DestinDave said:
The way it's been explained to me is with a digital camera let's say you have 8 megapixels. That's 8 million "pieces" of information for that picture. With a medium format negative (or transparency) if you were able to count all the grains of silver on the emulsion you would probably be in the tens of billions! So, in effect the difference is 8 megalixels -vs- 10 gigapixels...
Digital backs for medium format cameras necessarily have more megapixels for the same quality. It's sort of like you need a much bigger lens on a larger format camera to get the same zoom that you would with a shorter length lens on a smaller camera. Consider that you might have 8 megapixels on a camera body that's about the equivalent of a 35mm camera body. When you step up to something like a 6x7 or, dare I say, a 4x5, you're talking at least 22-24 megapixels just to keep the ratio of the resolution to actual image size (or canvas size in PS terms). But to address the original question of how digital compares to film, when you start talking 6x7 and larger, digital doesn't even come close. The native resolution of negative film is approximately 3000dpi. So take a 6x7 low ISO negative film for example, maybe something like PanF. The negative itself (more or less grainless) is 18,600 square pixels; no enlargement. When you start talking about films like Provia (probably the most "grainless" film on the planet), especially with the aid of something like a drum scanner, I'd argue that the native resolution is closer to 5000dpi. That means the original image, non-enlarged, would be about 31,000 square pixels. Now just imagine what the numbers are like when you start talking 4x5 or 8x10.
Just because I'm bored, I decided to do the math:
4x5 low ISO negative: 60,000 Square Pixels
4x5 low ISO color positive: 100,000 Square Pixels
8x10 low ISO negative: 240,000 Square Pixels
8x10 low ISO color positive: 400,000 Square Pixels
sweet jesus. eat it, digital.