Pinhole Camera Exposure Calculator
Start with a meter reading, then convert it to your pinhole aperture and optional film reciprocity correction.
Why pinhole exposure is different
Pinhole photography uses extremely small apertures (often between f/100 and f/300+), which means exposure times are much longer than with conventional lenses. A light meter may give you a reading at f/16 or f/8, but your pinhole camera often needs seconds or minutes.
This calculator converts that metered reading into a practical pinhole exposure by applying:
- Aperture conversion (meter f-stop to pinhole f-stop)
- ISO adjustment (if your meter ISO and film ISO differ)
- Optional reciprocity failure correction for film
How to use this calculator
1) Enter your metered exposure
Input the shutter time from your meter in seconds and the aperture used for that reading. For example, if your meter says 1/60 at f/16, enter 0.0167 seconds and 16.
2) Enter your pinhole aperture
If you already know your pinhole f-number, enter it directly. If not, provide focal length and pinhole diameter, and the calculator will compute:
3) Apply ISO and reciprocity settings
If your meter is set to a different ISO than your film/sensor, the calculator compensates automatically. For film users, select a reciprocity profile to estimate long-exposure correction.
The math behind the result
The base (uncorrected) exposure is:
If reciprocity correction is enabled and the base exposure exceeds about 1 second, a practical exponential model is applied:
Different films have different reciprocity behavior, so always treat this as a starting point and bracket your exposures when possible.
Field tips for sharper, more consistent pinhole photos
- Stability first: Long exposures demand a rigid tripod and minimal vibration.
- Use a cable release or cap method: Avoid touching the camera during exposure.
- Bracket critical shots: Shoot one at calculated time, one shorter, one longer.
- Track your results: Keep notes by film stock, weather, and development method.
- Check pinhole quality: Burrs or irregular holes can reduce sharpness and contrast.
Quick FAQ
Can I use this for digital pinhole cameras?
Yes. Set reciprocity to None. Digital sensors generally do not have film-like reciprocity failure.
What if I do not know my exact pinhole diameter?
Use your estimated f-number or test exposures. Small diameter errors can shift exposure and sharpness noticeably.
Are these reciprocity profiles exact?
No. They are practical approximations. Manufacturer data sheets and your own tests should be your final reference.
Final thought
Pinhole photography rewards patience. Use the calculated value as your baseline, then refine with real-world tests. After a few sessions, you will build a personal exposure guide that matches your film, camera, and creative style.