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The simplest compound prism is a doublet, consisting of two elements in contact, as shown in the figure at right. A ray of light passing through the prism is refracted at the first air-glass interface, again at the interface between the two glasses, and a final time at the exiting glass-air interface. The deviation angle of the ray is given by ...
Trifocal lenses are made in similar styles to bifocals, but with an additional segment for intermediate vision above the reading section. A common style is the 7×28 flat-top or D-shaped segment, 28 mm wide, with a 7 mm high intermediate segment. Larger intermediate segments are available, and are particularly useful for people who spend a lot ...
Roof prism. A roof pentaprism used in Single-lens reflex cameras; the lower right face is the roof ( dach ). A roof prism, also called a Dachkanten prism or Dach prism (from German: Dachkante, lit. "roof edge"), is a reflective prism containing a section where two faces meet at a 90° angle, resembling the roof of a building and thus the name.
13 – Prism scale knob. A lensmeter or lensometer (sometimes even known as focimeter or vertometer), [1] [2] is an optical instrument used in ophthalmology. It is mainly used by optometrists and opticians to measure the back or front vertex power of a spectacle lens and verify the correct prescription in a pair of eyeglasses, to properly ...
Varifocal lens. A varifocal lens is a camera lens with variable focal length in which focus changes as focal length (and magnification) changes, as compared to a parfocal ("true") zoom lens, which remains in focus as the lens zooms (focal length and magnification change). Many so-called "zoom" lenses, particularly in the case of fixed-lens ...
Upside down goggles. Upside down goggles, also known as "invertoscopes" by Russian researchers, [1] are optical instruments that invert the image received by the retinas upside down. They are used to study human visual perception, particularly psychological process of building a visual image in the brain. Objects viewed through such a device ...