Hands on: Make a digital pinhole camera

The internet age doesn’t mean the end for low-tech photography

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.

So the optimal-sized hole for a dSLR with a focal length of 50mm has a radius of 0.165mm – a diameter of approximately a third of a millimetre.

There are a number of other formulas but this one appears to be the most popular, probably because of its simplicity.

You’ll find some of the others on the sites detailed in the web links below, some of which have Javascript calculators.

Having determined the maximum optimal aperture, the obvious question is how do you make a hole one-third of a millimetre in diameter?

I inserted the smallest needle I could find straight into the foil to a sufficient depth so that the widest part of its shaft was buried.

Then I scanned the body cap pinhole assembly on a flatbed scanner at 1,200dpi, which, when viewed at actual pixel size, allowed easy measurement of the hole diameter – 0.6mm.

I made a second attempt using the same needle (it was the smallest one I had), but only inserting the tip. A second scan revealed this hole to be 0.36mm in diameter, though not exactly circular. Good enough, I reckoned.

Aperture and exposure
To calculate the effective aperture for your pinhole camera, you can use the formula f = v/d where f is the aperture, v is the focal length and d is the pinhole diameter.

For my modified pinhole EOS 300D this is 50/.33 = f152. This minuscule aperture is what gives pinhole photography one of its defining characteristics, virtually unlimited depth of field. Everything from the close foreground to infinity is in focus.

It does have one practical disadvantage though – it requires exposure times ranging from several seconds to a few minutes. Clearly there are some subjects for which pinhole photography is not well suited, but for landscape photography and even portraiture, excellent results can be achieved.

Using the camera
Obviously, with exposures measured in seconds, you’re going to need to mount the camera on a tripod or some other steady surface.

The low levels of light transmitted through the pinhole render the viewfinder virtually useless, so you just have to point the camera in the general direction of the subject and hope for the best. You can always adjust it if your first attempt isn’t accurately framed.

You’ll also need to experiment with exposures to find the right shutter speed. As a general guide, start by shooting outside on a bright day with an ISO setting of 100 and make an exposure of about 10 seconds.

You can go from there depending on how the thumbnail looks. I’m pleased with my first pinhole image, despite the fact that it’s poorly framed, overexposed and, because my pinhole wasn’t centrally located, vignetted on the top-left corner. One of the advantages of using removable foil pinholes is that you can adjust them like this to get them positioned in exactly the right place.

With the pinhole relocated and some exposure tests, I produced an image of a willow tree in my garden, with an exposure of two seconds at ISO 800. The Exif data for these pinhole images makes interesting reading.

In the absence of a proper lens, the focal length is shown as 0, the exposure details indicate two seconds at f0 and the maximum aperture value is f1,024. Other than that, all the other Exif data is recorded normally.

I conducted further experiments indoors. An image of some roses was made under halogen room lighting at 800 ISO, with an exposure of 20 seconds. As you’d expect, it shows the characteristic softness of pinhole photos. It’s also pretty noisy and there’s some sensor dust that’s a lot more visible than it would be with the lens attached.

I haven’t tried to improve my images using an image-editing program as this runs contrary to the whole ethos of pinhole photography. My digital pinhole experimentation has been great fun. It has even inspired me to make a genuine pinhole camera using discarded food packaging and a packet of Ilford photographic paper that’s been sitting in a draw for about 15 years.

Web links:
Worldwide Pinhole Photography Day Upload your pinhole photos taken on 27 April 2008 and see images from previous years.

Pinhole photography forums

Some good advice, pictures of the pinhole cameras he has designed and a Windows applet called Pinhole Designer, which helps with pinhole size, focal length and exposure calculations

Article and advice on the physics of pinhole photography

A history of pinhole photography and advice on building a camera

Pinhole cameras and kits on sale