The Machine
An enlarger projects an illuminated negative down onto paper. The light source alters the image quality.
| Type | Light | Effect on the print |
|---|---|---|
| Condenser | Collimated lenses | Higher contrast, sharper grain, visible dust |
| Diffusion | Scattered glass | Lower contrast, softer grain, forgiving |
This difference stems from the Callier effect. Silver grains scatter directed light away from the lens, boosting contrast.
Magnification and Geometry
Magnification is the print-to-negative ratio. A 50 mm lens at 5× magnification sits 300 mm from the baseboard.
Illuminance falls as the square of magnification plus one:
new time = old time × ((m2 + 1) / (m1 + 1)) squared
An 8-second exposure at 3× becomes 8 × 2.25 = 18 seconds (or 18 s) at 5×.
Working in Stops
Print exposures behave like camera exposures. Geometric steps—such as 4, 8, 16, 32 seconds—give equal one-stop increments. Arithmetic steps like 5, 10, 15, 20 seconds give shrinking tonal jumps.
- A one-third stop increase multiplies time by 1.26.
- A half-stop increase multiplies time by 1.41.
Focus wide open with a grain magnifier. Stop down two stops before exposure. Always develop for the full recommended time to ensure rich blacks.
Account for dry-down: dry prints look darker than wet ones.
Common pitfall: focusing stopped down. Always focus wide open for maximum brightness and critical sharpness, then stop down to expose.