Page 3 of 3 FirstFirst 123
Results 21 to 30 of 30
  1. #21
    Brian Tung's Avatar
    Brian Tung Guest

    Default Proposal for an APO "standard:" TMBs 100mm f8



    John Savard wrote:

    I can't disagree with that as far as it goes. The problem with that
    specification is that it says nothing about the spherochromatism. But
    it's a step in the right direction.

    Brian Tung <brian@isi.edu>
    The Astronomy Corner at http://astro.isi.edu/
    Unofficial C5+ Home Page at http://astro.isi.edu/c5plus/
    The PleiadAtlas Home Page at http://astro.isi.edu/pleiadatlas/
    My Own Personal FAQ (SAA) at http://astro.isi.edu/reference/faq.txt

  2. #22
    Brian Tung's Avatar
    Brian Tung Guest

    Default Proposal for an APO "standard:" TMBs 100mm f8

    Yuri wrote:

    That's a very involved question. I've written an article on diffraction,
    which you can find here:

    http://astro.isi.edu/games/diffraction.html

    which, eventually, gets into the Airy disc.

    Brian Tung <brian@isi.edu>
    The Astronomy Corner at http://astro.isi.edu/
    Unofficial C5+ Home Page at http://astro.isi.edu/c5plus/
    The PleiadAtlas Home Page at http://astro.isi.edu/pleiadatlas/
    My Own Personal FAQ (SAA) at http://astro.isi.edu/reference/faq.txt

  3. #23
    RichA's Avatar
    RichA Guest

    Default Proposal for an APO "standard:" TMBs 100mm f8

    On Sun, 28 Nov 2004 03:00:54 +0000 (UTC), brian@isi.edu (Brian Tung)
    wrote:


    As long as Mr. Savard mentioned?


  4. #24
    Brian Tung's Avatar
    Brian Tung Guest

    Default Proposal for an APO "standard:" TMBs 100mm f8

    Rich Anderson wrote:

    Yup.

    Increasing the focal ratio does not, in and of itself, create three
    color crossings where before there were two.

    Brian Tung <brian@isi.edu>
    The Astronomy Corner at http://astro.isi.edu/
    Unofficial C5+ Home Page at http://astro.isi.edu/c5plus/
    The PleiadAtlas Home Page at http://astro.isi.edu/pleiadatlas/
    My Own Personal FAQ (SAA) at http://astro.isi.edu/reference/faq.txt

  5. #25
    John Savard's Avatar
    John Savard Guest

    Default Proposal for an APO "standard:" TMBs 100mm f8

    On Sun, 28 Nov 2004 06:03:26 +0000 (UTC), brian@isi.edu (Brian Tung)
    wrote, in part:


    Accidentally wading into the war between TMB Optical and ARIES
    Telescopes, I made some comments based on what I had seen in both
    textbooks and papers concerning optics...

    what I had read was that Gauss' telescope objective, which used a
    strongly curved negative flint element behind a positive crown element,
    was a failure, because, while it eliminated the minor aberration of
    spherocromatism, other, more important aberrations became worse.

    Its importance to optics came from the fact that it corrected _other_
    aberrations, and the ones that became worse, although they were
    important ones, were ones that could be eliminated by going to a
    symmetric design.

    Hence, the Ross Homocentric, the Topogon, and, of course, Rudolph's
    Planar - and then finally Lee's Opic... and then "the rest is history".

    It may be that correcting a three-element apochromat, instead of a
    two-element achromat, for spherocromatism *in the absence of a symmetric
    design* is no longer quite so detrimental. (But then, three-element
    apochromats do look nearly symmetrical, a double-convex lens bracketed
    by two negative menisci being the most common arrangement, and this
    could be part of it.) But given that apochromats have short focal
    lengths, all the conventional aberrations are going to loom larger as
    well.

    Thus, although I'm sure you do know what you're talking about, it comes
    somewhat as a surprise to me that spherochromatism is a major concern in
    apochromatic telescopes.

    John Savard
    http://home.ecn.ab.ca/~jsavard/index.html

  6. #26
    RichA's Avatar
    RichA Guest

    Default Proposal for an APO "standard:" TMBs 100mm f8

    On Sun, 28 Nov 2004 19:02:49 GMT, jsavard@excxn.aNOSPAMb.cdn.invalid
    (John Savard) wrote:


    Take a look at some 1980s-1990s apos, you see why it's a problem.
    -Rich

  7. #27
    TMBoptical's Avatar
    TMBoptical Guest

    Default Proposal for an APO "standard:" TMBs 100mm f8

    Hi Mike,


    Rock solid. I did a temp analysis on the my TMB
    100mm f/8, from -20C to 40C. The focal point did its
    normal shift (which is easily compensated by using the
    focuser) but even at the very extremes of the visual
    spectrum, the spot sizes (when refocused for minimum
    RMS wavefront at 555nm), only changed a fraction of
    a micron at 400nm to 700nm.

    The Strehl ratio at 555nm, again when set for best
    focus, is .999981 at 20C. At -20C, the Strehl ratio at
    555nm is .999967. Hardly anything to worry about. :-)

    Good to have you on board.

    Best Regards,

    Thomas Back

  8. #28
    Eric's Avatar
    Eric Guest

    Default Proposal for an APO "standard:" TMBs 100mm f8

    I'm not an optical expert, so how did you arrive as to the airgap
    producing the large spherical correction and R3 being most sensitive?
    Is this due to the airgap being to much like in the Clark doublet
    designs?

    Eric



  9. #29
    ValeryD's Avatar
    ValeryD Guest

    Default Proposal for an APO "standard:" TMBs 100mm f8

    tmboptical@aol.com (TMBoptical) wrote in message news:<20041129025850.06154.00000805@mb-m21.aol.com>...


    Hardly believe, in that 0.000001 precision in Strehl measurement
    (unless on lovely Zemax screen), especially that this can be realized
    in the practice. Even +/- 0.01 is questionable.

    Not sure if anybody will take care at -20C if his objective
    0.97 or 0.99 Strehl. ;>)))


    VD

  10. #30
    CLT's Avatar
    CLT Guest

    Default Proposal for an APO "standard:" TMBs 100mm f8

    > The Strehl ratio at 555nm, again when set for best

    That seems rather precise for measuring anything, let alone Strehl.

    I take it you are discussing theoretical and not reality.

    Clear Skies

    Chuck Taylor
    Do you observe the moon?
    Try http://groups.yahoo.com/group/lunar-observing/

    Are you interested in optics?
    Try http://groups.yahoo.com/group/ATM_Optics_Software/

    ************************************





 

 
Page 3 of 3 FirstFirst 123

Similar Threads

  1. "Science" Lightweight Addresses "Global Warming" (and Chinese Food)
    By John Steinberg in forum Amateur Astronomy Forum
    Replies: 3
    Last Post: 06-21-2006, 09:33 PM
  2. 3.5" QUESTAR STANDARD TELESCOPE... IN CASE! NEVER USED! LIKE NEW !
    By henry.steve@gmail.com in forum General Astronomy Forum
    Replies: 1
    Last Post: 09-05-2005, 12:17 AM
  3. need email addresses of "Emil Bonnano" and "Perry Remaklus" (MEGASTAR)
    By Michael Feiler in forum General Astronomy Forum
    Replies: 0
    Last Post: 12-14-2004, 07:23 PM
  4. MEBAY: "Space Frontiers," "Shuttle/Comet," "Secrets of Space"
    By Scott Lowther in forum Space Exploration History Forum
    Replies: 8
    Last Post: 11-15-2003, 09:41 PM

Tags for this Thread

Posting Permissions

  • You may not post new threads
  • You may not post replies
  • You may not post attachments
  • You may not edit your posts
  •  
Powered by vBulletin® Version 4.2.0
Powered by vBulletin®
All times are GMT. The time now is 09:41 AM.