Collimation woes...Took off primary!!

DJVege · #1 06-01-2008, 03:04 PM

OK! So, I think the reason my collimation was off was due to the secondary not being square underneath the focuser. So, I've adjusted the focuser and all was looking good! However, the collimation was slightly off, so I took out the good ol' Astrosystems laser collimator, and the laser was about 3mm off centre. I do the usual, start undoing the 3 set screws, then start adjusting the collimation screws...but nada!! That mirror just won't move...no matter what I do, the laser stays in the same spot! ???

So, I did the unthinkable! I pulled the primary mirror straight off!! I've taken some pics and attached them below.

I read that the larger screws were for collimation, and the smaller screws were set screws, to hold the collimation in place. Is that right? If so, they why is this mirror not moving when I tighten either of them???

Help!

Thanks guys!

mill (Martin) · #2 06-01-2008, 03:24 PM

The screws are locked with nuts it seems.

edwardsdj (Doug) · #3 06-01-2008, 03:30 PM

When you say the laser was "about 3mm off centre" do you mean off the centre of the primary mirror spot?

DJVege · #4 06-01-2008, 04:00 PM

Yes, the primary mirror spot.

I have no idea...no matter what I loosen/tighten, the mirror doesn't move..??

edwardsdj (Doug) · #5 06-01-2008, 04:08 PM

The reflection of the laser on the primary mirror will not move when you adjust the primary collimation screws.

You adjust the secondary collimation screws to adjust the reflection of the laser on the primary mirror into the centre of the primary mirror centre spot.

Then you adjust the primary mirror collimation screws to get the reflected laser beam going back into the hole in the collimator where it comes from.

ballaratdragons (Ken) · #6 06-01-2008, 04:25 PM

Quote:

Originally Posted by DJVege

So, I did the unthinkable! I pulled the primary mirror straight off!!

Thanks guys!

Nothing unthinkable about taking the mirror out. You have to when you clean it. We all do

DJVege · #7 06-01-2008, 05:07 PM

Edwardsdj.....umm...jee, do I feel sheepish...that's right! Ooops.

* with head down and fake tail between legs * walks to telescope to collimate it properly!

I....am....an.....wait for it......little more......IDIOT!!!

Cheers mate! At least now I know what the back of a scope looks like.

edwardsdj (Doug) · #8 06-01-2008, 05:28 PM

Not a problem. There's is much that I don't know either.

How did you go in the end?

Gama · #9 06-01-2008, 05:29 PM

People have been hung and quarted for less !.

In the words of Derin Hinch "Shame Shame Shame"

But we all do things without thinking.
I spent 1 hour collimating my 22" to perfection one night, cool i thought, lets see if the collimation holds if i rotate the tube 180 deg..
Nope, went off badly. Spend another day pulling out the monster mirror and cell (All Steel), couldnt find anything wrong..

So another night collimating and the same thing.. This time i actually thought of what could cause it. Ended up being the seconday mirror would flop ever so slightly on its own weight as it rotated with secondary holder cell.
A little dab of silicone on the back of the mirror, here and there and now rock solid.
So please get in line for the banana membership.

Theo

DJVege · #10 06-01-2008, 07:58 PM

I'm collimated!!!!!!!!!!!!!!!!!!!!!!

Thanks Doug! And all....

It's probably not 100% perfect...but it wouldn't be far off it. At least all my collimating tools match up!

Just to sum up: The problem with my collimation was not my astrosystems laser, or the cheshire. The problem was that the secondary was not centered properly under the focuser. The laser collimator was not used to centre the secondary, only adjust it and the primary, which was why the cheshire didn't agree with the laser.

I'd also like to point out that I bought a skywatcher collimation tool from myastroshop. It's better than the cheshire due to the longer tube.

I'd also recommend this astrosystems laser collimator to anyone. It's brilliant. Makes aligning the secondary and primary very easy, as long as your secondary is centered (which is usually only done when you first get your scope, and rarely after, I believe).

Would you believe my luck...the clouds parted last night and I saw a great deal of sky, but the scope was not ready! Now, my scope is ready, and it's cloudy as!!!!!!!!

Thanks again everyone.

Omaroo (Chris Malikoff) · #11 06-01-2008, 08:26 PM

Brill Deej!

Clear skies old mate

Phil · #12 07-01-2008, 08:10 AM

Hay DJ you must be getting pretty good at collimation now. When you come up hear you can teach me how to do it probably Hope to see you soon .
Phil

DJVege · #13 07-01-2008, 09:19 AM

haha. No worries Phil! Got collimation down pat!

Dunno when I'll be up next, but I'll definitely come for a visit. And I'll bring the astrosystems laser collimator to show ya.

Tannehill · #14 07-01-2008, 02:21 PM

Great, thanks for the update. Makes sense now...I thought you were using the laser in barlow mode and couldn't quite figure why it disagreed with the chesire. A good learning example...

Regards,

DJVege · #15 07-01-2008, 02:33 PM

Yeah, sorry. Guess my explanations weren't great. The cheshire was out due to the secondary not being square. I wasn't keen to move the focuser a bit, but seeing as it's a new focuser, and attaching it was probably what caused the misalignment...

All is beautiful now. Nicely aligned....now if only I could get a view of something other than my white wall, I'd be ecstatic!

Omaroo (Chris Malikoff) · #16 07-01-2008, 06:01 PM

Quote:

Originally Posted by DJVege

Yeah, sorry. Guess my explanations weren't great. The cheshire was out due to the secondary not being square. I wasn't keen to move the focuser a bit, but seeing as it's a new focuser, and attaching it was probably what caused the misalignment...

Ah ha. As suspected. Logic states that the last thing you did is always the the problem..... Confucious