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Optical density is a result of the darkness of a developed picture and can be expressed absolutely as the number of dark spots (i.e., silver grains in developed films) in a given area, but usually it is a relative value, expressed in a scale. [citation needed]
AFAIK, optical density was originally defined by Hurter and Driffield as D = log10(O) to indicate the amount of an opaque substance suspended in a transparent medium: "For our purposes, i.e., in its application to negatives, the density is directly proportional to the amount of silver deposited per unit area, and may be used as a measure of ...
τ ν is the spectral optical depth in frequency, and; τ λ is the spectral optical depth in wavelength. Although absorbance is properly unitless, it is sometimes reported in "absorbance units", or AU. Many people, including scientific researchers, wrongly state the results from absorbance measurement experiments in terms of these made-up ...
Lenses of fixed tint are graded according to the optical density of the tint; in the UK sunglasses must be labelled and show the filter category number. Lenses with light transmission less than 75% are unsuitable for night driving, and lenses with light transmission less than 8% (category 4) are unsuitable for driving at any time; they should ...
Spectrophotometer for OD600 and Cell Density Measurements. OD600 (Also written as O.D. 600, D 600, o.d. 600, OD 600) is an abbreviation indicating the optical density of a sample measured at a wavelength of 600 nm in 1 cm light path (unless otherwise stated).
Spectral optical depth or spectral optical thickness is the natural logarithm of the ratio of incident to transmitted spectral radiant power through a material. [1] Optical depth is dimensionless , and in particular is not a length, though it is a monotonically increasing function of optical path length , and approaches zero as the path length ...
The granularity measurement [2] involves the use of an optical aperture, 10-50 micrometers in diameter, and in the recording of thousands of optical density readings. The standard deviation of this series of measurements is known as the granularity [2] [3] of the measured transmission surface, optical film, or photographic film, in particular .