The terraPin 6X6 is a pinhole camera for 120 film with a 6X6 frame, in a square format. This design consists of a slide-in replacement extension that changes the focal length of the pinhole camera. This affects "shutter speed", angle of view, and, possibly, depth of field.
Designed for 0.22mm diameter pinhole
f/115 center, f/132 nominal
Horizontal and vertical angle of view: 95.6°
This is a "fast", wide-angle extension for the terraPin 6X6. The Incher slides into the camera body with the terraPin Slider system. The shutter is a captive sliding vane that allows for easy control over exposure. The recessed design prevents interference if you prefer to uncover/cover the aperture with your fingertip.
Because of the short "focal length" of this extension, there is significant light "falloff" at the edges of the frame and the corners in particular. The geometric center of the frame is f/115, and a 14mm ring radiused around this point is f/132, which gives a good compromise between the frame's extremes of f/115 - f/172 (see diagram)
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There are only four pieces to this extension, and assembly should be obvious from the exploded diagram.
You will need:
0.22mm diameter pinhole in thin metal stock
2 X 10mm-long 3mm bolts and nuts (I used countersunk-head bolts for maximum clearance in the field of view -you will need to countersink the holes in the top trim ring)
misc finishing and shaping tools (files, sandpaper, X-acto, etc)
I recommend that the inside surface of wide angle extensions be painted with a flat black to avoid internal reflections and ghosting on your exposed film.