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New GT Hand Control

17 December 2001
Updated 21 January 2002 - see items in braces { }

In December 2001, Celestron started shipping a new version of the GT (computerized, goto) hand control for the NexStar 60/76/80/102/114/4/130 GT telescopes.  It is a much improved product.  In February 2005, Celestron announced a user-upgradeable hand control that is compatible with the GT and Tasco scopes - this hand control will be available for purchase through Celestron dealers late in 2005 - read this for more information.

Many of the improvements are 'trickledown' from the NexStar GPS line; thus the littlest NexStars benefit from some of the latest improvements designed for Celestron's top-of-the-line technological wonders.

Let me start off the review by stating that it has always been my opinion that the NexStar telescopes (all models) have been a clear step above any other computerized telescope (or self-contained computer add-on) since their introduction. The direct access to common catalogs, such as Messier and NGC, is far superior to anything else I've seen. This should not to be considered too lightly since ease of use directly affects how much time you spend playing with the hand control as compared to how much time you spend looking through the eyepiece. This new hand control makes many improvements in usability, some subtle, some quite dramatic.

First, here is the list of well-known flaws in the original GT hand control and the status in this new version:

  • No official RS-232 support due to several problems such as hand control lockup and inability to report coordinates above 12 hours Right Ascension or negative Declination - the new hand control includes the NexStar GPS RS-232 protocol, exhibits no lockup problems and accurately reports the current coordinates of the telescope. Use of the GPS control protocol means that any PC/Mac/Palm/Pocket PC program that works with the NexStar GPS scopes, works with this new hand control.
  • Won't save observation locations in the Eastern Hemisphere - fixed.
  • Won't save backlash settings - fixed.
  • Cordwrap feature not functional - still not included, but at least it has been removed from the menus to prevent confusion about it's lack of operation if selected.
  • Occasional lockups and runaway slews - fixed. I have not yet experienced a lockup or runaway.
  • Very touchy keypad that often leads to double key entries - fixed.
  • Light Control feature not functional - fixed.
  • Tracking Rate defaults to Solar - fixed. The default is now Sidereal. King rate has been removed but this tracking rate is not useful except with extremely precise tracking mounts used on an EQ wedge.
  • Error in the coordinates of M2, M10 and M110 - fixed.

Now, on to the review in general.

The first thing you will probably note is that you now select the model directly rather than using 'Custom' and entering encoder values. Moreover, besides setting the encoder values, model select also modifies the direction of movement for the up and down arrow buttons. On the 60, 80 and 4 settings, it reverses the direction of the up/down arrows at rates of 6 and below (direction remains the same for the 114 setting). This allows the up/down and left/right buttons to move in the same manner when looking through the Star Pointer (rates 7-9) and eyepiece (rates 1-6). The up/down buttons must be inverted on the 60/80/4 due to the inverted orientation imparted by the diagonal mirror. This is a great improvement that makes manual slewing much more natural.

A related feature that I will mention here is an added Utility item which allows you to temporarily change the direction of the up/down or left/right arrow buttons. This allows better control when using the scope with different combinations of visual and photographic accessories. For example, perhaps you have connected a small video camera to your NexStar 4's straight-through port, then connected this to a video monitor to give a group of spectators a view of the moon. Changing the direction of the up/down buttons would allow more natural control as you are now using the scope without the diagonal.

The next thing you will likely notice is that there are now two new alignment methods: Two-Star and Quick. While many will generally choose to use the original Auto-Align method - the telescope points out the required two alignment stars automatically - those who subscribe to the tips given in the NexStar Alignment Guide will be glad for the addition of Two-Star Alignment. This allows you to optimize the selection of the two alignment stars to ensure the most accurate goto performance possible.

Also, it won't take long to notice that when you are keying in numeric entries, the Undo button now works as a backspace key, rather than forcing you back to the beginning of a series of steps.

Quick-Align allows you to simply point North and level and with your supplied observing location and date/time, NexStar has a rough alignment to allow reasonable tracking performance. This is useful in two situations where goto will not be important. First, you don't want to take the 2 or 3 minutes for an Auto-Align, you will be manually pointing at easy-to-find objects (planets for example) and you want the scope to track the objects automatically. Previously we would simply by-pass alignment and point at the object, but then we would be forced to manually track the object as the Earth rotates.

Second, you want to observe a celestial object during the day (the Sun or Moon for example) and you want the scope to track the object automatically. In this case you cannot use the other two methods to any advantage as you cannot see the two alignment stars. Previously we would have performed an Auto-Align by simply accepting the two stars as NexStar pointed them out - Quick-Align has the same effect but we aren't forced to wait for the slew to the two alignment stars.

It should be noted that to use Quick-Align effectively it is important to level the tripod and the optical tube assembly (OTA). With the other alignment modes, it is sufficient to simply setup the tripod and start the alignment with the OTA orthogonal (perpendicular) to the altitude and azimuth axes - refer to the alignment guide mentioned above for more details.

The hand control now also stores your previous session's location and date/time settings. For example, if performing an Auto-Align, when you are prompted for location, the state/city or longitude/latitude you last used will already be displayed. You simply press Enter to accept. Same for date, time and time zone. This greatly speeds up the alignment process, particularly if you need to realign during the night due to the OTA making contact with the tripod or a mistakenly pulled power cord. The hand control does not keep time when it is powered off though, so when you go out the next night you will need to adjust the date and time. (The time zone will still be fine, unless you are on a roving vacation tour...) Also, the time zones now match international conventions and for areas outside of the United States they are simply your offset from UTC.

The Third Star Align feature has been renamed Re-Alignment and is now very easy to use. It now allows you to use any of the objects in the database as an alignment point. Simply slew to the object, Undo out of the menu and press the Align key. After that you follow the version simple instructions presented on the LCD to complete the operation.

Another improvement I noticed right off was in the speed of slewing at the different rates. With the original GT hand control, there didn't really seem to be 9 different slewing rates. Several of the rates seemed to be identical. With the new control, all of the rates are noticeably different. Also, with the old control, rate 9 was intermittently slower in Altitude movement than it was in Azimuth movement and rate 9 was not really the fastest slewing rate available; these flaws have been corrected.

The new control now does a much better job showing you what is going on. For example:

  • When you are manually slewing, the current slew rate is displayed in the upper right-hand corner of the LCD.
  • Menu items that already have settings will display them rather then leaving you guessing - i.e. - when you select the anti-backlash items from the menu, the current settings are displayed.
  • When you are in a menu that has items that you can scroll with the Up and Down buttons, a little two-headed arrow is displayed in the LCD.
  • When a slew is in progress, a little spinning stick appears in the upper right-hand corner of the LCD.

The Info presented on objects has also been enhanced. Most noticeably, the description of the object (the Info) is presented first so that you don't have to scroll down past RA, Dec, Size, Constellation, etc., before you get to read the description of the object. Also, the descriptions have been edited and provide a little better information, most noticeably for the double stars in the database.

As noted towards the beginning, the anti-backlash settings are now stored between uses of the scope - a huge improvement in usability. Improvements have also apparently been made in the smoothness with which the backlash compensation is applied to the motors as I find manual control is much improved. Note that the range of the anti-backlash settings is 0-99 now, where as the old control allowed 3 digit entries. With the old control, my settings were above 100, with this new control both axes operate best at about 85.

The goto slew has also been reworked - the telescope gets to its new coordinates a bit faster. This is most noticeable when you perform a second goto to the same object. With the new control, the familiar left-and-dip movement does not move as far from the object before returning and the final slow-rate movements are shorter.

In addition to the Two-Star and Quick-Align inherited from it's larger siblings, the new control also includes two other GPS-inspired features: Slew and Filter Limits. Slew limits allow you to set a maximum and minimum altitude (angle from the horizon) to prevent a goto from pointing below the horizon or pointing upward and possibly causing the OTA to make contact with the tripod. If you attempt a goto to an object outside of the Slew Limits, a warning will be displayed allowing you to abort the slew or proceed. If you proceed, be sure to watch the OTA and if it appears it will make contact with the tripod, simply press one of the arrow buttons to abort the slew. If the OTA makes contact with the tripod, you will most likely be forced to perform the alignment again.

Filter Limits will restrict the items displayed by the hand control to just those that are within the altitude settings of the Filter Limits. For example, if the Filter Limits are set to a minimum of 20 degrees and a maximum of 90 degrees and Mars is currently located at 15 degrees above the horizon, you will not be presented with Mars as a selection when you scroll through the Planet list. The various lists in the menu as well as the Tour feature are affected by the Filter Limits.

{ 21 Jan 02 - It should be noted that the Slew and Filter Limits are affected by an unleveled tripod.  If you experience times when they seem to be off, you might want to level the tripod and perform the alignment again. }

The Messier, Caldwell, NGC and Star catalogs have undergone some changes. It is now required to enter 3 digits for Messier and Caldwell objects. For example, to goto M42, you press the M button, then key in 042. The NGC catalog requires 4 digits and the Star catalog requires 6. A consolation to entering 6 digits for a star is that the star catalog now uses SAO numbers - no more cross-referencing NexStar specific star numbers. 

{ 21 Jan 02 - There is one 'gotcha' in the use of the NGC list.  If you enter an NGC object not in the NexStar database, the scope will slew to the next NGC item on the list.  Thus, you should always read the 'Info' on an object to be sure you got the object you entered. }

The new control now also provides menu items to view and set your current location (site) and time. The time option is useful if goto is missing the planets - you might find that you mistakenly entered the date/time during alignment.

There is also a handy menu item to show you the current Sidereal Time - the current right ascension at your meridian (directly overhead).

As you can hopefully tell from this review, I'm very impressed with the improvements in this new version of the GT hand control. It makes great improvements in mechanical operation, adds many features to make alignment easier and faster and includes many features to make everyday ("every night") use much easier. Celestron has taken the most friendly computerized telescope control on the market and made it even friendlier.

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Michael Swanson
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