Collimation issues

[Batfink]

Hi,
I was trying to collimate my 8" collapsible Skywatcher, the primary mirror, yesterday and not really getting anywhere, and was becoming confused and frustrated.

Then I realised what was going on, after loosening the locking screws, which I have converted to knobs, thanks to eqcradle, I would then try to loosen the adjusting screws which didn't seem to do anything, it was only when I put my hand on the mirror cell/holder and gave a little push that it jumped forward, so I assumed that the springs are not strong enough to keep the mirror cell under tension, am I right?

I got around the problem by using the locking screws to push the mirror cell as I loosen the adjusting screws, makes sense?

So I am thinking I need stronger springs, has anyone replaced these springs? and if so with what sort and sourced from where?

Thanks
Peter.

[erick]

Hi Peter

Try unscrewing the locking screws all the way back, and then pull the mirror back towards the bottom of the scope with the collimating screws, one at a time, a turn or two each at a time. This should compress the springs to where they are giving stronger support to the mirror and the compression should mean sag is reduced. I know someone who would screw one back until the spring at that screw was fully compressed, then just use the other two to collimate. I don't go that far - I like having three screws with adjustment, but I like to keep the springs under good compression.

This will drop your focus point a bit deeper into the focusser. Hopefully there is sufficient in-travel on all of your eyepeices before you pull the primary mirror back down the tube.

Bunnings have a good range of compression springs. There are some suppliers retro-fitting these scopes - usually sold as a package with better knobs?

[RAJAH235]

Feedback...
I always carefully "bottom out" the adjusters & then "let them off" by about 2 turns....
then start collimating.
That way, you have maximum tension.
But I have a Meade Dob with good heavy springs & no lock screws.
As stated, the springs can be replaced fairly easily.
Regs, L..

[Batfink]

Thanks, I think I'll try for stronger springs, I tried again by "bottoming out" the adjuster screws, then backing off, it only gets so far before the springs loose strength.

[barx1963]

When I added Bobs Knobe to my 12", I also purchased a set of springs. Bintel sell a comeplete set of spring, primary and secondary knobs fopr around $100. Was definitely worth it, collimation is much easier with these. The springs are noticeably stroonger than the ones supplied on GSO scopes.