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Determining the Altitude Backlash Compensation
All drive systems using gears have some amount of backlash. For astrophotography or CCD imaging, this backlash can be
a problem. Backlash appears to the user as the time period for which an object in the eyepiece does not move even though
the motor is driving. At CENTER speed (which is the fastest speed the tracking motors run) it takes about 1-2 seconds to
traverse the backlash dead zone. At 2 X SDRL speed it would take 3-6 seconds to traverse the dead zone. 1-2 seconds is
acceptable, but greater than 3 seconds would ruin an astrophoto. By setting the backlash compensation, the deadzone will
be traversed at CENTER speed. As the edge of the zone is reached, the speed will drop down to the pre-selected guiding
rate; either PHOTO or 2 X SDRL. When the motor is not activated, the compensation sets the drive system in the center
of the dead zone. This cuts the time it takes the motors to traverse the dead zone in half.
For a properly set backlash compensation, it should take about half to one second for the object to move in the eyepiece
when the rate is set at PHOTO or 2 X SDRL. The star should move smoothly without jumping. If the compensation is set
too high, the star will jump suddenly as it overshoots the deadzone, then slow down to the pre-selected guide rate. If it is
set too low, the motor will run at CENTER speed then drop down to the guide rate and it will still take a second or more
for the object to begin to move.
Here is a procedure for testing the backlash compensation.
1.
Set SPEED (under SETUP menu) to 2 X SDRL.
2.
Point the telescope at a stationary distant object (in the day) or at Polaris (in the night) and center it in the eyepiece.
3.
Press the up DIAMOND button while SPEED is set at 2 X SDRL. The motor will run at full speed for a brief
moment then slow down to 2 X SDRL. You know the motor is moving at full speed because you can hear it. When it
slows down to 2 X SDRL, you probably won’t be able to hear the motor. During the time the motor is running at full
speed, you should not see any movement of the object. Only when the motor slows down should the object start to
move.
4.
Release the button and the object will stop moving and the motor will run at full speed again (too center itself in the
dead zone) for a brief moment. The object should not move.
5.
If the object moves while the motor is running at full speed, then the backlash compensation is set too high.
6.
If the object doesn’t start to move after the motors stop running at full speed, then the backlash is set too low.
If the backlash compensation is set incorrectly, lower or raise the value (under the ALT BACK menu under the SETUP
menu) in increments of 50. When you get close to the correct value, use increments of 10. You do not need to get the
value more accurate then increments of 10.
Finding 90º Declination for Polar Alignment
For polar alignment, it is essential to know when the telescope is pointed straight up, relative to the forks. When the
telescope is on a wedge, this is 90º declination. You know when the telescope is pointed straight up, parallel to the forks
by using the POSITION menu. Here is how to do it!
BUTTON or ACTION
NOTES
DISPLAY
Set the telescope to its downstops.
Turn telescope and hand control ON.
Turning the telescope ON at the
altitude downstop, references the
encoder so it knows where it is.
MENU
ALIGN
Press DOWN three times.
Go down to the POSITION menu.
MENU
POSITION
