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Thread: TMB 100mm F/8

  1. #1
    ValeryD's Avatar
    ValeryD Guest

    Default TMB 100mm F/8



    Tom Back wrote:

    "In fact, the TMB 100mm/800mm SD triplet is the best
    corrected lens on the market now, from any company."

    This is not a fact. Of course this objective is too small
    and too slow to be compared with other, more practical
    F/# APO triplets.

    But I can state and place my reputation as optical designer,
    that such cheap combination as any well made 100mm F/10
    achromat (say, Sinta one) in combination with Chromacor-II
    (when properly collimated in a scope) will beat that 100mm F/8
    SD triplet in terms of secondary color correction and will be
    completely free of spherochromatism.
    If to see on spot diagram, all colors from 420nm to 656nm are
    INSIDE Airy disk diameter. This can't be achieved with that
    100mm F/8 SD triplet.

    OK, this is the case with F/10 achromat. No problem, let take
    100mm F/8 and again use a Chromacor-II. Again, color correction
    within 420nm to 656nm is better, than in TMB 100mm F/8 SD triplet.

    Let take 120mm F/8.3 achromat and Chromacor-II. The same result -
    color correction is better, than in TMB 100mm F/8 SD triplet.

    Even 150mm F/8 achromat being correctly matched with Chromacor-II
    show ZERO color on any object.

    Of course, for many such true APO as SD triplet is more attractive
    telescope design. But it is not the best in the color correction.


    Valery Deryuzhin
    ARIES.

  2. #2
    Tom Davis's Avatar
    Tom Davis Guest

    Default TMB 100mm F/8

    Valery,

    I never saw that level of correction from either the
    Chromacor, or the Chromacor II. I tried every spacing,
    every possible effort being made to get perfect collimation,
    and the 100/800 you refer to clearly outperformed them.
    The same is true with the 92mm 700mm FL Burgess
    Fluorite. Please don't get into this any further. I have
    enough first-hand use with multiple Chromacors that you
    sent me that you ust don't want to go down this road.

    The Chromacor works, but is a high maintenance item, and
    the two scopes in question are not. I don't have to go out
    and collimate my scope everytime I use it. I did not have
    to collimate the 100/800, and only had to collimate the
    92mm fluorite once, and that was because of a prototype
    lens cell. It holds collimation perfectly now.

    Thanks, Tom Davis

    "ValeryD" <aries@mercury.kherson.ua> wrote in message
    news:5c4a4ee7.0411240231.2ffb253@posting.google.co m...



  3. #3
    SweetGus the AssClown's Avatar
    SweetGus the AssClown Guest

    Default TMB 100mm F/8

    In article <5c4a4ee7.0411240231.2ffb253@posting.google.com> ,
    aries@mercury.kherson.ua (ValeryD) wrote:


    Good god......not you again.

  4. #4
    Mark D's Avatar
    Mark D Guest

    Default TMB 100mm F/8

    Tom Back wrote:
    "In fact, the TMB 100mm/800mm SD triplet is the best corrected lens on
    the market now, from any company."
    This is not a fact. Of course this objective is too small and too slow
    to be compared with other, more practical F/# APO triplets.
    But I can state and place my reputation as optical designer, that such
    cheap combination as any well made 100mm F/10 achromat (say, Sinta one)
    in combination with Chromacor-II (when properly collimated in a scope)
    will beat that 100mm F/8 SD triplet in terms of secondary color
    correction and will be completely free of spherochromatism.
    If to see on spot diagram, all colors from 420nm to 656nm are INSIDE
    Airy disk diameter. This can't be achieved with that 100mm F/8 SD
    triplet.
    OK, this is the case with F/10 achromat. No problem, let take 100mm F/8
    and again use a Chromacor-II. Again, color correction within 420nm to
    656nm is better, than in TMB 100mm F/8 SD triplet.
    Let take 120mm F/8.3 achromat and Chromacor-II. The same result - color
    correction is better, than in TMB 100mm F/8 SD triplet.
    Even 150mm F/8 achromat being correctly matched with Chromacor-II show
    ZERO color on any object.
    Of course, for many such true APO as SD triplet is more attractive
    telescope design. But it is not the best in the color correction.
    Valery Deryuzhin
    ARIES.
    ---------------------------------------------------------------
    Hello Valery, While I don't posess the knowledge that either you, or
    Tom Back posesses as a designer, I won't debate the possibility of an
    Achromat w/Chromacorr having better color correction than the LZOS made
    100mm F-8 Apo Lens, as this might be a possibility.

    What is debatable though is to think that any Chinese manufacturer right
    now would be figuring a lens as well as LZOS would, a sub-contractor of
    Zeiss.

    I'm sure Spherochromatism, and Strehl ratios are not the only things
    that make a good lens.

    On interferometer, I'm quite sure any of the Syntas would show rough
    zones in figure, and not anywhere near the P-V specifications as a good
    LZOS Lens.

    Doesn't lens smoothness, and adhering to proper design parameters
    account for anything?

    What good is a lens that is perhaps highly corrected for color, when a
    sample lens may only exhibit 1/2-1/3 wave figure?

    Then, is Chromatic abberation considered to be the only criteria of a
    good lens, and lens design? I think you know the answer better than I
    do. Mark



  5. #5
    Bill Meyers's Avatar
    Bill Meyers Guest

    Default TMB 100mm F/8

    Hello, Tom,
    I can't cfomment on the Chromacor nor on Valery's spot diagrams but I
    can give my own experience.
    I have used a TMB 100 F/8 belonging to an observing buddy, and I have
    posted about it on s.a.a., about a couple of years ago.
    I found that it gave beautiful star images, and was amazed to see that
    on Vega and other stars the image did not braak down at 600x, and it
    remained a perfectly round tight image.
    I have heard claims like this about other top quality apos and
    felt it was hyperbole by inexperienced observers, and I would not have
    believed it until I saw these images. This to my mind is a wonderful
    scope. I saw no secondarfy color in focus. I fail to see how those
    images could have been improved. I am speaking of images in focus at the
    eyepiece. I did not look at out of focus images, nor did I consult spot
    diagrams or use an interferometer. I am an observer.
    The TMB OTA at that time was heavy, and I felt it was overbult,
    but I would not call a four inch 32 inch focal length impractical.
    Clear skies,
    Bill Meyers

    Tom Davis wrote:



  6. #6
    ValeryD's Avatar
    ValeryD Guest

    Default TMB 100mm F/8

    "Tom Davis" <tdavis11@carolina.rr.com> wrote in message news:<DE1pd.649$Mu3.58384@twister.southeast.rr.com >...

    You didn't used Chromacor-II with 100mm F/10 achromat. F/10 is
    much more forgiving for collimation than F/8.

    Also, the fact, that you need to collimate Chromacor each time
    you use it does not say anything bad about Chromacor itself -
    this just indicate how bad can be mechanics in chinese telescopes.

    More, Chromacor was not purposed for constant removing from a scope.
    I was able to adjust mechanics in my chinese refractors - 100mm F/10,
    120mm F/8.3, 150mm F/8 that they never required Chromacor recollimation.

    All depends how good mechanics in your scope, how good your skill
    and patience are.

    You can ask Sol Robbins, who is not an engineer/optician, but he has
    enough knoweleges and patience to be able to choose right correction
    of Chromacor and to perform it's correct installation and he don't need to
    collimate his rig each time. Ask him if he can see any color on selestial
    objects. Note, that 100mm F/10 has about 3x less color influence on image.
    If he can't see any color in his 150mm F/8 scope, it is worthless to
    speak about 100mm F/10 + Chromacor-II.


    VD

  7. #7
    Leonard's Avatar
    Leonard Guest

    Default TMB 100mm F/8

    Valery wrote :



    Come on Val , kicking Tom Back again and again has
    got to be getting old even for you . Your own equipment reviewer does
    not agree with you.
    I know you have better things to do . Most people don't care if Tom
    Backs head is so full of himself as to be ready to explode. Most
    people only care about if Mr. Back is delivering on what he says he
    can . And it seem he can .

    So maybe you could :

    1- Make some more chromacorrs , there hard to find .

    2- You may have a review of your eyepiece the SPL vs. the TMB
    mono. coming up on the AP newsgroup. At least its said to be in the
    making . What if yours comes out second to the TMB mono. You could
    take some time and think about what your going to say .

    3- And last but not least , where are all the Aries APO's ?

    4- Don't forget all this may bring the " Old Judge " over here
    typing a longgggggggg boring disseration about what a bad boy you are
    .. Please save us from that !!!!!!!!!
    Leonard

  8. #8
    Tom Davis's Avatar
    Tom Davis Guest

    Default TMB 100mm F/8

    Valery,

    If you need to be an engineer to make the Chromacor work,
    you've answered your own question. Having no corrector is
    better than a corrector that needs to constantly be tweaked.
    Yes, the standard Chinese mechanics are an issue, but they
    are an issue that needs to be dealt with by anyone using
    such a scope with a Chromacor. As you add up the cost
    of upgrading a scopes mechanics, it becomes more and more
    expensive a proposition. The only answer is to have a
    pre-installed, permanent Chromacor, or a lens that does
    not need one.

    Sort of reminds me of the old Jaguar XKEs. When
    everything was right, they were great sports cars. When they
    had a problem, you needed a Jaguar specialist to fix one.
    Any refractor that needs an expert to keep working, is not
    going to fly with most buyers. Until you can get a scope
    with a Chromacor III pre-installed, with little user
    maintenance required, it is not fair to be bashing Thomas
    Back, or anyone else with a working triplet APO or
    doublet APO design. I'm very happy that Sol has a great
    scope, but that did not happen with my Chromacor II.
    I did not have a collimation issue. While the color correction
    was far better than the native achromat, I had a slight
    turned edge (which the Chromacor II could not fix), and
    no matter how I spaced it, I still did not get the level of
    color correction that even the pre-TMB 100/800, or the
    current 92/700 Burgess Fluorite could provide. The TMB
    100/800 is beyond this level, not just in color correction,
    but in all other areas of optical correction.

    I wish you well with pre-installed Chromacor III equipped
    high quality achromats. I think that product could provide
    what you discuss to the average buyer. Until then, let's
    give poor Thomas a break. He has enough pain with his
    neck problem. We don't need to give him any more pain
    by bashing products of his that have a proven track record.

    Thanks, Tom Davis


    "ValeryD" <aries@mercury.kherson.ua> wrote in message
    news:5c4a4ee7.0411241116.5802a817@posting.google.c om...



  9. #9
    TMBoptical's Avatar
    TMBoptical Guest

    Default TMB 100mm F/8

    V.D. passed gas and said -


    Wrong again Val. I really don't know why I am wasting
    my time with you, and you can be sure I won't again,
    but when you said you would place your reputation as
    an optical designer on the line, well, I had to respond.

    Yes it can, and the TMB 100 f/8 has all the wavelengths
    inside the Airy disk diameter from less than 420nm
    to 706nm, beyond your Chromacor-II performance,
    which is never truly achieved in the real world, only
    on your Zemax screen, as Tom Davis so well pointed
    out.

    I will be posting the spot diagram of the TMB 100mm
    f/8 on the TMB Yahoo Group, if anyone is interested.

    And for the people that think my head is too big, that's
    fine, but I do speak the truth, and if that gives me a
    big head, so be it. There was a better corrected lens
    at one time than the TMB 100mm f/8, the Zeiss 100mm
    f/10 APQ. But that scope has not been for sale for
    many, many years.

    Happy Thanksgiving s.a.a.ers!

    Thomas Back
    TMB Optical

  10. #10
    Ted Kord's Avatar
    Ted Kord Guest

    Default TMB 100mm F/8

    ngc7789@citynet.net (Leonard) wrote in message news:<58ee67ec.0411241127.67981bcf@posting.google. com>...

    If Valery spent as much time designing and building scopes as he does attacking
    other vendors, he could produce a scope that has zero CA, zero SA, perfectly
    smooth surface and polishing.

    You know, it's a general axiom that those who put others down do so to
    feel better about themselves for their inferiorities.

 

 
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