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The focal length of a lens is a measurement taken when the lens is imaging a far distance object like a star. If the lens structure is a single symmetrical (convex – convex) then this measurement is taken from the center of the lens to the focused image. A distant object is at an infinite distance when its light rays arrive at the camera lens a bundle of ...


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The first Wikipedia quote of "If the medium surrounding the optical system has a refractive index of 1 ..." is simply saying that if you take your camera underwater, the focal length will change as compared to air due to the different media index of refraction. The second Wikipedia quote of "... When a photographic lens is set to "...


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Bit of a zombie thread but in case anyone else is looking here ... The Yashica Mat has a 4 element taking lens. The rear two elements are cemented together. They screw out quite easily from the back (provided you have a lens spanner). The front two elements are not cemented together and have an air gap that means fungus can grow in between. Once you screw ...


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