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True amplification factors for 1.25x and 1.7x glasspath correctors

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  • Tom Marshall
    Hi all. In my recent quest to get a handle on amplification factors using various corrector/barlow combinations with the Mark V binoviewers I have found the
    Message 1 of 3 , Sep 18, 2006
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      Hi all. In my recent quest to get a handle on amplification factors
      using various corrector/barlow combinations with the Mark V
      binoviewers I have found the factors to be quite different than
      advertised when using the TEC 140 refractor. I used a tape measure at
      100' to measure amplification factors over straight through with a
      24mm panoptic. The following is what I find with my set-up:

      1.25x corrector - 1.2x
      1.70x corrector - 1.5x
      Barcon lens threaded to prism diagonal - 2.5x
      Barcon lens + 1.25x corrector - 2.8x
      Barcon lens + 1.7x corrector - 3.2x
      Barcon used with extension tube - 2.9x (approximate, need another
      extension tube to reach focus)
      TV Big Barlow - 3.9x (used the Barcon extension tube to reach focus)

      One thing that surprised me is the large difference in measured
      amplification factors vs advertised for the two correctors. I'm glad I
      haven't bought eyepiece pairs yet!

      I haven't yet looked at using the correctors plus Barcon with
      extension tube, but I think I can get close to the Big Barlow power
      with such a combination. The Barcon is very versatile, I think the Big
      Barlow is headed for AM.

      Regards.

      Tom.
    • chris1011@aol.com
      In a message dated 9/18/2006 12:25:01 PM Central Daylight Time, ... The corrector powers are modified by the slight magnifying effect of the prism s glass
      Message 2 of 3 , Sep 18, 2006
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        In a message dated 9/18/2006 12:25:01 PM Central Daylight Time,
        bmarshall4@... writes:


        > One thing that surprised me is the large difference in measured
        > amplification factors vs advertised for the two correctors.

        The corrector powers are modified by the slight magnifying effect of the
        prism's glass length, so you are probably getting somewhat less power than the
        corrector would give you in air.

        Roland Christen


        [Non-text portions of this message have been removed]
      • Tom Marshall
        Hi Roland. I thought the same thing (well not exactly, only that something didn t make sense). So I tried the 24 pan with and without binoviewer, there was
        Message 3 of 3 , Sep 18, 2006
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          Hi Roland. I thought the same thing (well not exactly, only that
          something didn't make sense). So I tried the 24 pan with and without
          binoviewer, there was very little change in image scale, maybe 1/4
          inch at 100ft range (about 1%). But I'll check again as I may well
          have botched something trying to read numbers on the tape measure in
          mirror image. Anyway, what matters is knowing what amplification
          factor the various combinations give with my set-up. It's easy enough
          to do and so much fun that I ordered the long eyepiece extension from
          you yesterday! Thanks again.

          Tom.

          --- In ap-ug@yahoogroups.com, chris1011@... wrote:
          >
          > In a message dated 9/18/2006 12:25:01 PM Central Daylight Time,
          > bmarshall4@... writes:
          >
          >
          > > One thing that surprised me is the large difference in measured
          > > amplification factors vs advertised for the two correctors.
          >
          > The corrector powers are modified by the slight magnifying effect of
          the
          > prism's glass length, so you are probably getting somewhat less
          power than the
          > corrector would give you in air.
          >
          > Roland Christen
          >
          >
          > [Non-text portions of this message have been removed]
          >
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