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Equipment & Techniques => Digital Cameras & Shooting Techniques => Topic started by: maxshafiq@gmail.com on February 01, 2017, 06:30:19 pm

Title: Using Spot Metering and Exposure
Post by: maxshafiq@gmail.com on February 01, 2017, 06:30:19 pm
OK folks I have a spot meter and exposure question.

I have an indoor scene where the sun is shining through the window and hitting some furniture. It casts a nice ray of light across the furniture.
I am trying to shoot the scene where the highlights are not blown out, and yet the darker parts are not lost either.

Here are the scenarios:
1/ If I meter only the highlight (100 ISO, 1/250s, F5.6) and expose for this in camera, the highlights come in nice but everything is dark. When I try and pull the dark in software I see noise.
2/ If I meter the mid tone (100 ISO, 1/15s, F5.6) , then the highlights get blown out.
3/ If I meters the dark areas (100 ISO, 1/4s, F5.6), then highlights still blown.

What technique (spot metering) could I use to get perfect exposure? I am using a Sekonic meter.

Thanks

 
Title: Re: Using Spot Metering and Exposure
Post by: BAB on February 01, 2017, 06:37:04 pm
you need two or three exposures or you need to add fill flash if not you can only expose for your cameras DR and do the rest in post!
Title: Re: Using Spot Metering and Exposure
Post by: maxshafiq@gmail.com on February 01, 2017, 07:11:36 pm
I understand the flash option and let's assume I want to keep it all natural light.

If I go the 2 to 3 readings route, how do I know/calculate which reading to use for the camera? I am assuming I have to calibrate my camera/sekonic meter to each other?

Thx
Title: Re: Using Spot Metering and Exposure
Post by: Slobodan Blagojevic on February 01, 2017, 11:11:50 pm
.... If I go the 2 to 3 readings route, how do I know/calculate which reading to use for the camera?...

If you do 2 or 3 readings, you'd do 2 or 3 exposures at those readings and then combine them in post.

Depending on your camera's dynamic range, you might be able to get away with just one exposure. Your 6 f-stops scenario shouldn't be such a big deal for modern cameras, especially for Sony sensors.
Title: Re: Using Spot Metering and Exposure
Post by: razrblck on February 02, 2017, 02:15:16 am
You can use a reflector to bounce some light in the shadows. If the highlights are too strong and they come from a window, try using a big diffuser (or a white, opaque cloth) to bring them down.

On the exposure side, ETTR might help minimize shadow noise.
Title: Re: Using Spot Metering and Exposure
Post by: stamper on February 02, 2017, 03:49:22 am
When you spot meter for the highlights you have to add +2 EV which will retain detail in the highlights and the shadows will be lighter, which means less noise if you have lighten the shadows further in your photo editor.
Title: Re: Using Spot Metering and Exposure
Post by: BrownBear on February 02, 2017, 05:56:28 am
Quote
...fill flash....

Quote
...reflector....

I've done a lot of this kind of shooting, and those are the quick and easy solutions that just flat work all the time. One big proviso on both- you have to avoid reflections off the window glass if the window is visible, especially if any outdoor scenery is visible through the window.

Another option is to ND gel the window to reduce the intensity of the highlights while "bringing up" the ambient indoor light. (gel sheeting is available from larger photo supply stores).

Speaking of gels, you could also CC gel the windows to match indoor light sources and crank up the indoor light to reduce the difference from outdoor. In architectural shoots an array of larger incandescent light bulbs (to sub for originals in a room) and rolls of CC and ND gels were critical accessories in my location kits.

You might also consider moving the furniture.

Given options on time of shooting, there's one more approach that can be even more pleasing when any outdoor scenery is visible through the window: I also adjust my shooting time until outdoor ambient light is lower and more compatible with indoor light, especially when spill light from windows elsewhere in the room helps illuminate the scene. Best results for me are when there's no more than about 2 stops difference between indoor ambient and window-sourced highlights on your subject.
Title: Re: Using Spot Metering and Exposure
Post by: pegelli on February 02, 2017, 07:02:00 am
2/ If I meter the mid tone (100 ISO, 1/15s, F5.6) , then the highlights get blown out.
jpg or raw? (of film?)
Title: Re: Using Spot Metering and Exposure
Post by: maxshafiq@gmail.com on February 02, 2017, 08:55:08 am
RAW
Title: Re: Using Spot Metering and Exposure
Post by: maxshafiq@gmail.com on February 02, 2017, 08:56:30 am
If you do 2 or 3 readings, you'd do 2 or 3 exposures at those readings and then combine them in post.

Depending on your camera's dynamic range, you might be able to get away with just one exposure. Your 6 f-stops scenario shouldn't be such a big deal for modern cameras, especially for Sony sensors.

Yup Sony sensor...was trying to avoid the HDR route for the time being :-)
Title: Re: Using Spot Metering and Exposure
Post by: pegelli on February 02, 2017, 09:06:49 am
Yup Sony sensor...was trying to avoid the HDR route for the time being :-)
Very strange you can't get 6 stops of DR from the camera, my 2010 Sony does better then that.
How do you determine the highlights are blown out in your second and third scenario? Are you using raw digger or are you judging by the default conversion of your camera in your raw conversion software?
Title: Re: Using Spot Metering and Exposure
Post by: SZRitter on February 02, 2017, 10:01:31 am
Yup Sony sensor...was trying to avoid the HDR route for the time being :-)

HDR isn't the only way to combine images. I sometimes prefer to hand paint in areas, or you can use a technique like luminosity blending. Or any combination of techniques.

For instance, and I am by no means as good at interiors as even a quarter of the guys in here, but to overcome window light vs incandescent, I'll typically make two conversions of the RAW, one aimed at each sources temp, then layer the two conversions in Photoshop. With the image that is my base (i.e. predominant light source) on the bottom, I'll mask out the other layer and start painting it back in. It's time consuming, but it has worked for me. Obviously, doing it at the time of the shoot would be better, but not all of us have that luxury.
Title: Re: Using Spot Metering and Exposure
Post by: scyth on February 02, 2017, 10:17:05 am
OK folks I have a spot meter and exposure question.

I have an indoor scene where the sun is shining through the window and hitting some furniture. It casts a nice ray of light across the furniture.
I am trying to shoot the scene where the highlights are not blown out, and yet the darker parts are not lost either.

Here are the scenarios:
1/ If I meter only the highlight (100 ISO, 1/250s, F5.6) and expose for this in camera, the highlights come in nice but everything is dark. When I try and pull the dark in software I see noise.
2/ If I meter the mid tone (100 ISO, 1/15s, F5.6) , then the highlights get blown out.
3/ If I meters the dark areas (100 ISO, 1/4s, F5.6), then highlights still blown.

What technique (spot metering) could I use to get perfect exposure? I am using a Sekonic meter.

Thanks

use camera's spotmeter and use rawdigger to find out how your camera's spot-metering is calibrated (rawdigger website has article with instructions)... then expose so that important lights where you still want details will be within say 1/2 EV to clipping in raw channel (most probably greens based on your illumination)...  you absolutely do not need to bother with Seconic, albeit 1 degree spot metering is nice (if your model has that)
Title: Re: Using Spot Metering and Exposure
Post by: maxshafiq@gmail.com on February 02, 2017, 10:58:45 am
I've done a lot of this kind of shooting, and those are the quick and easy solutions that just flat work all the time. One big proviso on both- you have to avoid reflections off the window glass if the window is visible, especially if any outdoor scenery is visible through the window.

Another option is to ND gel the window to reduce the intensity of the highlights while "bringing up" the ambient indoor light. (gel sheeting is available from larger photo supply stores).

Speaking of gels, you could also CC gel the windows to match indoor light sources and crank up the indoor light to reduce the difference from outdoor. In architectural shoots an array of larger incandescent light bulbs (to sub for originals in a room) and rolls of CC and ND gels were critical accessories in my location kits.

You might also consider moving the furniture.

Given options on time of shooting, there's one more approach that can be even more pleasing when any outdoor scenery is visible through the window: I also adjust my shooting time until outdoor ambient light is lower and more compatible with indoor light, especially when spill light from windows elsewhere in the room helps illuminate the scene. Best results for me are when there's no more than about 2 stops difference between indoor ambient and window-sourced highlights on your subject.

Some interesting techniques using GELS!! that I had not thought off :-)

Moving the furniture around to suite the style I am looking for is always an option.

Thanks
Title: Re: Using Spot Metering and Exposure
Post by: maxshafiq@gmail.com on February 02, 2017, 11:02:18 am
Very strange you can't get 6 stops of DR from the camera, my 2010 Sony does better then that.
How do you determine the highlights are blown out in your second and third scenario? Are you using raw digger or are you judging by the default conversion of your camera in your raw conversion software?

Just by looking at them after default conversion and zooming in. There is nothing but white...no data.
Title: Re: Using Spot Metering and Exposure
Post by: scyth on February 02, 2017, 11:11:04 am
Just by looking at them after default conversion and zooming in. There is nothing but white...no data.

dear, you need to use tools that can show clipping in raw - rawdigger, fastrawviewer or converters that can do the same like rawtherapee or rpp
Title: Re: Using Spot Metering and Exposure
Post by: Slobodan Blagojevic on February 02, 2017, 11:13:55 am
Just by looking at them after default conversion and zooming in. There is nothing but white...no data.

Just looking at them is not good enough. You would be surprised just how much data is still present in the area that looks totally white.
Title: Re: Using Spot Metering and Exposure
Post by: SZRitter on February 02, 2017, 11:19:15 am
Just by looking at them after default conversion and zooming in. There is nothing but white...no data.

Just to back up the other two who posted before me, on my main digital camera, I know that right as my white clips, I still have one stop I can bump up and recover data while maintaining color accuracy. This will vary by camera, so you just have to test.
Title: Re: Using Spot Metering and Exposure
Post by: pegelli on February 02, 2017, 11:42:39 am
Just by looking at them after default conversion and zooming in. There is nothing but white...no data.
I agree with the others before, white at default conversion doesn't mean there is no data. It's very likely your raw converter has only pushed that data over the edge in its default jpg conversion. Probably another example of "it's not the tool, but the ......"  ;)
Title: Re: Using Spot Metering and Exposure
Post by: EricV on February 02, 2017, 12:52:42 pm
If you cannot use your meter or camera histogram to find the right exposure, just take several bracketed exposures and figure out later which one is right.  Your scene is not moving, and there is no special prize for capturing the image in a single perfectly calculated exposure. 

In cases where the brightness range is extreme, there may be no single exposure which keeps highlights below clipping and simultaneously provides enough light in the shadows for adequate post-processing.  In that case, you will have to combine multiple exposures in post-processing.  This will let you do what you have already attempted (brighten the shadows), without the noise penalty.
Title: Re: Using Spot Metering and Exposure
Post by: BobShaw on February 02, 2017, 07:49:52 pm
When you spot meter for the highlights you have to add +2 EV which will retain detail in the highlights and the shadows will be lighter, which means less noise if you have lighten the shadows further in your photo editor.
The best answer here by a country mile. Using a reflector is also a good idea.
In short, the highlights are at the right end of the histogram so two stops over the reading taken should ensure they are not blown.

You are probably confusing people with your question as you are asking about spot metering which most will take to mean the Spot metering mode in your camera meter. However you then mention Sekonic so I take it that you are taking an INCIDENT AMBIENT light measurement at the subject using a hand held meter., which is much better anyway.
In either case this is a Photography 101 question and you don't need software to get it right.
Title: Re: Using Spot Metering and Exposure
Post by: mouse on February 02, 2017, 07:53:24 pm
The problem you pose is a classic example of a situation which just begs for multiple (maybe only 2) exposures and HDR blending in post processing.  Why are you so adverse to this solution?
Title: Re: Using Spot Metering and Exposure
Post by: BAB on February 02, 2017, 08:13:41 pm
You don't need to do HDR which by the way the is easy you should however do exposure blending with luminosity slices or just blend the shawdow with the mid tones and highlights it's also very easy non destructive and produces the best results.
Most interior shots even if you only make one exposure need blending at the very least. But as you can gather from all OP the hardest way to get the best results of an interior shot with mixed lighting, strong highlights especially from sunlight coming through an in filtered window is with one exposure your creating a monumental amount of post work.


At this point I would suggest you search you tube there are a few great videos on how to do, also luminosity blending interior shots.


Many pros shoot ten images filling in or highlighting certain important features or areas the your camera no matter what exposure you choose won't be lit right. And yes using gels, shoring the interior during the day and then not moving the camera and waiting four hours for the right ambient light to make the outdoor shot thru the window is all part of the job!


Sorry
Title: Re: Using Spot Metering and Exposure
Post by: BrownBear on February 03, 2017, 09:11:50 am
Some interesting techniques using GELS!! that I had not thought off :-)

Moving the furniture around to suite the style I am looking for is always an option.

Thanks


Our manta for commercial shooting was pretty straight forward:

"Computer time is unpaid. Better to shoot it right in the first place and move on to the next paycheck."
Title: Re: Using Spot Metering and Exposure
Post by: BobShaw on February 03, 2017, 06:34:34 pm
The problem you pose is a classic example of a situation which just begs for multiple (maybe only 2) exposures and HDR blending in post processing.  Why are you so adverse to this solution?
There are only 6 stops of range. Any camera made this decade should do that.
The question was about selecting exposure.
Title: Re: Using Spot Metering and Exposure
Post by: KMRennie on February 05, 2017, 11:36:51 am
I have a Sekonic L758DR and a Nikon D810. Having calibrated the meter to the camera I would spot meter the brightest point and open up by 3.5 stops. This gives me a file where the brightest points are just below clipping verified using RawDigger. From your measurements 6 stops below brightest should still be fairly noise free. Without calibrating the meter to the camera and using RawDigger or similar you are unlikely to arrive at an exposure that is just below clipping without a great deal of trial and error or a bit of luck. To answer which exposure, for me it would be the one that preserves the highlights. A bit of fill, either with a reflector or a bit of flash may give you a nicer looking file without PP but I would be surprised if you couldn't get a nice file with a proper ETTR exposure. Hope this helps. Ken
Title: Re: Using Spot Metering and Exposure
Post by: BobShaw on February 05, 2017, 09:30:19 pm
I have a Sekonic L758DR and a Nikon D810. Having calibrated the meter to the camera
Why. One is an incident meter and one is a reflected meter.
Title: Re: Using Spot Metering and Exposure
Post by: Martin Kristiansen on February 06, 2017, 05:57:51 am
Why. One is an incident meter and one is a reflected meter.

I am pretty sure the Sekonic is a dual incident and reflectance meter.  I have an older Sekonic and it seems much the same as the one quoted here.

I am not understanding the backwards and forwards on this thread. It's very simple. If you are using the 1 degree spot measure the brightest area that is causing all the concern. Measure the darkest area you want to retain some detail. How many stops difference do you have. If it is 6 stops I don't see a problem. If it is substantially more shoot an extra frame either a darker one to hold the highlights or a lighter one to hold the shadows. Many ways to combine in post.

Personally I would take an incident reading to give me an average exposure and then measure the highlights and see how many stops over it was. Three or less I would shoot the incident reading. Much more I would close down one stop and two stops using either shutter speed or ISO. It's not common to combine incident and reflective readings to build up a picture of the scene but we used to do it in film days on occasion. Easier than hunting that midddle grey if you didn't have a grey card.
Title: Re: Using Spot Metering and Exposure
Post by: KMRennie on February 06, 2017, 10:46:30 am
The L758DR  has both spot and incident meters. In this instance I would only use the spot meter but everyone to their own. Ken
Title: Re: Using Spot Metering and Exposure
Post by: BobShaw on February 06, 2017, 04:50:21 pm
Incident is measured at the subject position of light hitting the subject. It does not depend on the colour of the subject and is therefore accurate.
Reflected is measured at the camera position of light reflected from the subject. The reading therefore varies depending on the colour of the subject as well as the light hitting it.
It may be possible to take an incident reading at the camera or a reflected reading at the subject, but neither would be correct as the collection area is different.
Title: Re: Using Spot Metering and Exposure
Post by: BrownBear on February 06, 2017, 08:53:54 pm
We still have several Sekonic L758DR and more of its predecessors dating back over the decades. It's most definitely both a spot and incident meter. Because we used a lot of fill light balanced with ambient, I can count on one hand the number of times I used the spot meter indoors as proposed by the OP in this thread.

The combo of incident and spot makes for a whale of a light meter, saving us a whole lot of time onsite and on the computer, making money for us all the while. When you're gelling strobes as well as adjusting balance with ambient, they're priceless. 
Title: Re: Using Spot Metering and Exposure
Post by: SZRitter on February 07, 2017, 09:11:19 am
I wish they hadn't stopped the production of the 558R (I think that is the right number). I have one, which is also incident and spot meter, and it is amazing in situations where you want to see individual values. I would get a 758, but they seem insanely expensive compared to what the 558R retailed for.  :'(

To the OP: You should do a bit of homework with the spot meter and your camera(s). Personally, I would find something, with a bit of detail, and a bit of color. Spot meter that (so it's middle gray), then take exposures adjusting your camera one stop at a time until it's blown out. count the distance in stops between the initial reading and the last spot you preserved detail to your liking, and then when you are in the field, you'll have an idea of what you can expose for and retain highlights. Basically, you found (and I may have the number wrong) Zone 0 for your camera.
Title: Re: Using Spot Metering and Exposure
Post by: stamper on February 07, 2017, 09:48:29 am
I have been into photography for 15 years and I have never seen anyone using one. I was under the impression that they have little relevance to digital photography. Obviously some enjoy using one of them but are they really useful?
Title: Re: Using Spot Metering and Exposure
Post by: BrownBear on February 07, 2017, 11:12:28 am
Obviously some enjoy using one of them but are they really useful?

Priceless in the settings I described. If you don't have one when adjusting lighting ratios and balancing lights and light sources for indoor shooting, might as well take up golf. The OP is trying to set up an indoor shot.
Title: Re: Using Spot Metering and Exposure
Post by: BrownBear on February 11, 2017, 09:42:44 am
BTW-

If you want your mind thoroughly blown on lighting (and the use of incident meters), both natural and artificial as well as their mix, zero in on the teachings of the late Dean Collins.  I know of NO ONE before or since who understood and used light, subject form, tonality and texture so well.  I had the good fortune to work with him a couple of times, as well as attend a couple of lectures and a 2-day workshop.  All these years later my mind still reels at his brilliance.  Best place to start is with his DVD's, most notably this set (https://www.software-cinema.com/training/photography/dean-collins/4/the-best-of-dean-collins-on-lighting). Watch #4 first, or he'll submerge you like a tidal wave with all the info in the others. Here (http://strobist.blogspot.com/2006/08/review-best-of-dean-collins-on.html) is a good review at Strobist.
Title: Re: Using Spot Metering and Exposure
Post by: Doug Gray on March 26, 2017, 02:27:21 pm
dear, you need to use tools that can show clipping in raw - rawdigger, fastrawviewer or converters that can do the same like rawtherapee or rpp

^This is good advice. There is a great deal of margin built in to digital cameras. It's there to allow compression at the high tone end to simulate film. Digital cameras get better and better as the exposure increases - until they clip, then it's a hard clip. Very unlike film. These tools let you characterize it and know what you can get away with.

You can also experiment by taking various overexposures and dropping the exposure slider up to 3 or 4 ev or so in the RAW conversion. If the sensors are hard clipping you will see that happening and won't be able to recover dropping the slider any further.
Title: Re: Using Spot Metering and Exposure
Post by: Jim Metzger on March 30, 2017, 10:10:35 am
I would also like to know from the OP if you are using base ISO. The DR of the sensor drops as you increase ISO and makes it more difficult to extract all the info.

I would also look at noise reduction in just the shadow areas. What is your intended output? Small reproductions for web and actual prints tend to show much smoother output than zooming in to 100% or more of the RAW image at the computer.

I also recommend calibrating your camera with a Colorchecker Passport and making sure you get the white balance right (or at least close) in camera. My experience is the more you manipulate the file, even RAW, the less "headroom" you have to work with.
Title: Re: Using Spot Metering and Exposure
Post by: Doug Gray on April 02, 2017, 01:21:01 pm
Know your camera and shoot RAW. If the scene has a wide dynamic range set exposure using spot and add enough EVs to maximize light collection without sensor clipping. This is fast and isn't hard to do with a bit of initial experimentation on any new camera.
Title: Re: Using Spot Metering and Exposure
Post by: uuglypher on May 25, 2017, 07:53:27 pm
Several responders have approached this alternative using the full capabilities of raw image data capture.

If you have determined how much raw-accessible dynamic range your camera has beyond the point at which the jpeg histogram frame indicates clipping (varies camera-to-camera, but usually is between one and three full stops of extra raw-accessible DR (ERADR)  you may easily be able to avoid HDR.

Using the sensor's full available raw dynamic range, simply expose for the brightest possible image without clipping highlights, but coming as close to doing so as possible. The thumbnails will appear badly overexposed (as they WOULD be if they were jpegs) but in your raw converter will be easily tonally normalized by moving the Exposure slider to the left. A win:win technique: capture the absolute least possible noise, image data of the highest possible Signal-to-Noise ratio, and capture image data with the greatest potential breadth of creative and artistic interpretation...from high key to low key, and every variation in between.   Every brightness level in the scene is captured with the highest number of photons possible...from the brightest highlight detail to the darkest of shadow details, and delivers the maximum tonal and color spectra permitted by the bit depth of image file.

Some call it a "digital negative" but it is much, much more than that. It is analogous to an unlimited collection of unprocessed latent images.

It's a real shame the camera manufacturers don't provide an in camera raw histogram! But there surely would be a prohibitive per-unit cost, given the variation in ERADR that occurs from sensor to sensor. So it's up to you to determine, by test exposures, the actual raw-accessible DR of your camera.

But give it a go: it's well worth the effort!
You'll  like it.

Best regards,

Dave


Title: Re: Using Spot Metering and Exposure
Post by: uuglypher on May 27, 2017, 12:03:52 am
scyth
blagojevic
SZRitter
pegelli
KMRennie (mentions ETTR
Doug Gray
Jim Metzger..( mentions loss of DR with incr ISO)

Above are seven responders to the OP who indicate awareness of the "headroom" that digital camera sensors provide that  can be  "useful for recovery of some cases of blown highlight detail".

The remarkable aspect of "headroom" is that, even among cameras of the same make and model, that headroom can vary.  Three cameras of the same brand and model were tested: one had an extra  2/3 stop, the next one and 1/3 stops, and the third  had two and 2/3 stops of extra DR ....  indicating that each and every camera ought be tested for its actual raw-accessible DR.!

If any of the responders above have done such testing of their own camera to determine how much extra raw-accessible DR it has beyond the point that the JPEG clipping warning /blinkies is set off, I'm hoping they would report their results at base ISO. 

The loss of DR with increasing ISO is extremely variable. I have one camera with extra DR of one and 1/3 stops at ISO 100 that loses its first 1/3 stop at ISO 400, and another with one and 1/3 stop at ISO 100 that waits until ISO 1600 before it loses its first 1/3 stop of DR.

y'gotta test your camera!

Dave
Title: Re: Using Spot Metering and Exposure
Post by: Guillermo Luijk on May 28, 2017, 04:19:52 am
The remarkable aspect of "headroom" is that, even among cameras of the same make and model, that headroom can vary.  Three cameras of the same brand and model were tested: one had an extra  2/3 stop, the next one and 1/3 stops, and the third  had two and 2/3 stops of extra DR ....  indicating that each and every camera ought be tested for its actual raw-accessible DR.!

If any of the responders above have done such testing of their own camera to determine how much extra raw-accessible DR it has beyond the point that the JPEG clipping warning /blinkies is set off, I'm hoping they would report their results at base ISO.

I doubt such a variance exists. Do you have RAW files proving this for the same exact scene?.

RAW highlight headroom isn't such a simple concept as referred to in this thread since RAW files contain three colour channels which can clip individually (generally G is the first to fall). How they clip and how this clipping correlates to camera light metering, heavily depends on the kind of subject/light present in the scene.

In such a multichannel/multisubject/multisprectrum environment it's nonsense stating "this camera has 2,5 stops of RAW highlight headroom". Just spot meter over any other scene and the figure will vary because of the changing variables.

If the RAW highlight headroom is evaluated against camera JPEG instead of camera metering, variance in determining it increases exponentially because of white balance, tone curve, saturation,... and any other process involved in building the JPEG file than can clip some channel.

I did some spot metering tests on lab (uniform white surface under tungsten light) and real world scenes for the Canon 350D and 5D, and got these very different highlight RAW headrooms:

http://www.guillermoluijk.com/article/spot/index.htm

Lab 350D:
(http://www.guillermoluijk.com/article/spot/histomax350d.gif)

Lab 5D:
(http://www.guillermoluijk.com/article/spot/histomax5d.gif)

Real world scenes 5D:
(http://www.guillermoluijk.com/article/spot/nube.jpg)

(http://www.guillermoluijk.com/article/spot/nube.gif)


(http://www.guillermoluijk.com/article/spot/ventana.jpg)

(http://www.guillermoluijk.com/article/spot/ventana.gif)

While the lab test over a uniform surface and tungsten light provided 3,5 stops of headroom, this real world scene has 1 whole stop less highlight headroom, surely because the tiny dark areas on the wall fooled camera spot metering. More examples in the provided link.

So forget to accurately characterize your camera's highlight headroom and learn by practice how your camera's JPEG correlate to RAW clipping under different situations. UniWB may help.

Asking camera manufacturers for RAW histograms has demonstrated to be wasted time. Those interested in such things must be considered niche nerds by those splendid marketing departments.

Regards
Title: Re: Using Spot Metering and Exposure
Post by: bjanes on May 28, 2017, 09:27:16 am
The loss of DR with increasing ISO is extremely variable. I have one camera with extra DR of one and 1/3 stops at ISO 100 that loses its first 1/3 stop at ISO 400, and another with one and 1/3 stop at ISO 100 that waits until ISO 1600 before it loses its first 1/3 stop of DR.

y'gotta test your camera!

Generally speaking, with an ISO less camera (such as the Nikon D810 and other cameras using recent Sony sensors), one loses 1 stop of DR for each doubling of ISO. This is simple physics. In doubling of ISO, the amplifier gain is doubled and the analog to digital converter (ADC) overflows one stop earlier, halving the DR. The relationship between ISO and DR is shown graphically for many cameras on Bill Claff's Photographic DR page (http://photonstophotos.net/Charts/PDR.htm). Examples are shown below in the attachment. The interval between x-axis markers is 2.5 f/stops. For the D810 increasing the ISO by 25 stops from ISO 100 loses 2 stops of DR and the curve is nearly linear.

Many cameras not using Sony sensors have the DR at low ISO limited by high read noise, but the RN drops as ISO is increased and reaches a minimum at higher ISO. For the Canon EOS 1DX, DR hardly changes as the ISO is increased by 2.5 stops from ISO 100, but at ISOs above about 800, RN reaches a minimum and the curve becomes linear and 1 stop of DR is lost for each doubling of ISO.

The Sony 7RM2 uses Aptina variable gain technology, and the DR plot shows discontinuities when the gain is changed, but the 1 stop loss of DR for each doubling of ISO generally holds.

I find it hard to believe that any camera can go from ISO 100 to 1600 with only 1/3 stop loss of DR. What camera is that?

Regards,

Bill
Title: Re: Using Spot Metering and Exposure
Post by: uuglypher on May 28, 2017, 03:25:21 pm
The camera that looses 1/3 stop of DR BETWEEN ISO 800 and ISO 1600 is a sony a99.  Of course, one ought use the lowesst ISO possible, but should also depend on specific exposure tests at different ZISOs to determine DR loss, NOT theoretical predictions of a linear rate of loss. And this inconsistent rate of DR LOSS has been demonstrated not only in some Sony's , but also some Nikons , some Canons, a Pentax, and a Fuji,

My best recommendation, if one is seriously interested,  is to test each individual camera (sensor) yourself. It would be a shame if one consistently were to leave one...or two...or possibly three stops (i think that would be a record) of DR "sitting on the table unused...and thereby forfeiting significant image data quality (how much dependent on the bit-depth of the data!). The greatest unused DR I've found was Two and 2/3 stops in a Pentax (model?) and in a Nikon d800. I also tested a d800 that had only 2/3 stop of unused DR.

Which, incidentally, explains my surprise when I was told quite explicitly by dxO, that they test one ( count 'em , 1) camera of each brand and model for their vaunted test reports.

Curious, eh?

Best regards,
Dave
Title: Re: Using Spot Metering and Exposure
Post by: bjanes on May 28, 2017, 03:55:40 pm
The camera that looses 1/3 stop of DR BETWEEN ISO 800 and ISO 1600 is a sony a99.  Of course, one ought use the lowesst ISO possible, but should also depend on specific exposure tests at different ZISOs to determine DR loss, NOT theoretical predictions of a linear rate of loss. And this inconsistent rate of DR LOSS has been demonstrated not only in some Sony's , but also some Nikons , some Canons, a Pentax, and a Fuji,

Dave,
According to Bill Claff's Chart (http://photonstophotos.net/Charts/PDR.htm#Sony%20SLT-A99V) for the A99V, the DR at ISO 400 is 9.19 stops and the DR at ISO 1600 is 7.39 stops. Two doublings of ISO results in slightly less than 2 stops of DR. Where do you get your figures?

Regards,

Bill
Title: Re: Using Spot Metering and Exposure
Post by: uuglypher on May 28, 2017, 06:54:23 pm
I have seen the various charts and "official ratings" , but have found they vary in minor to significant degrees from what one will find by exposure tests on one's own individual camera or cameras. I'll admit that  It seemed puzzling until I was made aware of the phenomena of "process variance /process excursions" and subsequent "performance variance" that have plagued the semiconductor production iindustry from the time of Shockley's first publication on the topic in, as I recall, 1960 or '61 up to the present day. A study of the history of those phenomena disabused me of the idea that our cameras' image sensors were highly refined devices that deliver Dynamic Range within strictly defined limits.

Anyone willing to personally test the raw-accessible dynamic range of a number of cameras, including multiple cameras of the same brand and model will discover, as a number of us have, that there is considerable variation in the upper limit of DR delivered by ostensibly identical sensors. The camera manufacturers assure that their sensors will deliver at least the DR necessary to at least blow out highlights of JPEG files, but seem uninterested in how much more so-called "headroom" their sensors will deliver. That, of course, makes providing an in-camera raw histogram a pricy option evidently not-to-be-considered, what with how it would boost the per-unit price and all!

What amazes me is that so few have actually done the due diligence of conscientiously testing their cameras for the actual raw-accessible DR they can deliver. It's not hard. certainly not beyond the capabilities of those likely to be participating in these fora. They just need to do it.  Testing my own cameras and those of friends, and participants in classes, courses,  and workshops, I've personally seen a range of of extra raw-accessible DR of from 2/3 stop to two and 2/3 stops, with the great majority of cameras having at least one full stop of unused DR. There are rumors of some cameras with three stop or more of unused DR.

But even one full stop of extra DR is nothing to sneeze at. Failure to use it in raw image data capture results in forfeiture of up to 50% of tonal and chromatic spectra..or more, depending on scene DR. You all should be able to figure out what that amounts to depending upon 12-bit-depth vs. 14 bit-depth.

Best regards,
Dave
Title: Re: Using Spot Metering and Exposure
Post by: bjanes on May 29, 2017, 09:18:57 am
Anyone willing to personally test the raw-accessible dynamic range of a number of cameras, including multiple cameras of the same brand and model will discover, as a number of us have, that there is considerable variation in the upper limit of DR delivered by ostensibly identical sensors.

Bill Claff has addressed the possible variation in sensor performance of cameras of the same make and model through a collaboration where users around the world take a series of paired pictures according to his protocol and send them in to him for analysis using his custom automated protocol. When I first got my Nikon D3, I performed a series of tests as outlined by Roger Clark (http://www.clarkvision.com/reviews/evaluation-1d2/index.html) to determine the DR of the sensor and also sent files to Bill Claff. My results were quite close to his and those published for the D3 by Peter Facey (http://www.brisk.org.uk/photog/d3index.html) and others. No significant variation here. I have also performed a similar analysis of my D800e and my results agree with Bill's and the DXO results.
 

What amazes me is that so few have actually done the due diligence of conscientiously testing their cameras for the actual raw-accessible DR they can deliver. It's not hard. certainly not beyond the capabilities of those likely to be participating in these fora. They just need to do it.  Testing my own cameras and those of friends, and participants in classes, courses,  and workshops, I've personally seen a range of of extra raw-accessible DR of from 2/3 stop to two and 2/3 stops, with the great majority of cameras having at least one full stop of unused DR. There are rumors of some cameras with three stop or more of unused DR.

If you look at the linked sites by Roger and Peter, you will see that the methods are rather laborious and not at all as simple as you describe. You are new to this forum and do not have a track record by which we can judge your qualifications. Why don't you tell us your testing protocol and publish your raw data. Until then, I will give little credence to your posts, which are out of the mainstream here.

Regards,

Bill
Title: Re: Using Spot Metering and Exposure
Post by: uuglypher on May 29, 2017, 02:47:48 pm
...to get you started:

http://www.uglyhedgehog.com/t-262533-1.html

Dave
Title: Re: Using Spot Metering and Exposure
Post by: bclaff on May 29, 2017, 03:16:18 pm
Bill Claff has addressed the possible variation in sensor performance of cameras of the same make and model through a collaboration where users around the world take a series of paired pictures according to his protocol and send them in to him for analysis using his custom automated protocol. When I first got my Nikon D3, I performed a series of tests as outlined by Roger Clark (http://www.clarkvision.com/reviews/evaluation-1d2/index.html) to determine the DR of the sensor and also sent files to Bill Claff. My results were quite close to his and those published for the D3 by Peter Facey (http://www.brisk.org.uk/photog/d3index.html) and others. No significant variation here. I have also performed a similar analysis of my D800e and my results agree with Bill's and the DXO results.
 

If you look at the linked sites by Roger and Peter, you will see that the methods are rather laborious and not at all as simple as you describe. You are new to this forum and do not have a track record by which we can judge your qualifications. Why don't you tell us your testing protocol and publish your raw data. Until then, I will give little credence to your posts, which are out of the mainstream here.

Regards,

Bill
Bill, thanks for your help over the years in contributing files.
FWIW, I don't use image pairs. Image pairs can be used to remove Fixed Pattern Noise (FPN) to get more accurate results. There are others ways to accomplish this.
In any case, I'm more focus on what the photographer will actually observe so in most of my tests I consciously don't remove FPN because it will be in the image you take.

Regards,
Bill
Title: Re: Using Spot Metering and Exposure
Post by: uuglypher on May 29, 2017, 04:16:07 pm
Hi, Bill,
You asked for a description of my test exposure system. Have you tried what I described in the link provided? It certainly is not a complex procedure.

Attached are some examples of use of the extra raw-accessible DR determined by the described procedure.

It is a system that I and others have found to work well.

If you are satisfied that you are using your camera's full complement of extra raw-accessible DR, I'd be the last to suggest you change what you are doing.

If you do give it a try, I'd be interested in your results .

Best regards,
Dave
Title: Re: Using Spot Metering and Exposure
Post by: Guillermo Luijk on May 29, 2017, 05:14:00 pm
Your procedure depends on JPEG highlight clipping, which depends on the white balance set and other adjustments (saturation, colour space,...), so it will provide a different highlight headroom everytime is tested.

Moreover ACR is a fantastic RAW developer but a poor RAW analyser, so you can't trust its highlight warning be an accurate RAW clipping warning tool. Use DCRAW or RAW Digger instead.

Regards
Title: Re: Using Spot Metering and Exposure
Post by: bjanes on May 29, 2017, 05:58:15 pm
Bill, thanks for your help over the years in contributing files.
FWIW, I don't use image pairs. Image pairs can be used to remove Fixed Pattern Noise (FPN) to get more accurate results. There are others ways to accomplish this.
In any case, I'm more focus on what the photographer will actually observe so in most of my tests I consciously don't remove FPN because it will be in the image you take.

Regards,
Bill

Bill,

Since I haven't updated my camera since getting the D800e, it has been quite some time since I contributed files, so I didn't remember exactly what I contributed, but I was happy to contribute to your valuable project. I plan to update from the D800e to the D820 or whatever and will, of course, contribute to your project.

Since you have entered into the thread, have you noted much variation in DR among cameras of the same make and model?

Regards,

Bill 
Title: Re: Using Spot Metering and Exposure
Post by: bjanes on May 29, 2017, 06:06:19 pm
Your procedure depends on JPEG highlight clipping, which depends on the white balance set and other adjustments (saturation, colour space,...), so it will provide a different highlight headroom everytime is tested.

Moreover ACR is a fantastic RAW developer but a poor RAW analyser, so you can't trust its highlight warning be an accurate RAW clipping warning tool. Use DCRAW or RAW Digger instead.

+1.

As Guillermo knows, ACR uses a baseline exposure offset that has to be taken into account and PV2012 applies a tone curve and automatic highlight correction. I have found that if one uses PV2010 and a linear tone curve (sliders in main panel set to zero) I can get an approximate estimate of highlight clipping. Of course, I use Rawdigger to evaluate my raw files.

Regards,

Bill
Title: Re: Using Spot Metering and Exposure
Post by: uuglypher on May 29, 2017, 11:03:34 pm
"Your procedure depends on JPEG highlight clipping, which depends on the white balance set and other adjustments (saturation, colour space,...), so it will provide a different highlight headroom everytime is tested."
"...a different highlight headroom every time is tested" ???

Not so. In fact,  multiple re-testing of the same camera/sensor at the same ISO yields a great majority of identical results, only rarely evidencing 1/3 stop variation (usually the result of misinterpreting a specular highlight spike antecedent to actual clipping. The key is that the continuous test exposure series carries both the point of jpeg clipping, and includes enough exposure to cover the onset of raw image data clipping.
The testing procedure is straightforward and simple to understand.  The results are easily recognized. Above all, it is an easily performed process and the results obtained are reliable and are reliably employed  in routine use.

Theorizing about it is no match for understanding the process, trying it fairly, and putting it into practice.

Best regards,
Dave
Title: Re: Using Spot Metering and Exposure
Post by: uuglypher on May 30, 2017, 01:25:20 am
".

+1.

As Guillermo knows, ACR uses a baseline exposure offset that has to be taken into account and PV2012 applies a tone curve and automatic highlight correction. I have found that if one uses PV2010 and a linear tone curve (sliders in main panel set to zero) I can get an approximate estimate of highlight clipping. Of course, I use Rawdigger to evaluate my raw files."

Bill,
Thank you for your comments. Please see my response to Guillermo's comments .
Neither I nor others using similar procedures as that which I've described are, not in the slightest, given to repeatetitive use of what Guillermo suggests are practices predicted to yield unpredictable results.
The practices I summarized in the link that I provided are easy to repeat and yield useful results as the examples I provided illustrate.

best regards,
Dave
Title: Re: Using Spot Metering and Exposure
Post by: Bart_van_der_Wolf on May 30, 2017, 10:57:17 am
Theorizing about it is no match for understanding the process, trying it fairly, and putting it into practice.

Hi,

It seems you are preaching to a choir of people who know what Dynamic Range means.

What you seem to be advocating is overexposure, and reliance on (Lightroom's) highlight reconstruction ability (which usually works best with achromatic highlights). However, Camera histograms/blinkies show the amount of clipping after White/Blackpoint correction, White Balancing,  and gamma adjustment, yet the Raw data channels may clip at different exposure levels. So OOC JPEG histograms or histograms from e.g. Lightroom's Process 2012 offer poor general guidelines for true DR and Raw data clipping. This is usually understood by the choir, that's why many of them use RawDigger or Fast Raw Converter which do allow to see Raw clipping. A Raw converter like RawTherapee offers more control over the Raw channel data scaling before demosiacing as well as tone-mapping after demosaicing.

Having said that, if timing and storage space allows, it never hurts to use an exposure bracketing strategy if one can, to either pick the best exposed Raw data file, or use an over-exposed shot for improved shadow definition (in Exposure Fusion together with a highlight preserving shot, or by attempted highlight reconstruction of the overexposed/clipped Raw data).

Cheers,
Bart
Title: Re: Using Spot Metering and Exposure
Post by: uuglypher on May 30, 2017, 11:47:52 am
Hi, Bart,
Not preaching, just offering a practical and simpler alternative that usually requires but a single exposure.
And I am most definitely not advocating "overexposure" , rather accepting the premise that proper raw image data exposure is based on making the brightest possible exposure without clipping highlights, but coming as close thereto as possible, which, incidentally, requires using the entire DR...which, incidentally, requires that maximum available DR for each camera be individually determined at the most frequently used ISOs. Using the lowest possible ISO commensurate with intended image features is always recommended.

Also, to similarly characterize the live jpeg-adjusted histograms of all brands of cameras is complicated by the evident variety of the different manufacturers algorithms used to produce what each considers the "ideal" JPEG.

Again, the system I (and a number of others) use is offered for the interested to try, certainly not by way of proselytizing.

Take it or leave it, but a number of us think that not to give it a rigorous and fair try would be, indeed, regrettable.

Best regards,

Dave
Title: Re: Using Spot Metering and Exposure
Post by: BrownBear on May 30, 2017, 01:05:43 pm
Reeling this back to the original indoor setting involving multiple light sources and a handheld Sekonic meter, there's a much easier way to reach the Valhalla of perfect exposure.

Switch that little Sekonic gem to incident metering. Meter the two light sources. Add a tiny little splash of fill light to spice the image for exactly the exposure ratio you want and press the shutter release.

No handsprings with your camera, and no post processing.  Just shoot the image and free up all that post-processing time your spot meter indentures you to. 

Oh wait....  This isn't the Pro Business Discussion section, is it.
Title: Re: Using Spot Metering and Exposure
Post by: bjanes on May 30, 2017, 02:16:01 pm

+1.

As Guillermo knows, ACR uses a baseline exposure offset that has to be taken into account and PV2012 applies a tone curve and automatic highlight correction. I have found that if one uses PV2010 and a linear tone curve (sliders in main panel set to zero) I can get an approximate estimate of highlight clipping. Of course, I use Rawdigger to evaluate my raw files."

Bill,
Thank you for your comments. Please see my response to Guillermo's comments .
Neither I nor others using similar procedures as that which I've described are, not in the slightest, given to repeatetitive use of what Guillermo suggests are practices predicted to yield unpredictable results.
The practices I summarized in the link that I provided are easy to repeat and yield useful results as the examples I provided illustrate.


Dave,

Guillermo and Bart are two of the most knowledgable posters on this forum and their opinions should be disregarded at one's peril. From some of your examples I suspect that there is highlight clipping that has been "recovered" by ACR. As a learning exercise, I suggest that you take some of your ERADR images and look at the raw histograms in Rawdigger or Fast Raw Viewer and report back to us. Evaluation downloads are available, but I would think that any serious experimenter would want to buy one or both (I have both).

The Rawdigger site has 3 valuable posts that are well worth reading:

How to use the full dynamic range of your camera (https://www.fastrawviewer.com/blog/how-to-use-the-full-dynamic-range-of-your-camera)

How to derive the hidden baseline exposure applied by your raw converter (https://www.rawdigger.com/howtouse/deriving-hidden-ble-compensation)

Forcing a raw converter to render tones accurately (https://www.rawdigger.com/howtouse/overriding-raw-converter-default-adjustments-settings)

Regards,

Bill







Title: Re: Using Spot Metering and Exposure
Post by: uuglypher on May 30, 2017, 08:42:49 pm
Please, Bill,
Don't mistake considering and using alternative approaches with disregarding. Not a bit of it.
I am, however, impressed with the results I and others have achieved in practice of the techniques used and have been repeatedly bemused at being told that this ot that test or app, plug in , or program will explain why the images we achieve do not reveal what they do, in fact, reveal, particularly when told they can't possibly be satisfactory by those who have never actually put the described technique to the practical test.

The recent example was being told that testing for extra raw-accessible dynamic range as described cannot possibly yield uniformly repeatable results. That was proof positive that the source of that statement was experientially deprived as regards the process. If those results were not reliably repeatable
no one would be successfully using the described technique of EBTR.

Having done the due diligence of learning, testing, refining, and consistently using the technique and passing it on to others who have taken up its use, I am disinclined to discontinue its practice merely because one  authority or another proclaims that it doesn't...shouldn't ...won't work. Rest assured, as long as it does, those of us experienced with the technique will continue in its use.

I do thank you for your comments and links you provided.

Regards,
Dave
Title: Re: Using Spot Metering and Exposure
Post by: uuglypher on May 31, 2017, 12:13:32 am
And Bill,
I meant to add that I do, indeed have and use both Rawdigger And Fast Raw Viewer.
You asked that I provide you with results of both. You seem to have missed my point that I'm not trying to convince you to use the technique I've earlier described and use. I don't feel the need to do your due diligence. If you, or others, wish to speak more knowledgeably about the EBTR technique, rather than simply theorize as to why it cannot perform as I and others have described and illustrated that it does perform, the basic instructions are there to be followed.  Evaluate the resultant images and check them with Rawdigger and Fast Raw Viewer and draw your own conclusions.

Best regards,
Dave Graham
Title: Re: Using Spot Metering and Exposure
Post by: Guillermo Luijk on May 31, 2017, 05:51:27 am
Your technique has been used for years with success by hundreds of RAW shooters, including me. It simply consists of correlating the camera JPEG blinking lights with what you find later at the RAW development stage, to try to figure out an estimation on how much you can allow your JPEGs to clip before the RAW file actually begins to clip as well.

The wrong part of the story is your assumption that this is an accurate calculation that will provide perfectly ETTR'd RAW files under any situation. No way, and you can check that with the RAW analysing tools you already have.

Regards
Title: Re: Using Spot Metering and Exposure
Post by: uuglypher on May 31, 2017, 08:56:42 pm
Hi Guillermo,
Thanks for commenting.  I understand, but  disagree with with your conclusion that users
of EBTR operate under the mistaken "...assumption that this is an accurate calculation that will provide perfectly ETTR'd RAW files under any situation."   Whether you are referring to the calculation of one's camera's allotment of extra raw-accessible DR (ERADR) or are referring to determination of the exposure at which jpeg highlight clipping will occur (when the determined ERADR must be added to the exposure to accomplish EBTR) is unclear. It is essential that both be accomplished accurately to assure utilization of all available raw-accessible dynamic range.

However, the explicit statement is that the EBTR process as described will fail to result in "...perfectly ETTR'd RAW files under any condition."   "Perfect" accomplishment of the entire available raw-accessible DR?    Well...O.K....I'll admit that we work within the slop factor of  something less than 1/3 stop ...which we find to  be adequate on a practical basis but which you may consider to be an error level of insufficiently "fine grain".  In fact, some practicing EBTR 
users actually ignore the last  intact 1/3 stop of determined ERADR and use it as "cushion" and a ( likely unnecessary)  guaran-damn-tee against any clipping of highlight detail in the raw image data.  There is no question that ACR does an amazing job ( at least to my mind...)  of recovering image data in the event of clipping in one of the  color channels and I am not unduly concerned when FRV informs me of that happenstance.  Too uncritical?  Perhaps guilty as charged, but it is so rarely (ever?)  of practical significance that I relegate it to inconsequentiality. 

Now, I have long suggested  that EBTR is really a simple procedure, but your statement:
"It simply consists of correlating the camera JPEG blinking lights with what you find later at the RAW development stage, to try to figure out an estimation on how much you can allow your JPEGs to clip before the RAW file actually begins to clip as well." is a touch too misleadingly simplistic. 

The key to successful use of EBTR is to realize that cameras vary not only in their maximum raw-accessible DR, but also in the accuracy of their histogram, correlation of the right end of the histogram frame with clipping, and/or correlation of the onset of the "clipping blinkies" with the actual onset of highlight clipping of a JPEG file. However, your salvation is that when you
identify  a given camera's   most accurate indicator of actual jpeg clipping, THAT remains consistently accurate, and it is at that point that one adds the determined ERADR of that camera to accomplish EBTR. .           

I have two cameras that both provide one and 2/3 stops of ERADR.
  In camera A the accurate indicator that highlight clipping will occur with the next additional 1/3 stop of exposure is the first definitive climbing of the right end of the histogram up the right side of the histogram frame. (at which point the onset of "blinkies" has not yet occurred). 

 In camera B the first indication that highlight clipping will occur with the next additional 1/3 stop of exposure is the  onset of the blinkies ( which occurs immediately after the histogram' right extreme barely "kisses" the right side of the histogram frame but before it begins its climb
up the right side.

With another camera that provides one full  stop of ERADR I have found that spot-metering
the brightest finely detailed highlights (subject Value VIII) and adding three full stops arrives at the point of jpeg clipping (which is past the point of the onset of blinkies).

A good friend spot-meters detailed highlights (value VII) , adds two stops, and then adds his camera's two stops of ERADR.

These indices of the onset of jpeg highlight clipping, although at great variance with each other, are consistently reliable in each camera.

The unavoidable axiom of success with EBTR?    "Know your camera !"

There are a number of benefits that accrue to use of EBTR as I've decribed the practice, and
one that is often forgotten is the decreased frequency  with which it's practitioners find the
need for  HDR, particularly those whose cameras have one and 2/3 stops or more of ERADR. Happily, my two work-a-day cameras come in just at that line!    Although some decry its presumed lack of precision, experienced users of EBTR routinely rely on its demonstrated accuracy and repeatable reliability...and were that accustomed precision found to be
unreliable, EBTR would quickly fall from use.

Is EBTR useful under all conditions? It offers complete reliability only when the scene DR
is exceeded by the camera's full, raw-accessible DR at the intended ISO.

Again, Guillermo, I offer explanation and attestation to the utility of EBTR not as a proselytizer, but simply to present a practical alternative to the presumed necessity of a more technical approach to assuring proper exposure of raw image data.  Seriously interested photographers will try both approaches and make their choice. and I suggest that use of one path rather than the other is a choice born of personal experience and is not, by any means (as I have heard) an act of faith nor a character flaw.

Regards,

Dave Graham
Title: Re: Using Spot Metering and Exposure
Post by: Guillermo Luijk on June 01, 2017, 08:23:57 am
I get a bit lost in all those acronyms you invented Dave. Anyway what I mean is that figuring out an approximation of how much the JPEG can be overexposed to make sure you keep a relatively ETTR'ed RAW, is something most RAW shooters have already done for years through practice. If one wants to go a step beyond in accuracy, JPEG is useless and proper RAW histograms are needed (like those provided by Magic Lantern).

As you mention, nowadays with the increased DR of modern sensors, interest in ETTR and RAW histograms is vanishing. One can even play the game of introducing some deliberate underexposure just to make sure no higlights get clipped in the RAW file, and shadows will still retain a good SNR.

Regards
Title: Re: Using Spot Metering and Exposure
Post by: scyth on June 01, 2017, 08:39:31 am
If one wants to go a step beyond in accuracy, JPEG is useless and proper RAW histograms are needed (like those provided by Magic Lantern).

my experience with M43 and Sony dSLM cameras is that with OOC JPG set to use UniWB (plus some other parameters to get as low constrast as possible) precision from "blinkies/zebra" in raw is within 1/3 EV to clipping in raw (as checked with rawdigger)... raw (or ooc jpg) histogram shown on your lcd is useless, in place clipping indicator (in whatever form - blinkies, zebra, some colors) where clipping happens in the frame is what people need.
Title: Re: Using Spot Metering and Exposure
Post by: uuglypher on June 01, 2017, 09:59:55 am
Guillermo states:
"One can even play the game of introducing some deliberate underexposure just to make sure no higlights get clipped in the RAW file, and shadows will still retain a good SNR."

Which, of course, abrogates the principle that maximal raw image data quality is sbsolutely dependent upon use of the greatest possible amount of raw-accessible DR.

And I'm sorry you were confused by acronyms in use by many who use EBTR (Expose Beyond the Right) by adding to the exposure that would cause clipping of a JPEG file the ERADR (Extra raw-accessible Dynamic Range) which must be accurately determined for each camera and added to the brightest possible (yet non-clipping)JPEG exposure to assure use of the full available dynamic range available for a capture of maximal quality raw image data.

Best regards,

Dave
Title: Re: Using Spot Metering and Exposure
Post by: uuglypher on June 01, 2017, 10:06:07 am
Scyth,
Thank you for amplifying my point that for appropriate use of EBTR the most accurate and replicable index of JPEG file clipping must be determined for each individual camera.

Best regards,

Dave
Title: Re: Using Spot Metering and Exposure
Post by: scyth on June 01, 2017, 10:18:34 am
Scyth,
Thank you for amplifying my point that for appropriate use of EBTR the most accurate and replicable index of JPEG file clipping must be determined for each individual camera.

Best regards,

Dave

I 'd prefer naturally clipping indications done in place based on raw data... in some cameras using UniWB for OOC JPG settings in EVF/LV mode makes things difficult (like Sony dSLM and face detection - using UniWB makes it difficult... plus you need to swtich settings effects ON ... otherwise you are limited to post shot review of blinkies instead of using in in real time while looking in EVF... still way better than useless histograms in camera - raw or not)
Title: Re: Using Spot Metering and Exposure
Post by: uuglypher on June 01, 2017, 12:03:27 pm
Hi, scyth,

The methods I describe in an earlier response to Guillermo ( Reply #61 on: May 31, 2017, 08:56:42 PM)
are of the sorts that a number of EBTR practitioners have found to be of useful accuracy. Although useful indices vary from camera to camera, once determined, they have been found to be of repeatable useful accuracy. A bit of practice works wonders at making them second nature to use.

Obviously, subjects that are quickly moving between areas of differing lighting ( children at play and other wildlife, various sports)  militate against use of EBTR! But  conditions of consistent lighting seem made for EBTR. ( studio, landscapes, indoor sports "under the lights), zoos, museums, etc.)

Best regards,
Dave