dg401
I think you are correct. The collimation screws cannot be the cause of "pinched" mirror on those scopes (on either mirror). There is no direct contact or path for stress to propagate in any way between the screws and the mirror. Only the tightening ring with the rubber o-ring can cause stress on the primary mirror if you tighten it too much.
BTW, the o-ring goes on the outer edge of the tightening ring. There is a groove at the base that looks like the o-ring goes there but it does not. Just in case it helps someone who took it apart and did not pay attention (like me
).
EDIT: Oops! sorry for double post.
I had that happen once early on in my fooling around with my RC6. The O-ring sits stretched a bit on a narrow "shelf" and wants to slip off that shelf and sit more loosely around the smaller threaded tube. I just stretch the O-ring onto the "shelf" and run a finger around it a few times until it sticks in place. Then I just screw down the ring until the O-ring starts to engage the mirror and it can no longer fall off the "shelf". This problem will probably catch all of us once and after that we're wise to it.
When it comes to tightening down the O-ring, I'm going to have to reverse my mentality away from worrying about how tightly I have to crank it down to seeing how loosely I can get away with leaving it. Also, after enough fooling around, the O-ring tends to start to fray. I was able to buy 10 replacements from Amazon for 6 bucks. At that price, no sense using an O-ring with any wear showing.
It bears repeating because it's been a huge eye-opener for me: If you don't understand every mechanical aspect of your optical system... all the way down to the individual screws, their tension, and the wind direction, you're starting your collimation with at least one strike against you (OK, maybe that thing about the wind direction was an exaggeration, but you get the point). I still don't know if my scope will give good results with the procedure introduced here (and it will come down to how closely my optical centers coincides with my mechanical centers), but I do know that I can complete the steps of this procedure with precision and certainty. That's important because each of us has probably started into any number of written procedures and somewhere around step 3, we throw up our hands and say, "I give up!". The metrics are either hazy, the descriptions sloppy, or worse, the procedure is full of logical leaps where the author jumps from point A to point C and doesn't bother to say anything about point B along the way because it's wrongly assumed that you understand the unspoken point B as well as the author does (assuming the author understands it at all).
When it comes to the always sticky issue of compression rings throwing 2" to 1.25" adapters out of alignment with the focuser, or throwing a 1.25" Cheshire out of alignment with the 2" to 1.25" adapter, I can't stress enough how much GRAVITY IS YOUR FRIEND. Mount your scope and point the focuser straight upward. Let everything hang loosely and let gravity do it's thing to pull everything downward and square. Similarly, when adjusting for hall of mirrors, point the focuser straight downward. Again, gravity will do it's thing and you can loosen the primary push screws without inducing flex into the mirror cell. At the end, the push screws can be tightened gradually while checking and rechecking the hall of mirrors until they're sufficiently snug.
Bottom line, This procedure will give a fast and precise mechanical collimation. It might also give a precise optical collimation if you're among the fortunate whose mechanical and optical centers coincide. At the very least, you'll be close and maybe need only fine secondary tweaking to spiffy up your star test.
Edited by dg401, 01 August 2021 - 05:51 PM.
