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Celestron NexStar 102 SLT, The Perfect Grab And Go? - Almost

Posted by Tom McDonough   01/02/2006 12:00AM

Celestron NexStar 102 SLT, The Perfect Grab And Go? - Almost
The Background

I have been an amateur astronomer for 34 years and have an IT career, wife, two teenagers, and two dogs – my life is very busy! I’m sure this bio has a familiar ring to many in today’s astronomical community. My main telescope is a vintage Criterion RV-6 Dynascope with excellent optics which I fully restored a couple of years ago. With the hectic pace of my life leaving little room for observing, I started a search for a grab and go scope that would fulfill the following criteria:

1) Scope can be stored fully assembled to eliminate physical setup
2) Weight under 35 pounds for easy carrying
3) High quality, low maintenance OTA and mount
4) Sufficient aperture for serious observing
5) GOTO system for finding objects in light polluted suburban skies
6) Price under $500

From the outset I decided to search for a refractor since I didn’t want to deal with collimating mirrors. Also, small refractors are generally better performers than small reflectors. My searching ultimately led me to the Celestron NexStar 102 SLT.

The Optical Tube

The NexStar 102 contains a 4” f/6.5 achromat that nicely satisfied my desire for aperture. I am an avid double star observer, so both the diameter and focal length of the lens will give an edge towards resolution, magnification, and reduction of false color. The purple coatings on the objective were even and free of imperfections. Star tests revealed near textbook circular, concentric diffraction rings both inside and outside of focus. Bright point sources such as Sirius and Venus show the typical purple fringe, but on extended objects such as the Moon, it was not objectionable. The lens cell/dew shield and the exterior of the 2” focuser are plastic, with the rest of the tube components metal. Several internet forums have lamented the fact that the focuser in the new SLT series is not all metal. I tend to disagree with this due to the fact that with 2” accessories, the scope becomes very tail heavy and cannot be balanced with the 3.75” dovetail mounted on the tube.

The Mount

The SLT mount is a significant improvement over the previous GT series. It has the latest hand control which supports SkyAlign, allowing you to align on any three object visible without knowing what they are. This was my first GoTo scope and I was successful on my first alignment. I did have quite a learning curve getting everything set properly. At first the tracking was very poor until I input the proper backlash settings for the RA and Dec motors. After this was set, the tracking was excellent, keeping objects in the field of a 28mm eyepiece for over an hour. Most of the internal components including the gears are metal and operate very smoothly. The OTA attaches to the mount with the popular Vixen/Synta/Orion dovetail. This gives easy and exciting possibilities of mounting other equipment onto the mount. The tripod legs are now tubular stainless steel and include a bubble level. Vibrations damp out in < 5 seconds. No tools are needed to assemble the mount or tripod. Power is an issue with the internal AA batteries; they simply cannot supply sufficient current to adequately operate the mount for even a short period of time. I highly recommend getting a power tank to run the scope, and if you place it on the tripod accessory tray it cuts the damping time almost in half! I leave a set of batteries in the scope as backup power in case I have to unplug the power cord while slewing to prevent cord wrap.

The Accessories

This is the area where the 102 SLT really falls short. The 1.25” diagonal is all plastic and is easily damaged with set screws. Optically it is okay, I did not notice any glaring aberrations. The included 9mm and 25mm eyepieces are of an unknown design and are okay if you did not have any already. On the plus side, the barrels are metal, the lenses are coated and have rubber eye shields, and come with nice plastic cases. The StarPointer is the biggest shortcoming as it is almost useless under suburban skies. First magnitude stars are barely visible through it and I had great difficulty finding alignment stars.

The Mods

Fortunately Celestron apparently put most of the quality into the OTA and the mount, skimping on the accessories to meet a price point. This is the preferred situation since accessories can be easily upgraded. The first thing I did was to mount a 6X30 finder scope in place of the StarPointer. The mounting bracket on the OTA accepts the popular Orion style dovetail with a nice tight press fit. This is a huge improvement and makes the alignment process a joy. It also helps for centering objects if the GoTo is a little off. I upgraded to a 2” diagonal which is much nicer optically and mechanically than the supplied unit. Finally I mounted an Orion 8” dovetail bar to the OTA so I could balance the tube with the new accessories. NOTE: Disassembly of the OTA probably voids the warranty and could result in damage to the objective lens if a screw gets away from you. All modifications are at the users risk. The modified weight of the whole system including the power tank is 23 pounds.


I can have the NexStar set up, aligned, and observing in the same time it takes me to drag out and assemble my RV-6. Using an Edmund 28mm RKE I have gotten stunning views of open clusters, nebulae, and galaxies. M31 looks quiet impressive under dark skies. Planets give quite pleasing views although no small aperture short focal length telescope is suited to high power viewing. In the past month I have seen more new objects than I have seen in the past five years! With limited observing time in the evenings, having GoTo is an incredible advantage.


The Good

Excellent objective lens
Sturdy, mostly metal mount and tripod
Accurate GoTo, latest hand controller
Low weight and easy setup
Attractive price

The Bad

AA battery power is insufficient
Diagonal very cheap
Eyepieces mediocre but serviceable
StarPointer useless
Steep learning curve for GoTo newbie

In my opinion, with a little help, the NexStar 102 SLT easily qualifies as a perfect grab and go telescope. The modifications exceeded my target budget a bit, but it was money well spent to propel the NexStar into meeting my objectives.

Click here for more about this subject. -Ed.