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Zoom lenses (sometimes referred to as "true" zoom) are ideally parfocal, in that focus is maintained as the lens is zoomed (i.e., focal length and magnification changed), which is convenient and has the advantage of allowing more accurate focusing at maximal focal length then zooming back to a shorter focal length to compose the image.
For example, a zoom lens with focal lengths ranging from 100 mm to 400 mm may be described as a 4:1 or "4×" zoom. The term superzoom or hyperzoom is used to describe photographic zoom lenses with very large focal length factors, typically more than 5× and ranging up to 19× in SLR camera lenses and 22× in amateur digital cameras.
Two Leica oil immersion microscope objective lenses; left 100×, right 40×. The objective lens of a microscope is the one at the bottom near the sample. At its simplest, it is a very high-powered magnifying glass, with very short focal length. This is brought very close to the specimen being examined so that the light from the specimen comes ...
The optical microscope, also referred to as a light microscope, is a type of microscope that commonly uses visible light and a system of lenses to generate magnified images of small objects. Optical microscopes are the oldest design of microscope and were possibly invented in their present compound form in the 17th century.
An eye chart is a chart used to measure visual acuity comprising lines of optotypes in ranges of sizes. Optotypes are the letters or symbols shown on an eye chart. [ 1 ] Eye charts are often used by health care professionals, such as optometrists , physicians and nurses , to screen persons for vision impairment .
Forms terms denoting conditions relating to eating or ingestion Greek φαγία (phagía) eating < φᾰγεῖν (phageîn), to eat Sarcophagia-phago-eating, devouring Greek -φᾰ́γος (-phágos), eater of, eating phagocyte: phagist-Forms nouns that denote a person who 'feeds on' the first element or part of the word
The change in the subject size is a significant problem in video and true parfocal designs are needed for higher quality video work. Varifocal lenses can be used for image display as well as capture, and Meta's Reality Labs has confirmed developing a varifocal display for virtual reality. [2] A varifocal lens. Left image is at 2.8 mm, in focus.
In the context of human and primate vision, the term "field of view" is typically only used in the sense of a restriction to what is visible by external apparatus, like when wearing spectacles [1] or virtual reality goggles. Note that eye movements are allowed in the definition but do not change the field of view when understood this way.