Firstly I am rather new to concrete and casting so please forgive any glaringly obvious mistakes I make along the way, I know there are definitely some things I would do differently next time around (more on that later) but if you have ideas on how any of this could be improved please share in the comments. With that said, this is how I made my own concrete pinhole camera...
Step 1: Making the Cast - Part One
The body of the camera is basically a box shape with two walls inside that create separate compartments for the film to travel through. The first photo shows the dimensions of the inside part of the cast which I built out of laminated sheets of 5mm foam. I then created a box to enclose this inside part which when poured in concrete would create the walls of the camera. Finally I found a pen which had about the right diameter (12mm) to make the hole in the front - where the pinhole would be attached, and also the two holes in the top - used for advancing the film and rewinding the film once it is exposed. I glued these three pieces in place before pouring the concrete.
Step 2: Making the Cast - Part Two
The base fits snugly into the bottom of the camera to make it light tight. I made my cast being generous with the measurements then using a file I shaved the edges off the base until it fit snugly into place.