Urgent Lightbridge collimation help please!!

[Helen]

Help!! Anyone with knowledge of Lightbridge colllimation please..

A friend and I are in the middle of replacing the standard collimation screws on an 8" Lightbridge dob with Bob's knobs. Instructions say replace one at a time. We've done two with no problem, but on the third it appears we've lost something (the spring?) inside the mirror housing and so the screw has nothing to grip on. We're afraid to do any more for fear of doing some damage (took us a while to pluck up courage to get this far, but Gordon assured me it was easy!!). We assume the only answer is to remove the mirror cell. There are 6 screws around the outside of the bottom of the tube which we assume will release the mirror cell. Can anyone confirm this is what we should do please?

thanks

worried pair of Cardiff!!

[GordonCopestake]

If you've done two you are in no danger of anything terrible happening. Just fish the lost spring out from the mirror cell and try again As you've found out the springs can be a bit fiddly and you have to compress them to fit them in. There are 6 screws, from memory the smaller ones are the lock screws and the larger ones are the actual collimation screws (which you should be replacing)

If you need more info just shout

[Helen]

Thanks Gordon, was hoping you'd be online! We haven't taken the mirror cell off the bottom, we were just taking the screws out from the bottom. Should we take the mirror cell off now by undoing the side of the tube screws? as I can't see another way of getting at the springs!

thanks

Helen

[GordonCopestake]

Noooooo dont take the mirror cell off!

Did you buy the new stiffer springs? If so just unscrew the old collimation bolt completely and flick the old spring out (you can either keep these as executive toys or throw them away) to put the new springs in you have to compress them and slide them in from the side (takes some effort!) then screw the new collimation screw in. I found that it was easier to half screw the collimation screw in and then slide the spring in after.

If you've lost a spring inside the mirror cell (and assuming it isn't sitting on the mirror!) you can just lift the mirror cell up and waggle it about a bit till the spring falls out.

[Helen]

OK! got the message!!!! Will get the tweezers out..

feeling a little more confident now..

wait for further instalments

[GordonCopestake]

Good luck!

[Helen]

Decided to stop now (getting a bit tired and got to prepare for an early start tomorrow). Will give it another go with a fresh head (and a proper torch).

thanks for the advice

Will let you know when we sort it out

Helen and Jean

[GordonCopestake]

No problem, feel free to PM me if you need more detailed advice. It's always better to do these things in daylight where you can see properly. Doing it in the dark (ow err missus) is a receipe for disaster. The last thing you want is a spring bouncing over your mirror!

[Helen]

OK, Gordon, you can stop crossing your fingers for us now ... we've done it (we hope!!).

The first two collimation screws were switched with no bother at all. The third had it in for us!! First we lost the spring, then the bolt wouldn't screw in. Decided to leave and come back fresh and so to minimise the risk of the loose spring getting anywhere it shouldn't have we left the scope parked in the middle of the living room!! Went back today in the daylight, and while it was easier to see what was where, and with the advice from Gordon on wiggling things to get at the springs, and to locate the loose spring, I must say that the one screw still didn't really want to play ball (don't know whether the thread has a problem or what??).

Anyway, the good news is that after much juggling and frustration we got all three springs and all 6 screws successfully replaced and have done a rough collimation. And thankfully the effort was worth it as collimation is SO MUCH easier now! Think a collimation aid is now called for though to maximise the views.

Advice on a collimation aid anyone??

Thanks as always

Helen

[GordonCopestake]

great news Helen, glad you got it sorted in the end. I used a laser colimator with my lightbridge to good effect, however I understand that a cheshire eyepiece is just as effective.

[Andrew*]

Cheshire's are good. Scopes 'n' Skies still have a really nice astro engineering one in their bargain zone for just £24. Gotta go for that!

Glad you got it sorted finally.

Andrew

[Helen]

Thanks Andrew. We'll have a look at the link.

Helen

[Peto]

there is a cheap way of collminating the truss dob a laser pointer pushed into a piece of polystyrene that is cut to fit the eye piece holder. simply the laser should be in the middle of the primary and secondary mirror and then should reflect back on the middle of the mirrors and into the pointer itself being a cheap skate and not wanting to wait for another order to arrive this worked for my 12" light bridge and got me out into the cold pretty quickly. have fun pete