Pinhole exposure calculator
Your half of the negative gets exactly one exposure. To get it right, you choose three things: season, time of day and light. Aperture and paper speed are fixed on this camera, so those three are all the calculator needs.
Both In Time · ISO 5 · f/90 · guidelines, not a light meter.
How long do you expose a pinhole camera?
With the Both In Time camera, about 5 seconds at midday on a sunny summer day, and about 20 seconds under an overcast sky. Indoors by a window it runs to minutes: photo paper is slow, and a 0.3 mm hole lets in very little light.
Outdoors the rule is simple. Morning and evening take about four times as long as midday. Spring and autumn double the summer time, and winter quadruples it. Each step down the light list, from brilliant sun to shade, doubles it again. Indoors the calculator assumes smaller differences between seasons and times of day.
At the other end, a pinhole camera has almost no upper limit. The longest single exposure by Przemek Zajfert, the photographer behind this camera, ran eight years, from 2006 to 2014 at Münchner Freiheit in Munich. For your half of the picture, seconds to minutes are enough.
Why three choices are enough
On a normal camera you meter the light, then set aperture and shutter speed. Here both are already decided: the hole is the aperture, and the photo paper never changes. So the calculator works with fixed values, f/90 and ISO 5, and only time is left. It estimates the light from season, time of day and situation, and turns it into seconds. It is not a light meter: when clouds come and go, what the sky is doing right now is what counts.
Once the exposure is done, write the time under your hole, with the date and the place. That is how the second person knows how your half was made.
Reciprocity failure: when to add time
Beyond about 30 seconds, photo paper responds more slowly than the maths predicts. So between 30 seconds and 5 minutes the calculator adds roughly 50%, and above that it doubles the value. The corrected time appears under the result.
Questions about pinhole exposure
- How long do you expose a pinhole camera?
At ISO 5 and f/90, about 5 seconds on a sunny summer midday and about 20 seconds when it is overcast. Mornings, evenings, winter and indoors take much longer; by a window it is minutes.
- How do you calculate pinhole exposure time?
Time in seconds = f-number² ÷ 2^(EV + log2(ISO/100)). With f/90 and ISO 5, a sunny summer midday at EV 15 comes out at about 5 seconds.
- Do I need a tripod?
Yes. The calculator recommends a tripod for every time it gives, and from 5 minutes on it is essential. A steady surface works too; any movement ends up on the paper as blur.
- Can I expose under lamp light?
Better not. Artificial light differs from daylight in colour temperature and strength, and photo paper responds to it unpredictably. The calculator still shows a guideline, but advises against it.