----- Original Message ----- From: "Kate Hudec" <hu...@rcn.com>
> I was interested in Guillermo's recent post about the relationship > between number of rings and zone plate image sharpness. I have a > converted Lubitel with 75mm focal length. If I wanted a camera with > MORE distortion (which I understand from Guillermo's post would also be > a faster camera), would I need a camera with a longer or shorter focal > length? Thanks in advance. Kate, I don't think I mentioned distortion in my post. A faster ZP has more clear rings, but that causes no distortion, the ZP camera still is free of linear distortion (at least). The increased number of clear rings increase the ratio noise/signal, tho. Noise is the light that reaches the film without having suffered diffraction, therefore do not contribute to the "sharpness" of the image, this is the light mostly responsible for the characteristic "glow" of a ZP image. Signal is the light that grazes the edges of the rings, suffer diffraction and is "focused" on the film plane, this light is the one resposible for the "sharpness" of the image. As far as getting distortion using longer or shorter focal length: Very wide angles of view are considered distorting because of the radically altered perspective compared to what we are used to see with our own eyes. If this is the kind of distortion you refer to, then, with a 6x6 film format Lubitel, you would need to have (IMO) the lens (pinhole or ZP) as least as close as 30mm from the film plane (closer would be better). I too have a modified Lubitel and I believe that even carving the front of the camera and recessing the lens, it'd be impossible to install the lens 30mm or less from the film plane w/o having vignetting caused by the viewing lens. If you want to sacrifice the composing help the viewing lens afford, then I think it may be doable but it'd easier if you get a cheaper 6x6 folder camera remove the bellows and modify it as pinhole/ZP. Something like this one I made: ftp://penate:athx2...@members.home.com/penate/cameras/12.jpg or this ftp://penate:athx2...@members.home.com/penate/cameras/6x6.jpg Hope it answers your questions. Guillermo
