17
PART III : ALIGNMENT
Eyepiece
It is very important to put the alignment stars at the center (or the same spot) of the FOV of the
telescope’s eyepiece during the alignment process. Thus,
• It is recommended that a reticle eyepiece is used for alignment.
• If a reticle eyepiece is not available, try using an eyepiece with a shorter focal length to
yield a smaller FOV. Users can defocus the telescope to obtain a large star disk in the
FOV. Centering the star disk in the FOV is easier than centering a sharp star.
• During the alignment process, avoid changing or rotating the eyepiece and the diagonal
mirror.
Mechanical Backlash
All mounts have some mechanical backlash on both axes. To avoid introducing alignment
error from backlash, users should keep the following rules in mind:
• When centering an alignment star in the eyepiece, the operation should always end by
using the
UP
and
RIGHT
direction keys to move the axes.
• If there is an overshoot when centering alignment star in eyepiece with
UP
or
RIGHT
keys,
use the
LEFT
or
DOWN
keys to pull the star back to the edge of the FOV and then use the
RIGHT
or
UP
keys to center the star again.
Alignment Stars Selection
The choice of alignment stars might also impact the alignment accuracy. Please
refer to Sec-
tion 3.8
on the rules of choosing alignment stars for various mounts and alignment methods.
3.7 Tips for Improving Alignment Accuracy
Rules for choosing an alignment star:
• Choose an alignment star with smaller declination. It will help the user to obtain higher
resolution in R.A. movement in the telescope’s eyepiece.
• If there is cone error in the telescope-mount setup or if users are not sure about it, it is
recommended to choose an alignment star that is close to the object(s) to be observed.
Advantage: Quickest alignment.
Preconditions:
• An accurate polar alignment for the mount.
• Small cone error in the telescope-mount setup.
If the cone error is large, there will be noticeable offset in the R.A. when the SynScan
hand control locates an object that is:
1.
Equatorial Mount with 1-Star Alignment:
3.8 Comparison of Alignment Methods
»
On the other side of the meridian from the alignment star
»
Deviated significantly with the alignment star in declination.
