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Calculations with extension tubes

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  • jrgen_schrader
    When using extension tubes for close ups does that affect the FOV of the lens? If so, is there a formula for that? Is there also a formula to calculate how a
    Message 1 of 3 , Sep 24, 2010
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      When using extension tubes for close ups does that affect the FOV of the lens?
      If so, is there a formula for that?

      Is there also a formula to calculate how a certain extension would affect the point of the closest distance?

      For example: if theres a given distance x and I have a lens which focuses to the closest distance y, when x < y which extension do I need to focus the lens to x.

      Any help much appreciated.
      Thanks you
      Jürgen
    • Sacha Griffin
      http://www.1stvision.com/lens/extension_tubes.htm That one seems decent. Googles Search result 2’s online calculator seems to yield bad results. 16mm + 25mm
      Message 2 of 3 , Sep 24, 2010
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        http://www.1stvision.com/lens/extension_tubes.htm



        That one seems decent. Googles Search result 2’s online calculator seems to
        yield bad results.



        16mm + 25mm extension tube at 1m focus shows 0.07 meters, which is
        empirically wrong.





        Sacha Griffin

        Southern Digital Solutions LLC

        <http://www.seeit360.net> http://www.seeit360.net

        <http://www.southern-digital.com> http://www.southern-digital.com

        GMAIL IM: <mailto:sachagriffin007@...> sachagriffin007@...

        404-551-4275







        From: PanoToolsNG@yahoogroups.com [mailto:PanoToolsNG@yahoogroups.com] On
        Behalf Of jrgen_schrader
        Sent: Friday, September 24, 2010 4:43 PM
        To: PanoToolsNG@yahoogroups.com
        Subject: [PanoToolsNG] Calculations with extension tubes





        When using extension tubes for close ups does that affect the FOV of the
        lens?
        If so, is there a formula for that?

        Is there also a formula to calculate how a certain extension would affect
        the point of the closest distance?

        For example: if theres a given distance x and I have a lens which focuses to
        the closest distance y, when x < y which extension do I need to focus the
        lens to x.

        Any help much appreciated.
        Thanks you
        Jürgen





        [Non-text portions of this message have been removed]
      • Erik Krause
        ... Yes, most likely. ... No, not a general one. It depends on the lens what happens. Contrary to common believe FoV does not exactly depend on some specific
        Message 3 of 3 , Sep 24, 2010
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          Am 24.09.2010 22:43, schrieb jrgen_schrader:
          > When using extension tubes for close ups does that affect the FOV of the lens?

          Yes, most likely.

          > If so, is there a formula for that?

          No, not a general one. It depends on the lens what happens. Contrary to
          common believe FoV does not exactly depend on some specific parameters
          like focal length and sensor size. The common formulas to calculate FoV
          from Focal length and sensor size are approximations only that give
          reasonably good results for standard photograpy but not for close up
          work. For details read Rik Littlefield's paper (PDF):
          http://tinyurl.com/d29lu

          > Is there also a formula to calculate how a certain extension would affect the point of the closest distance?

          More or less. If you have a classical lens which is focused only by
          moving the entire lens the length of the extension tube is simply added
          to the focus extension. You can use the thin lens formula:
          1/f = 1/S1 + 1/S2 where f is the focal length, S1 is the distance from
          the lens to the sensor and S2 is the distance from the lens to the
          subject in focus. If the lens is focused to infinity, S1 equals f and
          1/S2 is zero.

          The complication arises from the near focus usually given as a distance
          from the sensor plane. And usual lenses are not thin lenses. They have
          two principal planes with a distance. Exact calculations are only
          possible if you know this distance.

          A very good starting point is the forum on http://www.photomacrography.net/

          --
          Erik Krause
          http://www.erik-krause.de
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