Langenbrettach, August 14th 2001
Matthias Bopp
Tips, hints and pending problems for Celestron Nexstar 114GT
(original handcontroller before the update):
1.) The optical tube was inserted backwards, but it is easily removed by unloosening the "tube holder" connected
to the arm. Remove and replace tube in the position as seen on your manual. If the tube is inserted correctly and
levelled horizontally you should be able to read the labels "NexStar" both, on the tube and the little round one on
the tube holder correctly. None of them must be upside down !
2.) The arm's tube holder clamp needs to be turned a 180 degrees as well as it was upside down. Again look on
your manual and you will see the brand name label right side up as mine was upside down. Both of these
problems were making the telescope slew down to the ground when Goto planet Jupiter was selected and other
preset space items to anywhere but to the object. In other words: Install the tube with the mirror end farthest
away from the tripod, and the hinge on the OTA clamp should be at the bottom.
3.) Another overlooked problem may be you are trying to enter military time and this model is not programmed
for that, so just enter as usual and enter pm or am plus the other parameters.
4.) The battery connector is not very high quality. I had to replace the connector the second day. I do now use a
chinch connector (RCA connector) because the jack suits exactly in the hole of the NexStar casing where the
original jack had been. So I did not have to alter the Telescope (respectively its casing). In case I have to return it
within the warranty time I can change it back in 5 minutes.
5.) An ac/dc adapter or a rechargeable battery pack is more efficient than batteries. I never used the battery pack
but do use a 12V, 7Ah rechargeable sealed lead-acid battery. This type of battery does not need trickle charging
and do not have a memory effect like NiCd accumulators. So you can just fix the supply voltage of the charger to
13.8V (at room temperature) and you can leave it connected to the battery as long as you like without harming
the accumulator by overcharging. Please do not make the supply wires longer than needed and use thicker wires.
6.) The time zone offset from GMT for Germany is not "01" as indicated in the German manual but "23" because
the time zones are counted the other way around.
7.) Storing and recalling an observers position (lat, long) in the memory does not work on (my) NexStar114GT.
The alignment stars are far off. It is much better to use one of the predefined cities, even if it is more than 100km
away. For instance I am using Frankfurt/Germany (which is approx. 120km away !). The little NexStars have a
bug which prevents stored long/lat from working in the Eastern hemisphere.
8.) The initial alignment is crucial. It is essential to align the whole tripod horizontally and the tube north. See
enclosed explanations from a friend: The issue is that the NexStar needs the lat and long data to find the
alignment stars for you to use. If the base is not level, then the "virtual" location of the scope is -different- than
the location described by the lat and long. To illustrate this, take a globe, put your hand on your location with it
perpendicular to the globe radius at your location. This is the condition the NexStar wants because it is the
location corresponding to the lat and long that you entered. Now, tilt your hand slightly. Move around the
globe until the globe radius vector is perpendicular to your hand (don’t move the globe). This is the "virtual"
location. The NexStar depends on the AZ and ALT axis (RA and DEC if you are polar aligned) being
perpendicular. There is no hard index in the system. So, you must tell it that piece of data each time you power
up. This means you must put the OTA perpendicular to the arm at each power up (NOT level). The encoder
accuracy is 20 arc sec so you should strive for that accuracy.
9.) It should be essential during alignment to take care of the backlash effect. However the backlash values are
not stored in memory as stated in the manual so they have to be programmed every time you power on the
telescope. Please program the 2 values first and then do the auto alignment ! For my telescope the value 25 is
optimum for AZ and the value 10 optimum for ALT. I first bypass auto-alignment and enter the backlash values.
Then I try to track a Star and the telescope will say "No Alignment". Pressing 3 times "Undo" will get me back
to the main menu saying "NexStar ready" and asking for auto-alignment. I centre the object in the viewfinder
also during auto-alignment and 3rd star alignment always by moving from left to right and bottom to top.
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