Hands on: Make a digital pinhole camera

Sunday 27 April 2008 is Worldwide Pinhole Photography Day.

Held every year on the last Sunday in April, this international event promotes and celebrates the art of pinhole photography.

A pinhole camera is a camera without a conventional lens. Instead, a tiny hole focuses light rays through a single point.

They are usually home-made devices – everything from shoe boxes and Coke cans to Pringles tubes have been requisitioned in the quest for pinhole perfection.

Photographic paper is commonly used in place of film, but I’m going to show you how to temporarily turn your digital SLR into a pinhole camera by making a ‘pinhole lens’ to attach to it in place of the conventional one.

After all, it doesn’t get much more hands on than making your own lens. Pinhole photos have a beautiful dreamlike quality, reminiscent of a bygone photographic era.

Adapting your dSLR to take pinhole photos only requires a little time and effort (my first attempt took me less than half an hour), and provides a great introduction to the subject.

It’s astonishing that you can make images of this quality without a conventional lens and perhaps a timely reminder that you don’t need expensive, sophisticated equipment to make great pictures.

If you become hooked, and want to make a real pinhole camera, I’ve listed some useful websites opposite. The first thing you’ll need is a body cap for your dSLR.

This is a plastic cap which fits into the hole that’s left when you remove the lens. If your camera doesn’t have a hole, or you don’t want to put a hole in the one you have, you can pick up a spare for a few pounds from most camera shops. Using the smallest drill bit you have, or some other sharp implement, put a hole in the exact centre of the body cap.

There’s no need to worry about the size of the hole at this stage, anything between 1mm and 3mm in diameter should be fine. Next cut a piece of aluminium foil. A disposable food container, or as I’ve used, a Mr Kipling mince pie foil dish, is ideal – ordinary kitchen foil is too thin.

Tape it to the rear of the body cap covering the hole – I used thin strips of masking tape, but electrical insulating tape or even Sellotape would work equally well. Then use a pin or small needle to make a hole in the foil. I placed a cork under the foil to help keep the needle straight and steady, and to minimise burring. If necessary, sand the reverse of the foil to remove any burrs.

Try and keep the hole as small and smooth as possible. Generally speaking, the smaller and smoother you can make it, the sharper your pictures will be. For the rough and ready version, just use the smallest needle or pin you can find, insert it no more than a millimetre or so into the foil and then withdraw it. For more detailed information on aperture size see below.

Aperture calculations
If you’re not interested in the numbers, you can skip this section and get straight onto ‘Using the camera’.

The great thing about pinhole photography is that getting a good result is largely a matter of trial and error, but the physics is interesting in its own right and, who knows, it may help you get better results sooner. Generally speaking, the smaller the pinhole, the sharper your images will be.

Beyond a certain point, however, images become less sharp due to diffraction. The optimum size of the hole (aperture) is related to the wavelength of the light passing through it and the focal length – the distance from the hole to the sensor.

For distant subjects, the optimum pinhole radius (r) is approximately equal to the square root of the wavelength of the light λ multiplied by the focal length (d). Or r = sqrt(λd).

The visible spectrum corresponds to a wavelength range of 400-700nm, so we’ll use 550nm as an average value. The position of the focal plane on an SLR camera is marked by a symbol consisting of a circle with a horizontal line through it. To determine the focal length, measure from the line to the front of the body cap – on my EOS 300 it’s 50mm.

Using the above formula with all measurements in millimetres:

r = sqrt (.00055x.50) = 0.165mm.

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