Archived posting to the Leica Users Group, 2002/12/17
[Author Prev] [Author Next] [Thread Prev] [Thread Next] [Author Index] [Topic Index] [Home] [Search]A simple calculation I did (based on some leaps of faith, of course) is that to match slow film (ISO 50 or so) you would need an equivalent megapixel amount of about 28MP. This is how I came to that number. With a decent lens and film such as Fuji Velvia you can expect a lpm of about 45. Multiply this by the long side of a 35mm neg (36mm) and you get 1620 lines across. This is theorhetically the maximum number of lines you could discern from the far left to far right of the neg (or slide). Nyquist theorem dictates that you need to double sampling resolution to record detail. But this only works for things that are in phase, such as audio. That's why CDs sample audio at 44.1kHz. People can hear up to 20k (at best) so to record detail that high you need to at least double that (and there's debate that 44.1k isn't high enough, but that's WAY off topic). Anyway, for resolution of an image, doubling is not nearly enough. You need to multiply it by 4 (can anyone say "Reciprocity Law"? lol. It's like doulbing in both directions (2x2=4). This link hints that it may be more like a factor of 6, but I'll be conservative with 4: http://clarkvision.com/imagedetail/sampling1.html If you multiply by 4 my 1620 lines of resolution with film, you get a CCD sensor that must be 6480 pixels wide (4x1620), which would make it 4320 pixels on the short side (to keep the 24x36 aspect ratio). Total pixels: 4320x6480=27,993,600 (about 28MP). If it truly is closer to 6 (instead of a factor of oversampling by 4), this number rises dramatically. This ONLY refers to straight resolution. There are other factors, obviously, in favor of both sides. My observations for the morning.... Randy - -- To unsubscribe, see http://mejac.palo-alto.ca.us/leica-users/unsub.html