Monday, 12 October 2009

Minor scope mods

My new collimation springs and secondary screws arrived from Bob's Knobs last week and today (I have no work at present, so I have plenty of time on my hands) I decided to make the necessary modifications. The secondary collimation screw change was as easy as I expected, quick swap, like for like, the work of less than a couple of minutes.

The primary collimation spring change was also a piece of cake, something I did not expect. I had read of people doing GSO/Lightbridge collimation screw/spring modifications by removing the mirror cell, taking the mirror out of the cell and then replacing the springs, a prospect which, frankly, filled me with horror as I did not want to be fiddling with the cell and mirror and, quite apart from the prospect of the risk of damage (and when you are dyspraxic like me breaking something is a real possibility!), I really did not want to bother with fiddly stuff, I just can't be arsed with fiddly stuff. However, you DON'T need to take the cell out. You can easily change the springs, one at a time, with the mirror and cell in situ. Obviously this applies to GSO/Meade Lightbridge scopes, it might well be different for other makes.

What you do need to do is slacken off the collimation screws (black) and the collimation locking screws (white) and then remove each collimation screw - one at a time. This leaves the spring to be slid sideways out of place and the replacement spring to be put in. Once the new spring's in place, all you do is screw the collimation bolt back in; repeat the process for the other collimation springs, tighten everything back up and there you are, job done. Just make sure it goes back in as it came out (the bolt has a kind of washer/sleeve thing which fits inside the screw hole on the circular black frame at the rear of the cell) and you won't go wrong. Bob's Knobs provide a leaflet with the springs explaining the process and it is advisable to follow their directions.

This pic shows the rear of the scope with the collimation screws (black) and the locking screws (white). The pale round area inside is the back of the primary mirror itself. Click on pic for larger version.

Re. the collimation springs themselves, the new ones from Bob's Knobs are far heftier and more robust than the, quite frankly, flimsy things which came with the scope. How the manufacturers expect their scopes to remain in alignment when the springs are so thin is anyone's guess. I am hoping - expecting, actually - collimation to be easier and less frequent with the new springs. I wish I had taken comparison shots between the two springs to show the big difference between them.

Now to recollimate the scope and hope this all works...


2110: How's this for frustrating? It has been a beautiful autumn day, without a cloud in the sky. It is still clear in that you can see stars, but as murky as hell with a wee bit of cloud about. Jupiter has a bloody great halo round it... I think the scope mods won't get tested tonight. I am not lugging the 12 inch out for anything less than a proper observing session.