Celestron NexStar 102 GT 102x1000 AZ, Instruction Manual

COMPUTERIZED TELESCOPE

SCOPE SETUP FEATURES

Setup Time-Site –

 Allows the user to customize the NexStar display by changing time and location 

parameters (such as time zone and daylight savings).

Anti-backlash –

 All mechanical gears have a certain amount of backlash or play between the gears. 

This play is evident by how long it takes for a star to move in the eyepiece when the Hand Control ar-
row buttons are pressed (especially when changing directions). The NexStar’s anti-backlash features 
allows the user to compensate for backlash by inputting a value which quickly rewinds the motors just 
enough to eliminate the play between gears. The amount of compensation needed depends on the 
slewing rate selected; the slower the slewing rate the longer it will take for the star to appear to move 
in the eyepiece. Therefore, the anti-backlash compensation will have to be set higher. You will need to 
experiment with different values; a value between 20 and 50 is usually best for most visual observing, 
whereas a higher value may be necessary for photographic guiding. Positive backlash compensation 
is applied when the mount changes its direction of movement from backwards to forwards. Similarly, 
negative backlash compensation is applied when the mount changes its direction of movement from 
forwards to backwards. When tracking is enabled, the mount will be moving in one or both axes in 
either the positive or negative direction, so backlash compensation will always be applied when a 
direction button is released and the direction moved is opposite to the direction of travel.

To set the anti-backlash value, scroll down to the anti-backlash option and press 

ENTER

. Enter a 

value from 0-100 for both azimuth and altitude directions and press 

ENTER

 after each one to save 

these values. NexStar will remember these values and use them each time it is turned on until they 
are changed.

Slew Limits – 

Sets the limits in altitude that the telescope can slew without displaying a warning 

message. The slew limits prevent the telescope tube from slewing to an object below the horizon or 
slewing to an object that is high enough that the tube might hit one of the tripod legs. However, the 
slew limits can be customized depending on your needs. For example, if you would like to slew to an 
object that is close to the zenith and are certain that the tube will not hit the tripod legs, you can set 
the slew limits to 90º in altitude. This will allow the telescope to slew to any object above the horizon 
without warning.

Filter Limits –

 When an alignment is complete, the NexStar automatically knows which celestial 

objects are above the horizon. As a result, when scrolling through the database lists (or selecting the 
Tour function), the NexStar Hand Control will display only those objects that are known to be above 
the horizon when you are observing. You can customize the object database by selecting altitude 
limits that are appropriate for your location and situation. For example, if you are observing from a 
mountainous location where the horizon is partially obscured, you can set your minimum altitude limit 
to read +20º. This will make sure that the Hand Control only displays objects that are higher in altitude 
than 20º. 

Observing Tip//

 If you want to explore the entire object database, set the maximum altitude limit to 

90º and the minimum limit to –90º. This will display every object in the database lists regardless of 
whether it is visible in the sky from your location or not.  

Direction Buttons –

The direction a star moves in the eyepiece varies depending on the accesso-

ries being used. This can create confusion when guiding on a star using an off-axis guider versus a 
straight through guide scope. To compensate for this, the direction of the drive control keys can be 
changed. To reverse the button logic of the Hand Control, press the 

MENU

 button and select Direc-

tion buttons from the Utilities menu. Use the 

UP/DOWN

 arrow keys to select either the Azimuth but-

tons (left and right) or Altitude buttons (up and down) and press 

ENTER

. Pressing 

ENTER

 again will 

reverse the direction of the Hand Control buttons from their current state. Direction buttons will only 
change the eyepiece rates (rate 1-6) and will not affect the slew rates (rate 7-9). 

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