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Orion SkyQuest¿ XT6 Classic Dobsonian (354 x 150mm) Telescope

Posted by Josh under Telescopes

The Minimum Minimalist Telescope Pros: Simple rugged construction. Good performance on Planets and the Moon.Cons: Saving $100 means a major cut in performance compared to XT8.The Bottom Line: Works well on planets and the moon: solid value for a low-end telescope. If you can afford to go from $270 to $370 consider the Orion XT8. The Orion XT6 Dobsonian Telescope is a smaller member of the XT series Dobsonian telescopes from Orion. Except for minor modifications these telescopes have remained unchanged since they were introduced and have been standing up to use. The XT6 is a third smaller in diameter 7 lbs and $100 cheaper than the Orion XT8. However given the additional capability of the XT8 I would recommend that scope over this one unless the money really is an impossible hurdle. These are currently sold for $270 which makes them a solid 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 Buddhist 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. The middle ground for the average user who wants a practical and simple telescope was vacant until Orion introduced the XT series telescopes in the 1990s which have proved to be a near-ideal commercial version of the Dobsonian concept. Description and Usage The Orion version of a Dobsonian uses high quality steel-tubed Newtonian and mounts 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 XT6 is a compact telescope with a relatively small barrel which 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 mount there is no 45 minute tedious polar alignment procedure (and yes I am only that fast on nights with superior mojo to help). 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 at the same time as the XT8. I had brought back a Meade Plossl lens and was thinking about trading it in for something else. This one was already set up so it was pretty easy to be able to slew it around and try it out then compare with a larger XT8. Like the other XTs 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 is fairly heavy at over 34 lbs and it is a bit unwieldy with the optical tube attached do the base. But if you are driving to an observing site most people should be able to handle the tube and mount separately without a problem. As with all Newtonian telescopes collimation is part of life. This appears to be the hardest part of using one of these since 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 lot 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 and kudos to Orion for offering such a useful accessory with an entry level telescope. 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 and put in a Celestron Ultima eyepiece I had tried out in the XT8. There was no distortion- the XT6 gave a perfect image. The lines in the bricks did not converge at the edges- a very flat field of view. Note the image is very obviously dimmer in this telescope than the XT8 since they both have the same focal length but the XT8 has a mirror 33% larger in diameter which gives it 77% more image brightness. In photography terms the XT6 is an f/8 while the XT8 is an f/5.9 and so the XT8 is pulling in a lot more light in the same size image. It wasn’t until later that I got to see what an XT6 is like under the stars. It is fun to use and the optical prescription is well adapted to giving sharp images of planets. Here the smaller size than an XT8 does not hurt as much since planets are fairly bright so this is actually a bit more comfortable to look at. This is a telescope which works best for things you can see some trace of by naked eye since it is a bit limited on its light grasp. Because the focal length is the same as the larger XT8 the image fields are the same magnification and the differences are due to mirror size. Since the XT8 still isn’t at the point of extreme focal rations of f/4.5 and lower there isn’t a big difference such as coma or other optical defects. The main difference I can point to is the XT6 shows planets with a lot of contrast and sharp focus. Luckily the night I got to give an XT6 a workout had a thin crescent moon in the sky and here as on planets the telescope delivered a color free image with sharp detail. In this case the image has an advantage over the XT8 which produces a painfully bright image of the moon. In this case the XT6 image jumps out with craters and fine features clearly visible. On brighter nebulas this telescope has a fairly good defense against light pollution. The limited brightness means you don’t have to push up magnification as far as the XT8 to get your eye to see through light pollution (this only works visually- this is not a photographic mount for dim objects). What you do is slowly move up in magnification and what looks like a slight blur on top of a light polluted sky will suddenly jump out when the eye is able to differentiate the image from the background (I know this sounds odd but it works well). So objects such as Orion or the Lagoon nebulas can be seen in the city this way. The Plieades star cluster just barely fits into a field of view unless you use a special wide angle eyepiece. Where this telescope ends up being somewhat wanting to my mind is it isn’t quite able to keep following the user to deeper sky and more difficult images the way the XT8 can. Because of this the $100 difference between the XT6 and the XT8 is essentially buying the ability to go deeper into the same size images the XT6 can produce. Of course if that $100 is the difference between having a telescope or none then of course the XT6 is the choice. What this telescope does for $270 was simply unavailable 10 years ago and it certainly is a massive improvement over the typical 60mm refractor labeled with the absurd claim of