Collimation Question??

[rmcpb]

I am having real problems with seeing small bright objects. The mooms of Jupiter have two " tails" as do stars, ie they are not pin points of light. I have collimated till I have run out of ideas, all the rings match up and the star test gives beautiful concentric circles.

I can easily go to 400x on the moon but the cloud bands in Jupiter at anything over 80x have no detail, I used to be able to see some of the festoony bits once.

Are my eyes stuffing up?? :help:

Any ideas please.

[vindictive666]

ive got no ideas but am getting the same with the jupiters moons i have checked and mine is still out of collimation ? so ill following this post :)

[iceman]

That's exactly the symptoms I had, on the moons of Jupiter. It turns out that my secondary mirror was pinched in the holder (very tight) and was causing this. My primary mirror could also have been a bit looser.

So after rectifying both of these problems, and re-collimating, the moons of Jupiter are now pinpoints of light to me.

Hope that helps. Geoff has done a how-to on fixing this, but i'm yet to load it onto the main site. Will do so in the next day or two hopefully.

[atalas]

Hey Rob ,maybe the seeing bad!can happen,

Louie:D

[Starkler]

After seeing the images from a few of the GSO dobs at the recent Vic iceinspace star party, it became clear that a how-to on detecting and rectifying these issues could help a lot of people.

I spoke to Dave47Tuc last night. After fixing his gso dobs astigmatism problem he is very happy with the image he is now getting.

Stay tuned !

[ballaratdragons]

Yeah, this collimation is an Art form.

Rob, I have good to very good images but the collimation tool is off centre. Weird huh!

Below is a drawing of my collimation results. The Cheshire dot is exactly in the centre of the Mirror centre-spot and they are both perfectly lined up on the cross-hairs. All the way it is supposed to be and yet the whole lot is off centre.

[iceman]

BD: I think that's a result of secondary offset. Apparently that's not so much of a problem and something you needn't worry about.

I'm sure one of the experts will chip in here with the reasons why.

[ballaratdragons]

Thanks Mike,

I know that a 2ndry needs offset, BUT that seems a loooong way off centre.

Any help?

Rob, sorry to cut in on your thread, but this might help any collimation problems you have too.

[ving]

ditto ken. mines the same but not off by quite that much. :confuse3:
and I htink I have the tight secondary prob too

[Starkler]

Ken maybe your focuser isnt square to the tube, or the spider isnt centred properly.

[ballaratdragons]

Geoff,

The Spider it centred. I checked that a few times. I think you may be right about the Focuser though. I will check it for square again.

[RAJAH235]

Hiya all, The 2ndary has to have offset. If you start with the basics of squaring your focuser tube to the optical path, (see below), then centering the 2ndary in the focuser tube & continuing on from there, you'll find the 2ndary will be offset towards the primary & away from the focuser.
The distances/measurements vary, naturally, with each t'scope. See these> (http://www.andysshotglass.com/Collimating.html)
(http://skyandtelescope.com/printable/howto/scopes/article_790.asp)
I start by blue tacking a white sheet of paper inside the tube, opposite the focuser, so that I can see 'AROUND' the 2ndary, which is then adjusted so that it is in the 'centre of the focuser tube'. ( in other words, the circle, between the focuser & the edge of the 2ndary). The rest of the collimation takes place from there.
Ken, the view that you are getting is correct, if the optical, (NOT Mechanical), centres are lined up. HTH. Regards. L. :D

[ballaratdragons]

Ok Laurie. It just looks too far off though!

[RAJAH235]

Hi Ken, Mine looks like yours too. But it's almost 'perfect'. Meade build the offset into the 2ndary holder. You just have to collimate it correctly!
If the views are great & the stars have good diff. rings, & you get pinpoints, who cares what the position of the mirrors looks like? It must be right!
Regards, L. :D

[rmcpb]

Not my eyes :)

Fell for the oldest trick in the book. The secondary was too low and not centred correctly. That meant it had to be off axis to bring the light cone into the eyepiece and the result... multiple tails on the images.

A good case for a truss setup, that would have been easily detected as I found it when I pulled the secondary out to see if it was pinched in the holder.

[Dave47tuc]

Hi :D

Found this site on collimation.http://www.andysshotglass.com/Collimating.html

Heavy download so have broadband.