Collimation required or something else?

[PaulR]

I can't seem to get nice 'disk and diffraction rings' star images with my Orion Optics 6" Newtonian; I tend to get a sort-of disk and a small coma regardless of how good the 'seeing' appears to be.

Using my home-made 35mm canister collimation tool it seems that the secondary mirror is somewhat off as the reflection of the 'tool' is a bit off centre.

According to the manual I downloaded (none supplied with scope) I should be able to see the primary mirror clips equally but I can't actually see any of them (at least I can't see any of them equally!). (I haven't yet got around to trying an out-of-focus star to see if that indicates that collimation is needed <blush>)

The scope spent about 9 months unused stored in the house although the focusser and main tube caps were on.

Is it likely to be collimation issue, might adjusting the secondary help, could it be a case of careful cleaning of the optical system, could it be the no-name Plossl eyepieces that came with the 'scope? Could it be all of the above or maybe my expectations are too high??

Any help appreciated

TIA

Paul.

[Kaptain Klevtsov]

There are loads of collimation threads in here, but to get to see the mirror clips, first check that you actually have clips by looking down the end at the primary mirror, then move the focuser all the way in to be able to see a wider view.

Kaptain Klevtsov

[The Warthog]

Not being able to see the mirror clips at all is better than being able to see only one or two of them. Probably the clips are just out of view, and close enough to even. I would concentrate on lining up the reflection of the mirror so that the centre of the primary, and the reflection of your eyehole in the canister are lined up. Mark the centre of your primary if it is not already marked. Use only two of the three collimating screws on the back of the mirror to move the centre into line. You'll be OK.

It is unlikely that you need to clean your optics. Even a very dirty looking mirror is reflecting most of the light back to your eye. If your eps are very cheap, they could be a problem. You'll want to get some decent eps anyway, and money spent on good eps is never wasted. Borrow some name-brand eps if you can, but do your best to improve the collimation first.

You may see some spikes on your stars due to the spider holding your secondary mirror in place. This is normal.

[PaulR]

Thanks Mr Warthog!

I've just downloaded and followed these 'no nonsense' instructions from Orion...

http://www.orionoptics.co.uk/collimation.pdf

It seems that my main mirror is fine but the secondary needed some adjustment which I've now done. Seemed pretty easy - the scope is outside cooling down right now so I'll see if my adjustments helped any in a little while.

After reading a couple of other threads about (not) cleaning mirrors I'm going to steer well clear of that idea.

I guess the EPs that came with the scope are pretty average but they don't seem appaling. When funds allow I'll certainly get some better ones... maybe one of those nice sets

Thanks again for the guidance.