Telescope Review – Celestron NexStar 102 SLT
Written by Tammy Plotner
Are you looking for a sweet little telescope that can take abuse and keep coming back for more? Designed for the advanced beginner, or for those interested in a highly portable telescope referred to as "Grab and Go", the Celestron NexStar 102 SLT automated telescope goes through a year-long Tammy Test and graduates with honors…
First off, I'm not too keen on the idea of a GoTo telescope – much less a refractor. In my early years I found refractors to be uncomfortable to use, easy to dew, and just plain not as much deep sky fun as a reflector. As for the GoTo? I genuinely feel you do yourself a disservice by not learning to use an equatorial mount and a star chart. Misgivings aside, it was time to take a look at new technology and see what a year's worth of use would do to it.
Assembling the Celestron NexStar 102 SLT
Unlike the variety of telescopes I've used over the years with complicated equatorial mounts and drive units, the Celestron NexStar is swift and efficient. The tripod is lightweight aluminum, and stands up to time. Despite repeated uses and even overtightening, the legs extend quickly and lock securely using the hand turn knobs. No wing nuts here to get dropped and lost in the dark. The center accessory tray bracket is permanently connected and folds down when the tripod is opened. What's more, the knob that connects the accessory tray is captive – it can't get lost. Even though these particular parts are some type of polymer, they are extremely durable and even the occasional cross-threading doesn't strip them out.
At the top of the tripod is the mount cradle. Again, extremely simple and captively elegant. There is simply no "wrong way" to attach the mount to the tripod and no way to lose the parts that connect it. The mount itself is fully contained. Nothing is exposed to chance or wear. As for durability? Surprise, surprise. The drive motors are contained inside the mount and despite being dropped hard enough to make the exterior cover come off, it popped right back on and absolutely no damage was done.
Once the mount is connected, the telescope optical tube assembly (OTA) comes next. Again, captive screws mean even arthritic hands will not fumble these parts. The OTA attaches to the mount with what is called a "clamshell". It's a hinged affair that you simply fold over the telescope body and tighten down.
Last, but not least, are the accessories. Supplied with the Celestron NexStar SLT is a red dot finder that slides on easily on a dovetail mount, a cheap – but serviceable – 1.25" star diagonal, and two excellent SMA eyepieces. The controller is easily attached into a port on the side of the mount with what looks like a telephone jack and the battery pack is internal to stop cord wrap. Set up time? Twenty minutes the first time… Less than five when you get used to it.
Aligning and Using the Celestron NexStar 102 SLT
So, here's where my misgivings with GoTo units usually start. I've played with a lot of encoders and a lot of different units over the years and I'd usually get frustrated because it would take longer to get the units working than it took just to starhop. In the case of the Celestron NexStar, I was pleasantly surprised to find that it didn't take a whole lot of learning to use the system. Simply use the keypad to level the scope pointed north (remotely close is fine), and set the date, time and location. Press Go, and the little beast is off and running on its own – seeking out an alignment star. Use the keypad to move the red dot center on the star and enter again. Now, go to the eyepiece, center the star as much as possible and enter. Guess what? That's all it takes.
The more accurate you are with your time, location (latitude and longitude) and centering – the more accurate the scope becomes. Even loosely set, and I do mean loosely here, folks… A low power, wide field eyepiece will bring almost everything into the field of view on the first try. After that, it's a joy ride of selecting objects from the data base. If it tries to go to something below the horizon? It will tell you. If it might tangle itself trying to go to what you tell it? It won't let you. If you try to slew it towards the Sun? A little hand reaches right out of the keypad and slaps you upside the head. It knows better! And it learns… Oh, yes… It learns each time you center a new object up and corrects itself.
What Can You See With the Celestron NexStar 102 SLT?
Everything in the database? No way, Jose. Before you go getting all excited about a 4,000 celestial objects database, remember you are using a 4" telescope here. We're talking about a limiting stellar magnitude of around 12 here, so objects much fainter than about magnitude 10 or 11 under average skies are about as good as you're going to get. However, if you ask it to go to an object, it says it's there and you don't see it? Try looking at the on-screen data. Chances are you're trying for something that is beyond this sweet little telescope's grasp.
Lunar and planetary performance is outstanding. Being a refractor, it could be no less. Because the Celestron NexStar 102 is driven, it's possible to drop in some ridiculously high power and get a decent image. Double stars are crisp and clean, and here's the kicker… Deep sky (nebulae, galaxies, and star clusters) are surprisingly well resolved for such small aperture. When I can pick out the dark dust lane in the Sombrero Galaxy with a 4" aperture? I'm delighted. When open star clusters sparkle? I'm enchanted. When globular clusters try to resolve? I'm fascinated. When nebulae smoke out of the sky? I'm hooked. A little scope that can!
Final Words On The Celestron NexStar 102 SLT: What's Good And What Isn't
The supplied 1.25" eyepieces are excellent – but the diagonal needs an upgrade. On a happy note, it comes with a 2" focuser, so do yourself a favor when you're ready to step up your optics to the next level and go with the bigger accessories. If you can't afford the full 2" line, at least start with the 2" diagonal and use a reducer to accept the 1.25" eyepieces. You'll have this scope for a long time and the upgrade is worth it.
Word of warning… It's a battery eater. Even the high buck batteries don't last. Having battery power is great when you're in the field where no electrical outlet is available, but it won't be long until you're purchasing a power tank. Happy note? You can connect it to your car battery via the lighter, and the AC converter is very inexpensive.
Dew? Yep. It's a refractor's worst enemy. But, surprisingly, Celestron thought of that and the dew shield is included. Just remember, that won't keep the fog monster away from your eyepieces, but taking care to cover them during the critical point means being able to stay outside and play a lot longer.
Again, don't ever forget this is a small aperture telescope and it's not going to reveal every heavenly treasure you dream of and what you see is going to be small. It does rich field, so picture yourself looking at the Ring Nebula about as big as a Cheerio on a dinner plate, ok? But small aperture has it's advantages… The whole thing only weighs 14 pounds, so it is incredibily easy to take with you as a carry on, or to sling over your shoulder and walk. There's definitely something to be said about a scope that you can carry everything, including your eyepiece case, folding chair and cooler in one trip!
Usability factor? Don't give the Celestron NexStar 102 to a small child – but do give it to anyone old enough to read and follow a few simple instructions. Durability factor? It's been carried around in a car trunk for weeks at a time, strapped on the back of a motorcycle, knocked over at a public outreach event, and traveled to many star parties and still performs flawlessly. It is not a Takahashi, but Celestron produces quality optics and you will not be disappointed with your investment in this $500 telescope.
I wasn't.
Filed under: Telescope Reviews
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June 17th, 2008 at 6:22 pm
Wow, this might just be the one. I'm a complete novice as far as scopes, can you relate how this one compares to the SkyScout Scope 90? Both in terms of the type of telescope, the expense, and the performance?
By the way, the equatorial mount link seems to be broken.
Thanks Tammy!
June 18th, 2008 at 2:17 am
Nice review.
June 18th, 2008 at 2:56 am
I've been thinking of getting a telescope myself, I've never had one but I'm incredibly fascinated by astronomy (Or I wouldnt be posting here). Would this suit me for a first telescope? The price seems right and I feel I'm technical enough to get devices working (I work in the IT business).
June 18th, 2008 at 6:20 am
Thank you, gentlemen… Let's answer your questions.
There are two ways in which the Celestron NexStar 102 and Celestron SkyScout Scope 90 resemble each other – they are both refractors and they are both built by-gosh Celestron tough. What sets them apart is the mount (the section that connects the telescope tube to the tripod and allows it to move) and the focal ratio.
Now, let's compare the two and try to keep the technicalities to a minimum…
Both telescopes have a similar aperture (the size of the primary light gathering source). While the extra 12mm between the 90 and the 102 won't make a whole lot of difference in some objects, it most definately will give you a slight edge (about 40% more light gathering power) in magnitude reach (capturing fainter objects) and resolution.
In the case of focal length (the distance it takes the objective – primary – lens to bring the light into focus) – the two are almost precisely the same despite the differences in telescope tube length. The focal length is where you pick up your magnification factor. Focal length of telescope divided by focal length of eyepiece equals magnification power. Here the two are identical. Anything more than about 240X is useless.
Now, here's where the real kicker comes into play – the focal ratio. The Celestron SkyScout scope 90 is f/7 and the Celestron NexStar 102 is f/6. Without going into a lot of equations (it's early and there isn't enough coffee in the world to make me do math at this hour!) it all boils down to what type of view do you want. A telescope with a low ("fast") focal ratio offers lower powers and a wider field of view with any given eyepiece while larger focal ratios ("slow" telescopes) give higher magnifications but the field of view is more limited. Small focal ratio telescopes are actually better for deep-sky observing because of the lower power and wider fields. (yes, virginia… it really is better to use less magnification – the objects will appear far brighter and much easier to find.)
Now, the editor in me comes into play. Let's see if I can say this so even my Mom would understand: What you see in the same eyepiece in both telescopes is like comparing a regular window to a picture window. You can see the tree outside in both of them – but the f/6 window will show you the tree, the fence 10 feet away to the left and the car in the driveway to the right.
Now, let's get down to the mount, shall we?
The Celestron SkyScout Scope 90 is altazimuth. The user manually manipulates it up or down, left or right, and needs to be moved manually as the object progresses. The Celestron NexStar 102 is a GoTo equatorial – it moves up, down, left or right via a user keypad – but it will also perform those functions on its own and track the object. Upgrades exist to make the SkyScout Scope 90 a GoTo for about $100 – about $600 for the total system.
Honestly? I love them both and trying to chose between the two is difficult. The SkyScout Scope 90 has some great gadgetry and is a virtual teacher… The Celestron NexStar 102 SLT is for quiet contemplation. Both are excellent beginner's scopes – but the NexStar is better suited towards technically minded adults.
The bottom line is they are both Celestron tough. Future reviews will show that a lot of similar telescopes look great sitting in the corner of your living room, but don't live up to their expectations when used!
And James? Yes! The Celestron NexStar 102 will provide a lifetime of fascination for those even remotely interested in astronomy. If there comes a point where you want to graduate to a larger telescope, you'll never sell it because it is so portable and durable. Solar filters are inexpensive and a 2" wide field eyepiece turns the night sky into a showcase!
June 22nd, 2008 at 4:29 am
I have a Skyscout 90. What upgrades would I get to make it a goto for around $100?
I'm finding manual higher power tracking frustrating and the only mounts with low vibration slo-mo controls seem to cost as much as the Skyscout itself!
If there was a decent goto with tracking with super-quick setup, like what you mention for the 102SLT, for around $100, I'd seriously consider it.
August 10th, 2008 at 9:20 pm
I also bought a Skyscout 90. I'd love to know what to buy to make it a Go-To scope?
January 22nd, 2009 at 12:03 am
For me the issue with this scope is the power. Runs out way too quick, and even using a car to do the job isn't really ideal unless you want the sound of your engine in your ear while your enjoying the magnificence of space. I am being nit picky though…apart from that, for me, this was a good buy.
February 7th, 2009 at 12:10 am
I have recently purchased the 102SLT. I am having some issues with it though. I have made several attempts on VERY BRIGHT stars to try and align the scope and all I can get is an "alignment failed. try again". Kind of a downer if you know what I mean. I have even used the moon as one of the points of reference. I did manage to "manually" navigate to the Great Orion Nubula the other night. I was using a 6mm 1.5" lens and could make out the "dust". What kind of filter, if any, could I use to get this puppy to show its true face in the scope? I would like to get closer if possible, but I always wind up not being able to get a semi-crisp or what might be a close focus of the object. I am VERY interested in the sky and what's up there, I think I just need a bit of coaching. It's a bit cold out this time of year to do any real gazing, but I cannot wait to get underneath a dark sky with the right temp for longer viewing.