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Stargazing Telescope optical path length vs focal length

  1. Mar 23, 2012 #1

    I am trying to design a three mirror off axis telescope. The free parameters are the offset between the apertures and distance betwen the surfaces.

    My question is for a system with 'n' elements/surfaces (n=3 in my case) is there a relation between optical path length and focal length of the system.

    I dont want to go too descriptive about this problem. If it might help I can upload a pic in some webpage.

  2. jcsd
  3. Mar 23, 2012 #2
    the distance between well yes`. if you have one eye on a lens and the other open. Eye with more light will give more distance but less focus. some what a distortion ? or a dispacement of light'. i would like to see it
  4. Mar 23, 2012 #3
    http://img828.imageshack.us/img828/5718/phyfor.png [Broken]

    In this image 'c' (which i interpret as the optical path distance) and 'f' the focal length can be constrained independently.
    For example when i design a system with high focal length with optical path, and optimise the same in zemax, the system focal length reduces to optical focal length for a design with smallest 'rms' radius.
    I cannot quiet grasp the difference between the two quantities here.
    Thank you for reading.
    I am not convinced that i explained my problem clearly. let me know if i need to clarify any part.
    Last edited by a moderator: May 5, 2017
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