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By the same token, if you set the autoguider aggressiveness to the maximum, you are likely to
get rapid fire jerky movements of the mount as the guiding software tries to completely correct
every detectable guiding error, no matter how small. This results in overcorrection and,
ironically, poor tracking. Usually, an aggressiveness setting of 8 out of 10 gives the best results.
It allows some degree of tracking error to occur before it makes a correction, but the error is
usually not enough to compromise image quality. Furthermore, the guide star is returned to its
intended position in a series of smaller, but smoother steps. If the mount is guiding in a rapid,
jerky fashion, try a lower aggressiveness setting. If the image is trailed, try a higher
aggressiveness setting. Bear in mind that the X and Y axes may require different aggressiveness
settings to get the best results. A setting of 8 is usually a good starting point.
Figure 19. Autoguider control menu showing places to select exposure, calibration, and
tracking. The windows for the aggressiveness settings for the X and Y axes are shown in
the right lower corner, set to 8 on a scale of 1-10, for both axes.
Other settings include the backlash correction in both X and Y axes (Figure 17). Backlash is the
time delay in correction that occurs while the drive motor is taking up any slack in the gear
system of that drive axis. Backlash is chiefly encountered when the drive motor has to make a
guiding correction by completely reversing directions. That is when any slack in the drive system
gears is most likely to become apparent. However, backlash is usually not a problem at all in the
X (RA) axis. This is because the clock drive is constantly pushing against the RA gear to move it
in the +RA direction at the sidereal rate. Thus, there is rarely any slack in the +RA direction and
any additional correction in the +RA direction will usually be immediate. Corrections in the –RA
do not invoke backlash either because they are not made by reversing the direction of the RA
drive gear. Rather, they are made by simply slowing the drive motor. The correction is provided
by allowing Earth‟s rotation to proceed without being fully compensated by the clock drive, and
so the response is immediate. A subsequent full reversal of correction back to the +RA direction
will also be immediate because although the clock drive gear was previously slowed, it was still
completely engaged with the teeth of the RA motion gear. Thus, it is usually best to leave the
backlash compensation in X (RA) set to zero. If there will be any problem with backlash, it will
likely to be in with the Y (Dec) axis drive, which sits idle between most X corrections. If the last
correction was in +Dec and the drive motor was left engaged against the motion gear teeth in that
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