"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.
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Richard Knoppow
Los Angeles, CA, USA
