Thanks for all the comments- all good questions. I plan on bringing what I have to the meetup tomorrow, so we can talk it over too.

The paper I'm using is ILFORD B&W: http://www.ilfordphoto.com/Webfiles/2006130200232336.pdf

The moisture issue crossed my mind as well-- I have extra silca gel packets laying around, perhaps I could secure one or two of them inside (in such a way as to not block the light path).

The expansion/contraction thing concerns me - perhaps it is reason enough to switch to a 7/8" cavity to allow for some more wiggle room. I was planning on using black caulk or silicon rubber to adhere the pinhole in position, which may help in its flexibility.

I made a sketchup model of the camera (and pinhole insert), feel free to take a look: http://www.bhs128.com/projects/pinhole/camera.skp

ok i can see that working pretty well.

the math is out there for sussing out expansion and contraction for the diameter of the tube at various temps, i'd find the min and max and route out the notch a hundredth or two wider. remember wind chill doesn't affect metal, but solar gain does. the CNC router would be ideal for putting that in as i don't believe we've a circle template for the router.

roofing sealant is not a bad choice, but it offgasses some fun things that might effect your paper or your better half. 100% silicone should hold up just fine though, and only offgasses acetic acid (vinegar) as it's curing. you'll want "food safe" or aquarium caulk. i believe only GE manufactures it anymore, but it's sold under GE, DAP and several spendy brands as aquarium sealant.

I know we couldn't get enough height on the CNC, but I do have forstner bits, I can bring down if that helps. I think some of that nice thick MDF cut at 45 degree angles would make a good v-block base for the drill press.


Pete