[LargeFormat] Curtis color-separation camera

[Richard Knoppow]

-------Original Message-------
From: Michael Briggs <MichaelBriggs@Earthlink.net>
Sent: 06/14/03 10:36 PM
To: largeformat@f32.net
Subject: Re: [LargeFormat] Curtis color-separation camera

> 
> 
On 15-Jun-2003 tripspud wrote:
> Hi,
> 
>       A few days ago there was a thread on early tricolor type
> cameras.  It looks like this one was designed to make only
> two plates, however:
> 
>
http://cgi.ebay.com/ws/eBayISAPI.dll?ViewItem&category=4701&item=2934392347
> 
>        There must be a mirror inside.  I might have a look as the seller 
is
> known to  me and in my area, but  I'm only curious.


Definitely there must be a beam-splitter mirror.

The color tabs on the filmholders show that one holder was for the blue
image
and another holder for red and green.   Since all silver halide is
sensitive to
UV and blue, the red/green film would have had a yellow filter in the
light
path.   The red and green sensitive layers were probably only sensitized
to
those colors (besides the blue, which was filtered out) so that they could 
be
combinded into one holder.   Or perhaps additional filtration was included 
in
one layer.

The superb book "The Illustrated History of Colour Photography" by Jack H.
Coote has a description of Curtis cameras:

"Besides making double mirror cameras .... also produced single mirror
cameras
and camera 'backs' using a combination of three films in a 'bi-pack and
one'
combination."

"Most of the single-reflector three-colour cameras sold in the US were
intended
for use with films supplied by the Defender Company and known as Tri-Color
Combination."

So don't plan on using this camera...

"The three films divided into a bi-pack for the blue and green
records and a separate red record.  .....  The two emulsion surfaces of
the
bi-pack were pressed into contact in a special spring-back darkslide."

This is a confusing since the holders shown in the auction appear to be
divided
into ones for blue  and ones for red/green.   Also, since all film is blue
sensitive it seems to make sense to have the blue separate.  The only way
to
include a blue sensitive layer in a bi-pack or tri-pack (modern color
films) is
to have a yellow filter built into the film so that the blue light doesn't
reach the other layers.

"There is no evidence that single-mirror cameras were used for
professional
work, but for a few years they did provide the keen amateur with a
relatively
cheap way of obtaining separation negatives of live subjects."

It would take a really "keen" amateur to use the 40 pound 5x7 model in the 
ebay
auction!


--Michael

  Curtis made several one-shot cameras. This one is interesting because its made from an Agfa/Ansco 5x7 Universal View camera. 
  The lens is a little unusual, the Goerz Dogmar being more common. 
  I am not sure it was balanced for Defender Dupack or Tripack film, I think more likely it was Kodak film, but the cameras could be balanced for various kinds of films or plates.
  Late cameras had beam splitting pellicles rather than mirrors. The thickness of the mirror is important. If too thick it procduces wedging, a sort of variation of density across the frame. The pellicle cameras used sheets of gelatin with deposited reflection material on them. Delicate but they worked. 
  The camera is probably still useable.
  One shot cameras were commonly used for advertising illustration in the 1930's and 1940's. They were partly supplanted by Kodachrome but continued in use until the mid 1950's because the plates did not have to sent out for processing. 
  The negatives were usually printed using the three color carbro method although dye transfer was used after it became available. 
   Curtis also made materials for three color carbon and carbro. The English made Autochrome materials were not reliable enough for the advertising business. 
   Similar cameras were made by National Photocolor and Devin Colorgraph. These two companies merged in the late 1930's.  Since Devin was located on the east coast and Curtis on the west coast the frequency of the two brands varies with the location. 
   I think the Devin camera was all metal. 
   Curtis made a press camera sized one-shot called the Curtis Color Scout. I think this was a single mirror camera. It was 3-1/4 x 4-1/4, equipped with a range finder and intended to be usable as a hand held camera. 
  Kodachrome became available in sheet film sizes about 1938 and rapidly displaced the one-shot and sequential color separation cameras. It could be used in any standard camera and processing was done by Kodak rather than the rather fussy processing needed for good color separation. For photomechanical reproduction the Kodachrome original could be used to make the color separation printing plates. The result was sharper and more saturated color than could be gotten by photographing the carbro prints. 
  I'd love to have one of these guys but can't afford it.:-(


Richard Knoppow
dickburk@ix.netcom.com
Los Angeles, CA, USA