Pirich's Full Review: Celestron NexStar 80GT (189 x 80mm) Telescope
The NexStar 80GT is a compact refractor with a computer driven mount. All of the structural elements are metal, yielding a very solid and stable platform despite the small size and modest cost. More general information on getting a telescope is in my article on Picking a Telescope.
Description
The NexStar 80 GT is one of six telescopes Celestron has built using the same miniature version of a NexStar robotic computer controlled telescope mount. This version has the same 80mm diameter f/5 or 400mm focal length refractor which as been sold for a bit over 5 years by Orion, Celestron, and various other companies in many colors on various mounts. These telescopes have come to be recognized as what a beginner's first scope ought to be:
(1) Inexpensive enough to give it a try
(2) Capable of showing the most impressive objects
(3) Easy to use
(4) Rugged
(5) Flexible
Unlike previous incarnations, this telescope is now equipped with a motorized drive base controlled by a small hand computer with 4000 of the most interesting astronomical objects in the sky built in for it to automatically guide to on command. It sounds cool, but my first question was "Does it really work?"
I bought one of these as a Christmas present for my sister and her husband. Whenever they are visiting my home (which, if you have inferred from my other reviews is a sort of telescope farm, my wife would concur) we always do some observing. Although they haven't been serious astronomers, they are interested in observing since the views are always very pretty compared to photos. But they have always found the knowledge barrier intimidating. I thought I would give this telescope a shot as a possible answer.
It came in a surprisingly small box. Inside we found a light weight tripod and the telescope attached to its mount separately. The telescope comes with every tool needed to put it together, including a real screwdriver which is only actually needed for 2 screws on the finder scope. We had it put together in about half an hour.
The tripod was finished in a gunmetal colored finish and the telescope tube is painted in a steel colored metallic finish. The mount had a small cover for its lower base which had come free in shipment, but just popped back in to place. The mount threads on to the tripod with a single knob, and the tray/hand controller holder threads on to the tripod with a single captive screw. I took this screw out and installed it from the top instead after looking at how it was going together. This is a different tripod tray than the one shown in the instructions (much easier to install). When assembled, it was extremely light at 11 lbs. I was reminded of years ago when I got the C90 and it changed astronomy for me since it was light enough to walk out and use it on a moment's notice, so I used it more than heavier scopes I have owned.
The telescope is fairly rugged with all metallic construction except for more minor fittings. The dew/glare shield slides off the front to make cleaning the glass easier if you are so unfortunate as to have to do this. (DO NOT TOUCH THE GLASS IF YOU CAN AVOID IT. SMACK FINGERS AWAY IF YOU HAVE TO). I was happy to find these scopes have improved with time. There is a baffle part way down the optical tube and all of the lenses are coated- they have even gotten rid of a small screw which protruded into the optical path in earlier versions of this telescope and degraded the image.
Usage
The telescope has a couple of odd features we noticed. First, the batteries don't go in the mount. The mount arm and base have an aluminum rigid structure with plastic covers sealing up the electronic parts. The batteries are stored in a little pouch with a small strap on it with a cord coming out. The plug on the cord is the same one any other nexstar power supply has, so you would use an AC converter or car plug cord by plugging it in to the same spot.
There is no ON/OFF switch- the scope is ON when plugged in (you can also plug it in to the wall or to a car with a nexstar 12V adapter). The hand controller has no start-up as most computer users are used to- it is immediately ready to start operation. It will ask what model telescope it is amongst the types using this mount when it is first powered up, but will never ask this again (it is easy to change in the utilities menu in case you put in the wrong one). The controller stores its last location and time of operation, but has no way of orienting itself without help.
To get the telescope ready to observe, the computer needs to know how it is positioned on the earth, and then the precise orientation of its mount as it is setting on the ground. To do this, it will first ask you where it is. You can answer this either in terms of your local latitude and longitude (if you have a good map or a GPS unit), or by looking yourself up in a nearby city from the list in the manual. It will then want to know what the local time is and what time zone you are in. It is actually able to resolve this for any spot on earth, so if you are in Fiji, it will work just fine.
The scope asked to be pointed North and have the tube leveled. We did this by dead reckoning. We were first setting this up in New Orleans, and I happened to know we were within a mile of 90W 30N, so I punched it in. It asked for the time and we punched that in. It then made a guess at where the star Aldebaran was and started moving. It goes at 4 degrees per second, which is actually pretty fast.
When it stopped, it was in the right general area of the sky, but was nowhere near being close enough to see Aldebaran in the eyepiece. The telescope asked to line up the object using the finder, which is a sort of miniature heads-up-display like a fighter plane uses, except this just projects a red dot in the window, as if you had a laser sight. However, when you haven't aligned the site with the tube, it won't work, and you can't do this until you get the telescope centered on a distant object to use for alignment. So, we moved the tube until it looked like it was pointing at the star by eye, and got Aldebaran into the field of view. The wide angle field this telescope has with a low power eyepiece makes this much easier since you will see the object if you get within 2 moon diameters of it. We told the controller it was centered in the finder, and it asked to center it in the telescope. We switched to the high power eyepiece and centered the star. At this point, we turned on the pointer and centered it so we could use it the next time. I have heard you sometimes have to adjust the dovetail where the finder grips the arm it is on, but it was actually pretty close in this case so all we had to use were the finger knobs on the finder.
The little red dot can be brightened and dimmed by turning the on/off knob. When we were done aligning the finder, we pressed the Align button and the telescope saved the position of this star. It then took off for the star Sirius. Now, if a star is below a tree or other object, you can press UNDO to reject it and it will pick something else. It will never try to slew to something below the horizon. After centering the second star, which was much faster with the pointer working, the controller said NEXSTAR READY. This mount does have a manual version of this alignment process where you do all the steering and a quick align which assumes you pointed it perfectly north and got it perfectly level to start. When alignment is done, it reminds you to turn the pointer off to save the battery. The pointing accuracy was good enough for every object to be in the field of view, so we didn't need the finder to go to a pre-programmed object.
The different number buttons on the controller all have other functions. For example, one button says Planets, another says M (for messier) and one says Stars, and so on. By pressing planets, the controller will offer up a list of the moon and planets above the horizon at this time. Interestingly, it won't do the sun- but you need a special filter to observe the sun, anyway.
[NEVER try image projection with this telescope- at this diameter, you will burn parts and maybe people. NEVER try to use an eyepiece solar filter, even if it says it came from Zeiss- they can and do fail suddenly without warning from tiny invisible wear scratches in the glass from handling. This causes instantaneous and permanent blindness to anyone looking when this happens. These should be smashed with a hammer to make sure a child isn't blinded by one).
On Saturn we were surprised to find it showed the Cassini division in the rings, the white cummerbund stripe around the middle, and one of the orange-brown stripes on the edge of the white stripe. Two of Saturn's moons also were visible. The focus was nice and crisp, and there was none of the false color people complain about when we popped in a barlow and took it up to 133 power, the limiting practical power for a telescope this size. It still looked good, and even showed some gradient detail in the stripes. Something else we noticed was the mount is very steady, even with the legs fully extended and the feet on hard concrete. Vibration damped out almost instantly when you let go of the focuser.
On Jupiter, the scope does show some false color. There is a blue-violet halo around the planet. The lens cap for the front of the telescope has a sub-cap in the center for stopping it down. We tried this and Jupiter dimmed down, became a bit clearer, and the blue-violet halo vanished. This is because stopping the scope down only uses the center of the lenses, where they are less curved. Although this theoretically reduces the resolution, it can improve the image for bright objects because full spectrum light doesn't come to a perfect focus at the eyepiece in this type of telescope. Saturn had looked clearer because it is mostly amber colored, while Jupiter has parts which range from red to amber to blue, and has large areas in white.
If you press the TOUR button, the telescope will make a selection of neat things to see in the sky from its other databases. For some reason it doesn't include the planets (perhaps because these are transient in their location). The best objects visible from where we were in the city were the Orion Nebula, Double Cluster, and the Plieades.
The Orion Nebula showed up as a fuzzy area in the center of the field of view at low power. From there, I remembered how other telescope behave when the power is increased, so I did so and the cloud detail popped into view at 40X. At 80X, the trapezium and cloud detail around it was extremely sharp. Interestingly, the chromatic aberation was gone on dimmer objects like this since they are mostly visible in only one color, anyway. This object was a real crowd pleaser. We found if you press the INFO button while the telescope is tracking an object, it will tell you what it is, what its coordinates are, how far away it is, and what its magnitude is.
On the Plieades, the scope showed the entire nearby star cluster at once. The stars had a diamonds-on-velvet appearance, and even had a large swath of sky around them visible. This was easily one of the more interesting views I have seen of this object. The stars came through as little pinpoints. The only complaint is some of the blue tint visible in a Schmidt Cassegrain or Maksutov was missing.
Double Cluster was another pleasant surprise as the entirity of the two star clusters together were visible at the same time. In the case of ancient star clusters like these, which have been orbiting our galaxy for billions of years, the stars are quite old and tend to be white, yellow, or red. The colors appeared to be very nice. I just wish we had had a darker sky so more of the dimmer stars could be visible.
We tried it out on some double stars, such as Polaris (yep- the North Star is a double star! Didn't know that? That's OK- if you look up double stars, the telescope lists it for you). The scope showed Polaris and its dim companion. It was even possible to split Rigel, which has a very close and very dim companion star. Epsilon Lyra, the benchmark double-double star wasn't in the sky. I will have to see if I can visit them during the summer to give that one a try.
Details to Remember
First, watch what is happening with the power cord and be ready to shift the battery bag. We just had it hanging on a tripod bolt at the top of one of the legs and saw the cord could get wound around the mount if you didn't pay attention.
Second, once it is slewing to something, wait for it to get there before pressing more buttons. A couple times this seemed to confuse it. It has a little spinning icon it shows in the upper right corner of the hand computer while this is going on, so just wait before doing more.
Third, remember the RATE button. Many times it will select a speed for the little cursor keys to move the telescope. Often it will be a rate slower than what you want. The rates are slowest at 1 and highest at 9. Too slow? Press rate and it will show the current speed, and the next number you press will be the new speed. Once you get used to this, it is pretty easy to do.
The scope knows where the eyepiece and back of the telescope go, and so it won't let you run them into the tripod legs by pointing it straight up. So, there are some objects right above you it won't track to. You can point at them manually if the scope happens to be between tripod legs, but keep track of where the focuser and such are so you don't crash into the tripod.
The telescope automatically guides at new rates at new locations in the sky if you drive it there with the electronic controls. It won't lose its alignment as long as you don't force it to move by hand (not using the motors). So, if you are out and see something cool bud don't know what it is, just drive the scope to it and take a look. The scope will automatically track with the earth's movement. Unfortunately, it doesn't appear to have the ability to ask it "What in your database is near this location?" You'll need to look it up on a map.
Something immpressive about the telescope is how quiet it is when tracking. When it is slewing around, there is electric motor noice, but if there is any sound at all- conversation, traffic, etc., it is so quiet that you may wonder if it is working. I personally find it far more agreeable than the strange crunching sound the Meade equivalents make. Because of this, I suggest leaving the lights on the display on. It uses a little more power, but you can remember it is running and not leave it on if you don't mean to.
Also, the controls were designed to be easy to use. If you ever press a button you didn't mean to, press UNDO until you see something familiar. The listings for functions are meant to be logical, so just look around. The instructions appear to be fairly good, so that helps, too.
Conclusions
All in all everyone was very happy with the telescope and how it performed out of the box. The two eyepieces it has are OK quality, but there are other options which aren't all that expensive. I would suggest getting a small set of Plossl eyepieces in about 6mm, 10mm, 15mm, 20mm, 25mm, and 30mm sizes with a short barlow to do everything this scope can do. If you want to get just a couple to start, 6mm, 15mm, and 25mm are probably a good spread.
A car plug adapter or AC adapter may be a good idea so you don't have to use the little battery pack. The scope is surprisingly easy to move around, so it can be taken along for a picnic or other outing. It has the ability to be put in hibernation mode, and you can add objects of your own (astronomical and on the ground). So, if you are leaving it set up somewhere for an extended period and have a cover to keep it clean, you could actually power it down and remember where it is and where objects you looked at before are. This perhaps could be done on an extended camping trip.
I have already found myself wishing these were around when I was a kid. I found it to be a lot simpler and quicker to get this telescope to do something than I expected. It is surprisingly capable and well made for something you can find for $250 from www.adorama.com. For someone who has been a purist about "You've got to learn the sky!" this telescope has been reason to re-think that position.
Updates
The biggest change here is on possible upgrades from this telescope.
First, the Baader Contrast Filter from Celestron. I have a review for this component. Essentially, it suppreses the false color in the image and improves contrast in images. Because it knocks down blue light, it is also acts as a light pollution filter.
Second, the excellent Celestron 80ED 80mm apochromatic refractor will instantly take the place of the 80mm tube the 80GT comes with because they have the same barrel diameter. you would remove the tube clamp the 80ED comes with and put it in just like the 80mm short tube. With accessories, the 80ED will balance with the tube forward in the clamp, and with its black gloss paint job, should look as good as it perfroms. This telescope is available for $408 from www.handsonoptics.com, and I have a review for it as well. This telescope has a 2" focuser so you could get wider field images and also has no false color. so better resolution is possible. This is, in my view, the most cost effective upgrade for a major change in performance. Hopefully, Celestron will offer this outstanding configuration in the near future.
Finally, if you want to do something completely different, the small NexStar GT scopes like this can be readily converted to take another telescope tube with what is called a Baader Bracket, from www.alpineastro.com. This takes the telescope and its mounting ring off of the mount and replaces it with a dovetail slot and bar. This lets any scope up to about 10 pounds take the place of the small 80GT tube. So, you could, for example, put a C5 spotting scope on, or anyhing else you felt like as long as it was relatively light and compact.
400mm focal length, with a 3.25-degree wide field of view 2 eyepieces (16x and 40x) Observe immediately with the computerized auto align feature Autom...More at Amazon Marketplace
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