Orion XT-10



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Date: NA
Price: $649.99
Design: 250mm Dobsonian, f/5 reflector with 1255mm focal length
Description: Description: Large reflector on a Dobsonian mount with 2" focuser and 1.25" eyepiece adapter. It ships with two 1.25" Plossl eyepieces (25mm and 9mm), a moon filter, and 8x50 finder scope. It also features Orion's proprietary Correct-Tension system to help with balance issues.  

The Review

After a wait of 2 months I finally received my Orion XT10 via UPS. I purchased the scope primarily for viewing from my home which is surrounded by local city light pollution (although my back yard is relatively dark). Upon initial inspection of the (2) shipping containers I found a fist-sized hole in the center of the tube assembly box. Thankfully there was no damage. As I removed the tube assembly and the base parts from their respective containers, it was apparent that the general construction and quality of the scope was everything I had hoped for. As it was early afternoon and clear skies were forecast for that night I knew I had time to put the scope together, let it cool down, and check the optics. However the base attaching parts were not shipped and I had to call Orion. It took six days for the parts to arrive. During that time I put a coat of polyurethane on the unlaminated surfaces of the base to help seal them from moisture.

Mirror Cleaning

I noticed that the mirror had a slight surface film so it was removed, cleaned, and center spotted. How to clean a mirror is a very subjective topic. I used a method provided by:


It was not necessary for me to touch the mirror with anything but water and alcohol. The above method worked beautifully. Mirror cell removal and assembly was quite simple. I did notice that the 4 mirror retaining clips were too tight as they were pressing on the mirrors surface. This

very likely would have introduced astigmatism. When reassembling the mirror cell I left the retaining clips loose enough to allow a business card to slip between the mirror and the clip (eyeballed). However I noticed that the two screws holding each retaining clip were now a little too loose. I placed three small lock washers over each screw between the clip and the mirror cell (I am now looking for small springs to replace the lock washers). This provided enough tension on the screws to keep them from coming loose. To assist in mirror cooling I did not replace the metal back plate.


After receiving the missing hardware the base went together easily and was very solid. I cut out 6, 3" diameter plastic milk carton washers and placed them over the center pivot pin. This helped to smooth out the azimuth motion (I used 5). They worked very well. I placed the tube assembly on the base and attached the tension springs. BTW - I felt the directions provided with the scope were very clear and easy to follow. I did not mount the eyepiece holder or the 8 x 50 viewfinder, as I will use neither. I did mount a Rigel viewfinder, which is my preferred spotting method when observing. I want as little weight as possible on the front of the scope for balance purposes. OK -- I did place the 8 x 50 viewfinder temporarily on the scope to verify a complaint I had read about -- that the two mounting nuts holding the finder to the tube assembly came loose too easily. I would have to agree. I didn't try it but perhaps a couple of lock washers would help tighten things.


Since I had lent out my Tectron collimating tools I was forced to visually center the secondary in the focuser. No adjustments were necessary. Using my Kendrick laser I adjusted the 3 secondary screws until the laser beam struck the center of the primary mirror. I then adjusted the primary until the return beam struck the center of the laser. This took about 3 minutes.

First Light

Transparency: ~ 8

Seeing: ~ 4-5 (a cold front had gone through earlier in the day)

Limiting Magnitude: ~ 4.4 at zenith, nada near horizon.

NOTE: I have yet to use the 9mm and 25mm eyepieces supplied with the scope.

The scope went from an indoor temperature of 70 degrees to 23 degrees and a wind chill of 11. I placed a small desk fan pointing at the primary and let the scope cool for an hour. I would have let it go longer but it was getting late (and colder), and all I wanted to do was check out the optics. Using a 19mm Panoptic I pointed the scope at Betelgeuse and focused. A nice pinpoint image appeared. I replaced the Panoptic with a 2x Barlow and a 10mm Radian. Both sides of focus showed nice circular diffraction rings (when the seeing permitted) with just a hint of astigmatism. The mirror did demonstrate a bit of under correction. I placed a 27mm Panoptic in the focuser and surfed the Pleiades - gorgeous! Back to the 10mm Radian I went after Jupiter and was not disappointed. In spite of the seeing, several equatorial bands and zones were very clear. Its moons were bright pinpoints. The GRS was very pronounced with the 2x Barlow/Radian. On to Saturn -- its rings clearly showed the Cassini division and Saturn itself was exhibiting subtle banding -- very nice. There were at least 4 - 5 moons visible. BTW, I used a #80A blue filter (Orion) for both Jupiter and Saturn. I went after the Orion nebula using just the 10mm Radian. The Trapezium was obvious but the stars were bloated due to the deteriorating seeing and its lower elevation. The nebula itself was being washed out due to the local light pollution. A later in/out focus check showed some obvious astigmatism so either the collimation slipped or the mirror was still adjusting to the falling temperature (I suspect the latter). I was getting too cold to find out and called it night after about 30-45 minutes. The 2" focuser was very smooth and there was virtually no backlash. All my eyepieces fit and came to focus (with the possible exception of my 19mm Panoptic). I will have to double-check the next time I observe.

All in all I am very satisfied with the scope. It will stay in my garage so as to minimize future cool-downs. I placed shower caps over both ends of the scope to keep out future summertime pests. I will also place some desiccant in the bottom shower cap to reduce any moisture. I will be flocking the interior of the tube and I am considering replacing the secondary with a smaller, heated unit. The current secondary has a 63mm minor axis (25% obstruction). I would like to decrease the obstruction to just under 20%. The weight of the scope (56 lbs) does not prevent me from lifting and carrying the entire unit by the base. However the tube removes quite easily from the base if you desire to move the scope in two pieces.

Submitted by Tom Zefo - tzefo@earthlink.net - St. Charles, MO

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