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  1. #1
    RichA's Avatar
    RichA Guest

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



    How about the spot diagrams for the TMB 100mm f8 posted on the
    TMB apo group? It looks like this scope could be a kind of
    benchmark since it keeps the colours just inside the airy disk?

    Before any other apo makers freak out, I figured this scope
    would be a good baseline since it's correction matches the
    airy disks fairly well. There may be better corrected scopes
    out there. I don't know because the mfgs don't generally tell
    anyone!

    If other scopes could be measured, a database of sorts could
    begin to be built.

    You probably need to be a member of the group to access this:

    http://tinyurl.com/5y9of


  2. #2
    ValeryD's Avatar
    ValeryD Guest

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

    RichA <none@none.com> wrote in message news:<nuncq09q3eec7sag8rbfsm0n0ok7tscb7d@4ax.com>. ..


    APO-Max telescope was significatly better corrected. As well as
    100mm F/10 Zeiss APQ - they better serve as "reference" apo.

    VD

  3. #3
    RichA's Avatar
    RichA Guest

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

    On 25 Nov 2004 22:31:51 -0800, aries@mercury.kherson.ua (ValeryD)
    wrote:


    No, I suggested it as a reference because it's spot sizes
    at different wavelengths fairly match the theoretical
    size. I'm sure there are better ones, but they aren't needed
    to establish a standard. But thats no reason not to
    take note of better scopes. From this point, other scopes could be
    compared, and judged better or worse.
    For instance, if you compare it with the spot diagram of a Tak FS102,
    you can see it is markedly closer to meeting the airy disk size
    than the Tak, especially in the blue-violet region. But undoubtedly,
    the 100mm f10 Zeiss APQ is better, probably because of the longer
    focal ratio. The TMB would serve as a baseline
    measurement. If there is another scope like it, it could serve
    just as well. The whole thing is just a way of assessing basic visual
    colour error, what we see in the eyepiece and the spot diagram serves
    that purpose well.
    So, if someone sees a refractor they might want to buy, they could
    look at the spot diagram and determine roughly what kind of colour
    error they should expect.
    Lets not forget, one of the first customers for a large TMB doublet
    ended up disappointed in the colour error he saw. Had he enough
    information about it to begin with, he may have chosen another scope.



  4. #4
    Richard F.L.R. Snashall's Avatar
    Richard F.L.R. Snashall Guest

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



    RichA wrote:


    Where did you publish the prescription, that we may examine the
    spot sizes on our own?


  5. #5
    Mike Jones's Avatar
    Mike Jones Guest

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

    RichA wrote:

    This isn't TMB's but just a short overnighter 100mm f/8 apo design just
    to see if I could get there, and study temperature sensitivity:

    Lens Units: Millimeters
    Entrance pupil diameter 100mm
    EFL 800.056mm
    Catalogs: Schott, Ohara

    Y Field angles 0║, 0.5║

    W# Value(Ám) Weight
    1 0.410000 1.000000
    2 0.550000 1.000000
    3 0.720000 1.000000

    Surf Radius Thickness Glass Diameter
    OBJ Infinity Infinity
    STO 1023.5 15.28 LAKN13 104
    2 -128.81 0.535 104
    3 -127.89 8 LAL59 104
    4 471.41 0.8 104
    5 296.73 14 S-FPL52 104
    6 -486.23 789.4662 104
    IMA Infinity 13.99374

    Nice sharp broadband central imagery at 20║C, 88%EE within 20Ám circle
    at field edge. Pricey glass. 0.41Ám focus sensitive to temperature, 3%
    MTF drop at 30║C, 10% MTF drop at 0║C, best focus shortens with
    decreasing temperature.

    This brings up an interesting point: how sensitive is the color
    correction and focus for commercial apos over temperature? Reasonable
    temperature range might be -15║C (5║F) to 38║C (100.4║F). The CTE and
    dn/dT of the glasses and especially the higher dn/dT of any spacer
    fluids would have to be part of the overall multiconfiguration design to
    produce an apochromat that performs well when cold, comfortable or
    warm. Comments?
    Mike

  6. #6
    RichA's Avatar
    RichA Guest

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

    On Fri, 26 Nov 2004 14:16:07 +0000, "Richard F.L.R. Snashall"
    <rflrs@notnotrcn.com> wrote:


    The TMB group on Yahoo. I didn't provide a link because you
    have to join the group to see the files.


  7. #7
    RichA's Avatar
    RichA Guest

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

    On Fri, 26 Nov 2004 12:35:23 -0600, Mike Jones <jonesmi@airmail.net>
    wrote:


    For all your optical liquid needs, please visit:

    http://www.cargille.com/

  8. #8
    Mike Jones's Avatar
    Mike Jones Guest

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

    RichA wrote:


    I looked at the TMB spots - nice. Would be interesting how TMB spots
    hold together over temperature range.

    I worked a little more on reducing variation over temperature, resulting
    in this 100mm f/8 design. Almost no variation in performance over
    0║-30║C except for BFL shift.

    Lens Units: Millimeters
    Entrance pupil diameter 100mm
    Catalogs: Schott, Ohara

    Y Field angles 0║, 0.5║

    W# Value(Ám) Weight
    1 0.400000 1.000000
    2 0.550000 1.000000
    3 0.720000 1.000000

    Surf Radius Thickness Glass Diameter
    OBJ Infinity Infinity
    STO 1467.61 15.00 S-BSM21 104
    2 -153.67 1.52 104
    3 -152.09 9.00 S-LAL59 104
    4 837.00 0.05 104
    5 370.89 15.00 FPL52 104
    6 -360.51 * Below 104
    IMA Infinity 13.989

    Temp EFL BFL
    0║C 799.661 792.668
    20║C 800.000 793.024
    30║C 800.173 793.207

    1/20 wave P-V central imagery over 0.4-0.72Ám, 87%EE within 20Ám circle
    at field edge - gives spots very similar to TMB's 100mm f/8, and over
    0║-30║C temperature range.

    Mike

  9. #9
    Chris1011's Avatar
    Chris1011 Guest

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

    Impressive theoretical performance, which comes at a cost of instability,
    however. The main problem I see with this design is a very high sensitivity to
    cooldown. During cooldown on cold nights the middle and rear elements lag the
    front one by about 20 fringes or so. If you change R3 by 20 fringes, you have a
    severely undercorrected lens.

    If you rely on an airgap to produce a large amount of spherical correction, as
    is the case in your design, the entire lens will be thermally unstable because
    airgaps are by their nature unstable. Unlike a lens element, where the rear
    surface will bend by the same amount as the front, the rear part of an airgap
    will not bend the same amount as the front part under changing temperature
    conditions. Only when the two glasses are at exactly the same temperature front
    and back, will the airgap have the exact shape that you wish it to have.

    Roland Christen




  10. #10
    John Savard's Avatar
    John Savard Guest

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

    On Fri, 26 Nov 2004 03:50:00 -0500, RichA <none@none.com> wrote, in
    part:


    Myself, I would favor using a different standard to establish what
    constitutes an apochromat.

    A basic triplet lens, crown, flint, and fluoride, will, for different
    focal ratios, provide a certain level of color correction. The longer
    the focal ratio, the better the correction.

    If that is set as the benchmark, then one can say how closely some other
    lens design, such as a doublet with special materials, approaches it.

    An f/32 reflecting telescope with a crown and flint doublet, for
    example, can also be sufficiently well-corrected for color to be
    diffraction-limited, but that doesn't make it an apochromat.

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

 

 
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