CNC & CAD in Buildling a Camera - Tri-Color Specifically
Lately I've been pipe dreaming about building a 3-color camera. This is not something I intend to do tomorrow exactly, but I still think there's some good that could come from talking about it and discussing the feasibility.
3-color cameras require a very precise optical path and placement of the reflectors/film-planes needs to be very exact. Since Computer Aided Design and Computer Numerical Control were in their infancy (if not still in the womb) when the last "one-shot camera" was made, it seems reasonable to assume that making one today might be much easier than it was then.
As I'm imagining it, the camera body could be assembled from a number of separate pieces, cut on some kind of CNC machine (?) and bolted together. The design would accomodate film holder placement; accurately spacing their distances.
The reflectors would then need to be mounted in frames that allow for fine adjustments and calibration after installation, with a provision to fit these frames in the aforementioned body.
The lens board & focusing standard would be fairly easy to make; requiring no great feat of precision. A well made bellows & focusing track would suffice. It'd be nice to connect this to a rangefinder as well.
Considering the need for low thermal expansion, excellent rigidity & an ability to be easily machined, what would be the best material? Steel, stainless steel, aluminum, brass, YbGaGe?
Knowing what kind of machines would be needed to do this work would help you choose a machine shop with the capability. Finding someone versed in CAD shouldn't be too difficult either. I've got at least 1 engineer friend I could bribe!
Try Invar. The alloy you mentioned is probably useless for structural stuff. Carpenter sell Invar in rounds, I don't know where or if you could get sheet and other shapes.
Originally Posted by holmburgers
I was totally joking about YbGaGe of course... but I appreciate you mentioning this alloy.
Invar would be great, but it'll be expensive and wonít come in many forms. Iím also going to take a wild guess and say that itíll be a bit difficult to machine since as far as I know nickel isnít known to improve machinability unlike lead in 12L14, etc.
I would recommend a good engineering plastic. Ultra-high molecular weight polyethylene (UHMW PE), nylon, or acetal come to mind. There are cheaper plastics like fiberglass reinforced resins and ABS but they aren't meant for machining.
If you get serious about this defiantly do your homework and compile a lot of data. I may be interested in helping from the CAD standpoint as Iím a mechanical design drafter by trade and have access to both 3D and 2D CAD systems.
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I think that there is no need to use esoteric alloys with the machining problems and costs involved. If you use the thermal coefficient of expansion for a metal; calculate the change in dimension of your longest piece say from 20 degrees celsius to 35 degrees. There will be such a small dimensional change that it probably is not a factor. I had an enlarger with a 12' aluminum column (bed) and did not need to take temperature into account between summer and winter even with precision work.
Why are there no speaker jacks on a stereo camera?
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.
Front-surface partial mirrors get cheaper as you go smaller; I'd suggest that medium-format is a good place to start. In particular, using RB backs gets you a simple (graflok) mounting system for your films.
The real problem (unless I'm missing something obvious here) is that the mirrors will take up a lot of room in the optical path (about twice as much as in a normal SLR, and that's without any SLR viewfinder!), which means you're limited to quite-long lenses. It will be difficult-to-impossible to build a wideangle camera, and you'll want to have lenses with a registration distance as long as possible. You may only be able to support quite narrow fields of view.
Quit worrying about thermal expansion; such details are an irrelevancy.
You can get free CAD programs. Hell, you can use google sketchup or Inkscape with zero training and a little practise. Design the camera to be built entirely from shapes laser-cut from flat material, make yourself some drawings, send them off to ponoko and they'll send you all the parts in a couple of weeks. If complex 3D stuff (cams, etc) are required, they can be 3D-printed.
What I have thought about, when looking at the old patents to find the angles and dangles for the reflectors, is the majority of the camera body requires very little precision, at least not for prototyping.
A large plastic clsmshell with a mounting pad, then a holder assembly with precision turnscrew adjustments.
We'll need three film backs, also with some kind of 3-point adjustment for planar perpendicular adjustment. But the 3 film gates can be rough with the precision limited to the mounting plate.
What I was sort of hoping would materialize is a community effort - and I nominate Chris as the librarian - to put together an Open Source Hardware Project. Hopefully one that will live on well beyond all of us into the future.
I suggest the project name K-15, as the successor to true three layer color process using B&W emulsions.
My suggestion, once you get beyond the initial design experiments, would be to use a vacuum formed plastic housing.
Originally Posted by richard ide
A determined tinkerer can do this in a kitchen.
Google vacuum forming and check out a few you-tube links.