I have a 30D and I find that my "functional" ISO maxes out at around 400 and sometimes even less depending on the shot / subject. I'd love to (plan to) move up to a current generation body but am a bit confused regarding the "functional" ISO capabilities. I know the current cameras have incredibly high ISO capabilities but how high can they truly be routinely used in ambient and low ambient light before grain becomes an issue. Since all my lenses are full frame I'd love to go the 5DIII route ($$$$) but might also consider a 7D (mkII ?). Love to hear any opinions on capability vs. reality. Cheers
Are you shooting RAW or JPEG?? Older cameras had really limited processors in them, so jpeg images were not all that good at higher ISO settings. Using RAW and LR 4 should let you use the camera at ISO 1600. Thats one problem with using jpeg, future software improvements do not help old images.
Back when I bought my 30D, I was using jpeg, and images at ISO 800 were good, and optimizing the ISO 1600 images in LR4 helped them out a lot. Not as good as raw, but will print very nicely.
Sometimes sensors do seem to get noise at high ISO's as they age, that might be what you are seeing.
I've owned the DCS 640, D30, 10D, 20D, 30D, 40D, 7D, 5D, 5D MK II, 5D MK III, 1D MK II, 1D MK III, and 1D MK IV. So I've watched ISO capabilities improve over the past 17 years. The jump to full frame and use of RAW will give the biggest improvement over buying a new crop camera.
All sensors produce noise, and need to have NR applied at ISO's above base ISO, so its a matter of how much detail remains after you apply NR.
If you turn off NR completely, even the 5D MK III will show some noise at ISO 800.
Here are some images I took earlier this year that vary from ISO 3200 to ISO 12800. Sensors are good, and so are the newer RAW converters.
5D MK II ISO 3200
5D MK II ISO 6400
1D MK IV ISO 12800
D800 ISO 12800 (ton of NR, but lots of detail left)