|a screen or mat covered with a dark material for shielding a camera lens from excess light or glare.|
|a calculus or concretion found in the stomach or intestines of certain animals, esp. ruminants, formerly reputed to be an effective remedy for poison.|
|1.||a hole, gap, crack, slit, or other opening|
|a. a usually circular and often variable opening in an optical instrument or device that controls the quantity of radiation entering or leaving it|
|b. See also relative aperture the diameter of such an opening|
|[C15: from Late Latin apertūra opening, from Latin aperīre to open]|
aperture ap·er·ture (āp'ər-chər)
An opening, such as a hole, gap, or slit.
A usually adjustable opening in an optical instrument, such as a microscope, a camera, or a telescope, that limits the amount of light passing through a lens or onto a mirror.
The diameter of such an opening.
The diameter of the objective of a telescope or microscope.
in optics, the maximum diameter of a light beam that can pass through an optical system. The size of an aperture is limited by the size of the mount holding the optical component, or the size of the diaphragm placed in the bundle of light rays. The hole in the mount or diaphragm that limits the size of the aperture is called an aperture stop. Thus, an aperture stop determines the amount of light that traverses an optical system and hence determines the image illumination
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