Chasing advice on removing primary mirror

TheoHE (Theo) · #1 24-01-2010, 09:11 AM

Hi, I finally received my 10" Lightbridge (first proper scope) just before Christmas, but it's not been entirely plain sailing. On first build one truss was not snug and had to re-arrange trusses to get it to fasten without slop. I checked the primary for collimation and it was out, but from what I read this is not uncommon so ajusted it. One of the primary collimation screws was very tight compared to the other two, almost like it was jammed. The views still did not look right and checked the secondary mirror and was surprised that it was also off quite a bit. I thought that this would have been almost spot on. I started to adjust it but it was all over the place (using no-name laser collimator). Then I re-read the intruction manual which stated that the offset was adjusted already by the munfacturer, DOH. Ayway by this time it was time to go back to work overseas. Since being away I have ordered Bobs knobs springs and catseye collimation set (as they say the offset will be set with their tools). They said also that the stick-on paper circles on the primary are also sometimes not centered correctly. I'm assuming I will need to remove the mirror to do this properly, and also apply the catseye triangle. Sorry it took me this long to get to my question - but I'd like to know if it is easy to remove the mirror, how to do it and if there are precautions I should take.? Pitfalls? I am really looking forward to the views through a properly collimated scope. Many thanks in advance. Theo

mental4astro (Alexander) · #2 24-01-2010, 09:23 AM

Hey Theo,

have you tried Unwinding the collimation bolts, rather than winding them up. They could already be up as far as they go. Unwinding works just as well as winding. You may not need to remove the mirror then. I've been guilty of this too.

If it's a collapsible scope, can't you access the mirror with the truss poles removed? Simpler and safer.

TheoHE (Theo) · #3 24-01-2010, 09:51 AM

Thanks for the suggestions Mental, the bucket it quite deep and the illustration I saw for re-centering the paper doughnut shows the mirror removed. I am not confidant that I could place the new triangle accurately by reaching in. I was wondering if anybody was in the same position and had done it. When I exchange the existing collimation screws with Bobs Knobs I will see what my problem was with the stiff collimation screw, Theo

Visionoz (Bill) · #4 24-01-2010, 02:54 PM

Perhaps you've gotten the CatsEye collimator, no?
Anyways go to this site and read the information available

HTH
Cheers
Bill

TheoHE (Theo) · #5 25-01-2010, 09:05 AM

Hi Bill, I've ordered the cateye collimation tools, they are on their way. I will not be back it perth until mid February. Just trying to find things out before I get home. I was hoping someone had removed a Lightbridge mirror themselves and get me on the right track. Meade (USA) does not have an email adress for questions, just phone numbers for technical advice. Cheers Theo

Kevnool (Kev) · #6 25-01-2010, 11:47 AM

There is no comparison about the views through a collimated scope to an uncollimated scope.

If it aint collimated it aint worth looking through.

Collimate your scope before you observe,the dividends will be rewarding.

You will have pinpoints of light.

Cheers Kev.

richardda1st (Richard) · #7 25-01-2010, 04:20 PM

I have never checked to see if the circle is properly centered, must do that the next time I take the mirror out.

The mirror is very easy to take out. But be very careful not to drop anything on the mirror.

1. Make sure you have the protective cover over the mirror, maybe also remove the struts for ease of handling.

2. Stand the tube upright on the floor/carpet maybe use a towel on the floor/carpet.

3. Unscrew the 6 small Philips head screws on the outside of the bottom cast ring securing it to the tube.

4. Just lift the tube straight up, which leaves the heavy mirror and cast cell on the floor, very easy.

TheoHE (Theo) · #8 28-01-2010, 06:32 AM

Thanks Richard that's exactly what I was hoping to hear. It does not sound as complicated as I thought it might be. My partner has nearly finished the shroud and I've ordered a polarising filter and two Vixen eyepieces which will give me some more viewing flexibility. Now all I need is for this job to finish and get back home and set up the scope properly so we can enjoy it.

richardda1st (Richard) · #9 28-01-2010, 11:20 PM

Hi Theo, can you let me know how the catseye collimation set works out.

When assembling the struts make sure the clamps are well seated and tight, also the screws that you remove from the cast rings for the mirror and also the cast rings for the struts to the upper and lower tubes must be tight (within reason). Otherwise you may find that the scope may loose collimation.

Be careful if you use the altitude tension adjustment assembly, as the nylon friction pad will scratch and gouge the aluminium altitude bearing. I have been advised to replace the nylon pad with Teflon. As none of my lenses are heavy I don't use the clamp anymore.

One of the primary collimation screws is tight on mine as well but not a problem. Add a small drop of fine oil to the threads of these thumb screws and the strut lock knobs, wipe of any excess oil immediately. This helps to tighten the strut clamps without the thread binding and little force is required.

astro_nutt · #10 01-03-2010, 10:42 AM

Hi Theo!
Have a magnet handy for keeping the screws in one place.
The area where you'll be removing the primary...make sure it's clean, no pets, kids,etc! All tools are clean.
Finding the primary mirror's centre? While the mirror is out, place a sheet of clean greaseproof or tracing paper on a level surface. Place the mirror shiney side up on the paper and trace the bottom with a felt pen. Remove the mirror and fold the paper into a quadrant. Nip (tiny) the corner of the fold with a pair of scissors, unfold the paper as flat and as cleanly as you can and you should have a squarish hole on the middle of the circle. Carefully place the paper on the mirror and align the circle to the mirror. Using a whiteboard marker make a dot through the squarish hole in the centre of the circle onto the miror. Remove the paper and you have a centre dot on the mirror in which to place a collimation stick-on circle. Clean the whiteboard dot off with a cotton bud dampened with some isopropyl alcohol and gently dab, not wipe, rotate the cotton bud on each dab.
Cheers!