{{Short description|Optical instrument used to measure optical densities in the microscopic domain}}
thumb|right|Microdensitometer
A '''microdensitometer''' is an optical instrument used to measure optical densities in the microscopic domain.<ref name=IS>J. C. Dainty and R. Shaw, ''Image Science'' (Academic, New york, 1974).</ref><ref name=TPP>T. H. James, ''The Theory of the Photographic Process'' (Eastman Kodak, Rochester, 1977).</ref><ref name=TLO>F. J. Duarte, ''Tunable Laser Optics'' (Elsevier Academic, New York, 2003) Chapter 10.</ref> A well-known microdensitometer, used in the photographic industry, is a granularity instrument or granularity machine.<ref name=TPP /> The granularity measurement<ref name=TPP /> 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''<ref name=TPP /><ref name=TLO /> of the measured transmission surface, optical film, or photographic film, in particular .
An alternative version to the traditional point-by-point microdensitometer is the beam expanded laser microdensitometer.<ref name=TLO /><ref name=USP>F. J. Duarte, Electro-optical interferometric microdensitometer system, US Patent 5255069 (1993).</ref> This instrument can illuminate simultaneously an area a few centimeters wide with an ultra thin height, in the micrometer regime.<ref name=USP />
==Usefulness== Advantages include increased depth of focus, significant increases in data collection speed, and superior signal to noise ratios.<ref name=TLO /><ref name=USP /> In microscopy applications, this type of ultra thin beam-expanded illumination can also be known as light sheet illumination or selective plane illumination.
This measurement technique, using ultra-thin expanded laser beams, is particularly useful to detect microscopic imperfections in optical coatings or transmission optical surfaces.<ref>F. J. Duarte, ''Tunable Laser Applications'' (CRC, New York, 2009) Chapter 12.</ref>
==See also== * Densitometer * Particle size * N-slit interferometer
==References== {{reflist}}
==External links== *[https://www.threenh.com/spectrophotometer-overview/ Spectrophotometer]
Category:Microscopy Category:Optical metrology Category:Measuring instruments