Being obsessed with subminiature cameras in general and Minox cameras specifically it is no surprise that I chose the Minox format for my first pinhole camera experiments. I have greatly enjoyed using the resulting camera and am presenting the general details required to construct one in this report. I also present a number of photographs taken with my camera.
In general, the camera is simply a pinhole and wind knob added to a Minox film casket. The wind mechanism is the real innovation that I stumbled onto at Home Depot. A 1/4 inch plastic wall anchor fits perfectly into the Minox cassette take-up side and engages the spool tangs without damaging them.
To convert a Minox film casket into a pinhole camera you start by drilling an 1/8 inch hole in the bottom of the film casket, as shown in Figure 1, installing a length of 1/8 inch dowel rod which is then inserted into cut lengths of 1/4 wall anchor. Since the film is safely inside the Minox film cassette no light is able to reach the film, but note that the wall anchor must have 3 expansion grooves and not 4.
Figure 1. Critical Dimensions For Pinhole Camera Construction.
A 1/4 inch hole is drilled into the front of the camera, behind which a pinhole in brass shim stock is taped inside the camera. A piece of corrugated cardboard is cut to fit above the film cassette to hold it firmly in place. A strip of flexible tin is then bent around the camera and wrapped in electricians tape. This serves to both clasp the camera closed and act as a shutter mechanism.
I then made a crude clip-on sports finder by bending wire to the correct size (note that the finder should be the same size as the negative and viewed at a distance equal to the "focal" length of the camera). I sized my finder to the Minox negative size of 8x11mm, which is undersized for the actual negative size of this camera, but allows for the inaccuracy of the finder and also lets me frame my photos as they will be enlarged in my Minox enlarger.
The camera has a focal length of 16.75mm which is roughly "normal" for the 9.2x14mm negative size. I used a non-optimized pinhole diameter of .15mm so that my base "sunny 16" exposure would be exactly one second for Kodak Techpan film (rated at 50 ASA). For these long exposures a tripod clamp was needed and I constructed one from a large "bull dog" paper clip, a 1/4 inch spacer and 1/4 inch bolt (see heading photo).
Camera operation is quite straight forward. After loading your film you wind one full rotation, then with the camera firmly in the tripod clamp you frame your shot using the sports finder. When you are ready to take the shot you slide the shutter up to expose the pinhole. Note that the "shutter" should be wrapped tightly enough around the camera so that it will stay open, but loose enough to slide smoothly. After closing the shutter you should advance the film. For the first ten or fifteen frame you should advance the film roughly 1/3 turn and after that about 1/4 turn. I get approximately 35 frames for my standard 50 exposure Minox load.