to find out).

That means Canon 5D's ISO3200 in DxO is double effective ISO than ISO1600. But 5D's ISO3200 is not a real ISO since it is achieved in that camera by multiplying (digital amplification) an ISO1600 shot. So 5D's ISO3200 is completely useless to the RAW shooter; you gain nothing in shadows SNR but can clip one extra stop in the highlights.

An interesting case is the Fuji X100 ISO range:



Unlike it could seem, this is a CLEVER form of ISO. When an ISO superior to ISO1600 is set on this camera, the ISO setting is stored as metadata to let the RAW developer know about it, BUT the shot is internally done at ISO1600. So you can save up to one (ISO3200) or two (ISO6400) stops in the highlights, that other cameras (like the Canon 5D) stupidly clip.

Recent Sony sensors (K5, D7000) could almost work this way from base ISO100. Since there is a negligible SNR improvement from pushing ISO, they could always store the ISO setting as metadata, internally shoot at ISO100, and display a JPEG according to the ISO set by the user but keeping in the RAW file non-clipped highlights. This is what Emil has sometimes refered to as an isoless camera.

Regards

[RFPhotography]

How does what is being said in this thread about ISO square with this article, http://www.digitalphotopro.com/gear/cameras/the-truth-about-digital-iso.html and the referenced video (link in the article)?

[ejmartin]

How does what is being said in this thread about ISO square with this article, http://www.digitalphotopro.com/gear/cameras/the-truth-about-digital-iso.html and the referenced video (link in the article)?

The author of the linked article is very much misinformed, for instance 160 is not the 'native' ISO of the 7D, nor is it 'less noisy' than its neighboring ISO's.  On the 7D, ISO 160 is derived by pulling ISO 200 via digital multiplication of raw values by 0.8 (160/200).  So it is not less noisy, it is the same analog amplification, rather ISO 160 meters 1/3 stop brighter, so leads to 1/3 stop more exposure, so is less noisy because more photons are captured.  The read noise test referred to in the link simply shows that if you take ISO 200 read noise and multiply it by 0.8, it looks 1/3 stop dimmer (duh!) but until this is considered in reference to some signal it doesn't mean much -- indeed, if you maintain the same exposure (Tv and Av) both signal and read noise are multiplied by 0.8 and so S/N remains the same.

Rather than giving you 'the truth about digital ISO', the article is instead promulgating a lot of misinformation 

[ejmartin]

From what I understood, DxO adapted the saturation-based technique, which would be described for rendered jpegs in the ISO norm, to the raw output, which is definitely what interest us raw shooters isn't it?

It would seem to me that this misuse (if we conform to the lettre of the norm) is indeed more faithful to the goal of the norm, which is (or at least should be?) to give photographers an indication of sensitivity with the greatest repeatability (hence, no rendered converter-dependant jpeg output shall be used but raw output only) and practical interest (hence the reference point taken on raw saturation, which should primarily base the exposure, rather than an arbitrary gray level).

But yes, I fully agree that all the above is subjective speculation rather than strict ISO norm.

There are I think a  couple of goals:

1) To know how much headroom you have in the raw data for a given scene illumination (the DxO 'ISO' figure gives you this directly)
2) To know the actual sensitivity of the sensor -- its quantum efficiency, the percentage of incident light that is recorded by the sensor (the DxO 'ISO' figure gives this indirectly, when combined with other of their measurements)

Unfortunately by calling the measurement 'ISO' misleads I think unless one understands what it is for.

[jonathanlung]

Most of the posts (apart from mine, of course ) in the FM thread linked to above are misinformed.

Haha! That was actually the thread I was looking for (but couldn't find after a cursory search)! So it turns out you were the author of the post I was actually trying to cite.

[bjanes]

DxO misuses the term ISO, which refers to what particular light intensity input yields a particular output brightness.  Since raw data is unrendered, ISO does not apply.  Their measurement determines what particular light intensity input yields a particular raw level in the raw data, which is something different.

From what I understood, DxO adapted the saturation-based technique, which would be described for rendered jpegs in the ISO norm, to the raw output, which is definitely what interest us raw shooters isn't it?

It would seem to me that this misuse (if we conform to the lettre of the norm) is indeed more faithful to the goal of the norm, which is (or at least should be?) to give photographers an indication of sensitivity with the greatest repeatability (hence, no rendered converter-dependant jpeg output shall be used but raw output only) and practical interest (hence the reference point taken on raw saturation, which should primarily base the exposure, rather than an arbitrary gray level).

DXO is using the original ISO 12232 saturation standard, where the ISO (S sat) = 78/Hsat. Hsat is the exposure in lux seconds necessary to saturate the sensor. This standard can be applied to exposures with raw files.

The newer ISO 12232:2006 standards also have a saturation standard (SOS) but it applies only to sRGB rendered files and is not of much interest to those of us who shoot raw. The only ISO 12232:2006 standard that can be applied to raw files is the REI (Recommended Exposure Index) which can be anything that the manufacturer wants it to be. My experience with newer Nikon cameras indicates that it is close to the older saturation standard and will give 12.7% saturation when exposed according to the camera light meter. This allows 0.5 EV for highlight headroom.

If one is exposing according to a hand held meter, corrections for light falloff and lens transmission must be made as explained in the DXO post.

Regards,

Bill

[BJL]

DXO is using the original ISO 12232 saturation standard, where the ISO (S sat) = 78/Hsat. Hsat is the exposure in lux seconds necessary to saturate the sensor. This standard can be applied to exposures with raw files.

The newer ISO 12232:2006 standards also have a saturation standard (SOS) ...

A little warning: all of that's talk of "true ISO" seems related to measuring the _lowest_ exposure index at which there is adequate highlight handling. It is thus utterly different that what we meant by the ISO/ASA speed of film (actually, a film+processing combination), which was about the _ highest_ exposure index that gives adequate shadow handling --- very crudely, noise floor about four stops below metered midtones. The two measures are roughly like the lower and upper limits of pull/push processing.

Frankly, I suspect that most of us are far more interested in the shadow handling, noise related upper limit on usable exposure index, which by the way seems to be at 1600 or beyond for all modern SLR-sized sensors. And even higher if you wish to compare noise levels after normalization to some moderate resolution level, say the 8MP used in some DXO measures.

[lowep]

Maybe somebody reading this very interesting thread can help shed some light on a mystery that has been confusing me for some time concerning an ISO bug that pops up when I run .dng images from my old MFDB that is not officially supported by C1 through this program.

The mystery is that differences in MFDB ISO settings (eg 100, 200) are identified and reported by C1 in the metadata of the .dng files but do not show in the visual appearance or histogram of the image when comparing two files of exactly the same subject shot at different iso (that I often get from bracketing the iso in a portrait session), though the differences in ISO is clearly visible when the same files are run through other programs apart from C1 that do support this MFDB. Now what does that mean?

This is a question I have asked before but got no answer. But at the moment I am more concerned with what follows:

Is it that the actual data of raw files shot at different isos is the same, the MFDB only records the iso data as metadata, then the iso data is applied to the raw file automatically when the computer program opens the file - unless as in the case of C1 the program has not been taught how to do that with the metadata from the MFDB?

If this were the case (a big if) then could I stop wasting my time adjusting iso of raw files in an ignorant attempt to catch the ideal combo of maximum data captured with minimal motion blur, and just do this in post, as adjusting iso while shooting would make no difference to the actual data captured by the camera (apart from the camera settings info. stored in the metadata)?

But come to think of it this must be poppycock, since the iso setting does effect the exposure setting (as reflected in the histogram) and surely this must make a real difference to the actual data captured in the raw file as well as the metadata, right.

Maybe this should be posted under beginners questions rather than here?