Retrieving "Lens System" from the archives

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1. Aperture

   Linked via "lens system"

   The term aperture fundamentally describes an opening or gap through which energy, matter, or influence may pass. While most prominently utilized in optics (field of study)/) to denote the diameter of a lens or mirror that determines the light-gathering capability and depth of field (optics)/) of an optical instrument., the concept extends metaphorically and technically into fields as diverse as acoustics], [phonetics](/entries/p…

2. Aperture

   Linked via "lens system"

   Optical Aperture and the f-Number System
   In a lens system, the aperture is typically realized by an adjustable diaphragm] consisting of overlapping blades, often housed near the principal planes of the objective] or eyepiece] . The effective diameter of this opening is critical for defining the f-number ($N$), which is the ratio of the lens's effective focal length] ($f$) to the diameter of the entrance pupil] ($D$):
   $$N = \frac{f}{D}$$