Densitometer
An instrument that measures the optical density of a negative, transparency or print.
Measured in
density units
In depth
A transmission densitometer reads through film, a reflection one reads off paper, and colour versions read behind red, green and blue filters to measure each dye layer. It is the tool that turns darkroom practice from guesswork into measurement, and it is essential for calibrating personal film speeds and development times.
Examples in practice
Measuring a step wedge with a densitometer establishes exactly how long to develop for a target contrast index.