Reciprocity
Ilford SFX 200 long exposures
What a metered time becomes on SFX 200, and the stops it adds — worked out from Ilford’s own data, never past it.
Your metered time
Tc = Tm^P for metered times over 1 s; 1 s or less needs no correction (P = 1.43)
At a glance
| Metered | Expose for | Added |
|---|---|---|
| 1 s | 1 s | — |
| 2 s | 2.7 s | +0.4 stops |
| 4 s | 7.3 s | +0.9 stops |
| 8 s | 20 s | +1.3 stops |
| 15 s | 48 s | +1.7 stops |
| 30 s | 2 min 10 s | +2.1 stops |
| 1 min | 5 min 49 s | +2.5 stops |
| 2 min | 15 min 40 s | +3 stops |
| 4 min | 42 min 13 s | +3.4 stops |
| 8 min | 1 h 54 min | +3.8 stops |
| 16 min | 5 h 07 min | +4.3 stops |