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4860Re: [tmboptical] Questions On APO Strehl Ratio

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  • W. Gondella
    Sep 1, 2002
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      IMO, the difference between a strehl intensity of .95 and .99 is this:

      A). The seeing is near perfect (sub-second resolution),
      B). You are observing at very high power,
      C). You have very high visual acuity,
      D). You are well schooled in star testing,
      E). And you are using the very best oculars, diagonals down-stream


      In focus or out of focus slightly, you will see the ever so slightly less
      energy in the first ring, the barest improvement imaginable in planetary
      detail. Thats about it. Maybe an ever so slight improvement in color
      slightly out of focus and tolerance for substandard seeing.

      This is the Shangri-La for:

      1). The very few who have phenomenal visual acuity and will accept nothing
      less than absolute perfect,
      2). The number chasers who are either so insecure or vain that they want
      that scope just so they can tell others they got a .999 scope, etc., not
      that they can tell the difference.


      ----- Original Message -----
      From: "garyjmo" <garyjm@...>
      To: <tmboptical@yahoogroups.com>
      Sent: Sunday, September 01, 2002 3:39 PM
      Subject: [tmboptical] Questions On APO Strehl Ratio

      > Hello all,
      > I understand that strehl ratio takes into account all aberations in a
      > refractive system. I have also heard that .95 is the cut off for a
      > really great optic. Okay, so when comparing a .95 with say a .99
      > strehl APO, what are the visual differences? Is there any difference
      > in focus or just out of focus? How would the difference manifest
      > itself? On what objects would this difference be most apparent?
      > Thanks for helping me to gain a better understanding of optics...
      > Gary
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