Author Topic: AETTR + DUAL ISO: The Ultimate Automated Perfect Image Exposure-Beginners'Guide  (Read 61096 times)

ibrahim

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For the past weeks I've intensively gone through all threads regarding dual iso and ettr and I still haven't been able to know exactly a step-by step approach in how to use both for video in camera and when to use or not to use the histogram for this purpose.
I've understood all parts, but still how do they work together 'in practice' (on camera) is something that I have been struggling with. Anyone mind sharing through an example with concrete values?  :)
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Luther

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For the past weeks I've intensively gone through all threads regarding dual iso and ettr and I still haven't been able to know exactly a step-by step approach in how to use both for video in camera and when to use or not to use the histogram for this purpose.
I've understood all parts, but still how do they work together 'in practice' (on camera) is something that I have been struggling with. Anyone mind sharing through an example with concrete values?  :)

Here's how I use it:
- Enable Raw Histogram (don't enable yet DualISO)
- Set your FPS and Shutter, don't change after that
- Use ISO and Aperture to bring the exposure to the maximum, without clipping.*
- Look your histogram, the right side should not be crushed
- Enable DualISO. Set the recovery ISO to +2 EV.
- That's it.

After you process the file, it will be overexposed, so you should bring it back to normal exposure (also using histogram to guide you).

* Whenever possible and appropriate, I personally set the aperture to the "sweet spot" (see the MTF chart for your lens, it's normally between f/2.8 and f/5.6). Then I set the lowest ISO that crushes the right of the histogram just a little bit and, finally, bring back with a Variable ND filter. This way you have the best precision and highest SNR and DR.

mlrocks

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Is there a way to tell the camera to meter on human subjects' skin tones like face and eyes as the basis, then auto ETTR and dual ISO accordingly?
I used auto ETTR and dual ISO together, and found out that they are good for the whole scene, like a street with high rising buildings under the noon sun, but the human faces may be darkened.

yokashin

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Is there a way to tell the camera to meter on human subjects' skin tones like face and eyes as the basis, then auto ETTR and dual ISO accordingly?
I used auto ETTR and dual ISO together, and found out that they are good for the whole scene, like a street with high rising buildings under the noon sun, but the human faces may be darkened.

Try with the zebra turned on. Maybe you can align it correctly by looking at the zebra.
70D.112 [main cam] | M.202 | S110 [CHDK]

mlrocks

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Try with the zebra turned on. Maybe you can align it correctly by looking at the zebra.

This is a good idea.

stef7

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IMHO Spot meter would be the best. You can set exposure very precisely. In other cameras would use False color. But on the tiny low res LCD of EOS M or Canon 5D Mark III with ML spot meter function would be my friend when trying to set correct exposure on human faces.

In my experience ML RAW is like Canon RAW photos. It has more latitude toward underexposure than overexposure. Which means you can miss and recover more stops when underexposed than when overexposed. That's why I never use ETTR method with ML RAW. ETTR is mainly for log profiles on modern cameras where you need to overexpose at least 1 stop even 2 in order to get rid of the noise.

Lack of monitoring in more interesting and high image quality modes as crop is the reason why I rarely use 5D Mark III and EOS M with ML nowadays. It's a major pain in the a.. . In 1080p can use external monitor which is much more comfortable for setting exposure and focus and even more importantly - framing. Every cheap Chinese monitor has False color and wave form as tools. False color is by far my favorite one, perfect for exposure of people and skin tones. I never missed correct exposure with False Color. Never, not even once. But again in ML land external monitors work only in normal 1080p mode. And are not usable or even work with higher image quality modes as crop and anamorphic.

mlrocks

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IMHO Spot meter would be the best. You can set exposure very precisely. In other cameras would use False color. But on the tiny low res LCD of EOS M or Canon 5D Mark III with ML spot meter function would be my friend when trying to set correct exposure on human faces.

In my experience ML RAW is like Canon RAW photos. It has more latitude toward underexposure than overexposure. Which means you can miss and recover more stops when underexposed than when overexposed. That's why I never use ETTR method with ML RAW. ETTR is mainly for log profiles on modern cameras where you need to overexpose at least 1 stop even 2 in order to get rid of the noise.

Lack of monitoring in more interesting and high image quality modes as crop is the reason why I rarely use 5D Mark III and EOS M with ML nowadays. It's a major pain in the a.. . In 1080p can use external monitor which is much more comfortable for setting exposure and focus and even more importantly - framing. Every cheap Chinese monitor has False color and wave form as tools. False color is by far my favorite one, perfect for exposure of people and skin tones. I never missed correct exposure with False Color. Never, not even once. But again in ML land external monitors work only in normal 1080p mode. And are not usable or even work with higher image quality modes as crop and anamorphic.

Thanks a lot for your great explanation and tips, Stef7.
When using ML spot meter for human skin tones, what choice do you recommend, like raw ev, percent, 0-255, etc?
ML also has false color like Marshall and SmallHD etc. ML also has waveform and vectoscope. You prefer external monitor's similar functions, is it because ML ones are too small or not accurate enough?
In terms of ETTR, I agree with you that 5D3 is actually good for underexposure but not so great for highlight. From my experience, if I do manual ETTR in a street scene with complicated lighting and fast pacing, I tend to overexpose some area. When I use ML's auto ETTR module in such a situation, it works much more accurately than my manual mode, i.e., much less possible to overexpose. As you mentioned, ETTR helps a lot with the shadow noise. I can see noticeable improvement in the shadow area.
From your experience, it seems that ETTR is not that important when taking human subject related shots, like portrait, event, etc? From my experience, I rarely think about using ETTR in event shooting, because there is no time, otherwise, I may lose the decisive moment. If using an ML camera, I may put the auto ETTR always on, then maybe it is practical to use ETTR for event shooting. Otherwise, manual ETTR in event shooting is very difficult to implement.


stef7

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Spot meter show %. But it basically correspond to IRE on the waveform.
40% is 18% gray. Actually measured 42-44% with Canon 5D Mark III and ML spot meter, but fairly close

For linear video profile as Canon RAW, typical values for human skin tones are:

Lightest skin: 60 - 65 IRE or 62-67% on the spot meter
Darkest skin:  45 - 50 IRE or 47-52% on the spot meter

It is easy to check those values if you load a part of the movie or video in resolve and check values on waveform scope. You'll see they fall most of the time within those values.

You have to put the spot meter on the brightest part of the face as it is rarely evenly lit

The nice thing with False color is that with a single glance I can also check if there are part of the image which are overexposed or underexposed and also if skin tones are within the range.

Why not use False Color in ML ? Many reasons:
1. False Color requires processing power so everything else slows down.
2. Many clicks to switch it on and off. On a monitor it is just one click of a button or on the touch screen. Maybe it can be assigned to a button on ML as well. Never tried. While spot meter is on all the time and you can immediately see the value. 
3. Low resolution LCD not practical for the purpose
4. Small LCD on the back of the camera - leads to limited monitoring and camera movements. Uncomfortable to monitor, frame and shoot that way unless on a tripod or monopod with a LCD viewfinder on LCD

mlrocks

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Spot meter show %. But it basically correspond to IRE on the waveform.
40% is 18% gray. Actually measured 42-44% with Canon 5D Mark III and ML spot meter, but fairly close

For linear video profile as Canon RAW, typical values for human skin tones are:

Lightest skin: 60 - 65 IRE or 62-67% on the spot meter
Darkest skin:  45 - 50 IRE or 47-52% on the spot meter

It is easy to check those values if you load a part of the movie or video in resolve and check values on waveform scope. You'll see they fall most of the time within those values.

You have to put the spot meter on the brightest part of the face as it is rarely evenly lit

The nice thing with False color is that with a single glance I can also check if there are part of the image which are overexposed or underexposed and also if skin tones are within the range.

Why not use False Color in ML ? Many reasons:
1. False Color requires processing power so everything else slows down.
2. Many clicks to switch it on and off. On a monitor it is just one click of a button or on the touch screen. Maybe it can be assigned to a button on ML as well. Never tried. While spot meter is on all the time and you can immediately see the value. 
3. Low resolution LCD not practical for the purpose
4. Small LCD on the back of the camera - leads to limited monitoring and camera movements. Uncomfortable to monitor, frame and shoot that way unless on a tripod or monopod with a LCD viewfinder on LCD

Thank you very much for the insightful explanation, Stef7. Regards,

mlrocks

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From my initial testing, without an external monitor, with an LCDVF, 5D3's 5.7k 1x3 and 3.5k 1x1 centered modes are very useful, can be practical enough for real world shooting. Thanks Danne for his great work.

mlrocks

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I did more tests, the external monitor has an anamorphic mode, but the HDMI outputs only the real time live view. Unless the real time live view has the correct framing, the in monitor anamorphic mode is not good for framing.

On 5D3 with Dnne's latest ML version, neither 1x3 5.8k nor 1x1 3.5k centered mode exports correct frame preview to an external evf. I test this with a Zacuto EVF. So external monitor is still not working with higher resolution presets on 5D3. Also, changing between presets freezes the camera. Sometimes I have to remove battery. Sometimes I have to recopy ML files from the computer onto the CF card to solve the issue. 650D is much more robust in terms of changing the presets.

mlrocks

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"Lack of monitoring in more interesting and high image quality modes as crop is the reason why I rarely use 5D Mark III and EOS M with ML nowadays. It's a major pain in the a.. . In 1080p can use external monitor which is much more comfortable for setting exposure and focus and even more importantly - framing. Every cheap Chinese monitor has False color and wave form as tools. False color is by far my favorite one, perfect for exposure of people and skin tones. I never missed correct exposure with False Color. Never, not even once. But again in ML land external monitors work only in normal 1080p mode. And are not usable or even work with higher image quality modes as crop and anamorphic."

650D's 1x3 modes, UHD, 4K, 4.3K, 4.5K, have correct framing real time previews, in camera, and in external monitor/evf. I tested these modes with a Zacuto EVF. No in monitor anamorphic mode is needed.
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