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Views on schimdt Cassegrain telescopes

  1. Jul 26, 2005 #1
    Hey
    Im looking to buy a fine quality telescope by either Meade or Celestron, a schimdt Cassegrain. I came across this one while I was browsing throught the Celestron website, http://www.celestron.com/prod_pgs/tel/nx8ise.htm
    it's really cheap in comparision to any other computerized schimdt Cassegrain 8'' by celestron or meade.

    Can any amateur astronomers give me their views on this particular scope?
    I am very interested in the 12'' or 14'' computerized schimdt Cassegrain, but I am only a 20 years of age college student and so I have to stay in a price range.
    Thanks
    Karl
     
  2. jcsd
  3. Jul 26, 2005 #2

    turbo

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    Hi, Karl. That is a cheap price. Let's take a look at the picture in the ad and see why. You get a cheap one-sided mount (not even a lightweight fork mount, which would outperform this one by at least 5-1 for rigidity and resistance to flexure), you get a cheap lightweight tripod, and you get Celestron's basic 8" optical tube. The software/firmware may be OK, the circuit boards may be available when yours fails, and the pointing accuracy may be OK, but I wouldn't bet the rent money on any of that. I would suggest that you can buy a nice Dobsonian with a pretty large aperture for that money, and not have to worry about crappy tripods and mounts or computer failure.

    Check out Orion Telescopes. You can by a decent 10" Dob for about $500, and for about $750 you can get a 10" with a Dob with encoders and a pointing database containing over 10,000 objects. If you opt for the basic Dob, you will have lots of money left over for decent charts (a MUST), a nice pair of 7x50 binoculars (another MUST in my opinion) and some eyepieces (go for at least one long focal length, fairly wide-field model with good eye relief - they are expensive, but are fantastic, especially for the non-astronomers trying to look through your scope for the first time).
     
  4. Jul 26, 2005 #3

    russ_watters

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    I'm of the opinion that a computerized scope will provide more bang-for-the-buck for someone with no experience with astronomy. It isn't easy for an absolute beginner to find objects. That said, it depends on what you plan to do with it. Ie, that scope may be ok if you're not planning on taking many pictures and mostly want to view planets and bright nebulae, clusters, etc. Its a lot of aperature for a scope with a mediocre mount, though.
     
  5. Jul 27, 2005 #4

    turbo

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    It's not only a lot of aperture - it's an inordinant amount of magnifying power for that mount. A beginner will generally tend to want to push the magnification on his or her new scope, and that flimsy mount will be a heart-breaker at high magnifications. Also, the Celestrons that I have viewed through have often exhibited excessive image-shift during focussing, which will only compound the problem.

    I know I sound like a broken record, but for the money, a beginner is far better off buying the best optics available on the simplest most solid mount, a decent sky atlas, a low-power or zero-power finder, and a pair of 7x50s binoculars. Dobsonians fill the bill, and offer lots of aperture for very little money. The difference in money can pay for some nice oculars. You don't need access to electricity to make them work, and all it takes is a little nudge once in a while to keep an object in view.

    High-quality folded-optics scopes like cats, Maks, and R-Cs can be optically fine; however, they are very expensive, and adequate mounts for them are also very expensive. Base-level consumer grade catadioptrics are relatively inexpensive, and the manufacturers cut corners in critical areas that new buyers will not realize or appreciate until they compare their 'scope to others. Then, they will realize that other designs do not have as much problem with image shift, vibration, long damping times, corrector plate dewing, long cool-down times, etc, etc. These are not inconsequential issues, and a newcomer to amateur astronomy should not have to deal with them, lest it turn them off to observing entirely.
     
  6. Jul 27, 2005 #5
    Ok so you guys are saying that I should set my eyes on a dobsonian rather than a schimdt cassegrain?

    I had the notion that the schmidt cassegrains where the best scope you can get? That they were the most powerfull?
    If you had the choice of buying a 10'' schmidt cassegrain or a 12'' dobsonian which would you choose?

    I was checking out this, SkyQuest™ XT12 IntelliScope®, what do you think?

    And also this, Meade 10" LX200GPS Schmidt-Cassegrain

    But whats the meaning of UHTC Coatings? There is one hell of a difference in price range with a telescope with UHTC Coatings over the same telescope with out UHTC Coatings.
     
  7. Jul 27, 2005 #6
    And as for a beginner scope, that is not what I want because im not a beginner of astronomy ive loved astronomy all my life and I want to do it as a career. So I want to buy a telescope that I will be proud of for life but that is around $3000. I plan to also do some astrophotography with it and to buy some imaging tools too.

    Another thing, I am living in Ireland, im planning to order the telescope online as it would be so much cheaper. Is it safe ordering from another country, I mean should I worry about the scope lenses being damaged during the transport process?
     
  8. Jul 27, 2005 #7
    Last thing, what sort of detail could I get out of this, Meade 16" Starfinder Dobsonian Deluxe. It looks interesting at a very reasonable price.
     
  9. Jul 27, 2005 #8

    turbo

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    Now you're talking! A 16" scope will gather 4x as much light as an 8" scope (ignoring secondary obstructions, reflections at the corrector etc, if you're comparing it to a Cassegrain). If you have the means to store and transport that scope, you will love tracking down faint objects with it. The low f:ratio means that you will get some coma off-axis, but the widefield views these big scopes offer is breathtaking.

    I would buy the big Dob and observe with it, and later when you can better afford it, supplement it with another scope - the best images available (in my opinion) in a relatively affordable scope can be had with apochromatic refractors. I've got one of Roland Christen's early 6" f:8 APOs and it is wonderful. These are expensive to produce and he always has a waiting list for both his mounts and scopes, but they are really fine. Takahashi produces some nice APOs, as do others. You will appreciate the nice scope when you can afford it, but you will never let go of that 16" light bucket. They are addicting. I have a short f/l Celestron Comet Catcher for casual observing, and I still take it out from time to time, and I am never far from my Nikon 7x50 binoculars.
     
  10. Jul 27, 2005 #9

    turbo

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    Russ likes computer controlled scopes, and the small SCs can be nice if they are paired up with an adequate mounting. The "half of a fork-mount" shown in your original post is woefully inadequate, especially if you want to hang some kind of imager on the scope too. As for "best", these are commercial-grade scopes we are talking about (Meade, Celestron, etc) and they have to be built to a price point. That means there is a limit to how accurately the manufacturers will test and figure the optical surfaces, and as you have found out, decent high-transmission coating aren't cheap, either. It is possible to get Cassegrain scopes that can rival the images of a decent refractor or Ritchi-Chretien (probably the two best designs available), but they are VERY expensive. You are not going to get that kind of quality in mass-produced scopes, since it requires testing and hand-figuring each optical surface.

    As for magnifying power - power is widely overrated. Within limits, you can divide the f/l of the ocular by the f/l of the scope to determine the power that ocular will give you. That said, the usable magnification of any scope is highly dependent on the aperture of the scope and the sky conditions where it is used. If the scope is small-aperture, pushing it to higher and higher magnifications yeilds NO extra resolution, despite the manufacturer's claims, and if the seeing is terrible, no scope will give you resolution near its design limits. I will go into this in more detail, if you wish.
     
    Last edited: Jul 27, 2005
  11. Jul 27, 2005 #10

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  12. Jul 28, 2005 #11

    saltydog

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    Here's my suggestions:

    First read "Sky and Telescope" and "Astronomy" magazines. You do that already huh? I'd say a year's worth and you'll know just what you want. Me personally, I wouldn't get anything smaller than a 12". Schmidt-Cassegrains are nice. My understanding is that you need an equatorial mount for good astrophotography but I'm not an expert. Really, if I were in the market for a good scope, I'd have $5000.00 to work with. Celestron, I believe offers some nice ones on an equatorial mount. Later get the other stuff like a good CCD, filters, eyepiece set, tent too you know (star parties) :smile: .
     
    Last edited: Jul 28, 2005
  13. Jul 28, 2005 #12

    turbo

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    Take note, Cyclotron. The Losmandy GM8 has a 30# capacity and the Celestron 9.25 OTA weighs in at 25#. Add a nice short APO finder/guidescope, a camera, field flattener, etc and you're pushing the 30# pretty easily. The GM8 mount sells for about $1500, and you'll add about $1000 to get GOTO capabilities. This is considerably more expensive than the entire scope in your original post, but this is the type of mount that you will need for an 7" to 9" catadioptric OTA if you want acceptible rigidity and stability.
     
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