Densitometer

A densitometer is a device that measures the degree of darkness (the optical density) of a photographic or semitransparent material or of a reflecting surface.

[2] It determines the density of a sample placed between the light source and the photoelectric cell from differences in the readings.

[3] Modern densitometers have the same components, but also have electronic integrated circuitry for better reading.

Such measurements enable the photographer to choose the right photo paper and the correct exposure, obviating experiments with test strips.

Once the papers and darkroom have been calibrated, the first print from a previously measured negative is a success at once.