Richard Knoppow wrote:
> That's quite interesting. I suspect the Rodagon and Componon designs are
> quite similar although I don't have the actual prescriptions. Since its
> likely all the relatively modern lenses were designed with the aid of
> computers I suspect the performance should be much alike. I think the
> Focotar is an older design. One of the characteristics of the generic
> Plasmat type, which is what the Rodagon and Componon are, is that they
> can be unusually well corrected for astigmatism. Forgoing an explanation
> of what exactly that is (different in a camera lens than in opthalmic
> lenses) it leads to being able to get a very flat field. While both
> manufacturers claim superiority I suspect its pretty much a draw. Some
> think the Rodagon is mechanically superior to the Componon. Do your
> lenses have metal or plastic iris blades?
>
When I first got into 4x5" work, in the mid 1970s, I got a Schneider
Componon-S f/5.6 to f/45 180mm enlarging lens, # 11 973 xxx. It works
fine.
Its diaphragm has lots of blades (about 19 of them), enough to make the
aperture look round, and they appear to be metal. At least 10 years later,
I
got a Componon-S f/5.6 to f/45 150mm lens, # 14 588 yyy. It has only 5
blades, so the aperture looks approximately like a pentagon (except the
edges are not quite straght. I cannot tell if they are metal or plastic;
the
180 blades are ****nier than the 150 and darker, reminding me of blackened
brass (but I do not know what they are for sure), and the 150 blades are
duller, but slightly lighter in color and rougher, reminding me of
anodized
aluminum (but I very much doubt they would actually be aluminum). Perhaps
that is what plastic blades look like.
For normal photograph use, is there any benefit to having a round
aperture?
I know in half-tone work with a sealed half-tone screen, there is a
benefit
to having a square aperture, but round holes work OK -- you just get a
little bit of a different transfer function from the original to the
half-tone.
Unless you use the lens in the hot sun or something, there might even be a
slight benefit to having plastic iris blades: less likely to rust or
corrode.
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