Reciprocity Calculator
Calculate compensated exposure times for long exposures. Film loses sensitivity during extended exposures due to reciprocity failure—this calculator gives you the corrected time for your chosen film.
Calculate exposure
Select your film and enter the metered exposure time
Enter time in seconds or mm:ss format
Enter a metered time to calculate compensation
Reciprocity failure occurs during long exposures when film becomes less sensitive to light over time. The relationship between exposure time and density is no longer linear, so longer exposures need additional compensation.
Select a film above to see its specific reciprocity characteristics.
When to compensate
Reciprocity compensation is needed whenever your metered exposure exceeds the film's threshold—typically 1 second for most films, though some modern emulsions like Ilford Delta and Fuji Acros maintain reciprocity to much longer times.
Common scenarios:
- Night photography — city lights, star trails, moonlit landscapes
- ND filter stacking — 10-stop or stronger filters in daylight
- Pinhole cameras — tiny apertures require long exposures
- Low-light interiors — available light in dim rooms
- Large format — small apertures for depth of field
Tips for long exposures
- 1Bracket your exposures — reciprocity data varies between batches. Shoot at the calculated time, plus half and double.
- 2Use a cable release — even with a tripod, touching the camera introduces shake during long exposures.
- 3Consider colour shifts — very long exposures on colour film may produce unexpected colour casts. Black and white is more forgiving.
- 4Reduce development slightly — compensating exposure increases contrast. Consider pulling development by 10-15% for very long exposures.