[LargeFormat] Curtis color-separation camera

[Michael Briggs]

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