will do the job. What is important is that this flat surface can be set
perpendicular
to the optical
axis, with a reasonable tolerance. Just check with a meter tape that different points of the frontal
ring of the telescope have the same distance from the flat surface, within a centimeter or so.
This is enough.
Collimation from scratch (or CFS, for short) is a 5 steps procedure:
1. Mechanical centering of the secondary mirror (Section 6.1).
2. Check the distance between mirrors (Section 6.2)
3. Secondary mirror tip-tilt regulation (Section 6.3).
4. Primary mirror tip-tilt regulation (Section 6.4 and 6.5)
5. Focuser (or camera) tip-tilt, if needed (Section 6.6).
Steps 1 and 2 are usually only just quick checks. It is very unlikely you will need to do any change
during those steps. Also step 5 usually requires no action from the user (it is more probable you
need to do something in RiFAST and RiLA telescopes, because of the lower f/ratio). The “core” of
the collimation process is only steps 3 & 4.
Steps 1 and 3 can be performed indoor. All other steps requires at least an artificial star, or (much
better!) a real star during night. The whole process will require two to three hours. The good news
is that after this procedure you will not touch the telescope collimation again for a long time – even
years, if you do not transport the telescope frequently. After a “normal” shipment, usually you have
to perform only step 4, as described in Chapter 5.
We strongly suggest to have someone who can help you, at least for step 3, otherwise you will
have to move many times from the back of the telescope to the front, where the collimation screws
of the secondary mirror are located.
Let's see each step in detail.
6.1) Mechanical centering of the secondary mirror.
This step is usually just a check. Each telescope is accurately set during manufacturing! Using the
vernier caliper, check the secondary mirror support is
mechanically centered
in the front ring of the
telescope; i.e. all four “spokes” must have the same length, within half a millimeter (0.02”). If it is
not, adjust the screws you have at the end of each "spoke" of the secondary mirror spider.
Tightening
a screw, you move the mirror assembly
toward
that screw. Before to tight a screw
loose the opposite screw of the same amount to permit the movement. Each turn of those screws
produces 1 mm shift of the secondary mirror assembly.
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