Blaster6 wrote in post #16533993
So what you are saying is if I need a specific aperture and shutter speed in a poorly lit area I can increase my ISO and that will result in less noise? Flash is not an option so I will not be changing the scene lighting.
In the lower range of ISOs on Canon DSLRs, the read noise relative to an absolute signal level peaks at ISO 100, at which it is almost 2x as strong as at ISO 200. With each doubling of ISO, the read noise reduces at a slower rate, until about 1600 to 3200, where it levels off, and the only benefit of a higher ISO setting is a brighter review image, and better cooperation from your converter, which may do strange things that it shouldn't when pushing deep shadows.
Keep in mind I am not at the lower range of ISOs -- I am in the 1600 - 6400 range. What you are saying is 6400 is cleaner? This does not make sense to me but I am willing to try anything if I am understanding you correctly.
If you're will to do the push in the converter (and your converter does it right), and you are willing to have a dark review image and a dark JPEG which won't push as well as RAW does, then "under-exposing" at these higher ISOs instead of using higher ones will give you an increase in highlight headroom, without any noise penalty. In that case, setting a max makes sense, in manual mode. There are more reasons to use a max in Tv and Av mode, because you may feel that a compromised shutter speed or DOF is a better choice than noise. Personally, I'd like an option to set manual Av and Tv values, and use auto-ISO, but have ISO thresholds settable which allow your Av and Tv values to break away, such as allowing a lens to open all the way to avoid ISO 51K, being that noise may reduce resolution as much as a wide-open lens (IOW, the value of maximum sharpness is not appreciated as well with a lot of noise).
In the past I have gotten a slightly cleaner final result from slightly underexposing and bumping the exposure a bit in post.
That is not likely if all other things are equal; the only benefit you should have from under-exposing a lower ISO is increased highlight headroom. Perhaps the converter in your case was doing more NR at the higher ISO setting, by default, and you didn't like it? Or maybe the situation was not completely equitable.