Scope Setup Features; Setup Time-Site; Slew Limits; Filter Limits - Celestron NEXSTAR 102GT Instruction Manual

COMPUTERIZED TELESCOPE

SCOPE SETUP FEATURES

Setup Time-Site –
Allows the user to customize the NexStardisplay 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 arrow
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 back-
wards. 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 (10) to select either the Azimuth
buttons (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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