Tools
Long exposures
Past a second or so, film needs more light than the meter says — reciprocity failure. 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.