This:
A few months back, I started wondering how I could challenge my photographic skills in a more complex way than by just using a film SLR. I started to research pinhole cameras and wondered if there was anyone making cardboard pinhole cameras. I stumbled across this page and was blown away.
After some more digging and exploring the interweb, I uncovered a PDF file of plans for a cardboard pinhole camera, and a PDF showing how to assemble it. Being a packaging designer and having access to aforementioned cutting table, I decided to have a crack. I started from scratch with only an A4 print-out of the plans. The PDF was pretty inaccurate and not terribly detailed. So I would design a piece, cut a sample and fold it up to see how it fitted together. Tweak it, cut it, try again. Gradually I started to assemble a collection of CAD files that were slowly fitting together to make a camera-shaped object.
Fast forward through about another fifteen to twenty steps of prototyping and re-sizing, and you have this:
With a copy of the Pinhole Designer software available for free download from Pinhole.cz, I was able to determine the best size pinhole for the focal length of my camera. In turn, this gave me the required exposure times, taking into account the film I'm using and reciprocity failure info. I am now in the process of testing it with medium format film.
Will let you know how it goes. :)