16" Lightbridge Problem

[Bart]

Hello All

Has a disaster of a night recently. Went to collimate the 16" Meade LB and where normally i only need a tweak, the dot from the laser was a goo 2 inches from the centre cirle ring on the mirror. I foolishly tried much adjustment of the secondary. Fine. But the return laser wasnt coming back anywhere near the target on the laser. Something was up.

Now for some time I have felt the collimation bolts a bit stiff at the back/botom of the OTA. When I looked more closely, I wasn't getting much movement of the screws within the mirror cell. In other words, I couldn't move the mirror much. It was almost the same on an 3, which made me think i was imagining it. After much messing, I gave up and went for the 10", telling myself I need to get stuck in when its bright and more organised.

I am worried though. I wonder have the bolts rusted or bent meaning I'm not getting much travel. It wouldn't worry me much with the 10" but manhandling the 16" mirror will be terrible.

Before I dissasemble the whole thing, I wondered if someone has had a similar experience with the LB. It might be that there is very little movement of the rear cell in any case.

Out of curiosity, I'll take a few pics if anyones interested.

Barry

[mdstuart]

Odd. it should move as you rotate each of the bolts. I have those fancy ones which makes it easy.

Put your finger inside the cell from the bottom to see if the mirror holder is approximately the same distance from the base on each side.

You can remove the tube of the lower part of the scope which would then let you see better what is going on.

Mark

[russ.will]

I'd forget it - we all have brain farts - and start again in daylight. If you can then see an problem - stripped threads, etc - then you have an issue.

Russell

[clarkpm4242]

As Russ said, daylight re-appraisal of the situation is so much easier.

Don't be afraid of taking the mirror out of the cell, if necessary.  It is fine as long as you think it through beforehand.

Good luck.

Paul

[astronymonkey]

I find the bolts on my LB cell to be stiff too and often found that over time if adjusted them out too much so they run out of travel. In the daytime see if you can wind them all the way back and start again.

Hope you get it sorted .

Cheers

[Bart]

Sorry all, forgot about this post. I have looked in daylight and seems the cell is slightly off centre from the bolts. Can't see why. Will need to take the scope down (I leave it up all the time and just wheel it out). Its probably not as bad as I first thought, at night, after a couple of beers, cheesed off etc

I'm hoping to tackle this soon. However, have felt recently the astro bug is fading for some reason, not helped by approaching shorter nights and earlier mornings.

Will post again here when I take it on. Sorry for not replying previously.

Barry

[albedo0.39]

Some good advice here.

Relax. Take the scope apart, in the light and just get to know how it all works - there is really not too much to go wrong. For the secondary alignment, I recommend the following

Look at where the 3 screws normally impact the silver disc of the secondary holder

Remove the secondary assembly (careful does it)

Take a large drill and SLOWLY add a countersink to the 3 contact points on the disc

Now, take the screws you normally adjust the secondary with and grind a point to each one... Not too sharp , but pointed. You can do this easily with a drill and some sandpaper.

Reassemble the secondary so that now, when you adjust, the 3 screws sit nicely in the countersink sections and do not walk across the surface of the disc. This transforms the ease and accuracy of collimation.

Rgds