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Impressions and Opinions of My NexStar 80GT

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11 November 2000

Following are my first impressions of the NexStar 80GT.  Additional use of the scope hasn't changed my impressions much other than I'm pleased to say that the goto and tracking capabilities of this little NexStar are every bit as accurate as those reported by owners of the NexStar 5 and 8.

You must also read the review of the new GT hand controller, as this is the controller now shipping with the NexStar 80GT and it addresses many of the small problems noted below.

The viewing was done from my back patio which has three bright local lights and in the middle of a city with extreme light pollution.  Comments in braces - { } -  were added as I have made new observations at a later time.

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Well built. For a $400 scope with a tripod, computer control, two eyepieces and a finder, it amazed me how well built it is. There is very little plastic and the places plastic is used, it has little or no consequence on the performance or longevity of the scope.

Well designed set of features for a scope this size. Everything was well thought out; from the tripod/scope mounting, to the finder. There is a single bolt used to hold the scope to the tripod and it is turned by the use of a large head that makes it as easy as putting a lid on a jar. The simple laser-pointer finder is so much easier to use than the usual cheap finderscope; it is particularly well suited for beginners as well as those who know their way around the sky.

Easy to assemble/disassemble. Little or no fumbling in the dark to thread tiny screws into obscure holes. The hardest thing to assemble was the accessory tray on the tripod. This is due to the desire to make it fit very tightly to add stability. As is the case with any scope, assemble it fully in the light a few times to get the hang of it.

Very good optical quality. As you must expect with a short focal length achromatic refractor, there was apparent chromatic aberration (false purple color right at the edge of bright objects like the moon). {Improve the views with Baader's Fringe-Killer filter.}  But, it was not overpowering at all. The detail I could see on the moon at 40x magnification was awesome. I also looked at Jupiter. Two clearly defined dark bands at just 40x, also the four major moons were razor-sharp. I also looked at Saturn. The rings and planet disk were also razor sharp. One moon was clearly visible. Also gave a nice view of the Pleiades. I did not attempt any faint objects. {Since this initial session, I received a 3.6mm Plossl and 2x barlow.  The scope does quite nicely on the moon and planets up to the 111x afforded by the 3.6mm.  Also, I've naturally sought out some deep sky objects since then and the brighter nebulae and galaxies are easily viewable.} 

{18 Dec 2001 - I now have a new suite of Celestron Ultima eyepieces (5, 7.5, 12.5 and 18mm) and they are great in this scope!  The 5mm with a barlow gives nice bright views of the moon, planets and double stars at about the limit of 160x on an 80mm scope. The only drawback is the short eye relief of the 5 and 7.5mm eyepieces, way too short if you use glasses when observing.}

Stable mount. A sharp rap on the tripod or scope is dampened almost immediately.

Very portable. Since most of us would like to take this with us to dark sites any chance we get, you’ll be happy to hear that coupled with the ease of assembly/disassembly, the overall compactness of this scope make it an easy traveler.

Alignment and Goto features. I am unable to even make out the north star at this site, so I was relying on an old compass with no idea the difference between magnetic and true north at this location. After running the auto-align several times, I now know it to be about 2 degrees to the west as each time it pointed to an alignment star that was the amount it missed. But keep in mind, the requirement to point north and level, only affects the scopes ability to point to a bright star for alignment. After that it doesn't affect accuracy. What will affect accuracy is entering a correct longitude and latitude for your position.  This will show up the longer you are attempting to track a single object (it will drift out of the field) or later in the evening when you are asking the scope to goto and object (it might not show up in the field). {Update - Discussions I've had regarding alignment and tracking issues have clarified the alignment accuracy issues.  Accurate longitude and latitude are not important, other than NexStar's ability to find the two alignment stars.  Download the Alignment Guide from the link at the top of the main page for more details.}

But, I can report that generally speaking, the NexStar 80 GT is very accurate in pointing. It was successful moving directly to the Moon, Jupiter, Saturn and the Pleiades. All were near the center of the field in the 10mm SMA eyepiece (40x).

Small complaints and other comments:

The first time I started the hand controller, the auto-align feature (you perform this once each session in order to use the goto feature) messed up the prompts on the LCD panel. I simply "rebooted" (unplug power and plug it back in) and it worked every time after that.

The controller has an option to save the longitude and latitude of your viewing location and thus you do not need to re-enter it when performing an auto-alignment, something you do each time you power up the scope. This doesn't work correctly. It records my supplied long-lat, but if I use it the next time I start up the scope and perform the auto-align, it is not using the location correctly. I haven't determined exactly what it is doing, but it is pointing more than a hundred degrees away from the location of the alignment stars it is seeking. This might be limited to my location in Okinawa, Japan, but I have seen mention of this at a couple of web sites. The fix is to enter long-lat manually each time you align. Not too bad, adds less than a minute to the alignment process. {It now seems apparent that the NexStar 60/80/114/4 GT controller does not store the long-lat correctly in the Eastern Hemisphere.  If you are in North or South America and the extreme western part of Europe, you should have no problems. Update - this bug was fixed with the release of the new GT hand control in Dec 2001.}

Like many scopes mounted alt-azimuth on a tripod, there are times when you cannot easily view things near the zenith (directly overhead) because the star diagonal (or bottom of a reflector) cannot clear one of the legs of the tripod. With a manual scope you might be able to reposition the tripod or come around from another direction, but with goto, you cannot move the tripod without doing a realignment. And also, you must keep an eye on things when the goto feature is moving to an object. The scope will be more than happy to try and move the star diagonal right through a tripod leg. Naturally it will be unsuccessful, but it will try anyway. To stop a goto movement, simply press one of the direction buttons on the controller. NOTE: this is not always successful if moving to objects on the Tour list. You may need to pull the plug!

At one point, my scope would no longer move in the altitude (up-down) axis, either with goto or with the direction buttons. I tried restarting (pull the plug) and it still wouldn't work. As visions of boxing it up to ship to Celestron were playing through my mind, I gently moved the scope by hand (pushed the optical tube) and things went back to normal. Also, another time, it totally lost it's alignment and I had to restart and realign the scope. {The scope continued to regularly stop moving in the altitude axis.  Celestron was more than happy to repair it by replacing the altitude motor assembly.}

While the eyepieces supplied are OK, good eyepieces definitely improve the image notably. For example, the 25mm SMA eyepiece supplied shows easily noticeable elongation of stars around the outside of the field of view.

Using the computer controller to manually point the scope activates a feature called backlash compensation. This is used to re-center the gear wheels between teeth to make moving in the opposite direction more responsive. The controller lets you adjust the amount of compensation and setting it to 40 seems to be about right. Unfortunately it doesn't retain the setting between sessions (contrary to what the updated manual says), and the default setting is way over compensated on my scope. {Update - the new version hand control now stores the backlash settings.}

The direction buttons for manual control take some getting use to. The up and down buttons move “opposite” of the direction indicated by the motion for the left and right buttons. There may be a configuration setting for this as well but I haven't been able to find it. Again it just takes some getting use to. {No configuration setting is available - the direction buttons behave as expected in the view of the erect image finder, and flipped upside down in the upside down view afforded by the refractor.  Update - this was fixed in the new version hand control.}

The default power, 8 AA batteries, is reported to only last for about 3-4 hours. That will be rather expensive, so plan on buying an AC adapter (<$20) and if practical for your intended use, a car cigarette lighter adapter (<$15). I have also made an adapter that will let me use D batteries and 6V lantern batteries, which are much more economical. The parts were about $4 - just some wire, spring-loaded clips and the power connector to the scope. You may also consider purchasing a rechargeable source. There are some very nice ones well suited for this purpose ranging from about $30 to about $70.  These will still require the cigarette lighter adapter. The connector to use for any power source is the 5.5mm outside diameter and 2.1mm inside diameter connector sold by Radio Shack as part no. 274-1569A (Thanks to Les for this info), with + on the inside. The more popular size for this connector (found on most AC adapters) is 2.5mm inside diameter and it will not maintain contact. Read more about power sources here.

All in all, I love this scope.  A year ago I would not have imagined I would be able to buy a telescope with these features for just $400. {$350 now!}  If this isn't the perfect beginner scope (or second scope for someone with a larger scope and a moderate budget), then the 80HC (motorized, but without the computerized hand control) certainly is.

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Michael Swanson
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