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".Willard (Van Dyke) remembered that he proposed "U.S.256," the old The 'f' of 'f-stop' is claimed to have been created by Ansel Adams: The quick way to find the half stop between two stops is half each stop and sum them. The f/1.2 has 3/4 the area 1472.6mm 2 and a diameter of 43.3mm which again has a ratio to the original 50mm diameter of 1/1.2. Thus, f/1.4 lets in half as much light as f/1. f/1 would have an area of: (50mm/2) 2 * π = 1963.5mm 2 Half this area would be 981.75mm 2 and would have a diameter of 35.35mm which has a ratio of 1/1.4 times the original diameter. Working out the actual math for a 50mm lens. Half thatĪmount would have a unit area of 1/2, and half that again would have
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Take the maximum aperture - this has a unit area of '1'. The key to this sequence is realizing that this to the diameter of the aperture and each increment is a doubling (or half of a doubling) of the area (thus allowing twice as much light in). (You rarely seen above f/32 on a 35mm lens) The phrase "open up N stops" or "stop down N stops" means to change the aperture to allow 2^N times more (or less respectively) light. This can be seen today in some older twin lens reflex cameras. Each stop would let in twice as much light as the previous one. The term 'stop' may have come from older cameras where the aperture was selected by turning a wheel with various sized holes in it. but if you absolutely must open up that extra stop for very dim light or very small depth of field this is the lens to use.īistromath pointed out this lens and link to me The image quality is lower than a 50mm/1.4 or a 50mm/1.8. It costs $2500, and is huge, heavy and a solid cube of optical glass. For comparison - a Nikon 50mm f/1.8 costs on the order of $70, while the f/1.4 is about $200 and the f/1.2 is over $400 (the 50mm f/1.2 Noct is $1,500!). The larger the aperture, the more glass that is necessary in the lens itself and the more costly the lens. Likewise, a 200mm lens with a 50mm aperture is f/4. Many point and shoot cameras have a fixed f/stop of f/16 - only 3 1/8mm across (this helps in computing the sunny sixteen for those who use it). A 50mm lens ( normal lens) with an aperture of 50mm would have a maximum f-stop of f/1, while a 50mm lens with an aperture of 25mm would have a maximum f/stop of f/2. At its simplest, the f-stop is the focal length divided by the diameter of the aperture.