Friday Daydreaming
I've learnt a bit about a unique kind of color camera by studying F.E. Ives'
Hess-Ives Hicro Camera (
found here, though many different models seem to have existed). It used a special tri-pack with one element that folded down at a 90° angle (the blue sensitive element) relative to the remaining two elements (green & red sensitive plates). Then, a yellow dichroic reflector lowers down from within the camera and bisects this right angle at 45°. It throws blue light onto the blue plate and allows green & red light to pass to the bipack behind it.
U.S.P. 1,287,327 generally describes the Hicro camera.
Then, patent
1,238,775 describes the dichroic reflector and how to make it (warning... it's super easy!)
980,961 describes the film pack I believe, though I haven't actually read this one yet.
Ives refers to this dichroic reflector as a "color selective transparent reflector", and it represents an advantage over a half-silvered mirror or beamsplitting prism in that
only one color is reflected and all else are passed. A half-silvered mirror would split all light 50/50 and this would require further attenuation by a color selective filter to isolate the primary light. The dichroic reflector takes care of both at the same time, resulting in less loss.
A dichroic reflector is an interesting thing; "...the sum of the reflected rays is in color substantially the complement of the sum of the transmitted rays."
I have some pictures of the Hicro camera interior that I will post if I get permission from the author of said
pix.
OK,
and now for something completely different...
Michaelbsc has mentioned several times about using a tri-color beamsplitter to achieve a very efficient separation of light into red, green & blue elements. It turns out these
Phillips prisms use dichroic reflectors (maybe you knew this... I didn't!). These might be inside every
old camcorder sitting in your closet and I'm wondering if you couldn't just open one up and cannibalize it. Or you can get them for mildly reasonable prices on eBay (at most $200, but O.B.O.). Or one could go for broke (or just broke) and call up
these folks.