The coordination between Camera EI (Exposure Index) and lighting.

[caiyichenweg]

Hi, dear Roger and all the friends on the forum! I’d like to inquire about the coordination between EI and lighting during your work. During my learning process, my teacher told me that if I want to capture low-illuminance images with rich details in the shadows, I should lower the EI and increase the lighting to match it. And when shooting images with rich details in the highlights, I should raise the EI. Roger, do you do it this way when shooting? Or do you mostly keep the EI at 800 for shooting and expose with your eyes and a light meter?

In addition, thank you so much for helping us beginners who are still at the starting stage! Thank you for your patience!

Topic

[mkrjf]

I have a related question – when shooting log and using a 1deg spot meter what ‘f-stop’ do you aim for in resolvable dark and resolvable bright (and skin tone) when shooting log?! I guess a grey card in each area but I want to use something like Adams 10 zone system to make sure every area on set is exposed the way I want as DP – do you switch meter to EV or just try to limit the range of stops between gray card in the dark area and grey card in the bright area? some in camera log (fuji flog2 on xH2 for example) are ‘impossible’ to overexpose or in case of flog impossible to underexpose – the histogram is literally lifted and capped so there is never 0 black or ‘100’ white.

[dmullenasc]

There is a certain logic to what the teacher is suggesting, which is related to ETTR (Expose To The Right) — if you have a dim scene with no bright highlights, you could shoot at a lower ISO for less noise in the shadows. And conversely if you have very hot highlights, you could shoot at a higher ISO for more highlight retention (of course, you could also not change the ISO and just expose so that highlight detail is not clipped, which might result in a darker image that will have to be brightened later.)

However, practically-speaking, if you are happy with the noise of ISO 800 and in a dark scene, do not think you’ll be attempting to bring up any shadow area in post color-correction, meaning your noise will not increase, plus you can light for exactly the amount of shadow detail you want at ISO 800 with your chosen LUT, then perhaps using a lower ISO is being unnecessarily cautious (I will admit when doing very dim scenes on stage, I might lower to ISO from 800 to 500 just to get a cleaner image for post.) Sometimes your dim or dark scene involves practical sources of a very low level, like a candle flame, a small flashlight, a streetlamp, or distant city lights, things that cannot be brighter, so lowering the ISO isn’t practical.

I also find that with the ARRI Alexa, especially now with the Alexa 35, it’s rare in bright exterior scenes where I find that the ISO needs to be raised above 800 to retain bright highlights. If I get into that situation, I’d probably just expose for the highlights I want to retain and perhaps get the DIT to make a ASC CDL adjustment to the LUT to compensate for the darker image, just so that dailies aren’t too dark-looking.

[gx42]

Hi David – Could you explain this a little further how a higher ISO would retain highlights? Intuitively, it would seem a higher ISO would push the sensor out of its optimal dynamic range and increase the intensity of highlights. Even with using ND, would you get more noise in shadows and less dynamic range? And is this characteristic camera specific for an Arri vs a Sony Venice or other camera for example, or do all digital cameras behave this way?

[dmullenasc]

The higher you set the ISO, the more you are underexposing the sensor.  With cameras like the Alexa, you always capture 14+ stops of dynamic range in any ISO setting (can’t vouch for extreme choices though.) So at high ISO settings, you are capturing more highlight information (because of underexposure) and less shadow detail. The opposite at low ISO settings.

Not all cameras are “ISO invariant” though.

Keep in mind that in real world situations, your scene may not have 14+ stops of information in both directions — for example, at a low ISO outdoors, you might be sacrificing overexposure detail but the shadows may not be dark enough to benefit from more information being allowed for them.

[gx42]

Very interesting and excellent information. Thank you!

[Juanlage]

Good morning,

I hope my contribution helps you; it’s another way to see things and has helped me understand it better.

When working with a camera in Raw or Log, the ISO and Cine EI are metadata. This means that even if you set the Cine EI to 2000 ISO or 200 ISO, the camera’s base sensitivity (let’s say it is 800) will not actually change. This can be seen in a WFO, where the signal does not change when altering the Cine EI. In reality, I could work without paying attention to the Cine EI and just look at the WFO, setting the signal close to the clipping point on the black side if there are many uncontrolled highlights or near the white clipping if I want to reduce noise as much as the scene allows. This is done, of course, by adjusting the aperture, opening or closing it while closely watching the waveform monitor.

However, this method has a problem: if you ignore the Cine EI, even if the signal is workable, it won’t have logical continuity because the camera has a metadata (ISO Cine EI) that is inconsistent with the exposure you’ve set using the waveform monitor, causing exposure jumps in the image. Another issue is that LUTs won’t work properly because they are associated with the Cine EI metadata to maintain coherence; you’ll see them more overexposed or underexposed. Additionally, no one will understand the intent of your photography.

Ultimately, the Cine EI is just a reference to ensure the workflow remains coherent and the exposure intent is clear. If your base is 800 and you lower it to 400, logically you open the aperture by one stop. When you do this, activate and deactivate the LUT; when the LUT is deactivated, you’ll see that the log signal is higher on the waveform monitor because you’ve compensated by opening the aperture from 800 EI to 400 EI. If you don’t compensate by opening the aperture, the signal will remain in the same place on the waveform monitor.

I hope this explanation is clear since my English is not good and this is translated by Google. Thank you and best regards,

[Author]

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