I really like the idea of a plastics. Low weight would be a boon and machining would likely be easier and cheaper. I'll look into those..
This question probably deserves a huge answer, but just for the sake of asking, what kind of data would you need to design something like this? If we understood the optical needs, then I could hand-draw something encompassing the basic design once I had reasoned it out in my noggin. It'd be nice to get a more in-depth look at the inside of one of these cameras and work from that.
FYI, the reflectors are not actually glass mirrors, but are ultra-thin pellicles that have been vacuum deposited with some kind of reflective coating. National Photocolor, a company who actually manufactured these cameras back in the day, still makes such pellicles to this day. You'd need 2, and a 5x7" one in a frame is about $250. A smaller one might even be less.
I think a camera designed to take 120 film backs would be an awesome first start; though 4x5" might make more sense at first.
Chris. I found the old patents to some of these once, and the drawings are pretty complete. I'm not sure where I dug them up, but it was with search engines.
I found those drawings very instructive. I'll see what I might have when I get a chance. But search away.
The National Photocolor connection is excellent. Much better than the stuff I tracked down. $250 is awesome.
Last edited by michaelbsc; 03-05-2012 at 07:09 PM. Click to view previous post history.
Google sketchup... ponoko.. what is this, the 21st century?! That's some crazy stuff; amazing what you might be able to build from an armchair. Duely noted.
Michael, you're thinking exactly as I am about mounts with precision turn-screw adjustments. The body can get you in the ballpark, the fine adjuster get you on the money.
Thermal expansion might've been a red herring, but I just meant to ask about materials in general, and CMB did once mention that Bermpohl tri-color cameras (made of teak) did have this problem. Plastic's the way to go...
Good call on focal lengths. This is an issue that these cameras tried to address in the past. I'll have to do some digging, but there were retrofocus lenses to somewhat overcome these difficulties... I'm gonna post a list of cameras and their lenses here in a few minutes...
. . .
Ok, here's a list of cameras and their lenses from Issue 15, Volume 3 (1942) edition of The Complete Photographer
Curtis Color Scout - 2.25x3.25" - 7.5" Goerz Dogmar f/4.5 (190mm) Curtis Color Master - 5x7" - 14" Eastman Ektar f/6.3 (355mm) McGraw Hand Camera - 6.5x9cm (2.5"x3.5") - 140mm Goerz Dogmar f/4.5 (5.5") McGraw Professional - 5x7" - "none" National Daylight (or Tungsten) Feather-Weight - 3.25x4.25" - 8.25" Goerz Dogmar f/4.5 (210mm) National Studio Deluxe - 5x7" - 12" Goerz Artar f/9 (305mm)
A much earlier model: Bermpohl Naturfarbenkamera - 9x12cm (3.5x4.75") - Hugo Meyer & Co. Gorlitz Doppel Plasmat 21.5cm f4
Sure enough, these are some pretty long lenses. Anyone care to find the film-diagonal:focal-length coefficient?
update:
This is promising, a Curtis Color Stellar 133mm f/5.3 on 4x5". here and here
Last edited by holmburgers; 03-05-2012 at 10:21 PM. Click to view previous post history.
I tried to think through the focal length issue once.
The geometry is difficult to conceptualize in my head. And I'm afraid I've never had time to really analyze it. But you could get a kinda short lens by bringing two of the film gates forward. But you have to stay out out of the image field. The camera would be unwieldy and awkward. And short is a relative term. You probably can't get 90mm.
That Curtis Stellar is the obvious arrangement with two mirrors in series, everything close to being at right-angles. Easy to build without much calculation.
However if you're happy for it to be "crooked", you can do a couple of things:
- bring the film planes forward toward the lens and at an angle, which means that the mirrors are steeper, which means less optical path length consumed, which means you can have shorter lenses
- put in three mirrors, which gives you four outputs and therefore a TTL viewfinder!
Of the first point, consider the Red film plane of the Curtis above, swinging it around to lie immediately to the left of the lens. You can imagine that the first mirror is steeper, which means you can bring the second mirror closer. Getting equal path length (for equal focus) means that the red film will actually be a long way out the front, next to the lens.
Of the second point, consider three mirrors in a tree topology. First mirror splits light into two beams, each secondary beam hits a second mirror, which splits it into two further beams. Net result is four copies of the light from the lens: one for each colour and one for the viewfinder. Each beam of light has been through exactly 2 mirrors and so has lost (assuming 50% silvering) 2 stops. Given that you need two mirrors in series for a basic tricolour camera anyway, this design shouldn't have any added flange distance (it makes the scrunching process described above harder though) and means you get a viewfinder.
I'm not sure how much help I can be from the other side of the planet but I do use CAD and CNC. Our CNC machine is intended for drilling and routing PCBs but I use it mainly to cut plastic sheet up to 10mm thick to make test fixtures and assembly jigs.
I use it to make cameras too - see the link below.
Another point to remember, which isn't really big, is that if the images do not have the same number of reflection then odd will be reversed from even.
Also the filter factors will not be the same so 50% may not be our friend. 67/33 might prove useful.
Steve, thanks for your offer of assistance. I think we're a long ways from actually doing anything, but this kind of group effort is just the type of thing that could make this project a reality someday.
Michael, I hadn't thought of that... does that mean in the typical arrangement, 2 of the images will actually not be mirrored, and the remaining plate, being struck by the % of light that was never reflected, only transmitted, would give a typical mirror image negative? I guess so..
If we pretend filter factors are all equal, then a 33/66 mirror at the front, followed by a 50/50 mirror would give equal exposures on all plates. 33% to the red (in the case of the Curtis above), and the remaining 66% split down the middle to green & blue. However, there might be a more novel arrangement if we consider filter factors.
Originally Posted by holmburgers
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