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: > I'm willing to believe things that are true ... Good. The data should speak for themselves, then. > Show me the data for "most" lenses. The standard for MTF lens charts shows modulation transfer for 5, 10, 20, and 40 lp/mm. The upper limit of 40 is chosen because it is close to the limit of visual acuity for 35mm images, and because few lenses really show outstanding performance beyond that limit. > Any way, who cares about "most", I only > care about the best lenses, since that's > all I use. The examples I gave were for Leica lenses, which are among the best in the world. > You need 5400 SPI to reliably sample 53 lp/mm. No, I do not. I have a 2700-dpi scan of a Provia transparency right here in front of me that quite obviously resolves lines covering individual pixels, thus resolving 53 lp/mm. Given this, I'm afraid I cannot give any credence to your assertion. The physical evidence cannot really be ignored. > Where is this information and for what films? You can find the technical descriptions of the films on their respective Web sites. I was looking at Ektachrome, Technical Pan, Provia 100F, and Velvia. > "Viewing distance" is only a stated condition, > and not valid for this discussion, and this is > therefore irrelevant to this discussion. The entire purpose of taking photographs is normally to display them for human visualization, so the limits and conditions of human viewing of those images are extremely relevant to this discussion. > You didn't tell me anything I didn't know. Sorry. You had not shown any of this knowledge thus far. In any case, it might be useful to others. > If that were true, you would not be insisting > that 2700 SPI can reliably scan 53 lp/mm. As I've said, I have the proof right here in front of me. Your isolated and unsubstantiated assertions really are of no value next to an actual scan that contradicts what you claim. > How convenient for you to leave out some of > the best lenses made from this discussion. It is not a matter of convenience. I simply have no data for Zeiss lenses. If you do, perhaps you can provide some of it here for comparison. For what it's worth, the scan I mention above, the one that disproves your assertions, is of a transparency exposed using a Leica Apo-Summicron-M 1:2/90 ASPH, one of the sharpest lenses ever made by Leica. It easily resolves 100 lp/mm throughout the field even when wide open, and it only gets better when stopped down. This is one reason why I am able to see an actual 53 lp/mm on the scan.