[pure-silver] Re: looking for a 240-300mm enlarging lens
- From: "Richard Knoppow" <dickburk@xxxxxxxxxxxxx>
- To: <pure-silver@xxxxxxxxxxxxx>
- Date: Sat, 19 Feb 2005 01:48:17 -0800
----- Original Message -----
From: "Peter De Smidt" <pdesmidt@xxxxxxx>
To: <pure-silver@xxxxxxxxxxxxx>
Sent: Friday, February 18, 2005 7:33 PM
Subject: [pure-silver] Re: looking for a 240-300mm enlarging
lens
> Shannon Stoney wrote:
>
>>
>>What is a process lens, as opposed to an enlarging lens?
>>
>>On ebay there was one 240mm enlarging lens for $200.
>>
>>--shannon
>>
>>
> A process lens was used on graphic arts cameras. They were
> usually
> optimized for 1:1 and, I think, F22. Enlarging lenses are
> often
> optimized for 6x enlargements, and are often at their best
> at about f11,
> at least for a 240mm lens.. I would only use a graphic
> arts lens if it
> was really, really cheap, as in free. If that's what you
> want, call up
> graphic arts places and ask if they have any lenses. I did
> that awhile
> ago and picked up a Goertz Dagor. I had to insist that the
> person take
> some money as he wanted to give it to me. I sold it on
> Ebay for $200 to
> someone in China. (No, I didn't think it would go for
> anything near
> that.) Still, look for a real enlarging lens. A while ago
> I bought a
> mint (and I'm not exaggerating) 240mm Nikon enlarging lens
> for $75. They
> simply are not that much in demand.
>
> -Peter De Smidt
> www.desmidt.net
If used for the orignal cross-screen half-tone process the
f/stop is chosen according to the magnification and the
nature of the screen. There are a couple of theories of how
the system works, I am not sure which is currently thought
correct. However, the f/stop is critical for good quality.
Many barrel process lenses have a slot for special stops or
filters. For color halftone work, for instance, the stop for
each color is of special shape, somewhat eliptical, and the
angle of each color is chosen to avoid a moire pattern in
the final printed image.
For pictorial work the optimum stop is around f/22 for
most of them.
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