My first GOTO scope....a Celestron/Costco NexStar 102GT

 The accidental discovery

This was totally unanticipated and was never in the works, well sort of, but not this way. One Friday evening, like we always do after having dinner, we would just go to our nearby Costco warehouse to window shop and get the usual stuff, such as groceries, clothes, etc. I usually walk my lil girl around, either in the trolley basket, or by foot. To keep the lil one entertained, I would usually bring her to the toy section. In that same alley, Costco also stocks electronics such as synthesizers, keyboards, electronic drums, you know the usual budget fare (well not everything is cheap though). This time round, whilst perusing the aisles, I chanced upon a gleaming grey scope on a GOTO mount. From its one arm fork mount visage, I immediately recognized it as Celestron's beginner NexStar series scope. From its rather fat OTA, I made it out to be at least a 4" scope. I was right! But from experience, I knew they were selling NexStar's in this size that were short tubes (i.e. 500mm or f/5 scopes). I have had in the past "briefly" owned such a beast of an OTA, after having such a blast with my Orion 80ST. While an achromat, the f/5 80mm scope was a pretty decent performer at high magnifications. There was of course the warm hues from the glass being achromatic, but the color was well controlled. There was no purple haze, or multi-colored neon lights hiding behind the moon. The planets look really nice and sharp, after using similar sized newtonians. It was not so much the sharpness, but more the contrast. Refractors just have superior contrast. Objects are usually framed by nice dark background. Its bigger brother, the 102mm f/5 was totally different animal though. For one the OTA was heaps heavier, making its use on a photo tripod unbearable. Color was also very apparent on every bright object, washing out minute detail. Needless to say I did not hold on to the OTA very long.

So I was really happy to find that this particular NexStar came with a longer focal length, two times the focal length of its short tube brethren. Clocking in at a nice 1000mm, this scope had a f/10 focal length. That translates to better color correction, sharper images and less edge of field distortion. Looking down the working end of the scope, I noted the nice green, purple coatings on the achromatic objective lens. There was minimal reflections coming off the objective indicating good multi-coatings for less light loss. Also I did not see a baffle directly behind the objective. Lesser quality scopes tend to have their full aperture stoppered down to minimize aberrations. Other accessories that came with the scope include a nice red dot finder, not so different from those Orion Ezy Finder's found on most of their beginner scopes. I used to scorn at these zero magnification pointers, but ever since using one that came on my Orion StarBlast, I have grown to appreciate them. While the glass is tinted and you cannot see anything but the brightest stuff through them, they are very intuitive to use, especially if your instrument is a wide field one. Getting the object of study in the ballpark, you can then pan around to find it. I guess by itself, the red dot pointer would be a poor  choice for a scope of this focal length. However since this was a GOTO scope, this finder made more sense. It also cuts down on the weight of the OTA, so the already inadequate mount would have better damping characteristics. The OTA also has a very nice focuser with metal focuser knobs (which is lined with rubber for a better grip).

This package comes with a nice foam lined plastic container with a five eyepieces set, a 20mm, 12.5mm, 10mm, 6mm and 4mm eyepiece. Unfortunately, the quality of the eyepieces leaves a lot to be desired. While they are the preferred 1.25" barrel size eyepieces, the optical design of these eyepieces are not in sync with times. They are of the Huygens and Symmetrical Ramsden designs that used to come with scopes of the 60's and 70's. These designs employ two lens elements to give very narrow field of views, very poor color correction and ridiculously tight eye relieve. While these eyepieces are okay for longer focal length scopes, they are very poor performers in faster scopes. I guess they would be okay for this OTA, but I could not use them as I need my glasses on when observing. Well this set would make a great upgrade set for a small long focal length refractor using a hybrid 0.965" to 1.25" diagonal. The other accessory this package came with was a correct image 45 degree prism telescope diagonal. While fine for terrestrial views, I found that its performance was less than starry (pun intended) under the night sky. This diagonal was firstly a prism diagonal. Testing it under the stars showed that it was letting less light through. Also the star images were not as sharp or as contrasty. I ended up replacing this with a Orion 1.25" dielectric star diagonal, and this greatly improved the views of night time celestial bodies. Jupiter looked surprisingly crisp, with abundant detail. More on this later.

The mount itself was very intuitive to setup. I like it how Celestron scopes now come with a very well written instruction manuals, as well as a pictorial quick setup guide (for dummies lol!). All one needs to do is look through the quick setup guide quickly, and one is ready to start assembling the scope. This was the same for the 127mm Celestron Powerseeker I obtained a couple of years ago in oz. Seeing how this was my first motorized/computerized mount, I was keen to get it setup so I could play around with it. The mount came in two pieces (not counting the accessory tray which is very easy to put on, the battery holder and the NexStar hand controller). All one needs to do is to unfold the three tripod legs, align the fork arm assembly base to the top of the tripod in the tripod mounting platform, and then attach  the assembly onto the tripod by threading the coupling screw into the hole at the bottom of the fork arm assembly. And wala the mount it ready. All one needs to do now put the accessory tray in place by aligning the tabs and then turning it till it clicks in place, plugging in the NexStar hand controller and then putting 8AA batteries into the battery pack and plugging that in. My gripe with the mount was firstly it was not adequate to handle a OTA this long. Celestron did try to remedy this by adding tubular legs to the tripod. However this was still not enough. They probably should have provided the mount with 2" tubular legs! To get the mount to dampen down quicker, one could possibly hang weights off the middle of the mount to weight it down, or use specialized vibration damping pads. Also this mount lacks an on/off switch. To turn off the mount, one would have to physically unplug the "external" battery pack (yup unlike its more expensive cousins, this NexStar does not have an enclosed battery holder) from the fork arm. Not so cool in my opinion!!!!

Under the Stars

Here comes the litmus test. I was keen to get the scope under the stars to firstly test out NexStar's three star alignment I have read so much about (sic) and how well the scope tracks.  Was also keen to check out how good the scope optics were and if the longer focal length made a difference in terms of chromatic aberration and contrast. First night out was under indifferent Los Angeles skies. Tried the three star alignment. Big FAIL. Did not try any of the other alignment procedures so spent the night checking out the optics. Looks at a couple of bright open clusters and Jupiter. My thoughts were meh...okay views...not great. Color correction was surprisingly good. It was on par with the Orion 80ST if not better. Okay views turned to great views when I replaced the correct image diagonal with a Orion Dielectric star diagonal. Images were wayyy sharper and brighter. Jupiter revealed a level of belt detail that rivaled my 6" Celestron/Vixen f/5 newtonian. All that you have read about the crummy correct image diagonal is true. This is one of the field things that needs replacing if all you want to do is look at stars. Open clusters looked gorgeous with the pitch black background thrown up by the refractor's superior contrast (and this from light polluted skies no less) . I spent quite a bit of time on M45, the Pleiades and the double cluster in Perseus.

Did not get the GOTO working till Terry stumbled on the two star align and got it to work. It seems that the three star align only works from pitch black skies (personal communication from Terry while testing his Costco scope out from the All Arizona Star party). Two star align works just fine from light polluted skies. The trick to get the GOTO to work properly is to make sure you get the location, date, and time as close to perfect as possible. Also make sure your mount is level (check the bubble level). Most important thing however is the batteries. they have to be fresh and not affected by the cold (as I found out when I was at Mount Pinos....GOTO refused to work!). Also when centering the alignment stars, always use high mag and defocus the stars to get them as dead center as you can. Trust me when it comes down to centering DSO's in the ep's, it really helps to get the alignment stars as close to the center as possible for accurate GOTO. I also found from personal experience that the NexStar align favour some stars over others. Not sure if it is just the placement of the alignment stars or something else. Once aligned, NexStar can place the object pretty close to the center, if not the center of the FOV. Have not tested to see how long the tracking motors can keep the object centered, but from my short forays, it seems to do a pretty nifty job.

The Verdict?

This has got to be one of the hottest deals in the telescope world right now. For the price, one could do far worse than purchasing this scope. In the price range, other good buys for beginners include Orion's battery of beginner scopes (70mm Explorer, Orion SkyScanner table top scope, Orion StarBlast 4.5 on either mini dob or EQ mount). This scope is, however a full fledged GOTO scope with tracking. Although I usually scorn at the idea of recommending a GOTO scope to a beginner (I myself am a "dyed in the wool hardcore" starhopper), this would make a great first telescope, when presented together with a good beginners book such as "Turn Left at Orion". Although the accessories are not the best, they are enough to allow newbies to gain access into the observing world of visual astronomy. If one is resourceful enough, one could also do some basic astrophotography with this setup, seeing how the GOTO works pretty spot on, and tracking seems to be pretty good. But more on this in a later post. Till then do yourself a favour and go out and buy one, if you have not already done so. remember that you can only get this special price at Costco. This scope sells for more than $200 on e Bay!