by Jim Havlice
I love my Meade ETX-125 GoTo telescope. It’s light enough to easily move from the garage to the driveway – or to pack it up for a star party. That means that I use it often. With 5 inches of aperture it has enough light-gathering capability to see a lot of the Deep Space Objects (DSOs) and I really like the GoTo convenience. After aligning the ’scope, just choose an object from a huge list, push a button and the ’scope moves reliably to that object.
Ah, but I am an amateur astronomer and I am afflicted with a disease. It goes into remission, but eventually reappears with serious consequences. That disease is “Aperture Fever.” At star parties I have enjoyed looking through Russ’s 12 inch Dobsonian and marveled at the bright, high-resolution images – the Ring Nebula is a great example. It looks so much better than through my 5 inch Mak.
For the visual observer, Dobs are a great choice of telescope. You spend most of your money on the telescope, not the mount. So, you get a large aperture ’scope at a very reasonable price. And they are very portable since the ’scope breaks down into a couple of component parts.
Dobs have had one limitation – they are not GoTo scopes. You need to find objects yourself by star hopping – an essential skill that every amateur astronomer should develop. With my GoTo Mak, I let the telescope find an object and THEN look through the finder to see where the object is located. This is the astronomical equivalent of an old gun joke: Ready, Fire, Aim! The finder is a 1-to-1 model (no lenses) that projects a red dot in the direction that the telescope is pointing. Later that evening, I go back and find several objects – this time using only the finder, not the computer.
Orion XT10 IntelliScope
Anyway, along comes Orion – the telescope company, not the constellation. They have equipped a Dobsonian telescope with position detectors and a computerized hand-held locator that helps you find objects in the night sky. These are sometimes referred to as “Push To” telescopes. I assembled a 10-inch model for display – a display that I walk past many times each day. That old “fever” flared up again. I just couldn’t resist taking the unit home to test it out.
The first test: how portable is it? The telescope tube and mount are the two main components. The steel optical tube is 47 inches long and weighs about 29 lbs. I found the tube very easy to pick up and move around and it fit nicely onto the back seat of my Jeep. The tube is circular and – duh – will roll around unless you fix it in place. A small length of rope looped around the tube and tied to a convenient point up and behind the seat kept the tube in place while driving and braking. This is really important – you don’t want the tube crashing into the front seats when you brake. The base (or mount) weighs 26 lbs and easily fit into the back area of the Jeep. I didn’t use anything to tether the base – and it stayed in place the entire journey home.
Assembling the telescope at home took only about 5 minutes – and that included carrying the two components to the far end of the driveway.
Alignment is very easy. During the initial assembly of the ’scope, the tube is made to be perfectly vertical when it reaches the hard stop on the base (or mount). This is the “home” position for starting the alignment. Choose two stars to align with. The manual suggests two stars that are at least 60 degrees apart. I chose Arcturus and Altair. (Unlike some GoTo telescopes, the computer does not choose the stars for you).
The telescope comes with a 9x 50-mm finder scope with a cross hair eyepiece. And here I ran into my first problem. My Mak uses a red dot finder with no lenses – basically a 1x finder. I had a problem finding things with the much smaller field of view of the 9x finder, mostly because I wasn’t sure where the tube was pointing. This is a problem that probably goes away with experience, but it took me a while to find two of the brightest stars in the sky. I suspect that Orion uses the much larger and heavier finder in order to help balance the weight of the mirror on the other side of the telescope.
Orion Computerized Object Locator
You align the telescope using the high-power 10 mm focal length eyepiece (120x) – carefully centering the alignment star in the field of view and pressing ENTER on the hand-held computer. The high-power eyepiece assures good accuracy in the alignment. Move the telescope to the second alignment star, center in the eyepiece, and press ENTER again. The computer “thinks” for a bit and returns a “warp” factor, basically a measure of how well the unit is aligned. A “warp” factor of 0.5 or less is recommended. I hit 0.5 the first time. Good but not great.
OK, now it’s time to see how well this system works. First, replace the 10 mm lens with a 25 mm eyepiece (48x). You want to begin with a large field of view. Each key of the keypad is labeled: M (Messier), NGC (New General Catalog), IC (index Catalog), Nebula, Cluster, Galaxy, Planet, Star, etc. This is very nice – to find a Messier object, click the key with M, type in the Messier Object number and hit ENTER. If the object has a name, the name appears on the second line of the display.
OK, let’s begin. I started with M13 – the Globular Cluster in Hercules. On the first line of the display is a set of numbers and arrows. The numbers are proportional to how far away the telescope is from the object in azimuth and altitude. The arrows indicate in which direction you should move the ’scope in order to find the object. When the numbers become zero, the telescope should be pointing at the selected object (M13 in this case). After pushing the telescope so that both numbers were zero, I looked through the eyepiece. Amazing. There was M13 in all its glory. It wasn’t exactly centered – in fact it was toward the edge, but it was there. I centered the globular cluster and marveled at its brightness. I could even begin to distinguish individual stars. Ah, the benefits of a larger aperture. Compared with my 5 inch Mak, this telescope has 4 times the light gathering capability, which increases with the square of the aperture. The ability to see individual stars rather than just a fuzzy cloud arises from the 2 times increase in resolution, which increases linearly with aperture.
I tried several more Messier objects and all were easily seen in the field of view of the eyepiece. The “find factor” for this system is excellent. The fourth object I “pushed to” was the Ring Nebula. Both my Mak and the Dob use a 25 mm eyepiece as the standard. Since the focal length of the Mak is 1900 mm and that of the Dob 1200 mm, the magnification of the Dob was 48x compared with 76x with the Mak. So, the Ring appeared smaller than with the Mak. Still, I could clearly see the hole in the Ring. I decided to change to the 10 mm eyepiece which provides a magnification of 120x. Oh my, this was one pretty sight. Because the aperture was larger, the Ring was still quite bright and the resolution was supurb.
I spent the next 30 minutes or so moving to other DSOs. All were either in the field of view or just slightly beyond it. I found all the DSOs I tried to find except for the galaxies. The moon has risen and the galaxies would have to wait for a moonless evening.
I decided to end the evening by viewing Jupiter. Ignoring the computer, I just moved the ’scope to this very bright planet. Jupiter’s moons were all visible and completely filled the eyepiece. I could easily see the equatorial regions on Jupiter itself. This is always such a magnificent sight. I wanted more! So, I reached for the 10 mm lens to up the magnification. Oops – after switching to the 10 mm eyepiece to view the Ring Nebula, I had forgotten to switch back to the lower magnification eyepiece. This was as big as Jupiter was going to get for this evening.
And then it dawned on me. For the last half-hour I had been using the “Push To” computerized telescope to find objects at 120x magnification. And in all cases, the object was either in the field of view or just slightly out of it. This is something I would never have tried with my Mak! Moving the telescope into the garage, I was enthused at the pin-point accuracy of the Intelliscope system.
If you have read this far, you can tell that I really liked this telescope. My goal for this test was to determine the pointing accuracy – and it gets an A+ from me. My driveway has limited angular visibility – so I couldn’t test the pointing accuracy for objects close to the horizon. I didn’t spend a lot of time judging image quality. In fact, I didn’t even collimate the telescope before using it. Still it provided beautiful bright images with no obvious aberrations. The great images, excellent pointing accuracy and easy portability make the Orion XT10 one fine telescope.
Now I have a case of really bad “Aperture Fever”!