by Jason Newquist
As I used the telescope over the course of the next two weeks, I had three issues which more or less impacted my two primary goals for this 10 inch telescope:
I'll cover each issue below, including some of the better features of the scope that are related. Don't let my approach fool you - I am very pleased with the scope. There is so much that is right with it that those things that are poor stand out. I'm highlighting what's wrong in this section for two reasons: (1) they are things that I noticed right away, and, once initially resolved, probably won't come back, and (2) I plan to give an overall taste of the pleasure of using this telescope in a later section. Having said all that, here are the problems.
First, the free laser collimator that came with the telescope was not properly aligned. Worse, the alignment changed as you turned the screw in the chamber which turned the collimator on and off. After a few hours of playing with this, I abandoned it and made arrangements to use the expertise and tools of some of the local observers when I would take the scope out for first light.
Initial collimation was easy. The positioning of the secondary in the center of the focuser looked good. It looked like I didn't need to shim the focuser, as it seemed to be square, too. Good. In the field, I first used a buddy's Cheshire eyepiece and dot laser collimator to collimate the optics. We did a pretty good job, too.
But another buddy came over toting a LaserMax holographic collimator. He slid that into the barrel, activated it, and I my eyes glazed over. My gadget gland exploded. Oooo! A reticule pattern and cross-hairs! Using this, we REALLY fine-tuned the scope's collimation.
The 3 spring-loaded screws of the primary mirror operate very well. Adjustments are very easy. The mirror cell assembly is very well designed, made from high-quality parts. I did notice one quirk, though, some days later, on my second night out. My 12mm Nagler Type 4 would not quite come into focus, when it had done so previously, even when the focuser was fully racked out. I sensed that I needed another quarter inch or so. Just a few minutes earlier, when collimating, I had noticed that the 3 primary screws were nearly fully extended. I must have been making adjustments all this time by loosening, rather than tightening them, causing the primary to move toward the front of the tube. If I had moved them too far, this would explain why the focal point had now moved out of the range of the 12 Nagler, when it was in range for this eyepiece on the night of first light. To solve the problem, I tightened down all the screws and re-collimated the primary from that baseline. The 12 Nagler was now coming into focus much further in. Voila!)
The night of first light, at Fremont Peak, a California state park, provided pretty good seeing and transparency. A number of experienced people came over and commented on the exceptional optics. The out-of-focus view of a star showed many concentric circles, with the obstruction of the secondary perfectly centered. One fellow who built his own f/4.5 10 inch dob said that the optics were outstanding, "just like a refractor!" Another guy, who owns a Starmaster with a Zambuto mirror, came by and said, "These are very sharp images. And just as contrasty as any scope here." I was pleased! Based on the performance at first light, it looked like the scope would meet the "outstanding optics" goal I had set for it!
The collimation misadventure was averted, and the results were excellent.
So good, in fact, that I could not contemplate not precisely aligning my optics every night. I opened my wallet, and got a LaserMax holographic collimator from Pocono Mountain Optics. This collimator is a gem, and I'd recommend it to anyone who has $240 to drop on a collimation tool.
Like the first problem, this isn't really a problem with the telescope itself, but it can be a problem if you opt for the 7x50 finder instead of the Telrad. I had previously bought a Telrad when I was considering the Orion XT10, so when I bought this scope from Discovery, I opted for the 7x50 finder. It looks okay out of the box, but I found two problems with it that make it hard to use.
The bracket that attaches it to the scope attaches to a single spot, and unless you're going to bolt it down hard and deform the tube, the bracket is going to stick out like a sore thumb and be subject to all kinds of jostling and tweaking. The bracket that attaches to the finder scope tube itself has 2 rings with 3 screws in each, providing pretty good adjustment capability. And while components were metal rather than plastic, the whole assembly seemed destined to be ripped out as I moved the scope from place to place.
Finally, the optics of the finder are sub-par. Things are not quite in focus, no matter how I adjust it. I admit I didn't spend a lot of time looking through it because I knew that it just would not be as convenient for me as the Telrad. By the end of the first night of observing, I had applied and aligned the Telrad, and was using it to find galaxies.
The third - and only real problem so far - is the scope's altitude motion. Out of the box, it was VERY stiff. I called Discovery to talk about this, and the rep on the phone indicated that the stiffness was there by design because many of their customers load the scope with finders and other heavy paraphernalia. Okay. Since I would only have a Telrad (and my heaviest eyepiece, the 35mm Panoptic, weighs in at 1.6 pounds), I decided that I needed to do something.
Before the star party where we had first light, I consulted the Discovery-Dob-Users Yahoo Group, read through the archives, and decided to apply ArmorAll to the altitude bearings, per certain recommendations. At home, this seemed to really help. Out of the box, I the scope required a stiff tug to get it moving, and was incapable of small nudges. After the ArmorAll, it seemed to respond very well. So well, in fact, that I could now perceive that the scope was out of balance, so I needed to adjust the location of the bearings.
After I was out in the field, the smoothness of the ArmorAll seemed to not provide smooth enough motion to make fine adjustments to, for example, conveniently keep something in the eyepiece. I needed instead to grab the end of the scope very tightly and apply pressure and strategically overshoot and recover the distance back. I got used to this a little, but it was clear that I needed to permanently remedy this so I could enjoy the telescope.
I also tried car wax with Silicon on the bearings, but this didn't work very well, either.
I worked with a local amateur telescope maker in my area to come up with a solution. The friction-bearing pads that come stock on the 10-inch Discovery PDHQ base are 3 / 4 inch square nylon. The Discovery rep on the phone says he believes they are Teflon, but is not sure. If they are Teflon, they're not the smooth milky white Teflon that are now installed on my base. The details are covered in another report available on my web site.
The jury is still out on this modification, but the motion feels a lot smoother. I'll post results here as soon as I've fielded tested things.
This report harps on two accessory issues and one quasi-design problem. Overall, with an outstanding focuser, excellent azimuth motion, and an overall feeling of quality materials, I think the scope gets a good rating on smooth operation. With the altitude issue addressed (hopefully!), I think the system should be excellent.
As for the other objective -- optical quality -- I think my observing reports can speak to that, especially the first light report where my observing buddies and I were blown away by the optical quality of the scope. I hope to capture another night like that soon, so I can continue to put the scope through its paces.
So far, after a month of ownership, I am very pleased. I have a telescope that has excellent optics, quality components, and good overall operation. Once I've proven to myself that the altitude motion issue is resolved, there will be nothing glaring that needs resolving. I'm sure there will be other things I'll want to tweak, but I'm not sure what they are right now -- and that bodes well.
After a few more observing sessions in good quality skies, I'll write a "Part III: Optical Performance." Stay tuned!
Return to The Discovery
10" PDHQ Page
Return to Jason's Amateur Astronomy
Updated on 06/10/2001 03:22:35 PM