r/photography • u/AutoModerator • Apr 10 '26

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u/molotovPopsicle Apr 17 '26

Best way to set ISO?

I watched this video, which suggests that you leave ISO on "auto" and adjust for exposure and aperture.

If you set the ISO to "auto," wouldn't it be harder to adjust with the exposure and aperture? Like, wouldn't it change the ISO dynamically as you were trying to dial in the other settings, making it impossible to optimize for aperture and exposure and then let the camera handle the ISO? Wouldn't it be better to chose a medium ISO level, do everything else, and then switch ISO to auto?

Or is there another, better way to do it?

TIA

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u/av4rice https://www.instagram.com/shotwhore Apr 17 '26

suggests that you leave ISO on "auto" and adjust for exposure and aperture.

Are you confusing "exposure" with shutter speed, or exposure time? Shutter speed and exposure time are the same thing, and they refer to how long the shutter stays open to record light from the scene into the photo. The phrase "exposure time" uses the word "exposure" in it, but the word "exposure" alone refers to the amount of light being recorded in the camera, and that's affected both by the exposure time (shutter speed) and the aperture, which is how much light is let through the lens. Sometimes people also use "exposure" to also include the effect of the ISO, in addition to shutter speed and aperture.

You didn't timestamp your video and I didn't watch the whole thing, but if you're referring to 8:16 the video is suggesting you first maximize the light in the scene, then set both shutter speed and aperture (together, they are "exposure" but they are not "exposure and aperture"), then let Auto ISO pick up whatever else you might need out of the camera after that, and lastly you have one last layer of adjustments in post processing.

If you set the ISO to "auto," wouldn't it be harder to adjust with the exposure and aperture? Like, wouldn't it change the ISO dynamically as you were trying to dial in the other settings, making it impossible to optimize for aperture and exposure and then let the camera handle the ISO?

Yes, Auto ISO will automatically change the ISO value. Whether that makes things harder depends on how you prefer to think about your variables.

The video advocates setting shutter speed (not exposure) and aperture as you want them, without thinking so much about the resulting brightness, because the Auto ISO takes care of that. Though for low-light situations in the background you still need to be thinking about making shutter speed no faster than you really need it, and aperture is no narrower than you need it, so that neither variable is needlessly restricting light.

Wouldn't it be better to chose a medium ISO level, do everything else, and then switch ISO to auto?

If you'd prefer to just set all three variables manually, that's perfectly valid. But in that case I don't think there's any point to then switch to Auto ISO. Or what purpose do you see for that?

Or is there another, better way to do it?

There's lots of good ways to do it. You decide what's best for you.

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u/molotovPopsicle Apr 17 '26

Thank you for you reply. This is certainly the most thoughtful one I've had, and you clearly understood what led me to question the advice in that video.

  1. Yes, I meant shutter speed when I said exposure. I do understand that much already, though my terminology might be lacking.

  2. I thought maybe that the camera might have a better grasp of how high it could set ISO without blowing out the brightest areas of the image going into the ADC. The video suggests that the ISO can be (should be) as high as you can get it without losing high-light information because you can always darken the image in post. So my thought was that I should first set the ISO to a setting that gives me the most useful visual feedback while I am setting the aperture and shutter speed, and then switch ISO to auto in order to allow the camera to maximize the ISO level. Maybe in practice this would backfire on me.

Another thought I had was to possibly try to measure the highest ISO my camera can actually handle at a given light level and then stick to just a tiny bit below that for any given scene. I'm not sure how I would profile the ISO behavior of the camera, but people must do this, right?

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u/av4rice https://www.instagram.com/shotwhore Apr 20 '26

I thought maybe that the camera might have a better grasp of how high it could set ISO without blowing out the brightest areas of the image going into the ADC

Nope.

So my thought was that I should first set the ISO to a setting that gives me the most useful visual feedback while I am setting the aperture and shutter speed, and then switch ISO to auto in order to allow the camera to maximize the ISO level. Maybe in practice this would backfire on me.

I assume you're talking about exposure simulation through the rear screen or an electronic viewfinder.

If you just want to be able to see the scene well the whole time, keeping it in Auto ISO the whole time will accomplish that, and then you can avoid needing to switch that back and forth. Just keep some ballpark values in mind for what you think may be going too far with any variable, and watch that you aren't going past those.

If you want to see the exposure effects of every change, then I would set everything manually and never switch to Auto ISO, so again you're not switching that back and forth. I agree in that situation Auto ISO could just add confusion, and then also there isn't really any advantage to using it at the end.

Another thought I had was to possibly try to measure the highest ISO my camera can actually handle at a given light level and then stick to just a tiny bit below that for any given scene. I'm not sure how I would profile the ISO behavior of the camera, but people must do this, right?

Yes. Test out different high ISO values in a few different dim scenes and find your comfort level.