Originally Posted by
Inkanyezi
Much ado about lenses "for film" vs "for digital". Actually, there are differences, and they are way simpler than that.
When we used film, there was very little light reflected back toward the lens from the film, and any such light was scattered, so we needed not worry much about light bouncing back and forth between film plane and lens, softening the image. Digital cameras is another matter, as there is a reflective filter in front of the sensor, effectively working as a mirror, and it does not scatter the light it bounces back toward the lens.
So why would that be a problem?
- Well, if the rear surface of the lens also is a mirror, there will be a lot of stray light from it toward the sensor, so AR coating is an issue with digital cameras, and it is quite noticeable. Many lenses from older days do not have the best AR coating, and they cannot produce as crisp images as lenses with good AR coating.
So I haven't touched "sharpness" or resolution yet...
Sharpness is a compound property, which depends heavily on contrast, and the stray light that old lenses cause to the sensor will decrease apparent sharpness, even though it does not affect resolution.
Then there is also another issue, which is in fact totally unrelated to the relative depth of film layers. That depth is irrelevant, although the unevenness when film is first rolled, then flattened, often making it bulge in an undulating fashion, may have some relevance to lack of sharpness at very wide apertures. No, it is not the depth, neither the unevenness of the film, but the simple fact that there are different criteria for different sizes of film or sensor.