Homemade pinhole camera

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An entirely homemade camera

A usable pinhole camera can be built using quite simple, even crude construction methods.

While a lensed camera must maintain precise distances between its optics and the image plane, pinhole cameras are entirely forgiving in this regard. Because pinhole exposure times are typically greater than one second, a complex mechanical shutter is not required. Instead, the photographer can manually open a simple flap or cover to begin exposure.

This low-tech approachability has inspired countless artists, tinkerers, and would-be inventors to try their hand at pinhole camera construction. This can be a satisfying project in itself, completely apart from the photographic results.

The only real requirement for a pinhole camera body is that it be a lightproof container of some kind. Everything from coffee pots, pumpkins, animal sculls, discarded luggage, and even entire delivery trucks have been tried. Many pinhole cameras have been built as showpieces of fine craftsmanship, whether in beautiful hardwoods or elaborately-worked metal. Others are defiantly ugly assemblies of cardboard and black electrical tape. In either case, the image properties will result from the camera dimensions and pinhole size, while the particular construction methods used will have minimal effect.

A pinhole camera using film or photo paper may contort its image plane into something far from flat; image proportions can be chosen at will; cameras may even use multiple pinholes to create a photographic collage in-camera. The design freedom of a homemade pinhole is practically limitless.

Roll film or sheet film

Cameras designed to make a single exposure onto sheet material are the simplest to construct; the iconic Quaker Oats camera is one well-known example[1]. But such one-shot cameras typically require that a photographer be able to develop the resulting image themselves. Often a pinhole photographer will use a sheet of photographic enlarging paper as the sensitive material. This may be more widely available than large-format sheet film, plus it can be loaded under an orange safelight. But enlarging paper has an extremely slow speed (ISO 6 is a typical starting point), and a tonal response that may be excessively contrasty.

In the digital era, access to darkrooms has become rarer; and so pinhole enthusiasts today increasingly use designs that expose 35mm or 120 film, which can be processed commercially.

Because a film advance adds some complexity to a home-built camera, it may prove a simpler option to convert an existing conventional camera for pinhole use. An older model with a damaged lens or a sticky shutter may not be economically repairable; but it can be usefully recycled by replacing its lens with a pinhole. Plastic "focus free" 35mm cameras appear at rummage sales and thrift shops, typically costing less than a roll of film; these may also be good candidates for pinhole conversion.

For someone with a bit more mechanical skill, a home-made film advance for 120 rolls is not especially difficult. The camera simply requires a peepsight on the back which aligns with the appropriate row of frame numbers printed on 120 film's backing paper.

Pinhole size and resolution

The diameter of the pinhole itself sets the limit on how finely details are resolved in the image plane. Up to a point, a smaller pinhole will record a sharper image—albeit at the cost of longer exposure times.

But the wavelike nature of light causes an effect called diffraction, where light rays stop following simple geometric paths. The smaller the pinhole, the more diffraction tends to blur the image.

Thus for any particular pinhole-to-image distance, there is one "optimum" diameter which provides the best balance between these two effects, and thus the sharpest image. Some of the greatest pioneers in optical science, such as Josef Petzval and Lord Raleigh, helped refine this analysis.

While the "optimum" diameter is often expressed in a very precise-looking formula[2], the casual experimenter need not find this too intimidating. it is rarely possible to measure a pinhole's diameter to better than 5% accuracy; and in any case small deviations from the "perfect" values will yield only minor differences in the photographic results. What follows is a table with measurements for optimal pinhole diameters, offering enough precision for all practical purposes. This list is tabulated by f-numbers which decrease in 1/2-stop increments.


Focal
distance
Pinhole
diameter
F-number
13 mm 0.14 mm f/90
20 mm 0.19 mm f/108
30 mm 0.23 mm f/128
40 mm 0.26 mm f/152
60 mm 0.33 mm f/181
80 mm 0.37 mm f/215
12 cm 0.47 mm f/256
16 cm 0.53 mm f/304
23 cm 0.63 mm f/362
33 cm 0.77 mm f/430
47 cm 0.92 mm f/512


F-ratios shown in bold are in the same whole-stop aperture sequence as f/11, f/16, f/22 and so on. For example, f/181 gives exactly 7 stops less exposure than f/16. This may be useful when using a light meter whose aperture scale lacks the tiny f-stops typical of pinhole cameras.

Assuming the "optimum" pinhole size is always used, a photographer will obtain the most detailed image (if this is desired) by scaling up the size of the camera, and using the largest image area that is practical. Naturally, this has to be weighed against the greater costs and inconvenience of handling large individual sheets of film or paper. A photographer who has no darkroom access may find that a camera based on 120 film (which can be commercially developed) gives the most satisfactory results.

While it is certainly possible to use a pinhole body cap on a DSLR, the typical 15 x 23 mm sensor size of an APS-C camera is comparatively small, and the resulting images may be disappointingly blurry.

Fabricating holes

While precisely laser-drilled holes are available commercially, it is not too difficult to fabricate your own. Since there may be some trial and error in this, it's usually best to create the pinhole separately from the camera body itself. This can done in a thin piece of foil, a section cut from a beverage can, or in a heavier-gauge metal piece with a bump sanded down to minimal thickness.

Despite the name "pin" hole, the shaft of a typical straight pin is about 0.75mm, much larger than the optimum hole diameter for most cameras. Instead, the metal should be held against a firm backing (a phone book works well) and just the tip of a needle poked through. A 10x loupe can be helpful in examining the resulting hole, which ought to be round and free from burrs or other debris.

It will often be necessary to poke several holes in order to get one of the desired diameter. Using a magnifier to compare the hole size to a millimeter ruler will give a rough measurement. But laying the pinhole on a scanner, set at its highest resolution, will provide a magnified view that can be measured more exactly.

Camera gallery

While the variety of pinhole camera designs is nearly infinite, the following cameras give some sense of possibilities.


Digital

Digital Pinhole camera? Usually the sensors of digital cameras are too small to make sufficient imagery with pinhole. But there is a digital option that might deliver a miracle of pixel resolution: The scanner camera, made of a common flatbed document & image scanner.

Notes and references

  1. The Quaker Oats camera originated in the period when the carton lid lid was still opaque cardboard. After about 1988, the oats carton switched to a plastic cap which is not light-tight; and thus metal paint cans or cookie tins may be a more practical alternative today.
  2. Selection of pinhole size at Wikipedia.


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