Tools
Long exposures
Past a second or so, film needs more light than the meter says — reciprocity failureReciprocity failure The loss of a film’s effective sensitivity in very long (or very short) exposures, so that more exposure than the meter says is needed. Read more in the glossary ›. Pick your film and type the metered time: you get the time to expose and the stops it adds, from the maker’s own data.
Work it out
Films with published data
- Ilford Delta 100 Pro Schwarzschild exponent · P = 1.26 · 1 min metered → 2 min 54 s
- Ilford Delta 3200 Professional Schwarzschild exponent · P = 1.33 · 1 min metered → 3 min 52 s
- Ilford Delta 400 Professional Schwarzschild exponent · P = 1.41 · 1 min metered → 5 min 22 s
- Ilford FP4 Plus Schwarzschild exponent · P = 1.26 · 1 min metered → 2 min 54 s
- Ilford HP5+ Schwarzschild exponent · P = 1.31 · 1 min metered → 3 min 33 s
- Ilford Pan F Plus Schwarzschild exponent · P = 1.33 · 1 min metered → 3 min 52 s
- Ilford SFX 200 Schwarzschild exponent · P = 1.43 · 1 min metered → 5 min 49 s
- Ilford XP2 Super Schwarzschild exponent · P = 1.31 · 1 min metered → 3 min 33 s
How it is worked out
A second or less
Exposed as metered. The makers’ data starts above one second, and nothing is corrected below it.
The maker’s formula
Where the maker gives a Schwarzschild exponent P, the time to expose is the metered time raised to P (Tc = TmP) — Ilford publishes its films this way.
The maker’s table
Where the maker gives a table, times between its points are read on log-log scales. Past the last point there is no answer: the table is never extended beyond what was published.
The same rules as NegaKit’s roll card, so the app and this page always agree.