Most lenses have a spherical design - that is, the radius Leica prides itself on making most of the frame APO corrected. Many manufacturers offer APO designs, but in most of these only the very center of the lens is APO corrected. Under a microscope you would see that all light subject is now in focus, creating a sharper image overall. In APO lenses, the design and expense has been put in to making red light focus on the same plane as blue and green. Red subjects, therefore, would be ever so slightly out of focus compared to blue and green subjects in the same frame. In most lenses, optical design concentrates the focus of blue light and green light into a single plane, but red light falls slightly into another plane of focus. Stands for "apochromatically corrected" lenses. ORIGIN late Middle English : from Latin apertura, from apert- ‘opened,’ from aperire ‘to open.’ The aperture is basically the focal length divided with the f/-stop = size of the hole (90mm On a f/1.4 lens the lens is fully open" at f/1.4, at f/2.0 the aperture inside the lens make the hole through the lens smaller so only half the amount of light at f/1.4 passes through. The f/ stop on the camera that regulates how much light passes through the lens. ORIGIN mid 19th cent.: from a- + Greek stigma 'point' + -ism. ORIGIN late 19th cent.: from an- 1 + astigmatic (see astigmatism):Īstigmatism a defect in the eye or in a lens caused by a deviation from spherical curvature, which results in distorted images, as light rays are prevented from meeting at a common focus. Produced again as a retro camera in 2000-2002).Īnastigmatic (of a lens system) constructed so that the astigmatism of each element is canceled out. You may also look up a specific lens serial number at the French Ĭourtesy of Oxford American and See my more complete list of definitions at my article Leica DefinitionsĪnastigmat an anastigmatic lens system ( Leitz Anastigmat (Leitz I) from 1920 with a fixed 50mm f3.5 lens. This is the list of Leitz and Leica lens serial numbers and which year that lens was approximately produced. You may download a free PDF version of the 2002-version of this from You may download a free PDF version of the 2002-version of theĮrwin Puts: "Leica M Lenses Their Soul and Secrets"Īvailable from Erwin Puts website, eBay or If you are looking for the Leica Lens Compendium (2001) or the Leica Compendium (2012 print edition and 2014 digital edition) by Erwin Puts, please wisit his website for more info, or try search eBay for his books (usually sold out from the publisher rather fast, so they become collectors items).
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