gjl711 wrote in post #5887269
It's kind of interesting that in digital it is the exact opposite of what it was in film days. With film large grain = noisy image and small grains = smoother image while in digital, large photo sites = smooth image and small photo sites = noisy image. 
There are still some similarities, though. The early ultra-fine-grain films gave up dynamic range just as do sensors with ultra-high pixel density. It took technological improvements in the film to overcome many of those issues, just as much of the noise issue with small pixels has been improved. But in the end, fine-grained films still required lots of light, because each grain needed to see its fair share of light to be sensitized accurately. That's exactly true with small photo sites on sensors with high pixel density.
For example, Panatomic-X was an ultra-fine-grain film of the earlier type, but many photographers thought the tonal range of it rather limited, compared with, say, Plus-X. And the ISO-32 film speed didn't help in terms of practicality. Then, we had T-grain films and they improved fine grain performance markedly (according to some), and they didn't have to be as slow. But fast films were always grainer than slow films.
All that is still true in the digital world. Small pixel sites need lots of light. If they don't have it, what little light is there has to be amplified a lot, and that amplification also amplifies noise. But at ISO-50 or 100, these may do fine. Technology will improve, but large photo sites will always have more light hitting them at a given exposure, and therefore a bigger and more accurate sample of the scene. And the only way to make a sensor with large photo sites have enough of them to support a large print is to have a larger sensor.
8x10 film photographs on Super XX had clumpy grain typical of early films. But the results were smooth and spectacular, because those grains were never enlarged very much. 35mm never could match that look--ever--even with Panatomic-X or T-max. The only reason anyone ever used a Minox (with 8mm film still bigger than the sensors in point-n-shoot digicams) was for the novelty of a zippo-sized camera, or the ability to sneak a camera in where they weren't usually allowed. The magic wasn't that the image was good, but that the image was possible.
A big sensor with big photo sites will always outperform a small sensor with the same number of small photo sites, assuming the technology is even approximately comparable. But that performance will be measured in smoothness and accuracy, not in convenience. A 500mm lens is easier to carry (and afford) than an 800mm lens, and that's why wildlife photographers and birders are interested in the smaller sensor. Small sensors do really well, and the results can be pretty impressive. I'm not unhappy with the images I've made with my 6-MP APS-C 10D. But if you could manage to drag that 800mm lens into the same spot and use a 5D, the results would be even better, assuming your arm didn't cramp up or your native bearer didn't abandon you.
You could, of course, use the 500mm lens on the 5D and just enlarge the center of the image, but then you have, in effect, a camera with a smaller sensor. Would the middle 5 million pixels of a 5D frame (covering 15x23mm) outperform the 10 million pixels of a whole 40D sensor (covering the same 15x23mm)? Depends on how much you enlarge the image, but probably not. The pixels might be more accurate, but if you downsampled the 40D's 10 million pixels to 5 million pixels, the noise would be averaged out and you'd probably restore the accuracy. So, unless you get (and can carry) the longer lens, the 40D is a more sensible package for situations that require long lenses and a lot of portability.
When asked what size camera he preferred, Ansel Adams famously said, "the biggest one I can carry." Sometimes that wasn't the view cameras for which he was famous, but rather a Hasselblad (as with Moon over Half Dome from late in his career), or even a Leica (as with Georgia O'Keeffe and Orville Cox).
Rick "who actually has a 500mm lens for medium format--equivalent when using 6x6 roll film to a 180mm lens on a 40D" Denney
