Trouble with secondary mirror collimation.

[Kirscovitch]

I was collimating my scope this afternoon. It was pretty close to being spot on. The laser was touching the rim of the circle on the primary and touching the edge of the bullseye in the the laser collimator.

I am having a heck of a time getting the secondary mirror to adjust. All three adjustment screws are so tight they almost feel like they are welded in place. I went on youtube and found a video of someone collimating the same scope I have and It didn't seem that you need that much force to turn the screws.

I don't want to force anything an break it or strip out a screw. What should I do???

[NGC 1502]

Hi Matt.  I think that the 130 SLT is a Newtonian ?  Most secondary mirror holders have a large central screw.  I'd slacken that off, then try the 3 adjusters.

If the centre screw is very tight, you may have to support the spider vanes as you turn the screw, so you don't bend the vanes.

Hope you sort it, Ed.

[ScottS]

Have you got any other means of checking your collimation first? The laser may not give entirely accurate results on it's own anyway. Especially for the secondary.

[cantab]

Try loosening one before you tighten any others?

[Kirscovitch]

Thanks Ed. I will try that. I didn't really want to mess with the center screw as in all the information I've read on it said not to touch it but I will try putting a little slack into it.

Scott, I do have a second collimator with a hole in the cap and it did seem off. The laser seems pretty accurate. as it doesn't "draw" a circle when rotated. It stays in the same spot.

[Kirscovitch]

Try loosening one before you tighten any others?

None of them will turn either way. I'm afraid if try to turn them that I will twist the vanes. The dot will move when try turning the screws, but jump back to the original position when I release the pressure.

[ScottS]

Thanks Ed. I will try that. I didn't really want to mess with the center screw as in all the information I've read on it said not to touch it but I will try putting a little slack into it.

Scott, I do have a second collimator with a hole in the cap and it did seem off. The laser seems pretty accurate. as it doesn't "draw" a circle when rotated. It stays in the same spot.

Do you mean it doesn't draw a circle on the primary when in the focuser? It may well not, but that in itself doesn't prove the secondary is correctly aligned. You've already said the collimation cap says otherwise. I would trust that more.

[Kirscovitch]

Do you mean it doesn't draw a circle on the primary when in the focuser? It may well not, but that in itself doesn't prove the secondary is correctly aligned. You've already said the collimation cap says otherwise. I would trust that more.

Sorry, I meant the cap showed that the collimation appeared to be off.

[mdstuart]

Is the secondary out of alignment? If not leave it alone.

Look down the eyepiece tube and you should see the secondary as a circle centrally aligned with the eyepiece tube.

I know how frustrating it is when things like this happen.

Mark

[wookie1965]

Have a look at these

http://www.andysshotglass.com/Collimating.html

http://www.schlatter.org/Dad/Astronomy/collimate.htm

http://www.astro-baby.com/collimation/astro%20babys%20collimation%20guide.htm

And read this very good guide by a fellow Lounger Moonshane

Collimation.pdf

[Peter Drew]

I would perservere with undoing at least one of the three small screws as they do not impart so much tension as the larger central one. The combined effort of these three screws, if tight, will add to the tightness of the central one. 

[Kirscovitch]

Thanks for all the tips guys. After a little more tinkering and bit more swearing I finally got it. I'm not sure what the deal was. Maybe they were over tightened at the factory? Almost felt like there was some sort of lock tite on them or something.

[astronymonkey]

definately slacken one a tiny bit before tightening the other a tiny bit ...... much easier with bobs knobs though