Collimation off?

[Kaptain Klevtsov]

Thought I'd got it spot on last night, red dot straight back in the hole etc. but it looks like I am getting odd shaped stars. Opinions guys and gals please, I need to figure out what's going on here.

I thought that it might be tracking, but the top right area seems to show some coma, this is 4 90 second subs stacked BTW, they all have the comet shaped stars.

TIA

Captain Chaos

[GordonCopestake]

Nice M51 CC! I would say it was tracking as all the stars are distored in the same direction. I would have thought coma would throw the distortion out from the center of view? I could be wrong. Was the polar alignment acurate? A guide scope would tell you for sure.

[Ambermile]

Hmm - not sure about it being collimation CC as the stars bottom left are OK. This rules out tracking too. I suspect your camera is not in the right plane to the mirrors. Are you sure the focuser is aligned properly?

Arthur

[geppetto]

Any chance that the primary might be pinched in its cell?

[Kaptain Klevtsov]

Thanks guys, that was quick!

Hmm - not sure about it being collimation CC as the stars bottom left are OK. This rules out tracking too. I suspect your camera is not in the right plane to the mirrors. Are you sure the focuser is aligned properly?

Arthur

I was under the impression that the nosepiece keeps it square to the focuser axis, and that collimation ensures that the focuser axis is in the right place. Could be that the frame flexes as it slews, or the whole shebang boings with the shutter slap enough to do this.

Pinched primary - sounds quite painfull!

The primary arrived stuck to a piece of chipboard with blobs of silicon of somesuch. I haven't even considered seperating that yet, but it could have bent the mirror ever so slightly (if that's what "pinched" means in this context).

Thanks for the PM'd link Arthur, I'll check that out as well.

Could also be wind - I'd been drinking lager.

Captain Chaos

[geppetto]

if that's what "pinched" means in this context

Yep... does sound painfull now you mention it :D

Worth a try if all else fails

[The Warthog]

I would use Occam's razor, and go witht he tracking theory. Simplest answer. When you hear hoofbeats, think horses, not zebras.

[Kaptain Klevtsov]

I'm thinking that you're right WH at the moment.

Reason being, I can run through the subs and watch the stars track across the frame between the subs.

I'm definitely going to have to build a pier for the EQ6 as its such a pain in the butt to align. I thought that I had it spot on last night, but the little tiny tripod that it sits on means lots of crawling about on the floor. At least with the HEQ5 I just sit it on the pier and it's aligned.

Thanks chaps, I think we have the answer, though it was staring me in the face all along.

Captain Chaos