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  1. #1
    Tony Flanders's Avatar
    Tony Flanders Guest

    Default Best planetary Scope?



    macman@whoever.com (David Dunn) wrote in message news:<8c8c835a.0308112009.d99cbdd@posting.google.c om>...



    I haven't seen the 6" LT, so I can't say for sure. But it is a mighty
    poor scope if it *doesn't* provide better planetary views than the 5" Mak.

    Planetary views depend on aperture (good), central obstruction (bad),
    and optical quality (very important). Orion's 5" Mak has modest
    aperture and big central obstruction which, at best, have to limit
    its planetary performance pretty severely. It is not unlikely that
    your 4.5" Newt could do better, if you collimated it properly and
    put it on a decent mount. Any decent 6" Newt should out-perform
    the Mak handily across the board. The benefit of the Mak is
    portability, not performance -- but you don't mention portability
    in your criteria. Anyway, the SVP mount isn't especially portable;
    it is overkill for visual observing with a 5" Mak.

    Have you considered Orion's 8" Newt on the SVP mount? A couple of
    people here have said that it performs pretty well, and 8" is a
    mighty nice amount of aperture, both for deep-sky and planetary
    work. And assuming that the mirror is well figured, I would
    rather have an F/5 Newt than an F/8. (In fact, I *do* have an
    F/5 Newt, namely the Starmaster 12.5" EL.) All things being
    equal, I would like F/6 even better in 6" or 8" size, but that
    isn't one of the options if you stick to Orion ...

    - Tony Flanders

  2. #2
    David Knisely's Avatar
    David Knisely Guest

    Default Best planetary Scope?

    Hi there. You posted:


    While the 5 inch Mak has a somewhat large central obstruction (around 30%
    linear), its performance is hardly "severely limited". I used one on Jupiter
    and it beat my 100mm f/6 refractor as far as the amount of detail visible
    and the overall quality of the image. It is a good lunar and planetary
    instrument, although a quality 6 inch Newtonian with a modest secondary
    obstruction (less than 25%) would probably beat it. Clear skies to you.
    --
    David W. Knisely KA0CZC@navix.net
    Prairie Astronomy Club: http://www.prairieastronomyclub.org
    Hyde Memorial Observatory: http://www.hydeobservatory.info/

    **********************************************
    * Attend the 10th Annual NEBRASKA STAR PARTY *
    * July 27-Aug. 1st, 2003, Merritt Reservoir *
    * http://www.NebraskaStarParty.org *
    **********************************************




  3. #3
    Mij Adyaw's Avatar
    Mij Adyaw Guest

    Default Best planetary Scope?

    David,

    You must have compared it to a low quality 100mm refractor. I have done the
    same comparison with the Orion 5 inch Mak against an AP 105. The AP 105
    provided much better contrast on Jupiter and Saturn and it was much easier
    to see detail. To equal a good four inch refractor, you will need a good 6
    inch Mak with a 30 percent CO.

    Regards,

    -jim

    "David Knisely" <ka0czc@navix.net> wrote in message
    news:3F394632.1070704@navix.net...
    Jupiter
    visible



  4. #4
    Jon Isaacs's Avatar
    Jon Isaacs Guest

    Default Best planetary Scope?

    >David,

    No doubt about it, I am quite sure David has a Orion 100mm F6 refractor. This
    is not a "low quality" refractor, rather it is a basic achromat that does a
    good job of doing what an Achromat can do.

    This thread is not about APO's and other expensive scopes. Here is the meat of
    the Original Poster's question:

    "I have been doing a little research and I am interested in Orions SkyView Pro
    127mm (StarMax 127mm with a higher quality mount) wich costs $650. So
    my question is, based on my criteria, wich scope do you think I would
    like best? The SkyView Pro 127mm, or some other scope for around the
    same price. I think I could go up to $1000 (mount and all).

    Clearly David's comparison of the 127mm MAK to the 100 F6 Orion refractor was
    relevent, especially since someone had previously suggested the MAK would not
    be a good choice. I have no doubt that a 4 inch AP scope would provide sharper
    images but....

    I believe it is important to keep things in context here and remember that
    simple and basic does not mean something is "low quality." Some of us have
    simple and basic and we like it, we are aware of its limitations but we are
    also aware of what "low quality" really is. Anyone who wonders, I have a 5x24
    finder from a Tasco scope I can send you.

    As far as recommending a scope to the orginal poster, I think the point is that
    aperture rules here so if he wants some decent planetary images, a 6 or 8 inch
    Newtonian is the obvious choice. A used 8 inch SCT with some accessories would
    also make a good choice.

    Jon Isaacs

  5. #5
    David Knisely's Avatar
    David Knisely Guest

    Default Best planetary Scope?

    Hi there. You posted:


    I compared it to my SkyView Pro100, but also compared it against a 6 inch
    Newtonian, so what I stated was factual. The Mak provided surprisingly good
    images with good contrast, showing 4 to 6 belts, the red spot, and some
    irregularites in the two equatorial belts. It showed no chromatic aberration
    and little if any spherical aberration, so optically, I would judge it as a
    reasonably good instrument. Again, an unobstructed Apochromatic (and
    multi-thousand dollar) refractor had darn well be somewhat superior to it at
    least to some extent (otherwise, I would want my money back on the APO
    refractor). However, the Mak is a much more cost effective alternative to a
    *much* more expensive refractor. In any case, the claim that "a big central
    obstruction which, at best, have to limit its planetary performance pretty
    severely" is a major overstatement. Clear skies to you.
    --
    David W. Knisely KA0CZC@navix.net
    Prairie Astronomy Club: http://www.prairieastronomyclub.org
    Hyde Memorial Observatory: http://www.hydeobservatory.info/

    **********************************************
    * Attend the 10th Annual NEBRASKA STAR PARTY *
    * July 27-Aug. 1st, 2003, Merritt Reservoir *
    * http://www.NebraskaStarParty.org *
    **********************************************



  6. #6
    andrea tasselli's Avatar
    andrea tasselli Guest

    Default Best planetary Scope?

    "Mij Adyaw" <NoSpam@NoSpam.org> wrote in message news:<G2k_a.43949$Bp2.17494@fed1read07>...

    Never in this world. A 6" quality Mak is considerably superior to any
    4" APO, be it from AP or otherwise. To match a 6" Mak with 30% CO you
    would need a 120 mm APO at least and possibly bigger.

    Andrea T.

    My Astronomy Pages at:
    http://www.geocities.com/andreatax/index.htm

  7. #7
    Tony Flanders's Avatar
    Tony Flanders Guest

    Default Best planetary Scope?

    David Knisely <ka0czc@navix.net> wrote in message news:<%Or_a.622$Q5.215@fe01.atl2.webusenet.com>...


    OK, I certainly won't quibble about words. A 127mm scope with a 30%
    obstruction should be roughly equivalent to an unobstructed 90mm
    scope for viewing low-contrast detail. Whether that counts as
    "severely limited" is up to you. On the one hand, people today
    spend thousands for unobstructed 85mm and 90mm APO refractors,
    and lots of serious planetary work was done up to and throughout
    the nineteenth century with smaller scopes than that. On the
    other hand, it is no match for a high-quality 6" Newt with a 20%
    central obstruction, let alone an 8" Newt.

    - Tony Flanders

  8. #8
    David Knisely's Avatar
    David Knisely Guest

    Default Best planetary Scope?

    You posted:


    The "subtract the obstuction" rule of thumb has never been highly accurate,
    although a loss of contrast does occur with larger central obstructions. The
    aperture of these smaller Maksutov's seems to be overstated. My StarMax 90mm
    EQ from Orion which I use for solar work has a true clear aperture of only
    87.5mm (the company states the size of the primary mirror, which is a bit
    inaccurate). The 127 Mak is probably more like 123mm in aperture. Overall
    the larger Maksutov compared very well to a fairly good 4.5 inch Newtonian as
    well as a 120mm f/8.3 achromatic refractor, being better than the refractor
    with the Mak's showing none of the faint but visible secondary color around
    Jupiter. In any event, the Maksutov was much more compact than the refractor.
    "Severely limited" would be performing something like the typical department
    store 60mm refractor, and the Mak is certainly well beyond this level. Clear
    skies to you.
    --
    David W. Knisely KA0CZC@navix.net
    Prairie Astronomy Club: http://www.prairieastronomyclub.org
    Hyde Memorial Observatory: http://www.hydeobservatory.info/

    **********************************************
    * Attend the 10th Annual NEBRASKA STAR PARTY *
    * July 27-Aug. 1st, 2003, Merritt Reservoir *
    * http://www.NebraskaStarParty.org *
    **********************************************




  9. #9
    Ian W's Avatar
    Ian W Guest

    Default Best planetary Scope?

    In article <20030813084811.13124.00001174@mb-m10.aol.com>,
    jonisaacs@aol.com says...


    I'd suggest you visit a local astronomy club on an open night, or a star
    party and try out as many telescopes as you can. Nothing beats a bit of
    hands on experience before laying down the $$.



    Never were truer words written. Given the choice between quality optics
    and a simple solid mount versus whizz bang features I'll take quality
    optics and a simple mount any day of the week.


    There's a few choices and the original poster may want to consider
    purchasing a good used telescope, for example saving up for a bit longer
    and going after an 8" F8 Newtonian on a GEM, or a Meade LX-50 series
    Maksutov. Or if you can find one a Cassegrain (so called 'classical
    Cassegrain').

    One thing that should be mentioned is the choice of eyepieces for
    planetary observing is nearly as important as the choice of telescope. I
    swear by Orthoscopics for serious planetary observing.

    Ian W

  10. #10
    Tony Flanders's Avatar
    Tony Flanders Guest

    Default Best planetary Scope?

    David Knisely <ka0czc@navix.net> wrote in message news:<3F3AA3F2.3080305@navix.net>...


    Heavens, I certainly never meant to imply that! A 127mm scope would
    have to be fantastically poor to be crippled down to the level of
    a 60mm scope. Having said that, those department-store scopes can
    perform better than most people think. When I was reviewing cheap
    scopes, I found that the $100 60mm refractors showed nearly as much
    planetary detail as my pricey 70mm Televue Ranger.

    - Tony Flanders

 

 
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