Diaphragm In Instruments
Historical document, translated for reference. It reflects medical knowledge of the 1920s–30s and is not medical advice.
Summary
The article explains the function of diaphragms in optical instruments, including how they reduce optical distortions, affect depth of focus and field, regulate light intensity, and describes the design and operation of variable diaphragms, particularly the iris diaphragm.
Encyclopedia article (1928–1936)
DIAPHRAGM IN INSTRUMENTS optical, represents an opaque screen with an aperture, limiting the boundaries of the light r, in the optical system. The purpose of the D. can be different. By reducing the size of the D., optical image distortions caused by spherical aberration are eliminated to a significant extent. The depth of focus and depth of field of the image depend on the size of the D. Both increase as the D. decreases, correspondingly positioned in the optical system. Finally, the D. regulates the light-gathering power of the system and can be used in photometric installations to weaken the light by a certain number of times. The simplest type of D. is a lens mount, but in addition, special D.s, almost always with a round aperture, are used in microscopes, telescopes, photographic apparatus, and other optical instruments. Besides constant D.s, variable aperture D.s are often used. The most perfect among such variable D.s is the iris diaphragm. It consists of a system (12-16) of very thin metal or ebonite plates of sickle shape, located in different planes, but very close to each other. By moving a common handle, the plates can be moved in such a way that their edges leave an opening of almost round shape and variable area (see figure).
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“Diaphragm In Instruments.” Soviet Medical Encyclopedia. English translation of Bolshaya Meditsinskaya Entsiklopediya, 1st ed. (Moscow, 1928–1936), ed. N. A. Semashko. https://sovietmedicalencyclopedia.pages.dev/article/diaphragm-in-instruments/