can't collimate lightbridge

[sejanus]

argh

So I have the trusty laser pointer in the eyepiece. The red dot appears about 4cm from the dot in the center of the mirror,.

No matter what I do to the screws on the spider, I can't get it in. I can get it to move around to the left, right, down, but not up.

The obvious answer is that I need to adjust the screws on the base of the mirror right? The problem is that adjusting these screws, the red dot doesn't move in the slightest.

What am I missing?

thanks

[erick]

Here's what I would do. BUT you'd better wait for more expert suggestions!

Laser in focusser and on. Loosen all three collimating screws in the spider a turn or maybe two. (Don't touch the centre screw) Reach in and grab hold of the secondary mirror holder and wobble it to move that red dot around to check you can get it on the centre spot. BE CAREFUL that the laser doesn't bounce off the primary, miss the secondary and hit you in the eye - keep your head to one side of the OTA. If you cannot get it on the centre spot, something is grossly wrong. Stop and think and observe the whole topend setup carefully for something out of alignment.

If you can get the red dot closer to the centre spot, hopefully on it, screw the three collimating screws back into place while holding the secondary on the alignment you want. I'm guessing the red dot will wobble around a lot while you are holding the since it is fairly fine changes to the angle of the secondary will move the red dot cm across the primary? But the object here is to convince yourself that the red dot can be made to hit the centre spot. Then, with the three collimating screws touching the secondary mirror holder again, start again from the beginning (sight tube through focusser) since you may have rotated the secondary a little and need to return it to correct alignment, square to the focusser.

Yes, adjusting the three primary mirror screws should have virtually no effect on the position of the laser dot on the primary.

But, I don't have a truss scope, let alone a lightbridge, just a small tube newtonian. I'm just proposing a gross approach for an apparent gross problem.

[Tannehill]

Sounds like your secondary collimation mechanics are awry. Like Eric said, the primary mirror bolts will have no effect on this, this is 100% adjustment of the secondary mirror.

If one of the bolts is not working, then you have either a stripped bolt, or some other issue.

My GSO and you lightbridge share the same 3rd party vendor of the spider assembly, I think.

Smooth collimation of the the 2nd mirror depends on the right tension
balance between the spring-loaded center bolt and the three collimation
screws. The center bolt at its top isn't fixed to the vane, but rather
wiggles and pivots a bit, thereby allowing the secondary to "wiggle"
when all three collimation bolts are loose. This wiggly center bolt is
holding the secondary to the vane, but the spring around it is pushing the secondary away. This degree of wiggle is determined by the tension of the
spring of the center bolt. The tighter the secondary bolt, the more
tightly compressed is this spring. If the spring is too loose then the
three collimation bolts, as they move down to push against the fender
washer, don't have much to move before they "push" the secondary beyond
the tension of the spring. The result is clunking of the secondary when
you try to adjust the collilmation bolts. You need a longer spring,
or a more tightly compressed spring anyway. The right dynamic tension is this system is necessary for smooth non-erratic and non-clunky collimation. Some springs are floppier than others; I needed to add some washers to my bolt to effectively over-compress the spring to get this correct degree of tension. That may not be your exact issue, however.

If one of the bolts isn't in contact with the top of the secondary mirror holder, that may explain why your one collimation has no effect, as you describe. A broken bolt, or its stripped (or the spider hole threading is stripped) and not really moving down when you turn it.

If you can't get it to work, try taking a picture of where the center bolt of the spider vane assembly screws into the secondary mirror holder itself. This should also show the three collimation bolts making contact with the fender washer on the top of the secondary holder.

Hope this makes sense and helps.

ST

[sejanus]

doesnt make a mega amount of sense :) but it might when I'm in front of it. thanks

[sejanus]

I'll have a closer look tonight. I did manage to collimate my other scopes ok, though I'm definitely still in the n00b category.

[sejanus]

well back from my play

discovered one of the screws is horribly bent which won't be helping

unfortunately during the mucking around i have completely stripped bare one of the other screws :( and it doesn't seem to want to come out! i did not want to use much force

the good news though is despite the carnage i have the laser dot bang in the center now, with a combination of doing a slight adjustment to the entire secondary position itself plus the 2 other screws. probably a huge fluke but it'll suffice until I work out how to fix the bent screw and the stripped screw.

[OneOfOne]

Just to be sure...I would also make up a jig to give the collimation of the laser a quick check unless you have already done this before...in which case forget I mentioned it :D

[Tannehill]

Ah-hah. Problem explained.

If that's a 16 LB, then it can't be too old and is probably (?) still under warranty. If that's the way the unit was delivered, you should be up for some repairs courtesy of Meade. What with the recent news of their "re-org" maybe that's not all that encouraging. But, perhaps with aide of the vendor, you can just swap out spiders. You can keep the secondary holder and even the center bolt, since those bolts and holes that are your problem are embedded in the spider itself.

I'd endorse getting some Bob's Knobs or comparable replacements to those collimation screws...much easier to adjust and no fear of over-torquing and stripping a head or such. Furthermore, the GSO-supplied springs on the primary are notoriously variable...maybe consider getting Bob's knobs for the secondary bolts and new stiffer springs from him also, for the primary. I did that for my 12 GSO and it's dramatically more predictable to collimate.

Regards

Scott

[JethroB76]

Not the greatest news...
Maybe not here in Oz, but in the US there has been some very ordinary experiences with the 16" LBs out of the box.

Would definitely agree with Scott on upgrading with the Bobs Knobs (or similar) kits

[Tannehill]

These are the knobs: http://www.bobsknobs.com/Meade/Newt/MLB16.htm

Could be you could make or find some locally, but he ships worldwide for the posted price. If you just stripped the head of the collimation screw, you can probably back it out. Remove the secondary from the spider by unscrewing it (the center bolt). Careful, a spring will pop off the back as you do....I'd just set the un-attached UTA on a table or something, not do it with scope assembled. Then you'll be looking at the business end of the collimation screws. You can either just wrap the threads in a rubber mat and vice-grip turn them out, or find a locking nut to put on the end to give you some traction and reverse it out. Just don't damage the distant end threads, or it'll hang as those threads back out through the spider body..

Cheers

Scott

[spacezebra]

Hi there

My LB 12 under went a total knob refit and a slight tweak to the spider, one thing that I did not use of bobs is the springs, opted for heavy duty ones from Bunnings. Collimation is now a breeze. Check with the supplier of your scope and have it checked out.

Cheers Petra

[sejanus]

thanks heaps for all the info guys

bobs knobs are the way. as it's sorta collimated ok I can wait the couple of weeks to have them sent from o/s then fix it all up properly.

scott I'll do what you suggest, taking the spider out when the time comes.

[Roger Davis]

Ensure that you check that the secondary is not rotated. A laser will not show this fault! You will need a Cheshire or sight tube.

Rotate your laser in the focuser. Does the laser dot waltz around the centre collimation dot? Then your focuser is not squared on to the optical and mechanical path. EVERYONE FORGETS THIS IMPORTANT POINT!!

Remember the order of collimation: FSP (Focuser/Secondary Mirror/Primary Mirror)

[sejanus]

ok well had a bit of success today!

took the spider assembly out of the scope and hacksawed off the bottom of the bent screw and used pliers to reverse it out as the thread was a bit marginal and kept slipping. Also used pliers to reverse out the one with the really screwed up thread. Had to use a bit of wd40 as they were pretty darn tight. Took about 20mins and a few 4 letter words but got there in the end.

Bintel had the bobs knobs handy earlier in the week so they are all fitted fine now and the spider and secondary are back in the scope and it's a 20sec job now to get the laser to hit the center dot.

however 2 concerns ;

- As Roger says above, when I rotate the laser pointer it dances around by about 5-8mm

- After adjusting the secondary with the new knobs, I can see the red laser reflected back out into the "eyepiece" off center. i.e. on the collimator/laser pointer there is obviously a hole where the light comes out, but the light does not appear to reflect straight back into that spot.

If I loosen the main screw on the secondary mirror a bit, adjust it so it does go back into that spot (and then retighten) - the laser is now a centimetre or so off the center dot on the primary. And when I recollimate it using the knobs, I'm back to square 1 i.e. the light is not reflecting back exactly where the laser originated.

is this a big deal? hope it makes sense. can take a photo if it doesn't.

Anyway, if it's clear tonight I'll do a star test.

cheers and thanks for the info

[Kevnool]

Also on the notes above put your laser colminator into a lathe and spin it you will maybe surprised to see its out of centre .....mine was brand new out of the box and straight into the lathe ..and there it was completely out of whack, with adjusting the colminator itself thats all the difference i need ....on my 10` lightbridge my 3 screws in the spider have wingnuts welded to them....the mirrorcell has the original screws but with extra compression springs added....these are a good scope only after little personel modifications....cheers happy viewing..kev

[CoombellKid]

Yes I've heard not particularly great reports either. My biggest turn off is the
design is top heavy when you put any premium ep in them. Since my ep's are
all XW or Nagler all up to and over 400gms each. I was quickly turned off the
idea. Not sure if the 8" 10" or 12" has the same problem, but I think the
discussions weren't particularly based on the 16".

Good Luck with fixing your problem. I'd be scared of buying anything Meade
these days.

regards,CS

[sejanus]

yes the top heavy problem surprised me - seems incredibly short sighted by meade

[JethroB76]

My comment was more directed at the amount of damage to the 16" that people have reported out of the box..though the top-heavy problem you mention is a pain and one that affects the 12" once you use big eyepieces/barlows/finders etc

[sejanus]

ok, so i just gave the scope a quick whirl

it's noticeably better than before. It's starting to look a bit more like a big scope now. good detail on tarantula and tucanae looks mega with the 7mm nagler.

however the image is still not really crisp. it is pulling in WAY more detail, but not as "sharp" or well defined as my old 11" celestron or my 10" dob did.

So in summary, it is looking good but I think it has a bit left in it yet.

btw, when you go to something bright like canopus - you can really see the spikes from the spider assembly quite clearly - I don't recall seeing this anywhere near as vividly in my 10" Dob - is this normal for a larger newt?

cheers

[CoombellKid]

sejanus,

could it be atmospheric quality, there doesn't appear to be a jet stream down
your way so it cant be that.

regards,CS

[sejanus]

There's a thought, although it was a bit soft even at 32mm which is pretty low mag. But yep thats possible, unfortunately it's my only scope at moment so i can't compare it side by side to another.

[Gargoyle_Steve]

You mentioned adjusting the secndary mirror back up there but didn't mention adjusting the primary afterwards, and the issue you talked about regards the return laser dot coming back "off centre" - that's primary adjustment.

If you've already tweaked the primary as well then please disregard what I've said. Hope you get it sorted out pronto.

[Roger Davis]

Do your final collimation on a star (obvious I know, but I thought I'd better state it). Whilst you are at it you can check the quality of your optics with a Ronchi screen held on the top of the focuser (no eyepiece) and rack the focuser in and out slightly. If the mirror is a perfect parabola you should see dead straight lines from one side of the mirror to the other. HOWEVER, should you see slight distortions to the lines it doesn't mean that your mirror is bad, just that there may be a turned down edge or a slight zonal error. Check out Dick Suiter's book: Star Testing Astronomical Telescopes
Check that your spider vanes are square onto the optical axis as well!