Collimation problem

[toml42]

I noticed this a while ago, but i think it's finally time to do something about it.

While collimating my skywatcher 200p, I find that no matter how hard i try, i can't get the secondary central under the focusser.

I have the central thread on the secondary as tight as it will go, and it is still quite a way off.

Is it possible that the focus tube is misaligned? and if so, can anyone give me any pointers on how to fix that?

[Nova]

Have you checked that the secondary is central to the diameter of the OTA? Done by measuring the distance along the spider vaines. I think (more advanced members correct me if im wrong) on a newtonian the secondary is supposed to be 5mm off center in the direction away from the focusing tube.

Also if you have the central mirror mount screw done up all the way then am I right in assuming you can not move the 3 adjustment screws at all?

[Moonshane]

assuming your secondary appears too far down the tube I think Nova has hit your problem. to move the secondary up the tube, you need to loosen the three collimation screws on the secondary housing to do so. the central bolt is only ever tight as the three bolts push on it.

at all times when doing this make sure you are holding the secondary (obviously keep yer mitts off the glass ) and have the tube close to horizontal. also, make sure there's enough thread left on the secondary central bolt to retain it.

hope this helps.

[NGC 1502]

I have the central thread on the secondary as tight as it will go, and it is still quite a way off.

Sounds like you mean that the secondary is too far down the tube

towards the primary ? Have you tried backing off all three secondary adjusters ? That will allow the central screw to draw the

secondary away from the primary.

Hope I've understood the problem correctly.

Regards, Ed.

[toml42]

yes, sorry, i should have been clearer. The secondary appears to be too far down the tube, I slackened all of the adjusters off then tightened the central all the way, but it still seemed wrong

[Moonshane]

might be worth slackening the focuser bolts and see if it will shunt down a little? but something seems wrong to me.

[Nova]

has it been a problem since you have had the scope?

[toml42]

yes, i noticed it the first time i colimated, but didn't think it was too big a deal, as i was able to complete the later steps and was getting great performance on star tests etc.

I'm guessing i might be losing a bit of light having it like this though, so i figured it was time to do something about it.

[Moonshane]

In all honesty, if you can see all three mirror clips and it's reasonably centralised then I wouldn't worry too much, especially if you only observe visually.

any chance you could take a pic down the focuser to show what you have?

sometimes doing this makes it look OK!

[Nova]

yeh. if your star tests are giving great results i wouldnt worry. after all its what we see when observing that really matters

[damnut]

Had similar issues with my 8" newt, in the end local astro shop RVO did all the hard work in perfectly re-collimating and cost a tenner.