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Nexstar 9.25" GPS

Posted by Richard Beasley   06/06/2004 12:00AM

Nexstar 9.25” GPS Review

In my seemingly never ending search for the perfect scope, I have ended up with a 9.25” Nexstar GPS. My wife is ready for this search to be over with, and frankly so am I. I guess I have gone through 30 + scopes since this all began. It all started innocently enough, my brand new Losmandy GM8 Mount had been sitting idle awaiting my 6” TEC MCT and actually I am still waiting. I saw an ad on Astromart for a 9.25” OTA with the Losmandy G11 type dovetail, and better yet the scope is ten miles away. Of course I take the plunge. The seller was kind enough to offer use of his 21# counterweight until I was able to get one. Thanks again Marty!

I ended up using the scope 6 days. After collimation, and cool down, the scope was ready. My first object to view, M13. I ended up viewing 20 or so of the more popular summertime objects, and I was impressed, very impressed. I made my mind up to get the GPS version, and sell the OTA, and Losmandy Mount. I did this because I am strictly a visually observer with no aspirations of doing photography. I prefer the goto, and constant eyepiece plane. The GPS version is also lighter than the OTA / GM8 Combo.

The scope arrived without damage, well slight damage to the plastic tripod spreader, but it looks as though it may break if you sneeze on it. I got the scope set up rather quickly, and everything appears to be in order. If you own one of these, you must remove the rubber feet on the tripod. A slight touch to the scope with the rubber feet attached, and it appears the scope is on a trampoline! Having owned a non-GPS LX200 I was anxious for a comparison. I owned the LX200 some time ago, so comparisons are from memory, so take this info with a grain of salt. I remember the LX200 tripod as being a little sturdier. A metal spreader of some sort with the Celestron may help. I have heard they are available aftermarket, and well worth looking into. The LX200 looked beefier due to the steel exterior. The Nexstar to me is more attractive, but looks more delicate. This is likely an illusion due to the plastic exterior, with the weight, I am guessing there is steel beneath the plastic. Three things with the Nexstar concern me, the plastic spreader already mentioned, the finder scope bracket, and hand controller. The finder scope bracket is a joke for a scope in the price range. It is made of flexible plastic, and looks similar to six point finder brackets, although it is a three point bracket. I would much prefer a bracket similar to the ones supplied with the low cost refractors, 2 adjustment screws, and the spring loaded pin. I must confess, the bracket has held alignment well so far, but it is cheesy. The hand controller just feels like it is ready to be damaged. The LX200 controller was constructed better.

Set up is rather easy. The GPS alignment does its thing, and then slews to the first alignment star. It was missing the star by 10 degrees or so. This problem can be solved by showing the scope where true North is. After a compass alignment the scope comes much closer. It still needs a little more tweaking. The scope does not make near as much noise as the LX200, however it does not appear to slew as fast. That may account for the noise difference. I initially had problems with the goto accuracy, and tracking, but that may be user error. It has pointed very well since the initial familiarization process. Accuracy appears to be in line with the LX200. Stability also appears to be in the same league.

The GPS is considerably more stable than the 9.25” OTA on the GM8 Mount with G11 Saddle. In fairness to the GM8, it was basically unused, therefore I never had taken the time to adjust the worm gears to rid the mount of backlash. Focusing is much easier on the GPS platform. All in all the scope works well. There is a problem with the image jumping every 20 seconds or so. I was advised by Celestron Tech Support I would have to buy a programming cable, and update the software to get rid of the problem. After my objections, they offered to repair the glitch in house if I send them the parts. This irritated me, maybe more than it should, why should I have to buy a cable to repair a defect in the scope, or do without my scope while I ship Celestron pieces of it. It just seems wrong to me. Celestron did agree to send out a new tripod spreader, and it arrived a week later. I caved and purchased the programming cable to repair the software defect. Fifty dollars later the tracking is now fine.

The biggie, how are the optics? Initial views and Ronchi testing show they are slightly better than the 9.25” OTA I had. Ronchi lines are straight, I perceive a slight bow outside focus toward the center, but at times they appear perfectly straight. I should clarify, the curved lines the Ronchi test has shown on most scopes I have tested is slight to non existent. The lines for this OTA are so slightly curved you really have to look hard to see it. I see no evidence of TDE, or zones.

I can only compare this scope to a 6” F5 Newt, MN61 Mak Newt, and C102HD at this time. Not a fair comparison. As good as the 6” F5 newt is, it is overmatched by the 9.25”. Fortunately, it was built to replace my TV85, and it does a remarkable job at that. The colors on Jupiter appear a little richer with the newt, and the image is a little sharper, however the 9.25 just uses its light gathering ability to show more detail. Since the 6” newt is better on planets than the MN61, and C102, the 9.25” is now the king.

Final thoughts are this is a great scope, at a good price. A new 9.25” OTA, and GM8 with appropriate plates, and weights would cost more than the GPS version. I miss being able to push the tube where I want it, but it is a small price to pay. The GM8 is more versatile however. Celestron could spend $20 more dollars building this scope, and improve the items I mentioned. Optically it is a winner, very good quality. No bloated stars as I have read about SCT’s showing, and decent contrast. I should mention for someone considering their first SCT purchase, I have found contrast to be lacking compared to a good quality newt, or refractor. For instance, my first view of M57with the 9.25, it did not stand out from the field of view as much as it does with a good refractor. It was clearly visible, and shows more detail than the smaller scopes, but doesn’t stand out from the background as starkly. It may be a function of the large central obstruction, or may be function of the amount of light the larger scope gathers, therefore scatters.

With my 6” quick look newt, and my 12” DOB coming soon maybe I have found the perfect scopes for me, or so I tell my wife.


Clear Skies
Richard Beasley

Click here for more about the Nexstar 9.25 GPS. -Editor.