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Author Topic: Optimal exposure  (Read 1962 times)

David Eckels

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Optimal exposure
« on: November 23, 2020, 10:58:20 am »

Read an excellent article on ETTR by Bob DiNatale over on PhotoPXL, https://photopxl.com/the-optimum-digital-exposure/
I knew about ETTR, but only applied it manually and got shy once the "blinkies" appeared. The attached image was shot on my D850 with EV at +1.3, bracketing at -3F 0.7 and matrix metering at 0 (Bob's methodology). This resulted in a 1/40, 1/25, and 1/15 sec series at f/4. So, if I've done my math correctly (no guarantee ;)) I was able to squeeze out 2 extra stops at ISO 400, way beyond where I would have started backing off, assuming the EV setting is taken into account by the matrix meter. That being said, I could even recover all the highlights from the 1/15 sec exposure, but I can't hold still that long! Bob also did a great job explaining how LR rounds off the highest channels to bring detail back into highlights. Please forgive if I've used the wrong terms; I'm sure my naive understanding has contributed.
Anyway, I decided to experiment with Bob's method at ISO 64 and ISO 400 under HDR conditions (really bright highlights and black blacks). So far, this has enabled at least a 1.3 EV improvement in exposure, which is what I wanted to understand. I know this is old ground for some, but it was kind of an epiphany for me and a straightforward methodology to achieve better exposures. Check out the article.
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faberryman

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Re: Optimal exposure
« Reply #1 on: November 23, 2020, 11:10:06 am »

So far, this has enabled at least a 1.3 EV improvement in exposure, which is what I wanted to understand.

What exactly is a 1.3 EV improvement in exposure and how did you measure it?
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digitaldog

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Re: Optimal exposure
« Reply #2 on: November 23, 2020, 11:40:10 am »

Read an excellent article on ETTR by Bob DiNatale over on PhotoPXL, https://photopxl.com/the-optimum-digital-exposure/
I knew about ETTR, but only applied it manually and got shy once the "blinkies" appeared.
The 'blinkies' are the JPEG and really tell you nothing useful about raw exposure. You really need a raw Histogram which RawDigger provides (more below).

Bob's piece is a good read, a few others:
Articles on exposing for raw:
http://www.onezone.photos
http://schewephoto.com/ETTR/
https://luminous-landscape.com/the-optimum-digital-exposure/ (Bob did a piece here too)
http://digitaldog.net/files/ExposeForRaw.pdf
https://www.fastrawviewer.com/blog/mystic-exposure-triangle
https://www.fastrawviewer.com/blog/red_flowers_photography_to-see-the-real-picture
https://www.rawdigger.com/howtouse/exposure-for-raw-or-for-jpegs
https://www.rawdigger.com/howtouse/beware-histogram
https://www.rawdigger.com/howtouse/calibrate-exposure-meter-to-improve-dynamic-range
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David Eckels

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Re: Optimal exposure
« Reply #3 on: November 23, 2020, 01:24:47 pm »

What exactly is a 1.3 EV improvement in exposure and how did you measure it?
I suppose it means one and one third (1.3 EV) of a stop extra exposure. More than double the photon collection.

Andrew, thanks. I am sure you would be more lucid than I. Didn't know Bob had done a piece on LuLa. Agree about the "blinkies" but looking at the same files with RawViewer and RawDigger with the highlight setting on, there appear to be blown highlights in the green channel at least, yet LR could recover same highlights. Recovery from one or both of the "unblown" chanels?
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digitaldog

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Re: Optimal exposure
« Reply #4 on: November 23, 2020, 01:27:34 pm »

I suppose it means one and one third (1.3 EV) of a stop extra exposure. More than double the photon collection.

Andrew, thanks. I am sure you would be more lucid than I. Didn't know Bob had done a piece on LuLa. Agree about the "blinkies" but looking at the same files with RawViewer and RawDigger with the highlight setting on, there appear to be blown highlights in the green channel at least, yet LR could recover same highlights. Recovery from one or both of the "unblown" chanels?
LR can recover highlight data if two of the three channels have some data. One or two channels are blow out. But tricks with some Process Versions in LR/ACR can slightly reconstruct some tone but it's hardly an answer for actual over exposure.
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bjanes

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Re: Optimal exposure
« Reply #5 on: November 23, 2020, 01:43:50 pm »

The 'blinkies' are the JPEG and really tell you nothing useful about raw exposure. You really need a raw Histogram which RawDigger provides (more below).

Bob's piece is a good read, a few others:
Articles on exposing for raw:
http://www.onezone.photos
http://schewephoto.com/ETTR/
https://luminous-landscape.com/the-optimum-digital-exposure/ (Bob did a piece here too)
http://digitaldog.net/files/ExposeForRaw.pdf
https://www.fastrawviewer.com/blog/mystic-exposure-triangle
https://www.fastrawviewer.com/blog/red_flowers_photography_to-see-the-real-picture
https://www.rawdigger.com/howtouse/exposure-for-raw-or-for-jpegs
https://www.rawdigger.com/howtouse/beware-histogram
https://www.rawdigger.com/howtouse/calibrate-exposure-meter-to-improve-dynamic-range

I think that your assertion that blinkies tell nothing about the raw file is overblown. If you do an exposure series with your usual camera settings (Nikon = picture control) and compare the onset of blinkies with clipping in the raw channels as shown by Rawdigger you can learn quite a lot from the blinkies. I find them useful in that context.

Bob's article urges extreme exposure to the right. He also rationalizes that the brightest stop of an exposure contains half the data with respect to the number of levels. The real issue is the signal to noise ratio as pointed out by Emil Martinec here, and not the number of levels as raw data are never posterized.

With current sensors as with Sony, ETTR is not as relevant as previously. Doubling the exposure only raises the SNR by the square root of 2 (1.4x), but risks blowing out the highlights with un-recoverable loss of image quality. Since the histograms and blinkies (at least on my Nikon D850) are somewhat conservative, I use them for helping to determine exposure; the raw file may be a half stop under clipping, but the image can be brightened in post with minimal loss of image quality.

Bill
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digitaldog

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Re: Optimal exposure
« Reply #6 on: November 23, 2020, 01:50:50 pm »

Bill, I don't need misinterpreted information (JPEG Histogram) to evaluate raw exposure any more today than when I shot transparency film. As a profession. It's a hack. Photographers have optimize exposure for a good hundred years before JPEG existed. Optimal exposure is photography 101. Or for many it always was and IMHO, should be.
With any sensor, optimal exposure is ideal: "Don't just learn the tricks of the trade. Learn the trade." -James Bennis
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kers

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Re: Optimal exposure
« Reply #7 on: November 23, 2020, 02:13:51 pm »

The 'blinkies' on a nikon react on the color temperature you have chosen. In that sense they are not always telling the same story.
Still i agree with Bill when used in a sensible way they are gicving relevant information especially when thesubject is moving and you cannot bracket.
Very often use the red channel blinkies when i photograph people in Tungsten light; overexposed skin is very ugly.
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bjanes

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Re: Optimal exposure
« Reply #8 on: November 23, 2020, 05:41:43 pm »

Bill, I don't need misinterpreted information (JPEG Histogram) to evaluate raw exposure any more today than when I shot transparency film. As a profession. It's a hack. Photographers have optimize exposure for a good hundred years before JPEG existed. Optimal exposure is photography 101. Or for many it always was and IMHO, should be.
With any sensor, optimal exposure is ideal: "Don't just learn the tricks of the trade. Learn the trade." -James Bennis

Andrew,

I have exposed Kodachrome and Velvia for over 40 years with good results before I moved to digital, so I know exposure pretty well even though I am not a pro photographer. I had the Pentax spot meter that Ansel used as well as a Gossen Luna Pro and a Sekonic incident meter. I really haven't used these meters for years. Sometimes I use the spot meter in my digital camera, but mainly use Nikon matrix metering checked in camera with the histograms and blinkies and in post with Rawdigger and FastRawViewer. Your mileage may vary, but I suspect that most of us do use the blinkies and histogram with good results.

What is your method for optimal exposure?

Regards,

Bill
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digitaldog

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Re: Optimal exposure
« Reply #9 on: November 23, 2020, 05:54:40 pm »

Bill, I provided my technique for optimal exposure previously.
If indeed you are able to expose optimally for transparency then you already know how to expose optimally for raw data. Test your media, test your meter, test your development, that’s it. From this point forward there is no need for a JPEG histogram.Just as you did not need one to optimally expose transparency film.
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Alan Klein

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Re: Optimal exposure
« Reply #10 on: November 23, 2020, 08:10:08 pm »

Andrew,

I have exposed Kodachrome and Velvia for over 40 years with good results before I moved to digital, so I know exposure pretty well even though I am not a pro photographer. I had the Pentax spot meter that Ansel used as well as a Gossen Luna Pro and a Sekonic incident meter. I really haven't used these meters for years. Sometimes I use the spot meter in my digital camera, but mainly use Nikon matrix metering checked in camera with the histograms and blinkies and in post with Rawdigger and FastRawViewer. Your mileage may vary, but I suspect that most of us do use the blinkies and histogram with good results.

What is your method for optimal exposure?

Regards,

Bill
Bill:  I've started using an Olympus E-PL1 micro 4/3 camera as a light meter to shoot 4x5 Velvia 50 and Tmax 100 and 400 film. What I do is adjust the E-PL1 settings so the picture looks OK on the screen and check the histogram so I'm not clipping.  I use center, not spot or matrix.  But regardless, I'll adjust the camera's settings to get the histogram in the full range improving the histogram away from light clipping for chrome film and away from dark clipping for negative film.  Then transfer the settings to the film camera.

Should I bother with blinkies?  Any other suggestions to improve my procedure? 

digitaldog

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Re: Optimal exposure
« Reply #11 on: November 23, 2020, 08:48:43 pm »

I've started using an Olympus E-PL1 micro 4/3 camera as a light meter to shoot 4x5 Velvia 50 and Tmax 100 and 400 film.
Should I bother with blinkies?
I've heard of some using a Kitchen Knife as a screwdriver.  ;D
Yes!
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bjanes

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Re: Optimal exposure
« Reply #12 on: November 24, 2020, 08:54:57 am »

Bill:  I've started using an Olympus E-PL1 micro 4/3 camera as a light meter to shoot 4x5 Velvia 50 and Tmax 100 and 400 film. What I do is adjust the E-PL1 settings so the picture looks OK on the screen and check the histogram so I'm not clipping.  I use center, not spot or matrix.  But regardless, I'll adjust the camera's settings to get the histogram in the full range improving the histogram away from light clipping for chrome film and away from dark clipping for negative film.  Then transfer the settings to the film camera.

Should I bother with blinkies?  Any other suggestions to improve my procedure?

Alan,

The blinkies add some additional information as they show where clipping is; also, small areas of clipping may not be apparent on the histogram. So, I would say you should look at them, at least when exposing Velvia.

What are your results? 4x5 Velvia film and processing are expensive, so it is desirable to nail the exposure. Andrew thinks your procedure is a bit unorthodox, but I would say use whatever method gives good results. Of course, the dynamic range of the monochrome film is much greater than that of the digital camera, but placing the exposure for the shadows is appropriate. The blinkies and right side of the histogram would not be that helpful in this situation. Using the Olympus is similar to taking a preview shot with a Polaroid.

Bill
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digitaldog

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Re: Optimal exposure
« Reply #13 on: November 24, 2020, 09:58:26 am »

Quote
Andrew thinks your procedure is a bit unorthodox

There seems to be some perverse human characteristic that likes to make easy things difficult.” -Warren Buffett
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Alan Klein

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Re: Optimal exposure
« Reply #14 on: November 24, 2020, 10:48:54 am »

Alan,

The blinkies add some additional information as they show where clipping is; also, small areas of clipping may not be apparent on the histogram. So, I would say you should look at them, at least when exposing Velvia.

What are your results? 4x5 Velvia film and processing are expensive, so it is desirable to nail the exposure. Andrew thinks your procedure is a bit unorthodox, but I would say use whatever method gives good results. Of course, the dynamic range of the monochrome film is much greater than that of the digital camera, but placing the exposure for the shadows is appropriate. The blinkies and right side of the histogram would not be that helpful in this situation. Using the Olympus is similar to taking a preview shot with a Polaroid.

Bill

Thanks for your advice.  I shot medium format Mamiya RB67 for years using a Minolta Autometer IIIf using its incident and 10 degree reflective.  But I read Alex Burke https://www.alexburkephoto.com/ when I got a 4x5 this year and whose photography I like.  I shoot landscape pretty much exclusively as he does.  He uses a digital camera as a meter.  The other advantages are I can switch to BW to "see" the BW view better.  I also find the upside-down view with 4x5 annoying.  I’d rather compose right-side up with my Olympus E-PL1 digital, for better aesthetics.  Then I set up the tripod exactly where I’m standing. That’s what works for me maybe not for others.  I use its zoom lens to determine the 4x5 lens I need before setting up my tripod and camera.  I also use it to snap the view I'll be shooting with the film camera so I have the settings or can record in video mode to transcribe when I get home.  The digital shot records the settings for easy viewing while I set up the 4x5’s aperture and shutter speed.  I can examine the histogram to see I’m not clipping and adjust it again and snap a second shot.  I keep the shots in the same folder in my computer after I scan the film.  So I can go back and see what was going on.  Some of it is a little anal.  But I’m still working on a procedure that works for me.

The last four Velvia shots I took were exposed perfectly using the camera as a meter.  Previous ones I screwed up at times but mainly because I failed to transfer the settings to the 4x5 correctly.  One problem with the digital camera meter approach is the aperture only goes down to f22 and ISO only to 100.  So I have to add or change stops from the digital camera to the 4x5 in my head.  Also, the camera gives aperture readings in tenths of stops.  However, I can change stop readings to whole, half or thirds in the digital camera.  So I may change those as well. So I’ve screwed it up especially since I'm learning movements and all the other things with a view camera I never dealt with before.  I'm switching over to Provia and Ektachrome, both ISO 100.  So I won’t have to worry about that ISO setting adjustment problem like Velvia 50. 
   
But it's a learning process and it seems to be working.  I'll flip the blinkies on to try it out. Currently, I pull the histogram from black clipping with negative film and white clipping for chromes and let the other ends fall where they fall.   

bjanes

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Re: Optimal exposure
« Reply #15 on: November 24, 2020, 10:49:31 am »

The 'blinkies' are the JPEG and really tell you nothing useful about raw exposure. You really need a raw Histogram which RawDigger provides (more below).

Andrew,

I agree that the raw histogram as shown by RawDigger is the proper tool for evaluating exposure, but that evaluation is retrospective (FastRawViewer can also show the histogram of the embedded JPEG preview). The camera histogram can be useful for evaluating exposure in the field, but there are situations where the camera histogram is quite different from the raw histogram. Image attachment 1 shows an example of a red flower where the red channel camera histogram is at clipping. The exposure was at base ISO of 64.

Looking at the raw histogram in RawDigger shows that the red channel is 2 stops short from clipping (attachment 2). Since the white balance multiplier for the D850 is 1.93 for the red channel, the histogram would move 1 stop to the right after white balance. What accounts for the extra stop? I suggest that it is from saturation clipping where the camera histogram is derived from rendering into AdobeRGB. I don't recommend using ACR to evaluate the raw file exposure since Adobe uses a hidden exposure offset (+0.35 EV for the D850) and the latest process version 5 employs automatic highlight recovery. Nonetheless, rendering the raw file into AdobeRGB shows a histogram very similar to the camera histogram. When one renders into ProphotoRGB, the red channel is well short of clipping (attachment 3).

In retrospect, the camera luminance histogram gives a more accurate indication of exposure since it represents primarily the green channels and the green channel WB multiplier is 1.0.

Regards,

Bill

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digitaldog

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Re: Optimal exposure
« Reply #16 on: November 24, 2020, 10:56:01 am »

Andrew,

I agree that the raw histogram as shown by RawDigger is the proper tool for evaluating exposure, but that evaluation is retrospective (FastRawViewer can also show the histogram of the embedded JPEG preview). The camera histogram can be useful for evaluating exposure in the field, but there are situations where the camera histogram is quite different from the raw histogram. Image attachment 1 shows an example of a red flower where the red channel camera histogram is at clipping. The exposure was at base ISO of 64.

Looking at the raw histogram in RawDigger shows that the red channel is 2 stops short from clipping (attachment 2). Since the white balance multiplier for the D850 is 1.93 for the red channel, the histogram would move 1 stop to the right after white balance. What accounts for the extra stop? I suggest that it is from saturation clipping where the camera histogram is derived from rendering into AdobeRGB. I don't recommend using ACR to evaluate the raw file exposure since Adobe uses a hidden exposure offset (+0.35 EV for the D850) and the latest process version 5 employs automatic highlight recovery. Nonetheless, rendering the raw file into AdobeRGB shows a histogram very similar to the camera histogram. When one renders into ProphotoRGB, the red channel is well short of clipping (attachment 3).

In retrospect, the camera luminance histogram gives a more accurate indication of exposure since it represents primarily the green channels and the green channel WB multiplier is 1.0.

Regards,

Bill
My point again is, in retrospect, no Histogram is needed to optimally expose an image. As was done by at least two of us for decades with transparency film.
A raw Histogram IS useful to get to the understanding towards learning how to optimally expose for that kind of data, and to see what, if anything, a converter develops from that in terms of brightness in highlights that may appear to clip (but are not) or those that do clip but shouldn't and can be minimally recovered. After that, no need for any Histogram. 
If Photographers would spend a fraction of their time ignoring JPEG Histograms for exposure and LEARN to use Spot reflective and incident meters, LEARN how they can be fooled, they would spend a lot less time doing stuff other than making images.
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Alan Klein

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Re: Optimal exposure
« Reply #17 on: November 24, 2020, 12:02:54 pm »

Is there any reason why spot metering can't be done with a digital camera rather than a stand alone meter?

digitaldog

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Re: Optimal exposure
« Reply #18 on: November 24, 2020, 12:13:34 pm »

Is there any reason why spot metering can't be done with a digital camera rather than a stand alone meter?
Did you read the manual (any manual you own) that covers the spot meter in any product you presumably own?
Did you even attempt to read URL's already provided that already answered your questions about using a meter?
Is there any reason why can't?
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Alan Klein

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Re: Optimal exposure
« Reply #19 on: November 24, 2020, 01:43:00 pm »

Is there any reason why spot metering can't be done with a digital camera rather than a stand alone meter?
If someone else can answer my question without forcing me to read nine treatises on Raw measurements and RAW digger, I'd appreciate it.
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