fivefish wrote in post #2077947
From my experience, a high 1600 ISO with flash that's correctly exposed gives pictures that are great.
An ISO 100 , 200 or 400 that's underexposed will show MORE noise than the 1600 ISO that's correctly exposed.
Again, that's just my experience.
DocFrankenstein wrote in post #2077992
That's the right answer from the physics point of view.
From tests I did a year or so ago, I didn't really see any difference between a properly exposed image shot at ISO 1600 and one that was underexposed at ISO 800. And that makes sense when you consider that in both cases, you are using the same image senosr and both are underexposing the image in the same way.
However, what I wasn't sure about was how the image would look at ISO 3200. After all, you have to go out of your way to use it so I thought maybe there was a reason for that. Maybe the image doesn't come out as well at that ISO compared to the other ISO settings? I don't know. So, I did a test to see if there really are a differences in images shot at ISO 3200, ISO 1600 and underexposed by 1 stop and ISO 800 and underexposed by 2 stops.
See for yourself. The test photos were shot in RAW and converted in DPP all using the same parameters except that the exposure of the image shot at ISO 1600 and underexposed by 1 stop was correct by +1 stop to compensate, and likewise, the image shot at ISO 1600 was corrected by +2 stops.
Also, other than changes to the ISO setting, all images were shot in Manula mode @ 1/25, f/5.6 and custom WB with camera on a tripod and cable release.
Resized full images:
1) Shot at ISO 3200
2) Shot at ISO 1600
3) Shot at ISO 800
100% crop of focused area:
1A) Shot at ISO 3200
2A) Shot at ISO 1600
3A) Shot at ISO 800