Figure 10
Figure 11
Figure 8
Try turning the main mirror collimation screws – when you are turning the right screw in the right direction, you will notice that the
distracting “tail” is getting shorter (figure 10):
Remember to recenter the star after you have turned a screw. When the telescope is perfectly aligned, you will see the picture of
figure 11 (when the air is perfect). During the use of your telescope you will get a feeling for this – it does not make sense to spend
a lot of time on collimation when the air is moving too much.
Important:
Outside the optical axis (the middle of the field of view) all stars will be distorted and show tails directed tot he edge
of the field of view. If you are using cheap eyepieces those star images will be even more distorted because the off-axis aberrations
of the telescope and the eyepiece will add up. For this reason it is essential to recenter Polaris after every turn of a collimation
screw because the turning of the screw will also shift the star from its centered position. As mentioned before it may not be possible
to get a sharp star image during periods of turbulent air. In this case try to achieve a symmetric image during collimation and abort
the process, if you don’t see any more improvement. During those nights it is not recommended to use high magnification. Try to
enjoy low magnification objects like nebulae, clusters and galaxies in those nights instead of fretting over the bad conditions.
Summary of Contents for Truss Tube Dobsonian Series
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