Re: Back to the original point:
Bob A L wrote:
Maybe on your cameras, but if I set my 1" sensor camera at f1.8, 1/60 sec. iso 100 and my apsc camera at f3.5, 1/60 sec. iso 100, and photograph the same subject illuminated by the same light, the photo from the apsc camera will be much darker than the one from the 1" camera.
Well, yeah, 'cause the ISO setting doesn't fit the exposure. Why would you do that? It's like saying if you leave the lens cap on one the photo is completely black.
Then I either would live with the darker photo, which might have even more noise than the one 1" sensor because of the dark image. Or, I could employ post processing techniques to raise the lightness in the apsc shot to equal the shot from the 1" sensor or lower the lightness in the 1" sensor to equal the lightness of the apsc sensor shot, and possibly add noise in either case due to the post processing.
But you wouldn't use an ISO setting that is appropriate for the exposure? Do tell!
But the difference in noise could vary simply because of sensor size or design. But then again, at my example of 100 iso, neither one would likely have much of a noise problem unless it was created by post processing.
*For a given exposure on a given camera*, lower ISO settings tend to be more noisy than higher ISO settings. How much more noisy depends *tremendously* on the difference in ISO settings and the particular camera.
That said, the *only* reason to use a lower ISO settings and lighten the photo in the RAW conversion is to preserve highlights at the expense of a more noisy photo. In "normal" usage, one chooses (or lets the camera choose) and ISO setting that is "appropriate" for the exposure with regards to how you want the photo to look.
In any case, f/1.8 on 1" has a 1/3 stop light gathering advantage over f/3.5 on APS-C. If you want to use a lower ISO setting on APS-C than 1" so you can preserve highlights that would be blown on 1", that's a *choice* that the APS-C photographer has, but it is not a mandate.