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P612v5.0

If you’ve browsed through this blog before you might have noticed a fondness for pinhole photography every now and then. For me it’s an extension of the process of taking the photograph all the way back from the developed film to designing the camera itself. There is something extra satisfying about holding up a roll of film to see a fixed image when the camera that took it was put together with your own hands, and pinhole cameras are the simplest way to achieve that. If I could make a functioning camera with a proper lens I’d certainly do that but I fear the precision required is beyond me.

The joy of pinhole construction is that the most critical component in any camera with a lens – the focusing system – is not required. A bonus is that since pinholes are tiny the effective f-number is usually very large, which means long exposures. While this can be a pain when actually taking photographs, it does mean that you can also dispense with precision when making a shutter – I can easily time a two second exposure with my watch, 1/500th: not so much.

Since I have a few excellent cameras for most “normal” purposes, I design my pinhole creations to do things that are a little bit different. For example there is the sprocket cam, that takes 72mm exposures across the whole width of 35mm film. Or the ultra-wide angle conversion of a Polaroid pack film camera.

One thing I have tried several times is a camera that takes 6×12 photos. The best effort was another wide-angle camera, with replaceable frame masks so that it can shoot 6×6, 6×9 or 6×12. It worked pretty well and I’ve used it for taking tri-chrome images too, but shooting 6×12 suffers from a big problem at short focal lengths like the one I used for that camera – vignetting.

As well as less light reaching the edges of the film because the pinhole is foreshortened to light coming in at an angle, the edges are further away from the pinhole than the centre of the frame. In one camera I built the frame edges are more than twice as far from the pinhole as the frame centre. This combination can lead to several stops difference in exposure between the centre and the edges. One solution is to curve the film around the pinhole so that all parts of the frame are the at same distance. This also reduces distortion in the extremes of the image since all parts of the frame are also perpendicular to the direction of light coming from the pinhole.

I have built cameras based on this idea before – using foam board as the main construction material. I got pretty good results, but the foamboard just isn’t durable enough, and is quite hard to light proof. So when some flat-pack shelf unit or other that I bought came with a big flat sheet of 5mm plywood as part of the packaging I thought I’d go the extra distance and make a wooden camera.

Here’s my initial sketch.
61250-1
The idea was to make it as compact as possible, so the film spools are crammed right into the corners, with the curve of the film plane meeting them as close as possible. In the end I dropped the idea to angle the sides in favour of a simple box shape, but the final camera is remarkably close to this now crumpled design.

P612v5.0 - interior, rear

There are two nearly semicircular plates that are held 60mm apart and form the film plane. The film travels from one spool around this curve to the other. Everything else is built around this – the base plate they are attached to, and the box that goes over the whole thing to make it a light-tight camera. The outer shell is held firmly in place with a wing-nut that threads onto a bolt fixed onto the top plate. There is a simple wooden knob for film advance, using a small window at the centre of the rear of the box to view frame numbers. The base plate has some little wooden feet, and a metal tripod socket.

The shutter is made from an L-shaped piece of plastic cut from an empty Polaroid film pack, pivoting about a small nail through the corner of the L. The long end of the L covers the pinhole, and the short end acts as the trigger. The L is sandwiched between two other pieces of the same film pack to make a snappy shutter action with a slim profile. The battery contact hole from the pack makes a conveniently sized and perfectly circular aperture for mounting the actual pinhole onto.

It took me about a week to put together in the evenings, using mostly wood glue, and a few small nails and screws. Since the cheap plywood turned out not to be very flat, and my woodworking not very precise the joints aren’t particularly snug, so I turned to my usual light proofing materials – 120 film backing paper and black electrical tape. After covering up the inside and outside of the joints I figured it was ready for a test and loaded up a roll of Fomapan 200, and went for a walk in the last of the August sunshine.

Forest track 6x12

You only get 6 frames of 6×12 on a roll of 120, so it was easy enough to shoot the entire roll and develop it when I got back, and scan it this morning. The results are very satisfying – it clearly works pretty much as I expected and there were only a couple of small problems I identified; a minor light leak, and the film appeared to gradually slide downwards as the film was wound on. The light leak I think came from around the film winder, so I’ve now added an extra flap to cover the gap between the wooden top plate and the film spool. For the film slippage I added some little tabs so that the film can’t move too far up or down, and some metal tabs to put a bit of friction on the film when it’s on the spools and prevent it unwinding and getting too loose.

Tiny trail ~ 6x12

Time for another roll! But already I’m very pleased with this – my best pinhole built to date.

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