The All-Purpose Space Viewing Machine
Written: Aug 10 '03 (Updated Mar 28 '07)
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Product Rating:
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Pros: Anything it does, it does well
Cons: Too bulky for quick-looks
The Bottom Line: It's still the answer to the question: If you were to get one scope, what scope should it be? It is beautiful, it works well, and the views are incredible.
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| Pirich's Full Review: Celestron NexStar 8GPS 11052 Telescope |
The NexStar 8 GPS is the descendant of a line of telescopes dating to 1970 when the first Celestron C8 appeared. It is the telescope which changed amateur astronomy. The 21st Century has seen this model become new again, and the results are amazing.
I had always wanted one of these, and now that I have one, it has become an interesting education. This review ended up being more difficult to write than I expected- this is a very capable piece of equipment in several unrelated ways, and this makes reviewing it complicated. More general information on getting a telescope is in my article on Picking a Telescope.
Background
I have already written about the genesis of these scopes in my review of the Celestar 8, so there is more information there. These telescopes were derived from a design Estonian optician Bernard Schmidt developed to make large photographic telescopes with flat fields of view in the era before hyperbolic mirrors could be reliably made. Hyperbolics are not cheap, so giant telescopes from the Keck to the Hubble space telescope are Ritchey-Cretiens with complex hyperbolic optics, but they are rare among amateurs.
In the 1960s, the people behind Celestron realized the Schmidt design previously used for observatory survey cameras was very practical for making an extremely compact telescope compared to its focal length. The spherical main mirror makes producing a high quality telescope easier since figuring and optical testing can be very accurate for this shape. The trick is to correct the light path with a specially shaped corrector plate which overcomes both the spherical aberration of the main mirror and eliminates the strong coma effect Newtonian telescopes have where stars to look like little comets at the edge of the field of view. This hybrid telescope was intended to be an all-purpose instrument where it would be a mid way between a long focal length (f/15 or higher) and short focal length (f/5 or below).
This results in an f/10 telescope which has a flat field of view across its available image. This optical design is the most physically compact available. A Schmidt Cassegrain Telescope, or SCT, typically has proportions similar to a mid-sized coffee can at any diameter. A Newtonian reflector or a refractor will be as long as or longer than their focal lengths. As a result, a moderate focal length Newtonian, a 6" diameter f/8, is around 4 feet long. A 6" f/7 refractor is typically even longer and an achromatic refractor optimized for planetary viewing will be longer still since it will operate between f/15 and f/20. These instruments are enormous and require giant sized tripods and mounts to wield them.
In comparison, an 8" diameter SCT is under 2 feet long and far lighter than either the Newtonian reflector or the Refractor in a smaller diameter. Even more interestingly, this scope is able to take in many deep space objects, but still has a focal length long enough to do something on planets.
This scope matured as the C8 in 1970, and changed everything. People could get a single large aperture telescope compact enough for one person to move, and cheap enough to get one. It changed amateur astronomy because it did some of everything, and did a fair job at it.
The NexStar 8 GPS
This variant follows several computer guided versions of this telescope. Most important of these was the Ultima 2000 from 10 years ago, the direct predecessor of this instrument. With the Ultima 2000, Celestron introduced a computer guided telescope capable of finding 10,000 objects with a fairly simple setup, and able to operate as an equatorial mount, or do something new- track objects in alt-azimuth mounting, where the telescope turns like a turret.
The NexStar 8 GPS is about two and a half generations later than the Ultima 2000. This new version of the C8 incorporates every innovation Celestron has developed for the telescope itself along with every development they have introduced for mounting one:
Optical Tube Assembly (the telescope itself)
(1) A carbon fiber optical tube. This saves weight, but more importantly it reduces the coefficient of thermal expansion between the front and rear of the telescope, so it stays in focus as the temperature drops at night.
(2) Fastar- The secondary mirror unscrews from the telescope and a special lens assembly goes in its place to turn the telescope into an 8" f/2 (yes, a 400 mm focal length) CCD imager.
(3) A large 9X50 finder- I ordinarily think of the finder as a sort of big peep sight, but this one gives a good enough image to mention. When Jupiter approached the beehive cluster earlier in 2003, the finder showed them together when the telescope couldn't.
(4) Clean-room assembly. I haven't been able to find one speck of dust in the interior. The glass appears perfect.
(5) Fit and finish is beautiful. The tube is a matt finish with clear resin so the carbon fiber is visible- very pretty. I design and build carbon fiber parts for a living- these are nice.
Mount:
(1) Twin arms with the scope mounted between. This is a new mount and all of the electronics are concealed inside the base and the arms with only the detachable hand controller
(2) Twin axis variable rate fine control electric drive system. It's accurate, and when in fine tracking, the telescope is so quiet I have to look for the glow of the hand pad to see it is on. This is a very nice feature compared to the RC car sound of the Meade LX200 scopesand their odd crunching sound while tracking.
(3) NexStar control (see my other reviews for more- all of them are similar in operation) with the refinement of GPS and an internal magnetic compass so the telescope can resolve its own location, the true local time, and basic directions without help. It can do this in the alt-azimuth mode or if it is on an equatorial wedge. When set up, it can slew to any of 40,000 preprogrammed objects, or items you store in its memory.
(4) The scope comes with a rugged adjustable tripod. After my experience with the Celestar 8, this stands out. The mount comes with vibration suppression pads (little disks you put under the feet to absorb vibration when the scope is on a hard surface), but I have found there is simply no noticeable vibration time if you set the scope down on a grass lawn.
As I mentioned in the Celestar 8 review, the way I came across this scope was a little odd. I had seen what looked like a really good deal on the Celestar 8, where you would be in business with a clock drive and the works for $1000. However, the tripod on it was too low, too wobbly, and getting another one was over 65% of the cost difference between that telescope, a bare-bones C8, and the $2000 NexStar 8 GPS, the fully loaded do-it-all home observatory. So, I talked it over with my wife, and she pointed out several things:
The NexStar could point itself. Even when you know where an object is, it takes a while to get to it, and this isn't the point of an evening's observing.
The NexStar is made for doing everything- it's the nicest version of the optical tube Celestron has ever offered.
The Celestar 8 had beautiful optics. No dust, and it even had perfect collimation on arrival. It showed the C8s are as good now as they have ever been, so I had reason to think the next one would be as good (believe me, it took some consideration and a leap of faith to send that tube away).
In short, the delta in cost came with all the cool stuff there was. I was only going to have one of these, so I bit the bullet and called up the folks at Woodland Hills, www.telescopes.net, and they didn't have a problem with me upgrading to the other scope. So, I carefully boxed up the Celestar 8, and a week later they sent me the NexStar 8.
The box which shows up for one of these is big. I mean small refrigerator big. A second box holds the tripod. They are packed like all of Celestron's other equipment with a box in a box with the hardware in conformal foam. Getting the boxes apart in this scale is a little bit of a trick. But the scope was in there, larger than life.
I am going to break with some and call this a large scope. Some have said the 8 is the largest of the small scopes, but I am going by another criterion here- a small scope is one which goes outside in one piece with its mount. Based on that, the largest small scopes are 5" to 6" depending on their design, and the 8" SCT is the small end of large scopes.
The NexStar 8 has integrated handles for picking it up and moving it easily, despite its 40 lb. weight (compared to others with handles seemingly bolted on as an afterthought). The arm away from the hand controller has a handle parallel to the arm, and if you lift here, the tube and fork assembly will hang sideways balanced on this handle. There is a "scoop" handle under the hand controller slot which lets you lift the fork assembly (FA) with the base down to go on the tripod. It is much easier to handle than the Celestar 8 was, and is easier to carry since the position of the handles lets you carry it with the tube pointed at the base. Three bolts hold the mount base to the tripod. A peg in the middle of the tripod top makes alignment easy. Here is what you do to take the scope outside:
First, unbolt the fork-tube and put the 3 bolts in your pocket or in a helper's hand.
Lift off the FA and set it on a table where no one can bump it.
Pick up the tripod and take it out to the observing area and set it where you will observe from (look up to make sure you are clear of obstructions).
Go back and get the FA and set it down on the tripod. There is a step in the center of the base, so getting on the peg may take a couple tries. The bolts go in from the bottom, but you need to have the base turned the right way for the holes to align. There are protruding foot-like features on the base which go midway between the tripod legs. feel for the hole underneath and have one bolt ready. When you feel it click into the threads, only thread the bolt in far enough to hold it in place. If you tighten it down, the others will not go in. Loosely thread the second bolt, and thread the third and now go around and tighten all of them finger tight.
Run the power cord, plug it the scope, and turn it on. The only difference between this controller and the other like this I reviewed is it comes up with GPS align as the first option. Lock the clutches with the tube pointed down and it goes through the alignment routine itself. The first time is longer since it is finding satellites and also has no true North declination for the internal compass. If you go a long distance, you will have the same situation. The compass needs to have a declination from true North, and this is setin the Utility menu after you have the scope precision aligned. This takes the precision North the scope has stored on that observing session and compares it to what its internal compass says to get a perfect local declination. The next time you align it, it will have a better first guess to start from.
Moving it back in at the end of the night is the same process as taking it out. I have found I need to look up and see a really clear looking sky to break this scope out, but the image when I do is always beautiful.
The mount moves at a top speed of 3° per second, so it is a bit slower than the other NexStar mounts, which top out around 5° to 6° per second. That said, it is still pretty fast. The one thing to remember is it must always be moved by the motors to keep its alignment. The Ultima 2000 had its encoders on its axles, so you could push it to a new spot by hand and it would pick up tracking when you let off. This scope will be totally misaligned if you do that and you will need to start over.
That said, alignment for this scope is easier than any other Nexstar in everyday use. You turn it on, tell it to GPS align, and wait for it to slew to the first star, center it in the finder, follow up by centering it in the telescope, then do the same for a second star it slews to, and you are ready to observe.
The tour has a large selection of objects to look at- stars, nebulas, clusters, and galaxies. Planets and the moon only come up on the Planets menu, not the tour. Different objects are listed different ways, and depending on how advanced an observer you are, you can get to them either by what they are, a catalog ID (like NGC 1421), or by the tour if it is a famous object, like the Sombrero Galaxy.
I have not seen all 40,000 objects in its database. In fact, I am pretty sure I haven't seen 10% of that. It will take me a long time to get to to them all, but actually the best thing about this is it lets me surf the sky. Yes, you heard me say that. I can find M57 in a few minutes. This telescope pops onto the Ring Nebula automatically.
The best part is the view it puts forward is very sharp, bright, and commanding. The telescope came out of collimation, and I had ordered a set of Bob's Knobs which I never installed in the Celestar 8. The Celestar had put out an amazing view of the Orion Nebula with 5 stars in the Trapezium. The new Nexstar, on its first night, only showed 4. The images of Jupiter and Saturn weren't as incredibly sharp, either. In short, I felt a sinking feeling. Then I put the scope onto Betelgeuse, near the zenith, and looked at the star's image at 400X. The bull's eye diffraction pattern was skewed to one side; the scope had been shaken out of collimation in transit, and I really should have checked this first.
I went back and put in the knobs and tried it out again after collimating the scope the next night. This time, it was a different experience The new NexStar was every bit as sharp as the Celestar 8 had been. Compared to other C8s I have seen, I would have to rate it as at the high end of capability. The Ultima 2000 scopes were similar in performance, and the story is they were screened for good glass. At this point, it appears getting free from Tasco (which had bought the previously independent company in 1998) may be the best thing ever to happen to Celestron.
This scope has the plusses and minuses any scope with a 2000 mm focal length and 8" aperature will have. First, it has a limited field of view. The Pleiades won't all fit. If you are looking at Double Cluster, you need to choose which one you want to look at. On the other hand, it really does fairly well on planets compared to wide angle Newtonians. I'd still have to say every serious observer needs to have a good SCT at some point. This is a lot of telescope, and for an urban observer, it will do a lot. It is also able to go fairly far down in magnitudes, so a large number of objects come through nicely. For example, the Blue Snowball, a blue colored nebula resulting from an exploded star, is obvious even in the middle of New Orleans. Saturn and Jupiter are drop-dead gorgeous through this scope. The view of these objects is intoxicating. The belts on Jupiter show their swirls and eddies while its moons are little colored balls. Saturn shows the Cassini division, its little moons, and the gradients in the rings.
The f/6.3 focal reducer stops the focal length to 1280 mm and it can be used with eyepieces up to 32 mm. I can report now it works well, and lets the Pleiades and Double Cluster fit in t a field of view. I will be posting a review on this device soon.
I have been using a Celestron binocular viewer (#93690 ) with this telescope, which splits the image up for two eyepieces so you can look with both eyes. The results are very impressive, though I have one friend who does not appear to be able to integrate the images. I wrote a review on it separately. All I can say is it makes a huge improvement in the observing experience with better visible detail and eliminates eye strain.
The 8", unlike the 5" SCT, does have some mirror shift. This means when you are focusing and reverse directions, the image will shift slightly. It is very slight on this scope, as it was on the Celestar 8, but is there. to focus it, you should move back and forth past focus a couple of times so you see what the image focuses to, and then approach from the direction where you are raising the mirror against gravity and stop at focus. It sounds complicated, but it isn't in practice. If you find the mirror shift unacceptable, there are add-on refractor type focusers available for these.
Tips and Improvements
(1) Have a plan before you try to move it. Think through exactly what you are going to do and what order you are going to do it in. Otherwise, you can find yourself holding the mount with one hand with it balanced on a knee while trying to get a door open.
(2) Make sure the clutches are tight before you start alignment. The position encoders are on the motors, so if it doesn't move with the motors, it loses orientation. It can still move some with the clutches off, so check. Keep this in mind because you need to loosen the clutches to move it without risking damaging the drive.
(3) Wait for the controller to finish a move before punching in new commands. It is possible to make it lose its place if you give it a string of commands while it is moving. The drive on the mount abruptly quiets down as it slows at the end of its slew to a new object and it is easy to think it is done moving when it is actually needs a few more seconds to finish its fine adjustment. Look for the little spinning "/" icon in the upper right corner of the controller display to disappear before giving it new commands.
(4) The telescope doesn't have a glare shield/ dew cap with it like a refractor. This lightens and shortens the tube, but leaves the scope vulnerable to dew forming on the corrector plate. You can spend $30 on one, or you can make your own. This works with any scope, so I have made the process generic enough to do it with others: Get 3 mm thick black art foam (in 11"X17" sheets at craft stores), a hot glue gun, and some sticky back velcro tape. Measure the circumference at the viewing end of the telescope. You can also measure the distance across the outside and multiply by Pi, 3.14159. You will make a cylinder of the foam to this diameter with a strip of velcro in it so you can open it up and wrap it around the tube for travel (cushion and stowage in one!) For a 5" scope, you will want to make 4 panels, for an 8" tube I recommend 6. Divide the circumference by the number of panels, and then add a half an inch or a centimeter to each one to make a glue land. The glare shield should be a few inches wider than the diameter of the telescope. What you want is to produce a sort of shade so descending dew laden air doesn't flow across the front of the telescope. The shield also helps by blocking off-axis light from shining in and dulling the image. Draw your pattern right on the foam with a pencil, so the glue lands you have in mind will be visible and help you align the pieces. Make one longer than the rest by another centimeter or half an inch to allow you to adjust the fit with the velcro. Glue the panels on top of each other with hot glue in a stair step pattern. Leave the long panel to be the Bottom step. Stick the velcro to the short end on the outside and wrap the glare shield around the telescope tube. Attach the other side of the sticky velcro where it touches down, and voila- you have a flexible glare shield for under $2. To use it, just put it together and then slip it over the front of the telescope by canting it and getting it started on one edge then working around the tube. It will be a little stretchy, and this is what keeps it on. Use the back edge of the metal corrector cell as a guide to get it evened up. It is light, so you won't change the balance. If you wrap it around the optical tube to store it, you will find it it stays nice and round and acts as a bumper while moving the telescope. If you want, you can make it out of a colored version of the foam, but you will need to paint the interior side black. I suggest flat black acrylic paint. Give it at least a week to dry in a warm place before you put it on the telescope.
(5) No direct battery provision- the scope comes with an AC power adapter, but using it away from a plug requires you to get either a car adapter or a battery pack.
(6) Get a set of Bob's Knobs (www.bobsknobs.com). They make collimating the scope easy, and the performance just isn't at its best until you get the collimation perfect. Simply put, the difference between seeing 4 stars and seeing 5 (ups- 6) in the Trapezium in Orion was recollimating the scope. It is worth the trouble.
Summary
This product is one of the most flexible observing devices ever made. For any task, there are accessories available from Celestron or other vendors to do it. In essence, it is the culmination of 35 years of trying to build the one telescope to have if you only had one. It is even handsome in the living room. With its tripod set to a comfortable viewing height, mine stands 66" tall, so it is pretty imposing. It shines under the night sky, it guides itself, and the images are beautiful. For about this much money, you can get a high end refractor which will produce similar images on planets, but will be dimmer on deep space objects, and will come with no mount or anything else. You could alternatively get a Dobsonian telescope with a huge mirror and a very simple mount. It will be harder to transport and can find nothing on its own, but will excel on dim objects. I'm not sure if this should be a first telescope, but if it is, it can do it all. Perhaps the best thing I can say about the NexStar 8 GPS is it has shown a jack of all trades doesn't mean master of none.
UPDATE 8/30/03: The Mars 2003 Star Party
On the night of August 27th, Mars made its closest approach to Earth. The astronomy club I am a member of, the Pontchartrain Astronomy Society, sponsored a public star party at the planetarium and observatory in Kenner (west of New Orleans). Quite a few of us decided to bring scopes oout so people could get a look (this was unpaid- none of us asked for or were compensated in any way). My wife and I brought two telescopes- a little C90 and the NexStar 8GPS. Where we set up with the other club members, there were large floodlights shining directly on us. Mars would be the only observing object, so this didn't hurt matters that much since the foam glare shield was long enough to keep the light from shining into the front of the telescope.
At 7:30PM, we had everything put together and had a moment to get a sandwich and a drink. These would be the last still moments for some time. I got the telescope lined up and started tracking. My wife ran the C90 about 20 feet away. Also present were a Meade 10" scope on a Losmandy mount which had a webcam and the live image diaplayed on a notebook computer. A Televue 102 4" scope, Orion 100mm, and even a Takahashi FSQ-106 refractor also came. Reflectors included a home made 6" Newtonian and another Celestron SCT. The observatory is equipped with a 14" Celestron SCT.
A few people came to look and I showed them how to look into the binocular viewer, which I started out with 2 20mm eyepieces, about 125X with Mars near the horizon. The image boiled from heat near the ground, but the ice cap and the dark areas were visible. I placed myself between the flood light and the observer so they could see. A few more people walked up and looked. A few minutes later, there was a crowd. I turned around and had a moment of shock when I found a line of about 30 people extending into the street.
What ensued was an experience I really wasn't prepared for, but it was definitely a good one. I estimate about 800 people looked through that telescope that night. By 9:30, the seeing was better as Mars pulled away from the horizon. I put a 2X apochromatic barlow in to boost power to 250X. Mars now showed its sandy-orange-red color clearly and the ice cap showed its comma shape. It was very beautiful. Some very nice people came back and brought us water bottles when they saw we couldn't leave the telescopes. The seeing was actually only fair as mist and clouds rolled over. However, we were lucky since it was just water vapor instead of ice crystals, so the image just became dim instead of blurred. Mars itself periodically disappeared to the naked eye.
By around 11:00, it had been quite an evening. I noticed some of the people were repeats. I asked one about it and he said, "I looked through all of them- this is the best view here, so I came back." That was a bit of a surprise, considering the competition. But perhaps it shouldn't have been.
The people were all very nice. I was thinking only a dozen or so would stop by. It seems a lot of people really like Mars. This was really a neat experience all around. The NexStar 8GPS has really come into its own, and I see I will be using it quite a bit more in the future (Saturn and Jupiter are coming up for Fall viewing!). After the views I had of Mars this time around, I will be looking again in 2020. Mars is still in the neighborhood, so I will keep looking over the next few months.
Updated usage tip: I have a work bench in the garage I have started using as a telescope staging point. What I do is take the NexStar off of its tripod indoors and take it out to reach the outdoor temperature when it looks like the seeing will be good that evening. Here in New Orleans, your telescope will be ruined by the humidity if you leave it out full time. This way, it is possible to keep it clean and dry, but not have to wait for it to warm up or cool off when going out to observe.
UPDATE 12/06/03: The NexStar in Winter
I have been doing more observing as the Winter stars have risen again. My favorite constellation is Orion and with its return I have started experimenting with photographing with the NexStar8 GPS. This is when the first problem I have had with it manifested itself. While tracking an object, the telescope would periodically jump in the altitude direction and then slowly return to the object. I called up Celestron about this and they said it was a known fault and I could either (A) get the interface cables and run a windows program to update it, or (B) I could send it to them to be reprogrammed at no charge other than shipping. Strangely enough, the cable is $30 and the shipping there and back was about $12.
So, I followed the instructions to unbolt the side of the left hand fork and found inside the controller board bolted to the arm with five bundles of cables plugged into it. I unplugged the cables, removed the board, and sent it away. Celestron upgraded the card, and now the telescope is back in business and all is as it should be.
The scope has even managed to be quieter than I remembered it. I have been observing the winter sky and learned a few more things about the telescope. Perhaps the most important of these is it becomes an even more flexible instrument with the focal reducer added- the Pleiades can all be seen at the same time, for example.
And, I have learned I was wrong about something after I returned to the Trapezium in the Orion Nebula. I spent some time looking around the four stars with the dim fifth, and looked for the sixth, and to my surprise, found it. Saturn is getting closer and rising earlier. I'll post more as I get a chance to do more in the cold clear skies of this time of year.
Recommended:
Yes
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Epinions.com ID:
Pirich
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 in Electronics |
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Member: Rich W.
Location: Tucson, AZ
Reviews written: 137
Trusted by: 40 members
About Me:
Dad, Engineer, Scientist, Astronomer, Traveler; order may vary.
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