----- Original Message ----- From: "Chris Harris" <cpharrisph...@hotmail.com>
> First, I can't see the image without a lupe. This makes composing on the > ground glass impossible. What f/stop is your zoneplate? if it were f/90 or f/64 (better) you shouldn't have problems composing your image, you must use a dark cloth though. You mentioned fresnel, that would also help, to see its effect before you buy an expensive one, buy one of those plastics reading fresnel lens you can buy at bus.depot, office depot, etc, they are just few bucks each. cut it to fit the back of your ground glass. > I should mention that I'm used to pinhole cameras without viewfinders, but I > thought I'd have the luxury of seeing an image on the 4 x 5 ground glass. If you want to see an image on the GG with a pinhole lens, have two pinholes, actually, 1 pinhole and one "nailhole", use the latter to compose and the pinhole to make the exposure. > The second problem is that the camera seems to be in focus through a wide > range of focal lengths. I can't see any difference between the focus quality > at 150mm (which the zone plate is designed for) and, say, 170mm. The > magnification changes, but the focus stays the same. I can set the focus at > infinity by measuring the distance from the film plane to the zone plate. > However, the fine adjustments of focusing with tilts and swings seem at this > point impossible. My suggestion is that you find the "actual" focal length of your zoneplate once and then use that distance everytime after. If you want to focus a zoneplate, is almost a must to do it viewing the aerial image and not the GG. BTW, you'll probably be amazed at how "nice" the aerial image projected by a zoneplate looks. Guillermo
