Originally Posted by
Roger Clark
I do take pictures with both cameras, and many more. The difference is huge if one changes the parameters of the test, which is what is commonly done, and what you appear to be referring to. But when one equalizes the test, there is no difference. Usually one changes exposure, and/or detail on the subject. For example, in a comparison of 500 f/4 on a 1D4 and 7D, the 7D has finer pixels which provides more detail. But the lens delivered only so much light. An analogy of only so much light: a single apple pie. There is only so much pie to go around. If you want more pieces of pie, each piece is less. In telephoto reach, to increase the 1D4 image detail to the same as the 7D, one needs a longer focal length. That longer focal length spreads out the light so there is less light per pixel (that is why exposure time increases when adding TCs). The lens hasn't collected more light when adding a TC. So the lens collects the light and the focal length + pixel size determines how much light per pixel and how much detail on the subject. When the two systems are equal (e.g, 7D and 1D4), one gets the same noise too. This is basic physics and is commonly applied in camera system design on spacecraft and aircraft remote sensing systems.
But this discussion is not appropriate here in a critique forum. I made the comment to dispel the common belief that the 7D is noisy. I'll post a more detailed explanation the gear forum.
Roger