Archived posting to the Leica Users Group, 1996/04/19
[Author Prev] [Author Next] [Thread Prev] [Thread Next] [Author Index] [Topic Index] [Home] [Search]On Thu, 18 Apr 1996, Eric Welch wrote: > I don't see how diffraction happens in film. Diffraction happens when > light bends around a sharp edge at a steep angle, like when the aperture > is set to a small size. You mean refraction? > > As far as it goes, 120 film can be "sharper" because the film base is > smaller, I haven't seen anything to say one way or the other, so I'll > take your word for it. BUT, MF lenses aren't as sharp as 35mm lenses, > because they don't have to be. Maybe Zeiss and Schneider lenses are, but > you're wasting contrast to have such high resolution with the > enlargements that are going to happen. Perhaps it is refraction, not diffraction, but upon reflection, I think that it could be both. I will try to find the stuff I was reading and post an answer. The point is that some light will pass through the emulsion and bounce off the back of the film, whether there is a black backing there or the dyes used in 35mm film. On its way back, some of this light will strike and expose some of the silver grains, rendering the image slightly less sharp. The light bouncing off of the backing will be refracted, but as it passes through the emulsion, some of it may be diffracted. These effects are small and I don't think that they make a very large difference to the quality of the image, but I believe that it is a problem that Agfa tried to address when it redesigned the AP film into the APX films. As for the sharpness of MF lenses, I agree that they may not have to be as sharp as 35mm films and that therefore they may improve contrast at the expense of sharpness when it is necessary to make this trade-off. My impression is that even the Schneider, Zeiss and Bronica lenses are not as sharp as 35mm lenses. Gary Toop