Density
A measure of how much light a processed negative or print blocks, expressed logarithmically.
Formula / rule
D = log₁₀(1 / transmittance)
Measured in
density units
In depth
A density of 1.0 transmits a tenth of the light, 2.0 a hundredth, 3.0 a thousandth. Because the scale is logarithmic, a difference of 0.3 corresponds to one stop, which makes density the natural language for describing negatives. Judging a negative means reading whether its shadow and highlight densities fall in printable range.
Examples in practice
A well-exposed negative typically shows shadow densities around 0.1 above base fog and highlights near 1.3.