[rollei_list] [digression] process lenses for mask making in the sixties
- From: Emmanuel Bigler <Emmanuel.Bigler@xxxxxxxx>
- To: rollei_list@xxxxxxxxxxxxx
- Date: Wed, 01 Oct 2008 08:51:53 +0200
Richard Knoppow a écrit :
----- Original Message ----- From: "Don Williams" <dwilli10@xxxxxxx>
To: <rollei_list@xxxxxxxxxxxxx>
Sent: Tuesday, September 30, 2008 6:59 PM
Subject: [rollei_list] Re: The new Fuji will be sold as.
At 07:48 PM 9/30/2008, Richard wrote:
The Apo Lanthar is a Heliar type. The older plain Lanthar is a
triplet. I also don't know if the Apo Lanthar was a true apochromat.
I don't know of any roll film cameras with Plasmat type lenses.
Their main virtue is wide field coverage and the ability to be very
well corrected for astigmatism but the Planar/Opic/Biotar type
probably has less spherical aberration which is important in
cameras using rangefinders because it minimises the shift in the
point of apparent best focus as the f/stop is changed. Excellent
lenses have been made using all three designs but the Planar and
Plasmat seem to be the favorites among lens designers.
Comparatively few lenses have been based on the Heliar.
From Don Williams:
.....Once in my career I had, in my department, a process camera.... We used
it to make a form of integrated circuit and the film was always
red-blind as I recall, just very high contrast. The camera was so
large it had a room of it's own, which was more or less part of the
camera.
Don
In addition to what Richard K. has said, I am happy to add a few
personal memories about that.
About film/plates used for making photomasks, I have used such high
resolution plates in the 1980's when I was a student.
The film I used was Kodak high resolution plates type 1A, square plates
2"-1/2 x 2"-1/2
The plates were rumored to be similar to the legendary Kodak
spectroscopic plates 649F, but non-chromatised.
Film existed also in the same genre of high-resolution, red-blind
silver-halide stuff.
>> After all of that, the question. The lens performance was
>> incredible, just superb, but was it an apochromat or just designed
>> for a narrow color band?
In the eighties, the industry had gradually abandoned film & plates to
make photomasks.
So the lab (where I prepared my Ph.D.) got for the price of a 'symbolic
French Franc' a mask-making bench exactly similar you yours. However the
actual price of the device was not so cheap since the price paid to take
the equipement apart, package it and carry it to the university was not
negligible. In addition a special room had to be re-arranged to install
the machine.
This copying bench was fitted with a high-performance lens made by the
French company CERCO. My understanding is that the company itself is no
longer in business, however the CERCO brand name seems to continue to exist.
The lens was clearly designed for green light, it was permanently fitted
with a green filter. The target was a classical drawing on paper
illuminated by ordinary white light.
It was not at all a dialyte and certainly not apochromatic, but
"monochromatic" or something like that. Moreover it was optimized for a
narrow range of magnification ratios. From memory, the resolution specs
were something like 400-500 cycles/mm, the lens was certainly
diffraction-limited so in order to achieve this resolution figure the
f-number had to be f/4 if the operating wavelength was 0.5 microns or so.
The real question is: if I find such a lens in a hi-tech flea market, if
I take the green filter off, can I use it for general purpose
white-light photography ?
In fact I have no idea of the actual image quality you can get !
---
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