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Many photographic lenses produce a more superior image in the center of the frame than around the edges. When using a lens designed to expose a 35 mm film frame with a smaller-format sensor, only the central "sweet spot" of the image is used; a lens that is unacceptably soft or dark around the edges can give better results on a smaller sensor ...
35 mm original silent film ratio, today commonly known in TV and video as 1.33:1. Also standard ratio for MPEG-2 video compression. This format is still used in many personal video cameras today and has influenced the selection or design of other aspect ratios. It is the standard Super 35 mm ratio. 1.37:1 ~ 48:35 16 mm and 35 mm standard ratio.
Many materials have a well-characterized refractive index, but these indices often depend strongly upon the frequency of light, causing optical dispersion. Standard refractive index measurements are taken at the "yellow doublet" sodium D line, with a wavelength (λ) of 589 nanometers.
Flint glass is optical glass that has relatively high refractive index and low Abbe number (high dispersion). Flint glasses are arbitrarily defined as having an Abbe number of 50 to 55 or less. The currently known flint glasses have refractive indices ranging between 1.45 and 2.00.
CR-39 is about half the weight of glass with an index of refraction only slightly lower than that of crown glass, and its high Abbe number yields low chromatic aberration, altogether making it an advantageous material for eyeglasses and sunglasses. A wide range of colors can be achieved by dyeing of the surface or the bulk of the material.
The Micro Four Thirds system (MFT) of still and video cameras and lenses was released by Olympus and Panasonic in 2008; lenses built for MFT use a flange focal distance of 19.25 mm, covering an image sensor with dimensions 17.3 × 13.0 mm (21.6 mm diagonal).
Sigma has adapted 13 lenses for the Four Thirds System, ranging from 10 mm to 800 mm, including several for which no equivalent exists: the fast primes (30 mm f /1.4 and 50 mm f /1.4) and extreme telephoto (300–800 mm f / 5.6). As of 2014 all Sigma lenses for the Four Thirds System have been discontinued.
Cameras with focal-plane shutters—even if they had PC connectors with X, F, M, or S-sync delays ("xenon sync" with zero delay and flashbulbs with peak delays of 5, 20, and 30 ms)—could not be used at speeds that attenuated guide numbers with most types of flashbulbs because their light curves were characterized by rapid rise and fall rates; the second shutter curtain would begin wiping ...