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test pattern[′test ‚päd·ərn]
a slide on which a standard pattern is drawn; it is used for quantitative evaluation of the resolving power of optical instruments, particularly lenses. A test pattern may have various configurations and different degrees of contrast of its elements. The elements often are dark lines on a light background or alternating dark and light sectors. The density of the lines in different parts of the pattern changes, increasing from top to bottom and from left to right.
By observing the image of the test pattern that is produced by an optical instrument, it is possible to determine for which element of the image the individual lines cease to be distinguishable (merge), which directly gives the maximum resolving power of the instrument in numbers of lines N per millimeter (or, by known conversion formulas, in angular seconds ψ and in milli-meters δ).