Print Exposure Calculator
Calculate adjusted darkroom print exposure times for f-stop printing, enlarger height changes, and test strip planning. Built for silver gelatin printers.
Calculate print exposure
Choose a mode to calculate adjusted exposure times for your darkroom printing
Adjusted exposure
20.0
10s +1 stop = 20.0
F-stop scale
Each stop doubles or halves the exposure. Click a cell to select it.
F-stop printing uses logarithmic (geometric) exposure increments. Each whole stop doubles or halves the total light reaching the paper, giving perceptually even tonal steps.
This is the preferred method for dodging and burning because a +1/3-stop burn will have the same visual effect regardless of the starting exposure time.
F-stop printing treats exposure time logarithmically, the same way your camera's aperture ring works. Instead of adding fixed seconds, you double or halve the time for each full stop.
Formula
t' = t x 2n
Where t is the base time and n is the number of stops (positive = more exposure, negative = less)
The advantage is that each stop produces a perceptually equal change in print density, regardless of the base time. A +1/3 stop dodge on a 4-second print produces the same tonal shift as +1/3 stop on a 30-second print.
When you raise the enlarger head, the same amount of light spreads over a larger area. The intensity at the paper surface drops with the square of the distance.
Formula
t' = t x (new size / old size)2
Using the diagonal measurement for each print size
In practice, lens fall-off, condensation, and refocusing all affect the result. This calculator gives a strong starting point, but always confirm with a small test strip at the new size.
Darkroom printing tips
- 1Always make a test strip first — even experienced printers test. It saves paper and chemistry in the long run.
- 2Warm up your enlarger — let the lamp stabilise for a few minutes before timing critical exposures.
- 3Dry-down compensation — prints darken by roughly 5-10% as they dry. Consider exposing slightly less than your wet test suggests, or do dry test strips.
- 4Use a focus finder — critical focus on the easel is essential, especially at large magnifications where depth of focus is shallow.
- 5Keep notes — record your exposure, filter grade, dodging and burning for every print so you can reproduce results.
Quick reference
| Stops | Multiplier | 10s base | 20s base |
|---|---|---|---|
| -2 | 0.25x | 2.5 | 5.0 |
| -1 | 0.50x | 5.0 | 10.0 |
| -1/2 | 0.71x | 7.1 | 14.1 |
| -1/3 | 0.79x | 7.9 | 15.9 |
| 0 | 1.00x | 10.0 | 20.0 |
| +1/3 | 1.26x | 12.6 | 25.2 |
| +1/2 | 1.41x | 14.1 | 28.3 |
| +1 | 2.00x | 20.0 | 40.0 |
| +2 | 4.00x | 40.0 | 1m 20s |
| +3 | 8.00x | 1m 20s | 2m 40s |
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