Archived posting to the Leica Users Group, 2001/07/26
[Author Prev] [Author Next] [Thread Prev] [Thread Next] [Author Index] [Topic Index] [Home] [Search]Austin writes: > It is an inaccurate statement. It is an accurate statement. I'll explain further, since you seem unwilling to believe it. Let's look at a typical lens, say a Summicron-M 1:2/50, set wide open. Already, on the optical axis, the modulation transfer at a mere 40 lp/mm is only about 45%. At the edge of the frame, it's down to 20%. And this is for a very good lens, a _Leica_ lens, not some entry-level Nikon G-series zoom. At f/5.6, the situation improves, but the MTF at the frame edge is still down to 50% for 40 lp/mm, and is only about 80% on axis. So, most lenses really just barely manage 40 lp/mm, much less 53 lp/mm (53 lp/mm isn't even plotted on most MTF charts, because the frequencies between 5 and 40 lp/mm are the most important ones for the subjective impression of image sharpness). Even if you have a perfect lens, try looking at film. A typical slide film may be down as low as 20% modulation transfer by the time you get out to 53 lp/mm, with some colors more affected than others. All of this is true _before_ you allow for camera shake, which makes things far worse, unless you are shooting from a heavy tripod. You can cut some of these resolution figures in half just because of camera shake. This can already happen at 1/125 with a 50mm lens, for example, and even in the hands of a well-practiced photographer. Finally, examine the limits of human vision. Under ideal conditions, a person with perfect vision can see details as small as 1/6875th of the viewing distance in a photo. In practice, though, this ability is diminished by a factor of 2-5. At a standard viewing distance equal to just over the diagonal of the image, 2700 dpi yields just about the limit of what a person can actually see, or 53 lp/mm. Does this make things clearer? > Provide the exact source of this claim. Erwin Puts, for the Leica MTF charts. Eastman Kodak and Fujifilm Ltd. for the film MTF charts. Norman Goldberg and Nikon Japan, for information on camera shake amplitues. Various sources that I don't recall for the vision data, since it is very widely acknowledged and cited in texts on the physiology of vision, and I've looked at many such texts over the years. > I didn't say it was wrong, just back it up > with some reality, not just your belief. See above. I work with facts, not beliefs. (That's why I've never believed in a "Leica glow," for example.) > What about Zeiss lenses for Contax 35mm SLRs? I have no data for Zeiss lenses. > Some of them have better MTFs than comparable > Leica lenses? Maybe, but unless their users also have much better eyes, and they somehow obtain much better films, and have the world's steadiest hands or specially damped tripods, it won't help. There are a few Leica lenses with outstanding performance, and even a few that are diffraction-limited (and you can't get any better than that). But there are no films that can take advantage of such performance, except for a few specialty emulsions like Technical Pan, and even Tech Pan cannot handle the very high resolution of diffraction-limited optics. And in any case, you cannot see resolution that high in an actual photograph, because your vision just isn't that good.