Why pinhole exposures are so long
A pinhole camera has no lens, only a tiny hole, so its effective aperture is extremely small. That aperture is usually somewhere around f/100 to f/300, compared with f/16 or f/22 as the smallest setting on many lenses. Very little light gets through, so exposure times are measured in seconds or minutes rather than fractions of a second. Many pinhole cameras have no mechanical shutter, so you typically uncover and cover the hole by hand.
Pinhole cameras do work. The tiny hole forms an image by letting only narrow rays of light through, producing a soft but recognizable picture with very wide depth of field.
Step 1: find your f-number
The f-number of a pinhole camera is the distance from the pinhole to the film divided by the diameter of the hole.
f-number = distance to film / pinhole diameter
For example, a camera with 50 mm between pinhole and film and a pinhole of 0.25 mm has an f-number of 50 / 0.25 = f/200. Measure the diameter as carefully as you can, since small errors matter a lot at this scale. Many commercial pinhole cameras state their f-number.
Step 2: convert a meter reading
Standard meters do not go up to f/200, but you can meter at a normal aperture and scale the time.
- Meter the scene for your film speed and note an aperture and shutter speed, such as f/8 at 1/125 s with ISO 100 film.
- Work out how much smaller the pinhole is. The light reaching the film drops with the square of the f-number ratio: (200 / 8) squared is 625, so the pinhole passes 625 times less light.
- Multiply the time by that factor: 1/125 s x 625 = 5 s.
So in that scene the base exposure would be about 5 seconds. A simpler way is to use an exposure table, a pinhole calculator app, or a printed chart for your own f-number.
Step 3: allow for reciprocity failure
At long exposures, film responds less than expected. At exposures of a second or more, many films need extra time, and the longer the exposure the more correction is typically needed. The amount depends on the film, so check the manufacturer’s datasheet. If you cannot find data, add generous extra time, then bracket. The same idea applies to other long exposures; see our guide to exposure on a film camera.
Rough starting points
Treat these as rough guides for a pinhole camera around f/150 to f/250 with ISO 100 to 400 film. They are not exact.
| Light | Typical range |
|---|---|
| Bright sun | Roughly a second to under a minute |
| Overcast | Roughly a minute to a few minutes |
| Deep shade | Several minutes |
| Indoors by a window | Many minutes, sometimes tens of minutes |
| Night scenes | Hours |
Photographic paper is far slower than film, so expect times many times longer. Check the paper manufacturer’s data if you can.
What happens if the pinhole is larger?
A larger hole lets in more light, which shortens exposure times, but it also makes the image less sharp. A smaller hole is sharper up to a point, after which diffraction makes the image soft again. There is an optimum diameter for each camera depth, often a few tenths of a millimetre for cameras a few centimetres deep.
Step by step: making a pinhole exposure
- Load film or paper in subdued light.
- Work out your f-number, as above.
- Meter the scene and calculate the base time.
- Add time for reciprocity failure if the exposure is long.
- Steady the camera on a tripod or a solid surface.
- Uncover the pinhole, time the exposure with a watch, and cover it again.
- Bracket by doubling and halving the time on additional frames.
Bracketing and tips
- Bracket more widely than with a lens camera, for example one and two stops either way.
- Keep your fingers and straps out of the front of the pinhole.
- Moving subjects blur or disappear over long exposures, a result many people enjoy.
- Keep notes on time, light, and film for each frame so your next calculation improves.