1. Remove the eyepiece from the focuser and look through it. The secondary should appear round. If the secondary does not
appear round, tilt it with the three collimation screws that are located on the back side of the secondary holder.
2. Next check the reflection of the middle point of the main mirror in the secondary. If the reflection of the mark on the main mirror
is not in the center of the secondary, center it by using the three collimation screws like you did in step 1.
Figure 7
Adjusting the main mirror
Once the secondary appears round and the mark on the main mirror is centered, check the collimation of the main mirror. If the
reflection of your eye and the reflection of the secondary on the main mirror are not concentric, insert the collimating tool into one
of the collimation screws that are located on top and on each side of the main mirror. When you turn the collimation tool you will
notice that the hexagonal head of the tool will lock into the hexagonal head of the collimation screw. Now you can adjust the main
mirror by turning the collimation tool (see figure 8). Adjust the screws until the eye and the reflection of the secondary are centered
in the main mirror. Practice this until you get a feel of what a turn at one of the collimation screws is doing.
Fine Collimation
During fine collimation, locate Polaris and view it with high magnification.
Note: Please take care that the telescope has time to
adapt to the ambient temperature before starting collimation – this will need up to 30 minutes (otherwise you will not get a good
star image). You may use the fans to speed up this process.
If the telescope is collimated well, you will see a system of dim rings of light surrounding a central bright spot — the so-called airy
disc. You will also notice a dim cross of light coming from this airy disc. This is the diffraction that is caused by the secondary
spider vanes. We have left this cross out off the next figures for clarity. What we want to see is shown in figure 11 – a central airy
disc that is surrounded by concentric rings. However, it is much more likely that the picture will be different – more like figure 9. It
is essential that you always center the star because outside of the optical axis all stars do show some distorted images. Note:
You will get those images only during moments of perfect steady air because air turbulence will distort this image. However the
collimation goal remains the same – getting a concentric star image. So let us assume you have good seeing and your eyepiece
shows you something like figure 9:
Содержание Truss Tube Dobsonian Series
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