Celestron Ultima 8 Instruction Manual page 42

ALT GEAR
Altitude Gear Ratio: This works the same as AZM GEAR.
AZM BACK - Azimuth Backlash Compensation
There is an enormous gear reduction between the tracking motor and the telescope. Highly accurate tracking is best
obtained by running the tracking motor at a relatively high speed. (If an electric motor is run too slowly, it runs at an
inconsistent speed, and can burn the brushes.) The high speed of the tracking motor requires a very large gear ratio, on
the order of 600,000 to 1. When the tracking motor changes direction, there is a slight delay before movement is visible
in the field of view due to the high gear ratio. This phenomenon is referred to as backlash. The Ultima 2000
automatically compensates for backlash, and this compensation is settable. The displayed number is the specified width of
the backlash deadzone (the time where the telescope is motionless) in eighths of a tracking motor revolution.
The backlash compensation is preset at the factory to zero. When the telescope is equatorially mounted (on a wedge), the
azimuth backlash does not matter. So the AZM BACK value can remain set at zero. The azimuth compensation is only
needed for Alt-Az tracking and for most people, it still won't be needed. To change the setting see the next section, "ALT
BACK".
ALT BACK
For astrophotography or CCD imaging, the altitude backlash compensation is critical. The azimuth compensation is only
needed for Alt-Az tracking.
It is easiest to set the backlash compensation in the daytime on a distant object with a high power eyepiece. For step-by-
step instructions on how to determine the backlash compensation, see the chapter called Procedures. Here is how to set
the altitude backlash compensation value on the hand control.
ACTION
Go to the SETUP menu
Press ENTER
Set SPEED to 2 X SDRL
Press DOWN 7 times
and note the setting
Press ENTER
Press ENTER twice
Press UP
Press ENTER
Press DOWN 4 times
Press ENTER 2 times
Press MENU
For more information see the section "Determining the Altitude Backlash Compensation" in Chapter 8.
42
NOTES
Example: Set the ALT BACK to 400 from 340
Enter into the SETUP menu and change the SPEED setting.
Scroll down to the ALT BACK mode.
The cursor is at the first digit of the azimuth backlash value.
Place the cursor at the leading number.
Change the 3 to a 4.
Move the cursor to the next digit to the right.
Set the 4 to 0.
The compensation is set to 400.
Return to the main menu.
DISPLAY
MENU
SETUP
SPEED
2 X SDRL
ALT BACK
00340
ALT BACK
00340
ALT BACK
00340
ALT BACK
00440
ALT BACK
00440
ALT BACK
00400
ALT BACK
00400
MENU
SETUP