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Wollensack 15" f/10 Apochromatic
Is this worth having a lensboard drilled? I was thinking of trying it
on the 5x7 for a bit of a tele feel, but if it's one of those dogs that pass as enlarging lenses, maybe not. |
#2
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Wollensack 15" f/10 Apochromatic
"Ken Smith" wrote in message m... Is this worth having a lensboard drilled? I was thinking of trying it on the 5x7 for a bit of a tele feel, but if it's one of those dogs that pass as enlarging lenses, maybe not. Its an apochromatic process lens. Process lenses had to meet quite high standards so its likely a very good lens. Wollensak was capable of making excellent lenses, I don't know why some of their post WW-2 lenses were so poor. This is not an enlarging lens although process lenses work very well for enlarging. A true apochromatic lens is corrected so that it comes to a common focus at three colors and is corrected for spherical aberration at two colors. Most lenses are achromats, chromatically corrected for two colors and for sperical for one color. While this doesn't mean that an apochromatic lens is necessarily better than an achromat apochromatic process lenses are generally slow, symmetrical types with excellent correction for all aberrations. They were designed for making three color separation printing plates where the thee images had to be of the identical size and very sharp. Most of these lenses are of the four element air spaced type known as a Dialyte. One property of a Dialyte is that its corrections do not change much with change in object distance so they generally will perform well at infinity focus even though designed for unity magnification where object and image distance are the same. However, dialytes also have rather narrow coverage, usually an image circle no larger in diameter than the focal length of the lens. I don't have information on the specific construction of this lens. -- --- Richard Knoppow Los Angeles, CA, USA |
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