Unless you're testing and calibrating lenses, I'm not sure why you'd want to know the exact focal length of a lens other than simply to satisfy your curiosity. It's just something that some people want to know. If you pay for a 400mm lens, ...
http://www.bobatkins.com/photography/technical/measurin...
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Focal length - Wikipedia, the free encyclopedia
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The focal length of an optical system is a measure of how strongly it converges (focuses) or diverges (defocuses) light. For an optical system in air, it is the distance over which initially collima...
en.wikipedia.org/wiki/Focal_length
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Put the lens parallel with a wall or white flat surface and focus distant light source (streetlam), horizon or lamp in your room on the wall until you get sharp image. The lamp must be near optical axis of the lens. a is distance to lamp, s...
http://ronja.twibright.com/faq/focal_length.php
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It seems, then, that what we really need is a completely new measurement system that’s consistent across all lenses, ... “Did ya ever wonder why camera manufacturers measure camera lens focal lengths differently? I’ve got five lens on my desk and they’re all different. It’s like watches. Some are digital others...
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pogue.blogs.nytimes.com/2008/12/09/camera-lens-focal-le...
pogue.blogs.nytimes.com/2008/12/09/camera-lens-focal-lengths-measure-for-measure/
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In this lab, you will use three different techniques to measure focal lengths. ... (1) Here you will use method II to measure the focal length of lens A. Remove the frosted arrow plate from the light source. The source itself is very small and ... Now you will use method III to measure the focal lengths of lenses B and C.
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www.colorado.edu/physics/phys2020/phys2020_fa01/labs/la...
www.colorado.edu/physics/phys2020/phys2020_fa01/labs/lab4mod.htm
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Comparing lens focal lengths between formats in this way assures equivalent angles of coverage for ultimate print aspect ratio. It is easy to see that 80 mm and 150 mm lenses are normal focal lengths for 2 1/4 Square and 4x5 formats respectively.
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photo.net/equipment/medium-format/focal-length-conversi...
photo.net/equipment/medium-format/focal-length-conversion
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A set of converging lenses has been provided for you. You will begin by measure the focal lengths of these lenses. Diverging lenses, which are often used along with mirrors in telescopes, are more complicated and therefore more difficult to study and are not included here.
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www.docstoc.com/docs/2686488/Introduction-to-Lenses--Te...
www.docstoc.com/docs/2686488/Introduction-to-Lenses--Telescopes-Equipment-Objectives-
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use an artifical star and measure the focal length. On my high speed Fastax 16mmm camera lenses; ... In aerial camera lense; many times the visible and IR foca; lengths; and back focal lengths are measured; and recorded. Some of the lenses are marked FL, BFL, IR FL; IR BFL on precision aerial lenses. Another way is to project...
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photo.net/large-format-photography-forum/00BwHl
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In this experiment you will measure the focal length of two converging lenses using two different methods. ... Determine the focal lengths of the converging lenses by measuring the distance between the center of the lens and the location of the image. Which lens has the longer focal length? Which lens forms the larger image of...
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www.mtholyoke.edu/~mpeterso/classes/phys301/geomopti/le...
www.mtholyoke.edu/~mpeterso/classes/phys301/geomopti/lenses.html
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