Learning collimation can be frustrating but once you got it, you got it.
Read up on the milk jug washer modification which helps make secondary rotation easy (be careful if you do remove the secondary not to touch the mirror or drop it or worst of all drop it on the primary). Also note that if the secondary collimation screws have been over-tightened they can put dents in the secondary stalk that cause the secondary to want to take up only one position (this can be fixed with a steel washer).
Make sure the tube is always horizontal so you don't drop tools in.
Put a piece of paper behind the secondary on the tube wall (I prefer orange, blue, green (not white)).
To collimate with a laser!!!:
1) Put a collimation cap in the focuser tube and look at the secondary. Slightly loosen the secondary collimation screws (only very very slightly) Rotate the secondary such that it is visually a perfect circle and has no visible oval shape when looking through the collimation cap (Make a collimation cap if you don't have one). Don't worry about what the primary looks like in the reflection yet. Gently tighten each of the secondary collimaiton screws so they are just barely tight.
2) Check and set the rotational position again. The rotational position is very important.
3) Take the collimation cap out and look down the focuser draw tube. Make sure that the secondary is not angled up or down in the focuser (the secondary screws being threaded in unequal distances can lead to the secondary being askew up or down). If it is angled, loosen all three secondary alignment screws and make sure that when you tighten them against the stalk (again only slightly tight) the secondary does not go askew and all screws are threaded in about the same amount (thread them in slowly one turn each on each screw at a time). If you found the secondary askew and have corrected it go back to #1.
4) Using the collimation cap make sure the secondary is correctly rotated such that it is round (again the secondary collimaiton screws should still be just barely tightened). Once the secondary is round. Then adjust the secondary collimaiton screws by gently tightening them until the reflected image of the primary mirror clips are equally visible (you can move the focuser in and out so the clips appear at the edge of the secondary mirror).
5) Check to see if the secondary is centred in the focuser tube. See if there is equal amounts of coloured paper visible all around the secondary between the edge of the secondary and focuser tube (if you move the focuser in and out you can make the ring of colour smaller (note: a portion of the ring of colour will be missing at the secondary stalk). Usually if the secondary is out of position, it will need to move toward or away from the primary mirror. If you do need to move the secondary loosen off the secondary collimation screws and tighten or loosen the centre screw to move it up or down the tube (clockwise is away from the primary and counter clockwise is toward the primary). You will need to hold the secondary stalk (without touching the mirror) to prevent it from rotating. I would do only a half turn on the centre screw at a time. If you have to move the secondary position, repeat 4 and 5 (you might have to do this a couple times). Note: this process only has to be done once!!! Once the secondary is centred you should not need to adjust its position again.
Note: if the secondary is too far up or down with respect to the focuser tube, the spider may not be sufficiently centred (ask again here if you need to do this).
6) Put the laser in the focuser and by only adjusting two secondary collimaiton screws get the beam to the centre of the primary mirror (this should not take very much turning of the secondary screws as it should be very close at this point.). During this process the secondary collimation screws should be slightly tightened to "lock" the secondary in place. Do not over-tighten or you will put dents in the secondary stalk.
7) Put the collimation cap back in and check the primary mirror clips are still visible at the edge of the secondary mirror. If the clips are not equally visible, you still have a slight tilt and/or rotational error and may want to go back and do 4 and 5 again. This does not have to be perfect. If 75% of one of the clips is visible and the other two are at 100% your are fine (or 2 are 75% and one is 100%) You may have 4 clips (I have 3). Work on perfection another day.
Just as a side note, a sight tube (long collimation cap) is the best tool for centering and rotating the secondary mirror. It allows you to more easily centre and round the secondary. The laser can then be used to tweak the secondary tilt only very slightly.
8) Once you are confident your secondary is in position, only then try to collimate the primary by using the collimation knobs on the back of the mirror cell to get the laser reflection to the centre mark on the laser collimator target.
If you have a barlow consider doing a laser barlow primary collimation (put the laser in the barlow and centre the shadow of the centre marker of the mirror on the laser collimator target).
9) Do a star test to see if you have it correct. Using the above method my star tests are usually perfect. If the start test is not perfect collimate the primary using the star.
Everyday collimation is just doing steps 6 to 9 above.
Just a note on the laser and secondary collimation. The laser will never show if the secondary is in the correct rotational position. If you try to collimate the secondary with a laser when the mirror is not in the correct rotational position, the laser will not address the rotation error. The first step in collimating the secondary is always to get the rotation correct.
Edited by MellonLake, 02 July 2020 - 08:45 PM.