A pinhole on the pier
A pinhole camera is the cheapest long lens-less exposure there is: a body cap with a hole drilled through it, a square of brass shim taped behind, and a hole in the shim made with the tip of a needle. Nothing focuses, so nothing is ever out of focus; everything is equally, gently soft from the wet boards at your feet to the horizon.
How big a hole
There is a best diameter for every distance between hole and film. Too large and the image is a blur of overlapping discs; too small and diffraction smears it instead. The usual rule of thumb is 1.9 times the square root of the distance multiplied by the wavelength of light, which for green light gives the figures below.
| Hole to film | Best hole | Works out to |
|---|---|---|
| 25 mm | 0.22 mm | f/112 |
| 50 mm | 0.32 mm | f/159 |
| 75 mm | 0.39 mm | f/194 |
| 100 mm | 0.45 mm | f/224 |
| 150 mm | 0.55 mm | f/275 |
A hole a tenth of a millimetre off is not worth a second attempt. A ragged hole is: sand the dimple flat with fine wet paper and look at it against a lamp through a loupe. It should be round and have no burr.
What the exposure is
Meter at f/16 and count stops. From f/16 to f/159 is a little over six and a half stops, so a metered 1/125 s becomes about three quarters of a second before the film's own reluctance is counted, and at those times it must be counted. On an overcast afternoon the metered 1/30 s at f/16 turns into three seconds on the dial and something like five on the film.
What goes wrong
- Wind. A fourteen-second exposure on a pier that hums under every wave is a recording of the pier. Hang the bag from the tripod and stand upwind.
- Flare. There is no lens hood because there is no lens. Keep the sun behind a post, or accept the star it draws.
- Dust. At f/159 every speck on a digital sensor is in focus, which is one more reason to use film here.
- Counting. A cable release with a lock and a watch with a second hand beat counting elephants in a cold wind.
The first roll is always for calibration. Bracket by a whole stop either side, write the times on the back of a hand, and read them against the negatives a day later.