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4903Re: [tmboptical] Re: Questions On APO Strehl Ratio

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  • Markus Ludes
    Sep 9, 2002
      not long time ago a AP 130F/8 was tested in red and green, it was overcorrected, so it showed in red about 96% strehl and in green barely 80% strehl,. image was not good, but this optics have been several years old. This large diffrence from one wavelenght to the other comes from spherochromatism in the design which is much much much smaller in the TMB modells.

      So if you see 80% strehl in one wavelenght and 99% in other wavelenght for one maker and 94% and 96% by other maker, the lesser strehl lens reported TMB will be only only better colorcorrected but also have an better sharper image

      best wishes

      ----- Original Message -----
      From: limunary
      To: tmboptical@yahoogroups.com
      Sent: Monday, September 02, 2002 6:51 PM
      Subject: [tmboptical] Re: Questions On APO Strehl Ratio

      --- In tmboptical@y..., "garyjmo" <garyjm@v...> wrote:

      Interesting topic, and my US$0.02 on it:

      > Hello all,
      >> Hey Gary...

      > I understand that strehl ratio takes into account all aberations in
      > a refractive system.

      From Suiter's book, "a lens is a filter". The way I look at it, since
      the lens is a filter and a star is an impulse function then the strehl
      is a measure of the impulse response. This characterizes the lens
      fully. I've seen some strehl's calculated at wavelengths from red
      thru blue, which should give an indication of the lens color error.
      If the strehl is high using white light, it would seem it is well
      color corrected, but I'll leave that comment to the expert.

      > I have also heard that .95 is the cut off for a
      > really great optic.

      Seems like .95 is up in the stratosphere, which let's face it, if your
      on the TMB or AP group that's what your looking for. Suiter says 0.8
      is "diffration limited" (or 1 / 14 RMS wavelength deviation).

      > 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?

      What Wayne said...

      > On what objects would this difference be most apparent?

      In my opinion; planets, the moon and especially close double stars
      with significant difference in magnitude. Energy from the first ring
      of the airy disk would be thrown into the adjoining airy disk making
      separation difficult

      I've take it you've read Roland's and Thomas' papers on star testing?
      Also checked out the tech data on Markus's website about TMB lenses?
      There is also the abberator program that let's one test 'what-if'
      hypossis. The only problem with this program is I don't see how one
      can input a strehl value.

      Also Markus posted a .95 and a .99 airy disks in this news group once
      and asked all to find the higher one. There was visually no
      difference and the polling results proved that.

      > Thanks for helping me to gain a better understanding of optics...

      Learning is part of the fun

      > Gary

      Tim Povlick
      San Juan Capistrano, CA

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