Simplicity, Quality, and Performance [Update 6/24/07]
Written: Oct 05 '01 (Updated Aug 19 '07)
Product Rating:
Pros: Well made, great optics, beautiful views, incredibly inexpensive.
Cons: Physical size, weight
The Bottom Line: A fantastic deal for a first telescope. It's got the performance, the price is right, and it's built to last. The XT8 is a classic design for learning the sky.
Pirich's Full Review: Orion SkyQuest XT8 Dobsonian (480 x 203mm) Telesco...
The Orion XT8 Dobsonian Telescope shows what standing the test of time is all about. Except for minor modifications, these telescopes have remained unchanged since they were introduced, and have been standing up to use. Some have been all the telescope their users needed, while others have been a gateway to other scopes, but they are at a useful size and work well, so generally they stay in use. These are currently sold for $370, which makes them an amazing value for the money considering what they can do. More general information on getting a telescope is in my article on Picking a Telescope.
Background
Dobsonian telescopes are the most famous creation of John Dobson, a one-time Bhuddist monk who realized the night sky would be far more accessible if a large telescope could be made cheap enough and simple enough to operate for people to view it. The telescopes bearing his name, Dobsonians, have been a revolution in amateur astronomy. The concept behind the Dobsonian telescope was to find a way to put all of the money and effort into improving the telescope's performance with as little spent on the mounting and other hardware as possible.
The configuration Dobson arrived at was to make as large a Newtonian reflecting telescope as possible and mount it on a simple turn table with a fork to support it. The telescope was designed to be simply pushed in the direction an observer wanted to go. There was no gearing, no precision bearings, no tripod, no drives, no equatorial heads; just a telescope on the minimum of equipment needed to point it. This configuration makes them look sort of like large artillery pieces aimed at the sky.
This led to a movement in San Francisco, CA, in the early 1970s, where amateurs ground their own telescope mirrors and built telescopes out of cardboard carpet tubes and plywood. What they let people do was take in high quality views of large celestial objects with very little investment. In the mean time, Dobson and the church parted ways. The legacy of this has been a group of avid sidewalk astronomers in San Francisco and these amazingly user-friendly telescopes.
When telescope companies started building Dobsonians, several refinements appeared. Teflon pads in the bearings allowed telescopes to glide more smoothly and higher quality mirrors improved performance. However, they made an unusual split- on one end, extremely high quality truss tube telescopes with fine woodworking appeared. Other manufacturers produced rather shoddy scopes made from cardboard with lousy optics. There appeared to be no true middle ground for the average user who wants a practical and simple telescope. That was until Orion introduced the XT8.
Description and Usage
Then Orion's folks started thinking about this and decided to do something about it. What they came up with was a taking a high quality steel-tubed Newtonian and mounting it on a laminated plywood stand. The mount has teflon pads and a very smooth turntable. To make the telescope more stable, it has a set of tensioning springs which pull the telescope against the teflon bearing pads. Teflon has an unusual property where its sliding friction and starting friction are about the same. As a result, something sliding on a teflon pad will not jump when it starts. The springs overcome the balance problem many Dobsonians have which results in the telescope trying to dip or rise depending on what is in the eyepiece holder.
The Orion XT8 moves very easily- when going to objects, you take the tube and just push it the way you want it to go, and it will move there. After an object is in the field of view, gently nudging the tube is all that is needed to keep it centered. The later versions of this telescope have a drawer-pull sized knob near the front end to give the user something to hold on to (easier that trying to grab the barrel over and over). My main complaint on this feature is it is black, so it doesn't show up at night- it should be white so it would be visible in starlight. The tube will stop when you stop pushing, and it is easy to make fine corrections. This is literally a telescope where you can walk outside, set it down, and just point it at something immediately. Unlike a Go-to telescope, there is no setup or slewing to wait for. And especially unlike an equatorial, there is no 45 minute tedious polar alignment procedure.
The first time I saw one of these was at the local telescope shop in New Orleans. This was a brand new product and had just shown up. I had brought back a Meade Plossl lens and was thinking about trading it in for something else. The XT8 showed up at the same time I arrived with a shipment from Orion. So, I helped set it up since I was curious. The construction is first-rate. The end fittings are well made die castings to hold the tube in-round. The steel tube was covered with uniform black enamel. The focuser was surprisingly well made and very robust. It moves smoothly and is very solid. It has a locking screw to adjust its tension so it won't slide out of focus.
The assembly was easy, though I can see the size of the components will keep you from hiking with them. But, if you are driving to an observing site, most people should be able to handle the tube and mount separately without a problem. The next step was collimating- and this appears to be the hard part simply because it isn't possible to look in the focuser and adjust the screws at the back of the telescope at the same time. So, plan on lots of iterations, and make sure you do a good job and lock it down so you don't have to do this as often. If you are using a laser collimator, it makes it a little easier, but more importantly, all you need to do is put the telescope where you can see where the return beam is hitting. Since it currently comes with a laser collimator, this is the way to go.
Across the way from the shop is a mall where one of the buildings a quarter of a mile away was brick. I slewed the telescope to it to see if the mirror had distortions and dropped in the Meade eyepiece I had brought. To my chagrin, I found a large distortion to one side. However, when I rotated the eyepiece, it moved. I wondered if the telescope was OK. The shop manager had a Celestron Ultima eyepiece and I dropped it in. There was no distortion- the XT-8 gave a perfect image. The lines in the bricks did not converge at the edges- a very flat field of view. I took the Ultima eyepiece home in place of the Meade, BTW.
It wasn't until later that I got to see what an XT-8 is like under the stars. In short, it is really fun to use. The best place to start is to look around for something interesting and just point it at it- you will be rewarded by a bright crisp view. After looking at the ring nebula and a few other dim objects, I was really impressed. However, the person who owned this one had another trick. He simply said "OK, the space station Alpha is going over in ten minutes- watch this."
What he did was drop a little CCD camera into the eyepiece holder and hook it up to a monitor. He focused the telescope on a couple of stars to get it prepared. then the space station appeared looking like something between a jet flying over and a bright star. He moved the telescope into the path of the space station and waited for it to appear in the field of view for the monitor. As soon as it did he started pushing the telescope to track. The station was visible with its solar arrays as a small + in the monitor. Needless to say, I knew that would be a difficult trick otherwise, and this was really cool.
One concern many people have is not knowing where things are in the sky to look at. However, something to keep in mind is the telescope acts to take an image and make it brighter and larger. So, if you can see something is there, then it's going to get better when you use the telescope. The upshot is the good stuff is visible to your eye. The Moon, Jupiter, Saturn, the Pleiades, The Orion Nebula, The Lagoon Nebula, Double Cluster, and Albiero are all naked eye objects. If you just point the scope at anything that looks like a bright star (not the sun) or a fuzzy patch in the sky, and look at the moon as it goes through its phases, you'll get to see more.
Conclusion
There are a lot of pieces of equipment available for use with Dobsonians these days. Any observing event today will have several showing up. The Orion is a beautifully executed version and I would expect it to last indefinitely. Eventually the base may start to deteriorate, but that will take a lot of hard use. While some complained about the steel tube early on, this means they aren't starting to fall apart after a few years of getting dew on them from time to time. Remember to dry it off if it gets covered with Dew and this will be less of an issue. Since the XT8 is currently a $370 telescope, this is an incredible value, especially since Orion has started bundling more accessories with it, including a laser collimator.
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