What is a good Dobsonian telescope for less than $500?

Question

I'm new to the hobby and am trying to avoid the usual mistakes noobs make. From what I have read many of them come with a cooling fan....can anyone shed some light on why a light box would need a cooling fan?

Answer 1

This is a good price point. You have several ways to optimize, I shall explain.

1. I am ruling out tracking. At this price point there is no good alternative for tracking that includes optics.

2. I am NOT ruling out a digital computer. It's very nice to have something to help you tour the sky.

3. I am bearing in mind that the "comes with" stuff, especially the eyepieces, aren't always the best.

4. I am thinking about new prices, but you should REALLY consider buying used. I saw a 10 inch dob on Astromart for $300 not too long ago and it doesn't get any better than that.

In all cases I am recommending Orion over other alternatives such as Hardin. It has good name recognition and better resale value (do join Astromart, one time fee of $12). People pay the money in part because ebay is well known for ripoffs and fraud: I saw an ebay instrument for sale in Montreal, tried to offer to go up and buy it and take it, only to discover that the exact same instrument had been sold in England earlier, same pictures, same description, everything.

Orion shipping costs (direct form Orion) are pretty high, you may well find you get a better price (on Orion's products!) from Highpoint Scientific, so call them first.

OK--

Option 1. Throw everything you can cat a light bucket and use the "comes with" eyepieces until you get more cash. Most people prefer the "get as much aperture as possible approach." Orion XT8 classic will get you there.

Option 2. Get the Orion XT6 instead and get it with the computer.

Option 3. Get the Orion Star Blast for $175 and a 24 mm Pan Optic eyepiece for about $300. It seems insane to spend more on the eyepiece than the telescope, but some day you'll upgrade and you'll still have the eyepiece. The Pan Optic gives, in this scope (direct experience), a panoramic 3.5 degree field of view that is well corrected. You will be able to get wide, sweeping views that are better than most binoculars and certainly easier to use (your arms won't get tired). With the "comes with" eyepieces you achieve higher powers, you'll get nice views of the moon and "reasonable" (not top notch) views of Jupiter and Saturn (which are only available a few months of the year in any case, and Jupiter is so low for N hemisphere observers that there is little point in "optimizing" for looking at this planet until two or three years from now--plenty of time to upgrade; ditto for Saturn, whose rings are moving into edge-on). So this little scope will help you learn how to navigate and point a scope under the sky.

It will be objected that "you can't be see much" in a 4.5 inch scope. To this I respond that there are thousands of devotees who spend thousands of dollars on 80, 90, and 102mm refractors. I personally agree that it is best to have access to aperture, but the merits of a small scope are also obvious: ease of setup, panoramic wide fields, and in the case of the Star Blast, good quality packaged in a low price. Try to get a new or used copy (abebooks.com) of Sue French's Celestial Sampler. This book is basically designed for the four inch aperture, and there is years of observing to be done in its pages. The famous sky artist, Stephen O'Meara, has also published work done with a four inch telescope (his main instrument). A four inch instrument will bring in ALL of the Messiers and several thousand of the NGCs.

As a final point, I'm not saying that you should get a four inch scope and keep it for the rest of your life and use that and that alone. But in fact this is a very easy way to decide if astronomy is for you. If you get the bug you'll eventually get something bigger (maybe keep the small one, maybe not) and probably devote a regular budget to astronomy, just as some people have a budget for bowling.

So there is no single configuration to which you need to be tied for the rest of your life, and all of them will have something to teach you. Of course, you also should consult Sky and Telescope's web site for a club near you so you can see many different configurations at work. You may see one that says to you: "I gotta have something like that."

And I can't emphasize enough that, although many people are horrified at the idea of spending $12 to join Astromart (one time lifetime fee), you could easily save $200 on your first purchase, and if you get your feet wet you won't feel nervous about buying any particular scope, because you'll know THE place to sell it if you decide to move on to something else. Preserving your sense of flexibility is important.

Answer 2

Most materials expand when heated and contract when they cool. Telescopes are typically taken out at night, during which time the temperature of their environment changes, usually from warmer to cooler, and the materials they're made of begin to change shape as they cool.

Because the different parts of the telescope are usually made of different materials, they will cool, and thus change shape, at varying rates. You don't want this to occur while you are trying to use the telescope because the distortion of the ratios of the dimentions of the telescope and it's optical system will cause you to get a poor image.

This is why it's important to let your telescope properly cool before you make any small collimation adjustments and use it. The mirror is glass, which is an insulator, and will tend to not cool as quickly as some of the other parts of the telescope, and in non-truss tube telescopes, the optical tube will retain a considerable amount of heat, and so the fan aids in the cooling process.

A good dobsonian for less than $500...
Well if you want the largest one you can afford, that would be a 10" Zhumell.

http://www.telescopes.com

Other than that, Celestron and Orion both make very good dobsonians.

http://www.oriontelescopes.com
http://www.celestron.com

Answer 3

Yes.

The reflector telescope uses a large mirror at the base of the tube. In some cases that mirror is eight to ten inches or more wide. In the evening, dew will begin to set onto things like windshields, car mirrors, telescope mirrors and so forth. So one thing you need to do is circulate air to prevent the formation of dew (moisture) on the mirror, or you will never be able to see andything.

The second situation is that large mirrors have large mass...certainly more than the hollow plastic or fiberglass tube which holds them. Where ever the telescope was during the daytime, it was at one temperature. At nightfall, temperatures begin to drop and you will get some flexing in the surface of the mirror which will throw off all your focus adjustments and make for crazy viewing. A fan evens out this cooling and makes it happen quicker than if you depended just upon normal convection air currents, which, inside a closed tube, might not be all that great.

Seeking a good Dob??? Go to Astromart dot com.
Go to EBay dot com. There are many other places, but
those are two easily accessable ones. Astromart wants you to pay $12 to join...Ebay does not. Look at what eyepieces come with your Dob...That might make the difference in which one you select. A nice set of eyepieces can set you back up to $1000 or more...Cheapos might cost $120 for a set ($20 Each). Baader Planetariums are around $140 each.

Don't listen to the ding-a-lings that say a fan is a "must have" to keep the cigarette smoke or bugs from settling onto your mirror.

Join a local Astronomy Club and you will meet all kinds of folks who trade equipment often. That is probably your best bet for finding a good Dob which you can look through and play around with before buying. Avoid the NEW WalMart products...Look for something with real quality...it is out there. Good optics cost MONEY.

Answer 4

Look up GSO (Guan Sheng Optical) on the Internet. They are Taiwan firm that builds for Meade and Orion. they used to build Celestron's Star-hoppers before big C was bought by Synta Optical.

Check out this 10 inch dob that comes in around $500 with a 1/12 wave mirror. Excellent optics and excellent price. I guarantee they are the most inch of aperture for any dollar price. they have US dealers so you won't get stuck for foreign shipping.

http://www.gs-telescope.com/content.asp?id=83

The cooling fan is just to speed up temperature equilibrium. While a scope is cooling down, its mirror is "over corrected" (too deep of a curve" for perfect focus. Once it is within about 5 degrees F of ambient temperature (1/2 hour of cooling with the fan) switch the fan off and both the night air and the telescope will stay nearly at the same temperature for the rest of the night. My 12 inch Meade Lightbridge would take 2 hours to cool without the fan and only 30 minutes with the fan.

Answer 5

Lots of good info already here. Maybe I can simplify a few things.
I concur that Orion would also be my first choice for a beginner as they not only have excellent equipment at a good price, but great customer service as well, which could be a big help if you have any questions later on. If there is a Dealer near you who sells Orion Telescopes, even better.
BTW, a "Dobsonian" Telescope is really a Newtonian Reflector on a simple alt-azimuth mount made popular by a fellow named John Dobson from San Francisco.
As to size:
Bigger is not always better, and this is an important point.!
If the thing is a chore to set up or transport, it will spend most of it's life in a closet, instead of outside being used.
So if transportability is important to you, make sure you get a size that you can easily handle. It is no fun to haul 75lbs of equipment half way across the backyard or load it in and out of the car if you have to drive to an observing site.
Also, the conditions at your observing site make a difference. If there is lots of light pollution, such as street lights, shopping malls near you etc. a larger scope will not necessarily be an asset.
Accessories: All electronic gadgets come under "nice to have". None of them make your scope see any better.
The accessories that come with the Orion telescopes are perfectly good. The Ploessl eyepieces are state of the Art modern eyepieces and will serve you very well. The super premium eyepieces ( with super premium prices ) are also "nice", but hardly necessary. The only accessory I would add up front is a low power eyepiece such as a 32mm Ploessl for wide field viewing.
I feel that in your case the Orion XT8 would be an ideal telescope. It is large enough to do some very serious observing of both planetary and deep sky objects. It is easy to set up and operate.
I also have the 10" Version and can tell you that it is a handful, but still managable. ( I am 6', 220 lbs.) This is about the maximum practical size for light polluted skies. My 16" cannot show me any more from my backyard, since the fainter objects are overwhelmed by skyglow. For larger scopes, you need really dark skies.
I feel strongly that a beginner should start with the basics and go from there as he gains experience. You can spend an awful lot of money on various accessories only to find out later that you don't need or want them.
Take something as simple as eyepieces for example.
Let's say that you've had your scope for a while and that you are fascinated with planetary observing, possibly even Solar work.
(ONLY with special equipment !!!)
Now, the fancy priced wide angle super eyepieces are great for panoramic views and all that, but that is NOT what is needed for planetary observing where the most important part is finely detailed views. In this case you want the eyepieces with the Sharpest views.
And here eyepieces like orthos and Radians are way ahead of the wide field eyepieces.
Ploessl eyepieces are the best for all round work. They are pretty good at just about everything. So, until you know what you want, they are perfectly fine. Buy accessories once you have enough experience to make informed choices.
Whether to get the XT8 with or without the electronic setting circles?
These do NOT turn this into a "goto" scope. They tell you which way to move the telescope to get to the object you have selected.
Unfortunately they cannot be added to an XT8 classic, so you have to make your choice up front.
But your Telescope comes with planetarium software which is also a great help in teaching you how to find things in the sky.
You have to decide that one for yourself. Personally, hunting stuff down in the sky is part of the enjoyment, but that's just me.
All in all, you can't go wrong with this choice.
If you want to find out ahead of time what's involved in setting up and operating this scope, go to the Orion website at www.telescope.com and in the search box type "manuals". Scroll down to the manual for the XT8 and download it. Read the assembly and operating instructions to get a good idea of what to expect.

Adolph

Answer 6

The fan is to cut down the time needed to have the inside temperature of the tube and the mirror the same as the outside (ambient) temperature.
If there is a temperature difference (even single digit degrees)
you will have unwanted refraction between denser and less dense air that will distort your picture at higher magnifications.