Native ISO

[Eric Coughlin]

A lot of cameras have a native ISO of 800. So, going below the native ISO you gain dynamic range in the shadows and lose it in the highlights, and vise versa when going above native ISO. Also, at lower ISOs the images tend to be less noisy. Okay. Now, if you've got a shot or are shooting a film where the lighting is such that you have plenty of room in the highlights to avoid clipping and plenty of light to expose with, assuming you want the cleanest image possible, why would you not shoot at the lowest ISO on the camera (say ISO 160)?

I often shoot at the native ISO, but I'm not afraid to change it up and go below native, which it seems many DPs seemed trained to avoid, and of course most DPs will raise the ISO when needed if there isn't enough light to the scene otherwise. But I'm just wondering why the big aversion to lower ISOs if these lower ISOs are giving out cleaner images?

I also feel like a lot of DPs don't understand how ISOs below native affect dynamic range and noise levels; they've just been told a certain ISO is native and turn that into a religion.

 

[Liam Hall]

I always rate my FS7 at least 2/3rds of a stop below it's native ISO.

 

[david dominguez]

The image is still going to be super clean at the native. I'd rather have the extra latitude than going down to 160 for a cleaner image. most don't care about how "clean" an image is when they're talking about the difference from 160 to 800

 

[CharlesPapert]

I regularly shoot on Varicam at the 5000 ISO native setting and under-rate it. On my current series my standard ISO is 2000 down from 5000. Gives me plenty of latitude in any direction I choose--1 1/3 more stops over if I need it, or switch to 800 and get 1 1/3 stops under (or more if required).

 

[Mitch Gross]

If your camera has a native ISO of 800 and you set it to 400 ISO, then you are reducing the dynamic range by one stop, clipping off the top. On the VariCam this would mean going from 14.7 stops (8 under / 6.7 over) to 13.7 stops (-8/+5.7). What’s special about the VariCam is that it has two native ISOs one can select, 800 & 5000. Both have 14.7 stops of DR, at least until you start gaining up or down.

The exception to this is the way Canon changes ISO. Those cameras change digital and analog gain with each ISO so that there is a consistent dynamic range no matter what ISO is selected. But what that means is the artifacts from different gains are inconsistent between ISOs. I would much rather lose dynamic range than bake in different gain signatures, but that’s a choice Canon made.

 

[Eric Coughlin]

I guess my point is, if you're shooting an eight stop scene that falls well within the dynamic range of your camera even when the dynamic range is shifting around based on whatever ISO you set it at, and you have plenty of light for exposure, why would you not want to shoot at the lowest ISO in order to get the cleanest image?

Having extra dynamic range beyond what you need for a given shot has no benefit while having a cleaner image (assuming you don't prefer more digital noise) does have benefits.

 

[cpreston]

If your camera has a native ISO of 800 and you set it to 400 ISO, then you are reducing the dynamic range by one stop, clipping off the top. On the VariCam this would mean going from 14.7 stops (8 under / 6.7 over) to 13.7 stops (-8/+5.7). What’s special about the VariCam is that it has two native ISOs one can select, 800 & 5000. Both have 14.7 stops of DR, at least until you start gaining up or down.

The exception to this is the way Canon changes ISO. Those cameras change digital and analog gain with each ISO so that there is a consistent dynamic range no matter what ISO is selected. But what that means is the artifacts from different gains are inconsistent between ISOs. I would much rather lose dynamic range than bake in different gain signatures, but that’s a choice Canon made.

After having grown use to Canon's programming, I actually have the opposite response to having to deal base ISO's shifting exposures on other cameras. I appreciate being able to use the ISO to compensate for changing my depth of field with the aperture without it noticeably affecting the exposure. For run & gun and documentary, I would assume most people would prefer being able to use an incremental ISO rather than being stuck at one or two base ISO's. Heck, even in situations where I can control the light, I will sometimes realize that the scene I just lit for an f/2.8 is really only going to work at an f/4 or f/5.6 and I can immediately just adjust the ISO to compensate.

Regarding shooting at ISO's below the base, I figure it is really just the same as the photography idea of ETTL. At least on the Canon's, the RAW image at 800 ISO and 200 ISO is exactly the same other than the curve being compressed for 200 ISO. You could just create a LUT for exposure at 800 ISO that crushes all of the blacks and drops the general viewed exposure level and it would be the same as shooting at 200 ISO with a standard LUT.

I've started to think that bigger problem in some cases is that as the DR on cameras increases, DP's are spending more effort trying to increase the contrast in their light set-ups rather than just shooting for a REC 709 contrast in post. What was maybe a five stop key vs fill ratio now needs to be a seven stop ratio in order to look right in the monitor. So they need more powerful lights for the key and more negative fill. But they don't realize that the those nice shadows they see in their smaller monitor is going to look like a noisy mess on a larger screen. And those sharp highlights are going have a bunch of CMOS smear in post.

Or, at least that is my feeling on some shoots.

 

[Mitch Gross]

For run & gun and documentary, I would assume most people would prefer being able to use an incremental ISO rather than being stuck at one or two base ISO's. Heck, even in situations where I can control the light, I will sometimes realize that the scene I just lit for an f/2.8 is really only going to work at an f/4 or f/5.6 and I can immediately just adjust the ISO to compensate.

You’re not stuck at either native ISO unless you choose to be. You can add or subtract gain to either on the fly just as you would from any other camera. But when you leave the native ISO it will trim dynamic range. That’s all.

 

[Mitch Gross]

I guess my point is, if you're shooting an eight stop scene that falls well within the dynamic range of your camera even when the dynamic range is shifting around based on whatever ISO you set it at, and you have plenty of light for exposure, why would you not want to shoot at the lowest ISO in order to get the cleanest image?

Having extra dynamic range beyond what you need for a given shot has no benefit while having a cleaner image (assuming you don't prefer more digital noise) does have benefits.

Not all ISOs are treated equally.

 

[cpreston]

You’re not stuck at either native ISO unless you choose to be. You can add or subtract gain to either on the fly just as you would from any other camera. But when you leave the native ISO it will trim dynamic range. That’s all.

I might be wrong about how other cameras work, but as an example to what I mean, the other day I was shooting a two camera interview on Canon at 800 ISO and f/4.0. During the interview, I realized that both the background looked artificially out of focus and that the interviewee had a tendency to sway back and forth enough to leave the depth of field on one of the cameras. So I just switched to f/5.6 and ISO 1600 during a question. On the Canon, the only thing that changed was the depth of field. On most other cameras, I am assuming that you would actually have a redistribution of the visible exposure.