DIY one-shot trichromie camera?

[Ben Syverson]

This sort of came up in the trichromie thread, but I thought I'd break it out to a separate thread... How possible do you think it would be to build a DIY one-shot camera?

Edmunds Optics has some large beamsplitters that seem like they could work:
http://www.edmundoptics.com/images/catalog/2035.jpg (http://www.edmundoptics.com/onlinecatalog/displayproduct.cfm?productid=2035&showall)

I sketched out a design that would allow a bellows range of 300-500mm in 8x10 or 150-250mm in 4x5, so you could theoretically go from infinity to 1:1.5. The sketch shows the bellows fully extended.

[Dan Fromm]

Can you work to high enough precision? Does your design allow a short enough greatest flange-to-film distance for the shortest lens you want to use? You know the answers, we don't.

Cheers,

Dan

[Ben Syverson]

I'm totally unsure about how much precision is required. If I were to build this (I probably won't) I would put primary emphasis on RGB focus, and less rigorous emphasis on registration, since that's easily done in Photoshop.

Such a camera could never be very flexible, due to the angles involved. At first I tried a design that went from 300mm (infinity) to 600mm (1:1), but it's not possible. 500m is only barely possible, as you can see from the tight corners in the design sketch. It might have to be narrowed down to 475 or 450.

You can put whatever lens you want on there as long as you can get the focus you want with a flange distance of between 300 and 500 (or 150 and 250 for 4x5). So a 300mm would have a fairly full range (infinity to 1:1.5). A 240 would not be able to reach infinity focus, but you could get 1:1. A 360 would have infinity but would be limited to 1:2.5 on the close focus.

The biggest question mark for me is how much the beamsplitting mirrors. They're 3mm thick, which leads me to think there will be some refraction. I don't know what that will do to the image or how it would affect the angles I sketched out.

[Robert Hughes]

You may wish to look up information about the old Technicolor cameras - they were bipack (red and blue one negative, green the other) and used beam splitters.

[Struan Gray]

Trichrome cameras are cheapest and easiest to build in small formats. The need for large beamsplitter plates is just one of the reasons.

There are two problems with the plate beamsplitters you have linked to. First, they work best at one angle of incidence (45°), which is less of a problem for your camera because you are limited to longer-than-normal focal lengths. A wide angle lens would probably show colour shifts across the field. Second, as you say, they have a thickness, which will shift focus (easily compensated) and introduce spherical aberration (less so, although again, less bad for long lenses).

If you're tempted to have a go, Edmund have some other beamsplitters worth looking at. The pellicle splitters are best, because they are so thin they won't interfere with the optical character of the lens. In practice though they are delicate, which makes them hard to clean. The polka dot beamsplitters are robust, and nicely wavelength and angle insensitive. They would be my choice if I wanted wide angles of view.

My perfect device would use dichroic beamsplitters, eliminating the need for seperate filters, i.e. the mirror *is* a filter. I would also try and use one of the Rodenstock digitar lenses corrected for a glass cover plate in front of the sensor. Traditional designs have alignment and adjustment screws for everything, but I suspect with CNC machining of a solid block or casting you could eliminate the need for them. 6x9 would be my sweet spot in format size/practicality/cost.

PS: if you're going to be printing with a hybrid workflow you can skip one of the colour filters and just expose full-spectrum. The missing colour info can be recovered by subtracting the two filtered frames from the full-spectrum one. Not only do you need to buy one less filter, but it can help when juggling exposure factors too.

[cjbroadbent]

A great project! Here's the Vivex (and the Cunningham) described in Practical Photography.

[jb7]

And here's one I came across-

http://www.flickr.com/photos/25384265@N04/4082110408/

[Henri Gaud]

http://trichromie.free.fr/trichromie/index.php?category/Matriel-trichrome

Trichrome one-shoot camera

I have buy 12 camera trichrome, and I have beginning the restore, and i can test them in 2010.

You can see these tests in the blog in few month

Excuse my bad english