It's the biggest misconception in digital photography. People think a
smaller sensor somehow changes the optics of the lens. Film or digital --
it's the same light projected through the same lens, you just use a smaller
piece of it with the digital.

Bob-

Funny you should mention that. Another related misconception is that sensor
size is not as important as the number of megapixels. In other words, it is OK
to have a small sensor if you have enough megapixels.

Thirty years ago lenses were rated in "lines per millimeter". I don't fully
understand the more modern modulation transfer ratio (MTR), but I can relate
lines to pixels. So, above a certain number, no matter how many pixels you
have, the image resolution is limited by the lens resolving power. Fewer
sensor millimeters means fewer "lines" in the resulting image. This is another
flaw in the claim of 35 mm equivalency since you would divide lines per
millimeter by the cropping factor.

Perhaps it wasn't a significant factor when sensors were no more than one
megapixel, but is certainly is in today's eight to ten megapixel world.

Fred