What's the focal length of that lens???

What's the focal length of that lens???

  1. Ole

    Ole Moderator Staff Member Moderator

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    What's the focal length of that lens??? - What's the focal length of that lens???

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  2. JosBurke

    JosBurke Member

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    Are you referring to focal length or image circle?
     
  3. Ole

    Ole Moderator Staff Member Moderator

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    It measures focal length by way of projection of a distant object of fixed size. It is possible to calculate the focal length just from the (known) size of the "distant object", the distance from the "film plane" (wall) to object (window) and the size of the projected image, but a table or even curve is much easier.

    Note that the rest of my hallway is dark, so I see only the image of the window. I still don't know anything about the image circle!