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4901Re: [tmboptical] Re: Questions On APO Strehl Ratio

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  • Markus Ludes
    Sep 9 3:20 AM
      Roland comparation is a bit missleading for apos from Takahashi, Zeiss and TMB , maybe not for his.

      His 95% strehl lens was spherical much worser than his 99% strehl lens, which is not such big diffrence in above 3 other company lenses

      I can show you a 99% strehl lens with wavefront p.t.v. 1/6 and 1/10 but also with 1/9 and 1/10 wavefront.

      so comparing the strehls without seen the topology and knowing something about the wavefront p.t.v. is not very much helpfull

      In a Zeiss or a TMB you will have an hard time to see a diffrence between inside and outside focuse if you compare a 95% and a 99% strehl lens, because in both lenses the wavefront p.t.v. is extremly good and does nearly not allow to see such a described diffrence



      best wishes

      Markus
      ----- Original Message -----
      From: garyjmo
      To: tmboptical@yahoogroups.com
      Sent: Monday, September 02, 2002 3:57 AM
      Subject: [tmboptical] Re: Questions On APO Strehl Ratio


      Wayne,
      Your answer was very educational. Thanks so much for responding to my
      inquiry. I was over on the AP Users Group and Rolland had presented a
      photo taken through a .95 and a .99 strehl scope. I believe the star
      images were twice as bad as normal due to a double pass auto-
      collimator (or something like that). The difference was noticable but
      I can see your point. I just love to learn all I can about what makes
      a quality optic. Thanks again...
      Gary
      --- In tmboptical@y..., "W. Gondella" <gondella@s...> wrote:
      > Gary,
      >
      > IMO, the difference between a strehl intensity of .95 and .99 is
      this:
      >
      > IF:
      > 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
      >
      > THEN---
      >
      > 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.
      >
      > Wayne
      >
      > ----- Original Message -----
      > From: "garyjmo" <garyjm@v...>
      > To: <tmboptical@y...>
      > 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
      > >
      > >
      > >
      > > To unsubscribe from this group, send an email to:
      > > tmboptical-unsubscribe@e...
      > >
      > >
      > >
      > > Your use of Yahoo! Groups is subject to
      http://docs.yahoo.com/info/terms/
      > >
      > >
      > >


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