Dismiss Notice
Join Physics Forums Today!
The friendliest, high quality science and math community on the planet! Everyone who loves science is here!

Refractor or reflector

  1. Aug 3, 2008 #1
    what is the best telescope? refractor or reflector?
    is the principle of reflecting is better or the reflacting?
     
  2. jcsd
  3. Aug 3, 2008 #2

    russ_watters

    User Avatar

    Staff: Mentor

    That's an impossible question to answer, there are just too many variables. Not the least of which is money.
     
  4. Aug 3, 2008 #3
    Here ya go
     
  5. Aug 4, 2008 #4

    HallsofIvy

    User Avatar
    Staff Emeritus
    Science Advisor

    Generally speaking, for a fixed amount of money, a reflector is going to be larger and better than a refractor. That is true for two main reasons:

    Light passing through a refractor lens has to pass through the lens: the glass has to have no defects all the way through. Light in a reflector does not: only surface defects are relevant.

    The lens, especially in larger telescopes, is the heaviest part of the telescope. For a refractor the lens is at the end of the telescope pointed up toward the stars, for a reflector, it is at the other end and so is lower. The support of a refractor has to be much heavier and more stable than for a reflector.
     
  6. Aug 4, 2008 #5

    Borek

    User Avatar

    Staff: Mentor

    Not to mention the fact, that large refractor lens will bend under their own weight, distorting the geometry. Mirror is much easier to support in such a way that it doesn't bend.
     
  7. Aug 5, 2008 #6
    If you're just starting out, I highly recommend a refractor, it's much easier to use. To me personally, a reflector takes a lot more time to set up and use, which would make me not feel like using it as much... but if you want the largest possible telescope and willing to put in the time to set up then a reflector might be better.
     
  8. Aug 6, 2008 #7

    Borek

    User Avatar

    Staff: Mentor

    In my experience there is no huge difference. Perhaps aiming refractor is more intuitive (at least when compared to Newton system).
     
  9. Aug 6, 2008 #8

    turbo

    User Avatar
    Gold Member

    No huge difference, perhaps, but I have a 6" Astro-Physics Apo refractor and a 90mm Vernonscope Apo refractor (as a finder/guidescope). I have a very massive AP mount with no setting circles or any other type of aiming aid but by sighting along the tube, and star-hopping with a decent set of charts, I have no trouble finding even very faint objects. You can learn to use Newtonians this way, too, but it's tougher to eyeball and star-hop with short-tube cats. Tube flexure is not a real problem with refractors of modest aperture like mine, nor does the weight of the glass cause problems in a well-designed objective cell.

    Of course, the OP is not going to jump into the hobby with a 6" Apo, so the point is moot. There is a very well-known astrophotographer from Austria who photographs with a folded-tube 9" TMB APO with world-class results. This design takes a lot of the potential flexure out of the picture, even with a massive objective cell, and makes the OTA mountable in a reasonable-sized observatory.

    Here is Diet's web-site:
    http://www.stargazer-observatory.com/
     
    Last edited: Aug 6, 2008
  10. Aug 6, 2008 #9

    DaveC426913

    User Avatar
    Gold Member

    Just remember the one rule of telescope shopping:

    Magnification is nothing. Aperature is everything.

    Do NOT get fooled by claims of large magnifications. What you want is the biggest aperature your money can buy.
     
  11. Aug 6, 2008 #10
    For larger telescopes, refractors have more aberration let alone weights and other things.
     
  12. Aug 7, 2008 #11

    Chronos

    User Avatar
    Science Advisor
    Gold Member
    2015 Award

    Schmidt Cassegrains are an economical compromise. Their big advantage is portability. They are much smaller and lighter than either a refractor or reflector of like aperature. This is a major advantage if you don't have an observatory.
     
  13. Aug 7, 2008 #12
    thank you all for your infos
    but im not asking about the money........
    ...asking about what is difference between the principle
    of refractor/ reflector telescopes
    and what to recomend
     
  14. Aug 7, 2008 #13
    i know this
    i gotta ask you about magnification:
    a telescope magnification is 36x-675x
    what is the measure of magnification?? meters?
    and what's the meaning of "Brightness" in telescopes?
     
  15. Aug 7, 2008 #14

    russ_watters

    User Avatar

    Staff: Mentor

    So you are asking what telescope you should buy? We need more information:

    Skill level.
    Intended use (do you want to take pictures?).
    Money.

    Yes, money is important. Turbo-1 mentioned a scope that is considered by many to be the premier amateur scope. It costs somewhere around $100,000.
     
    Last edited: Aug 7, 2008
  16. Aug 7, 2008 #15

    russ_watters

    User Avatar

    Staff: Mentor

    Ok, now we're getting somewhere. So your skill level is complete novice. Now how 'bout that budget?

    Magnification is a relative thing. With twice the magnification, an object will appear twice as big. If you want that in a size, it wouldn't be meters, it would be degrees of arc. The moon, for example, covers 0.5 degrees of your naked eye field of view. Magnify it 36 times and it will cover 18 degrees of your field of view.

    Writing "36x-675x" magnification is very specific: no doubt you read that off the advertising for a telescope. Please note again: this is completely meaningless as a way to compare scopes. First, it is easy to get pretty much any mangification you want. Second, no beginner level amateur scope can resolve anything at 675x magnification.

    For brigtness, the biggest determining factor is focal ratio and it is a square relationship. Ie, an f4 telescope will produce objects 4x as bright as an f8. And what this means, quite simply, is that dim objects will appear brighter and you'll be able to see things with the f4 telescope you wouldn't see with the f8.
     
  17. Aug 7, 2008 #16

    Borek

    User Avatar

    Staff: Mentor

    Think about it this way: there are interesting objects on the sky that are barely visible with the naked eye, even if they are large enough - I am thinking about famous Andromeda galaxy M31. To see it you don't need huge magnification, but you need to see it much brighter. Thus you want a telescope with a large diameter - so that it can collect as much light as possible. Magnification is not that important, especially when you take into account that the more magnified object is, the darker it seems to you - so it will be too faint to be visible.
     
  18. Aug 7, 2008 #17

    DaveC426913

    User Avatar
    Gold Member

    Yes, as Russ and Borek point out, so will I concur:

    1] The challenge with astronomy is not about seeing small things, it's about seeing dim things.

    2] A telescope that brags a 36x-675x mag uses what's called a Barlow lens. The actual mag of the scope might be only 135, but a 5x Barlow is simply a tube of plastic they throw into the box that moves the focal point 5x father away. It also means everything is 5x dimmer and 5x blurrier - and that's not even counting the ultra-crappy plastic lens they provide. Except under specific circumstances, Barlow lenses are arguably worse than nothing at all.


    As for which is better, IMO, you can get a bigger reflector scope than refractor for the same money. Again, go for aperature.
     
  19. Aug 7, 2008 #18

    russ_watters

    User Avatar

    Staff: Mentor

    I guess I'll repeat what everyone else has said now, but in a different way: for a beginner scope, the best bang-for-the-buck is with a (usually Newtonian) reflector.
     
Know someone interested in this topic? Share this thread via Reddit, Google+, Twitter, or Facebook

Have something to add?



Similar Discussions: Refractor or reflector
  1. Refractor Telescopes (Replies: 8)

Loading...