"Jean-David Beyer" <jeandavid8@[EMAIL PROTECTED]
> wrote in message
news:rbfVj.1212$OT1.79@[EMAIL PROTECTED]
> 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 shinier 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.
>
> --
> .~. Jean-David Beyer Registered Linux User 85642.
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