Orion XT10 IntelliScope Telescope

The Orion XT10 Dobsonian Telescope is part of a series of telescopes showing 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 $550, 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.

In the beginning, none of the hardware for something like this was available, and amateurs had to build their own. 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. Something to keep in mind here is there is a scarcity factor in telescopes as they get larger and the price increases exponentially. So, while you can know the local observatory has a 30" diameter telescope, the average person simply never had a chance to look through something anywhere near that size, so getting a large number of these telescopes built was revolutionary in that it put a lot of very dim celestial objects on common observing lists. In the meantime, 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.

Eventually the Dobson design was adopted by telescope manufacturers, and given how difficult it is for the average person to grind a good mirror, this had the potential to make large scopes even more available. 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 combined with very expensive optics. 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 the case until Orion introduced the XT series around 2001.

Description and Usage

When the Orion XT Dobsonians were introduced, they were a clear departure from other designs with a high quality steel-tubed Newtonian in place of a cardboard tube, and it was mounted 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 moving. The springs overcome the balance problem Dobsonians had until this deign was introduced which results in the telescope trying to dip or rise depending on what is in the eyepiece holder. Previously, Dobsonian owners had to become adept at difficult techniques like carefully shifting the heavy primary mirror to balance the telescope when collimated.

The Orion XT10 moves very easily- when going to objects, you take the knob on 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 earliest versions of this telescope didn't have the drawer-pull sized knob near the front end to give the user something to hold on to. 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 Deep South Regional Stargaze, an annual star party held at Percy Quinn State Park in Mississippi. Here the telescope was under nice dark skies, so it is a perfect environment to try it out. The telescope is very obviously larger than its sibling, the smaller XT8 8" diameter telescope. The F/5 focal ratio still yields a telescope low enough to the ground for most people and kids to be able to look through it fairly easily. The eyepiece is on the left side of the barrel, so guiding tends to be with the left hand.

The telescope is large enough for collimating it to be a two step process between the main mirror at the back and the secondary at the front. Since the telescope currently comes with a laser collimator, this is a lot easier to do than it would be using other methods which require going back and forth to look in the focuser for each adjustment. The Orion laser collimator is basically a centered laser pointer with a target drawn on it. The way it is used is to simply move the mirrors until the beam from the collimator hits the center of the main mirror, and then bounces back to the center of the collimator. What makes this easier is the reflection target in the collimator is now visible from the outside, so you can see where the spot is hitting while moving the primary mirror. Since this telescope is at f/4.7, it isn't very forgiving in performance for misalignment, so checking this after a significant move (like a car trip) is time well spent.

The 1200mm focal length of this telescope is close to the 1250mm focal length of a scope I have, the f/9.8Celestron C5. What is interesting here is the XT10 has twice the diameter and four times the area, but the magnification and field of view with any given eyepiece is almost exactly the same.

So, the XT10 was able, like the C5, to just barely fit the entire Plieades in a field of view. But the image is very different. The C5 has a flat field, and the Plieades definitely have a diamonds on velvet effect. But having said that, the image in the XT10 is very obviously brighter and more stars are visible. On another favorite object of mine, the Double Cluster, it is a similar story. The C5 does well for a telescope its size, but the XT10 makes it easy. If I was to nitpick, it is pretty clear the image in the XT10 is a bit curved compared to the C5, but that really comes from one of the reasons the Schmidt Cassegrain design of the C5 exists- for photography, where a flat field means better focus. Since Dobsonians are visual instruments, this isn't so important. On brighter objects, like planets, the difference isn't quite so clear. The XT 10 does show more detail, but when going between the two, the feeling I got was it was clarifying features the C5 hinted at rather than showing things not visible in the other scope. Something to keep in mind here is the XT10 brings in a lot of light, and planets like Jupiter are so bright they can be painful to look at. The moon really should be viewed with a dimming filter or else it will feel like staring at a flood light.

The XT10 is fair sized, though I think it will be able to fit in most SUVs or minivans, the fit in smaller cars is going to cause problems. The reason is the barrel of the optical tube is getting fairly large, and, of course, you need to load it so nothing is setting on top of it where it can get dented. Since it is a foot in diameter and 4 feet long, it's going to take up some volume, and the base is the size of a dining room chair. This comes to a critical point in comparing this telescope with the coffee can sized C5; it's a lot bigger and more difficult to move. And that is important, because it will need to get to the countryside to really show what it can do. In comparison, the C5 is less affected by light pollution, so I have found it to be quite useful in the city.

The trick the XT10 has the C5 doesn't is being able to accept 2" format eyepieces. The larger barrel allows a bigger light column into the lens, which means a bigger apparent field of view can be seen. Where this is useful is a large format eyepiece like the Celestron 32mm E-Lux will give a very comfortable open view with dim objects like galaxies far more visible than with just about any other type of telescope. This is the mode where a Donsonian really is the most fun to use. Unfortunately, though the telescope has the nice 2" focuser, Orion only includes two 1.25" format Plossls (the 25mm lens does OK for sweeping, but nowhere near as well as one of the 2" format eyepieces can).

The 9X50mm finder works reasonably well for getting into the ballpark of objects, though I personally like being able to sight along the barrel. The finder's 90 degree diagonal is convenient for getting the image near where you will be looking into the telescope, but getting it close enough to the object is the real trick. A lot of people use a device called a Telrad or the smaller Rigel systems Quickfinder [they both are sort of like miniature heads up displays from fighter planes] as finders. Another option is a red dot finder. Any one of these is under a $50 addition, so if you find pointing to be a problem, there are things you can do about it.

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, or look at the moon as it goes through its phases, you'll get to see something nice. And something to try with a Dobsonian like this telescope is to just putting in a 2" low power eyepiece and sweeping along the sky. This will cause you to run over a lot of neat objects. For example, if it is summer and you follow along the ecliptic (the plane the planets travel in- identify a couple planets in the sky, and you are in business), and cross the milky way in the vicinity of Saggitarius (it looks like a teapot), you will run into the Lagoon Nebula as well as several star clusters. A little sweeping in this area has several more bright nebulas, like the Trifid. Another area to try this in winter is the region around Cassiopia, which looks like a stretched "W" across the north pole from the big dipper.

A more subtle comparison for this telescope is with its sibling, the excellent Orion XT8. The most obvious difference here is $370 for the XT8 versus $550 for the XT10. They come with the same accessories, and the designs are otherwise very similar. The XT10 is more telescope, with 60% more light gathering capability, and about 25% more resolution, and is at the same focal length as the XT8. This means the real difference is a lower focal ratio, and greater ability to go after dim objects, or to make nebulas and star clusters significantly brighter at the same magnification as the XT8. The frustration here is you will need to get under the stars away from the city to really appreciate the difference. Yes, the higher light gathering capability of the XT10 will make the image hold up better if using a light pollution filter, but the XT8 will show less need for the filter in the city.

The question here is if the XT10 should be a beginner's first telescope. Going over $400 is a big deal for a lot of people experimenting with astronomy as a hobby. In truth, the f/6 prescription of the XT8 does an awful lot. In the past, I have had no trouble in a recommending the XT8 over the smaller XT6- the difference between them in cost is small, while the performance difference is enormous. Between the XT8 and the XT10, the cost difference is a bigger step, but the performance difference isn't so obvious. In absolute terms, the XT10 is more capable, but I expect most beginners will find it takes quite a while to feel like they are outgrowing the XT8.

Conclusion

The Orion XT10 is a beautifully executed version of John Dobson's vision for making deep sky astronomy accessible to everyone. This telescope is well built, and from looking at ones which are several years old, I would expect it to last indefinitely. Eventually the base may start to deteriorate, but that will take a lot of hard use, first. Remember to dry it off if it gets covered with Dew and this will be less of an issue. 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. The XT10 is a very good value at $550, especially since Orion has started bundling more accessories with it, including a laser collimator. If cost is a driver, the XT8 is certainly a capable alternative. Otherwise, the XT10 is more telescope for visual observing than $550 have ever bought in the past.