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

Orion's XT8 8 Dobsonian as a good beginner scope

  1. Jun 30, 2003 #1
    Orion's XT8 8" Dobsonian as a good beginner scope

    hey all... question!

    i posted this thread a while back and got some mixed reviews on what i should get as far as a telescope... well I really would like to get one before mars gets nice and close this summer.. i figure that will give me a pretty nice target...

    I also read http://www.scopereviews.com/begin.html about getting a first telescope.. what to expect etc, etc.. i found this article very good because a lot of the things he said most beginners think, were what I was thinking..

    Also he recommends Orion's XT8 8" Dobsonian as a good beginner scope... so I was wondering what you guys think of this.. and what would be a good eyepiece if I were to get a scope like this..

    Last edited by a moderator: Apr 20, 2017
  2. jcsd
  3. Jun 30, 2003 #2
    For eyepieces, get a 26mm super plossl and a 9.6mm and maybe a 15mm. The 26mm is standard for scopes of that size and the 9.6mm provides an almost optimal magnification. If your scope does not have a drive, then using the 9.6mm eyepiece can be a pain because it will be hard to keep the subject centered. The 15mm eyepiece is much easier to handle than the 9.6. Get all three if you can afford it. Some will recommend getting a wide field lens as well, but you can wait for that.
  4. Jul 1, 2003 #3
    what about the scope itself?
  5. Jul 1, 2003 #4


    User Avatar
    Science Advisor

    Of those mentioned, I would go with the Orion 8 inch. Several people in my astronomy club have one, and they are all quite good with NO dogs among them.

    You mentioned "Mars time" (August/September) so you need one from stock, like Orion. But, the eyepieces mentioned before, down to the 9.6mm, will only give you 125X, and an 8" scope with good seeing conditions should be able to go to 240X, which takes a 5mm eyepiece, or a 10mm plus a 2X Barlow lens. At 125X, Mars will still be just more than a very small red disk. Getting to 170X and higher will let you see some detail like the polar caps, dark areas, etc.

    An 8" has a maximum useful power of up to ~400X (50X per inch), but most "seeing conditions" will limit useful powers to about 30X per inch, which is 240X.
  6. Jul 1, 2003 #5
    thanks labguy... so lets say i get the orion... I should also get a 5mm or 10mm/ 2x barlow lens

    i dont mind spending a few extra bucks on an eyepiece that will allow me to get a better view... do you recommend a brand/model of eyepiece that i should get along with the scope? remember i am very new to all of this.. also what did you mean by I will need one from "stock" ?

    Thanks for your help
  7. Jul 1, 2003 #6
    If you're going to be viewing at high magnification a lot, you're going to want an equatorial mount. A dobsonian might be rather cumbersome for your purposes - to be fair, I've never used one, so I'm merely speculating. I once had a alt-az refractor, and it was particularly annoying. It depends on how much you're willing to spend. My personal opinion is that for a beginner, you don't need a huge scope. You just need something to force you to go outside and explore the sky. I own an 85 pound 10" reflector, and sometimes it's just too much for me. It takes me three trips to bring everything outside. I was considering buying a smaller scope from orion. I like Orion, especially for beginners, because they have some excellent deals.
    Orion has some equatorial refractors, which are nice, because they don't have to be collimated. For $499, you can get a 4.8" refractor. That's a little more expensive than the reflectors, but something worth considering.
    The scope I am probably going to buy is the AstroView 6 EQ for $369. As far as I'm concerned that's an excellent deal. Overall, it weighs 39lbs, so that's a big difference for me. 6" may limit how well you can see Mars, but I don't think you want to limit yourself to just the planets anyway. The planets constitute maybe 1x10-100% of what there is to see.
    I guess my main bit of advice is to get an equatorial mount for your telescope. Whatever rests on that mount is a matter of preference and budget. Don't sweat so much over the details. This first scope is a learning experience.
    Also, make sure you get something that is easy to carry from place to place. Sometimes, you may want to move your telescope in the middle of a session due to some trees. That happens to me almost everytime I'm out, and everytime I leave the telescope right where it is because it's just too much of a hassle to move it. I once had a 26lb schmidt-cassegrain, and as far as convenience was concerned, it was much more enjoyable.
  8. Jul 1, 2003 #7
    do you get better views with a refractor?? i mean i know that the size doesn't always mean its a better scope.. but a refractor about half the size of the Dobsonian.. will that yield similar viewing results? I don't really mind the lugging part.. and eventually I would probably get a more portable scope... I think I will be able to spend around 800 bucks for scope and eyepieces...
  9. Jul 1, 2003 #8
    The bottom line is, the bigger the aperture, the more you see, so with Dobs you get the most for your money. But you want observing to be fun, and if you're just beginning, I recommend an equatorial mount. Even a manual EQ mount is better (to me, anyway) than a motor-driven alt-az. I say save the Dob for when you're ready to nail some really deep sky objects.
    Let's say you spend $200 on three or four eyepieces. You've got $600 left for a scope. Now for $600 you can get a huge Dob, maybe 8-10"; maybe a 5-6" EQ reflector; maybe a 4-5" EQ refractor. I'm not so familiar with Dobs, but there seems to be a reason they're so cheap. There's no tripod, so you need level ground to work on. Dobs are usually low focal length, and so have other problems like coma associated with them. Refractors are expensive usually because they require special construction to correct for different refraction indices for different wavelengths, but they're easy to take care of and use, and they give nice views of the planets. Cassegrains have to be collimated a lot, so I'd stay away from those. So if it were me, I would get a 5" EQ refractor, but EQ reflectors are nice too. The advantage to buying an EQ reflector/refractor/cassegrain is that thereafter you can buy OTA's and attach them to your mount.

    I want to warn you that I am no expert on the subject - I've been using and buying telescopes for just over a year now. I would hope someone else would give his opinion. I don't want to steer you in the wrong direction.

    For some really good information on telescopes and accessories, visit www.astronomics.com and click on "how to pick a telescope." This site was an enormous help to me when I was starting out.
  10. Jul 1, 2003 #9


    User Avatar
    Staff Emeritus
    Science Advisor
    Gold Member

    High-end reflectors will likely beat most newtonians on crispness and field flatness. Low-end refractors will likely be beat handily by almost any decent newt. Low-end refractors suffer from chromatic abberation (objects, particularly bright objects like planets, will have a very annoying purple halo around them) and just as many optical defects as newts.

    It's actually easier to make a superb 8" mirror than it is to make a tolerable 4" lens. As a result, in low-end gear, the newt will almost always win -- IMO. Also, as has been said, you will likely grow to use all of your available aperture -- bigger is better.

    I would also like to point out that newts need collimation at least as often as do cassegrains -- the difference is that the cassegrains are more sensitive to poor collimation. You can be a little more sloppy with a newt, but you'll get your best views only if you collimate often.

    - Warren
  11. Jul 1, 2003 #10
    Isn't a newtonian a reflector?
  12. Jul 1, 2003 #11


    User Avatar
    Science Advisor

    Yes it is. They call it a "Dob" when mounted on an alt/az mount and call it a "Newtonian" when on an equatorial mount. I don't know how that habit started, because both are the same reflector.

    Also, see this site for a long discussion on smaller refractor vs larger newtonian. All of these guys spend big money on their gear, some well over $30,000.

  13. Jul 1, 2003 #12
    Heh, I'll add a few things:

    The most important thing to remember about telescopes is that the best telescope bought is the telescope that you will use reguarly rather than leaving it in a closet to gather dust!

    There are so many things that go into buying a telescope, escpecially a first scope.

    What do you plan to observe with it? That is one of the most important questions. If you are wanting to look at planets, comets, solar system objects, then a dobson is probably not the best scope to get. For these things you need a scope with a clock drive; dobsons usually don't have them except for the very expensive types or the ones made by amature telescope makers that really know what they are doing. Without a clock drive, by the time you get the object centered in the eyepiece, it drifts out of view very quickly. This (and getting the object into view) can be very frustrating for a first time telescope user.

    The large mirror size per cost of the dobson is not going to help much either. Dobson's usually have a low focal ratio. That is not the best for looking at planets. Usually for that you need a scope with a higher focal ratio. To get the dobson to a level that you can seriously look at planets, you have to "stop down" the mirror .. that is, cut out a circular mask and put it over the opening of the scope, but in that mask make a round hole, off center and smaller than the diameter of the mirror (these can be purchased). That limits the amount of light coming in, makes it a higher focal ratio, and gets rid of the diffraction spikes caused by the spider vanes, all making the seeing better. But then, say you stopped the scope down to 4" -- well, that's like looking at the planet with a 4" scope (refractor) -- you've basically lost all the additional area that other 4" provides to catch the photons! The extra money paid for that extra aperature is not doing you any good.

    Also, generally, you cannot use high power yield eyepieces with a dobson. I wouldn't consider buying a high power yield eyepiece for a dobson. Generally, they are made for viewing extended, extra-solar objects like nebulas, galaxies, and the like, with a wide field of view. And objects that you take a causal look at, and move to the next object. If you are going to do any serious study -- in depth looking at "an" object, you need something with a clock drive.

    Though a scope with a clock drive adds complexities to viewing. You do have to set it up, and align it with the polar axis, or have computer assisted alignment (more $), where you can point it at a couple of obvious objects, tell the computer what object that is, and then let the computer "internally" know the offset from the polar axis that you have the scope at.

    Also, you need to consider where you are going to use the scope at. To get the best views you have to take it to a dark site -- setting it up on your driveway in direct line with the neighbor's night light is not going to let you see too much except for the moon! If you are going to take it out to a dark sight, lugging around a heavy telescope and placing it in your vehicle can be the pits.

    A few other ideas you might consider:

    1) If you are not sure you will use it much, buy a good but cheap telescope first time. That usually means a reflector (Newtonian/dobson). You may not want to worry about getting a clock drive .. it's extra money. A good cheap scope is the Orion Fun Scope. This one is only 3" aperature, but there are similar scopes with a larger aperature, maybe up to 4". You can cradle it in your lap and support it against your body, to locate and center objects. It's a natural to use like that. It doesn't have a finder scope though. This is a very good scope for a beginner, one that is exploring if they might like astronomy as a hobbie, and won't set you back the big bucks if you make a mistake. If you find out you do like astronomy, then you'll find out that wasn't a bad investment, and (probably) always cherish that scope. This scope also as a mount/cradle that you can place the scope on too, for better/more steady viewing. It's small and lightweight. You can take it anywhere, on a moment's notice.

    2) Consider getting a small Meade refractor like the http://shopping.discovery.com/stores/servlet/ProductDisplay?catalogId=10000&storeId=10000&langId=-1&productId=11810&categoryId=22563&interCategoryId=22516&parent_category_rn=1109&partnumber=610105 [Broken]. These are smaller aperature scopes, in the range of 2.5" to 4", but they have superb optics, a built in table top mount, built in drive, computer database of objects, flip mirror for astronomical or terrestrial viewing, optional tripod mount. You can also take this anywhere. A good finder scope is an essential option on this scope. Heh, I saw last year that even Walmart were selling these scopes. Most would turn their nose up at buying a telescope from a department store, and I would too a few years back, but these scopes are good scopes. Just be sure that you get what you need to effectively use the scope in the base package, and that the things they are offering as "options" are not actually essential to the operation of the scope.

    3) Orion also has a "Short Tube EQ Reflector", that should be looked at seriously. They are quite comparable (usage wise) to the Meade ETX scopes. I noticed this scope has only a small reflect sight. These are good finders for someone starting out .. you can sight what you are trying to look at straght through .. and that is natural to try to do first time viewing. You will quickly move to a finder scope though .. I would recommend a good finder scope added to this telescope, as in the Meade ETX.
    Last edited by a moderator: May 1, 2017
  14. Jul 2, 2003 #13
    i cant believe you would suggest the fun scope??? isn't that a kids toy? i mean its got a 30x magnifying power on it??? and it is 90 bucks.. how good could it possibly be?
  15. Jul 2, 2003 #14
    Magnification is not everything .. it's only 1 piece of the puzzle in finding the right scope for a given person .. I think you'll find that out pretty quickly once you do get your scope.

    High power magnification does you no good if you can't locate the object, can't keep it centered in the field of view, the object you are looking at is low on the horizon and you're looking through upteen layers of air currents in Earth's atmosphere, or you have an unsteady mount. The times that you can use high power magnification are few and far between, and very brief, and if you are wanting to view high magnification, you need to know that and plan for/anticipate those brief moments.

    One thing I was trying to get at, and let you know, that a lot of persons that buy a scope use it quite a bit when they first buy it, then it's to the closet for it, and doesn't come out too often (I know by experience!). I'm not saying this will happen to you, and hope it doesn't.

    Portability of the scope is a big issue. I'm saying you [anybody] would more near use a scope that you can bring out at a moment's notice, and is not hard to lug around and set up.

    The "first scope" met all the ideas that I had: good optics (a must), easy to use, readily accessible, and cheap .. important if you're not sure it will be an ongoing hobbie. It is not a toy by any means.

    The other scopes I [[recommended/suggested]] are a step up, with other/extra features. If a couple hundred extra dollars is not an issue, they are good to buy. They still have the two most important features (besides low price!) that I can think of: good optics and portability.

    Extra (high power) eyepieces can come later, and can be used on different scopes if you decide to purchase an upgraded one (considering that you don't move from a 1.25" to 2" focuser).

    Also I'd suggest, that if you haven't started this already, that you get some beginner guides to observing and learn the sky/constellations. Without being able to glance up at the sky and knowing exactly where you are at, the chances of you locating "an" object is not too good, or will take you a long time. Remember, the features and orientation of the sky changes .. roughly every month the sky is a lot different than it was last month. You need to be able to look up at any sky and know whats up there .. you have to know your way around the sky.

    i'm just trying to help :0)
    Last edited: Jul 2, 2003
  16. Jul 2, 2003 #15
    i know you are trying to help.. and you have made several good points.. I just would never even consider getting that scope.. it seriously has to be just a play toy for kids...
  17. Jul 2, 2003 #16


    User Avatar
    Science Advisor

    This is just my 2-cents worth, But the Meade 70mm with computer is in "department-store" quality. It is a total dog and has no chance to gather enough light to see much at all. The Orion "Fun Scope" I saw at a dealer who came to our annual star party in March. I looked it over, and I can't imagine why anyone would buy one for any reason. Whatever the price is for it, you will be getting your money's worth.

    The other thing I saw posted somewhere above is that Dobs usually have short focal ratios (F/ratio). Almost every 6 inch reflector you can buy is f/8; plenty good for planets. Many of the 8" and 10" scopes range from f/5 to f/8, and sometimes higher. Discovery has been selling their 8", f/8 "Mars scope" faster than they can make them. A lot of the 10" and larger scopes run from f/4.5 (too low and too much coma) to f/7 which is a great all-around scope. Most 8" reflectors are made as f/6, but they go as high as f/10, honest. If the optics are high quality, an f/6 can be a killer on the planets and good for "deep-sky" objects as well. I have made three f/6 reflectors in the past year, but the optics were made by a "custom" and well known optician. When you pay $600 for just an 8" mirror, and $800+ for a 10" mirror, you do get your money's worth.

    But, as I said, that's just 2-cents worth.......
  18. Jul 2, 2003 #17
    so if you didn't own a scope.. and you had about 800-1000 bucks.. what setup (scope/mount/eye pieces) would you buy?
  19. Jul 2, 2003 #18
    My one and a half cents. These are all scopes I've considered in the past. I consider them all fine scopes - mostly it depends on how much you want to spend. As for eyepieces, I would think 3 would be enough and usually one will come with the scope. Just make sure you have a range - one low, med, high mag for whatever instance.

    Celestron Firstscope 114EQ - $160 - you can't beat that value - as far as I'm concerned it's plenty to get you started and keep you busy.
    http://www.optcorp.com/cart/ProductDetail.asp?PR_ProductID=1310 [Broken]

    Meade 6" SN - if you insist on spending more. I think they still have that ridiculous eyepiece deal running too.
    http://www.optcorp.com/cart/ProductDetail.asp?PR_ProductID=1740 [Broken]

    Again, Meade - I would really like to try this one out someday.
    http://www.optcorp.com/cart/ProductDetail.asp?PR_ProductID=1742 [Broken]

    Celestron - looks OK
    http://www.optcorp.com/cart/ProductDetail.asp?PR_ProductID=2047 [Broken]

    And don't forget those Orion scopes I mentioned.

    Bottom line is no matter what you buy, there will be something to see. I personally recommend the Celestron firstscope 114. I burned too much money on my first scope and I didn't like it.
    Last edited by a moderator: May 1, 2017
  20. Jul 8, 2003 #19
  21. Jul 8, 2003 #20
    Looks great. Nice choice. Hurry up and buy it before summer's gone! I would have suggested other ones, but this one looks excellent.
Share this great discussion with others via Reddit, Google+, Twitter, or Facebook