That's right Tom. It seems we're going back in time with regards to color film, and so someday I figure this will be the only way to obtain analog color capture.
By the way, here's some info on UHMW-polyethylene and other plastics. Sheet sizes are available, and machining appears to be easy:
They look fantastic.
Originally Posted by holmburgers
There are enough ways to go wrong with just one sheet of film. I can't begin to calculate the opportunities for error with three!
Let's not let the potential for errors deter us. Basically the only things we have to worry about are distances and angles. If we design-in the ability to affect these things, it's not that daunting.
A note about Bermpohls; since they use glass mirrors, refraction errors are introduced when the light strikes these at angles. You'll notice that two of light paths have slanted glass in front of the film-holders to correct for this. Pellicles though, are so thin that they don't introduce any appreciable error.
Ok, some more on the Curtis Color Stellar from the author of that website.
Curtis' solution to this problem was to design a retrofocus wide angle lens. This lens was named the Curtis Color Stellar. It has a focal length of 133mm (5.25 inches), but its back focal distance is approximately 210mm (8.25 inches). Thus the lens could be positioned 8.25 inches away from the focal plane, but it possesses the angle of view of a 133mm wide angle, which in this case is 60 degrees. Prior to introduction of the Color Stellar lens the standard lens on Curtis 4x5 cameras was 8.25 inches, with an angle of view of 38 degrees. It's obvious that 38 degrees is too tight for a variety of news images.
US Patent - Des. 115,165 - Curtis Color Camera
Not very exciting though. Haven't found the goods yet.
edit: Adding some as I come across them; haven't read any yet though.
USP 1,895,555 - Emil Reckmeier 1933 - (example of camera)
USP 1,951,896 - Bermpohl 1934
The 1951896 is the one I just found in my archives. There are pics of the mirror arrangements, but not specific angles and dangles. I had planned to get a protractor to get close, then calculate the needed angles necessary. But time never presented itself.
Originally Posted by holmburgers
The advantage of these over a straight 90 degree splitter is the focal path is shorter, so you can get wider lenses, and the body is smaller.
As far as my earlier statement that one of the three would have the image reversed, that's of no real consequence, and was an attribute of many commercial systems of the day. Printers simply dealt with it.
I had the idea that the first mirror needs to have slight registration marks in opposing corners so you can easily line things up later. Frame generously.
My original thinking was to learn to process the three images in the K-14 chemicals, without the requirements of doing it in the real K-14 process, then aligning the three sheets to make a transparency. Hence my suggestion for K-15 name.
Of course, one could always simply develop for color separations to print.
Yes, that Bermpohl is pretty much what I was thinking in terms of a crooked/folded implementation. I was expecting it to be more-crooked, but it still looks pretty compact.
Anyway. I don't reckon it would be too hard at all to draw up the casing for one of these and have it laser-cut from birch or bamboo plywood. Total cost of the body should be well under $200; the hard part IMHO will be obtaining large, high quality separation filters.
Edit: not to mention an all-analogue tricolour printing process!
My thought was that the beginning experiments for me would be tri color bromoil matrices. It seems far simpler to start than dye transfer or carbon.
Originally Posted by polyglot
Of course, not having done it I could be completely underestimating how hard tri color bromoil really is. But if perfection isn't the goal, then it should be manageable as a way to get the camera hardware figured out.
My enemy is time management.
There's a precedent for plastic bodied tri-color cameras. The 1945 version 4x5 Curtis Scout camera had a welded acrylic body. The philosophy behind this was that if the camera was dropped it would be sent in for repair. It has been said that a frequent complaint of the Devin camera was if it was dropped the metal would bend and registration would be lost. The earlier version 2x3 Scout (1940-41 model) body was an aluminum casting. The final model, the 1950s Press Special had a body of cast magnesium.
Worth noting that burgers has crossposted this to LFPF and got a very cool reply suggesting the use of a 3-way compact prism for beamsplitting. Such an arrangement should be on a similar order of depth as a traditional SLR mirror, which means you could maybe use retrofocus SLR lenses (RB67) to get normal/wide views.
Anyway, I suspect it'd be a good idea to implement decent tricolour printing (from consecutive shots on a rollfilm back) before building a camera like this. To me, the camera looks like a minor mechanical challenge of a similar order of complexity as a traditional camera build, just with a few more parts. The camera is of no use unless you can print (scan?) the separations, and the printing I think will be a real challenge.