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4x5 Pinhole Project

Terry Lee

New member
I've been wanting to do this little project for several years, and finally forced myself to sit down and do it. I've been wanting to use my mad CAD skills to whip out a laser cut pinhole camera for 4x5 standard backs. Why? I dunno, I guess I just enjoy the fun part of photography?

So I picked up a laser cut pinhole off the web, .5mm in size which equates to about 155mm focal length for 4x5. That meant I needed to design a box with that approximate focal length, and the aperture would be around f295 or so. (There are tons of pinhole calculators out there to play with online)

The box part was simple, the tough part was the light trap for a standard 4x5 holder:
Pin1.jpg


As this was liteply being cut on a laser cutter, the gotcha is that a laser can only cut in two dimensions. Anything needing three dimensions, like a light trap, requires layering. Luckily the laser cutter is so accurate I could build in retaining/alignment tabs into each layer. This worked like a charm and aligned it perfectly.

Pin2.jpg


The rest of the camera is a simple box, nothing too hard to do in CAD. I designed the tabs such that the boards would only go one way, like a puzzle, so there was no confusion about an inside/outside face to the board.

Pin3.jpg


To be continued.....
 

Terry Lee

New member
Since this was my prototype, I had a few issues as all prototypes do. But for the most part it went together very quickly, I had two cutting errors that are easy to fix, and made a couple of work around in the prototype.

The key was the back design, and the light trap appears to fit and work correctly:

Pin5.jpg


I used poly based glue, great stuff but it foams, and I didn't have good clamps. End result was a couple of light leaks. Next version I'll use CA glue to weld up the seems. You can see some filler material I ran into the joints.

But the good news the film holder fit perfectly into the back light trap. I hammered in some Tnuts into the inside face of the back, and an cut some simple retaining tabs out of the same ply that the camera was made from. A simple screw runs up into the TNut on the inside, and provides the pressure to hold the film holder in place:

Pin6.jpg


I only used 3 screw tabs for the back, mostly because I was lazy. Reality is it doesn't need any pressure at all just to be snug and the holder sits nicely.

Pin7.jpg


To be continued.....
 

Terry Lee

New member
The final chapter!

As I mentioned there were a few kinks. I didn't cut the pinhole opening correctly on the prototype, but it isn't anything some black tape can't fix! For the shutter, I also used a Tnut on the inside, with a screw thru the laser cut shutter. It is only snug, allowing the shutter so move easily, but still enough tension that the shutter won't fall closed with gravity:

Pin8.jpg


I also installed tnuts allowing placement of the tripod to either a horizontal of vertical position. If it is going to be a simple camera, it better at least be functional!

Pin9.jpg


I was surprised how sturdy it all works out to be. The wood, being ply, is very strong, and locks into the tripod with authority!

Pin11.jpg


Now for the test....I discovered another light leak! This time a pinhole sized leak on the side, again due to the glue used, but some quick black tape sealed up that side. On the final version I'll take some black silicon to the inside seams and make double sure it is light tight, but for the prototype tape works fine:

All set up and ready to test:
Pin10.jpg


If you've never shot pinhole before, you should give it a try. You really get to exercise your light math, fstops and such. I was using Foma 200 speed film (the Freestyle EDU version at least) and this shot was a 5 min exposure! We had no light, cloudy day, my EI for the EDU film is 100. Base exposure was 3:30 but I figured there was almost another stop of reciprocity failure for the film....I think I was pretty close:

Pinhole5.jpg


Next steps? To rework the CAD file to a "production" version and do a final Version 1.0 test! The building is fun but the photographer in me likes the testing part!
 
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