Funny shaped stars!

[spanky]

Can anyone help me out here?

Everything seemed to be going pretty good until last night when my stars started going funny at the edges of my images. It's not coma as I have the MPCC fitted.

Yesterday I did install the Synscan upgrade to my mount, but I can't think that would have had an effect like this would it?

I've just had another quick go outside, thinking that maybe I didn't have the camera in the focuser properly but it's still doing it.

Here's the four corners of my image, see how it's worse at the top corners?

I'm worried someone is going to mention the dreaded "C" word and I'm going to have to start buying lasers and allsorts!

*edit* I should add that the centre is spot on perfect

On on the plus side though, GOTO is awesome!

[spanky]

Anyone???

[Ant]

TJ had a problem a while ago that at first appeared to be collimation... from memory it was the weight in the focuser...

You collimate with an EP or cheshire which compared to the weight of a DSLR or CCD is quite light.

So although collimation is spot on, it's not when you add the camera. So maybe try collimating with a similar amount of overall weight hanging off the focuser.

It may not be that of course, but certainly something to rule out.

Cheers

ant

[rfdesigner]

How accurate was your origional polar alignement?

(thinking image rotation)

Derek

[spanky]

Alignment was easy good enough for 60 second subs. If it was rotation, then wouldn't it be in the same direction on all the stars rather than spreading out from the centre?

What does it actually look like when collimation is out? I can find lots of pics of defocused stars but nothing about an actual image.

Think it could be collimation then? Only had it a couple of months and it seemed to work great right out of the box. I guess with moving it about the mirror could have slipped??

[rfdesigner]

If it's image rotation then the first and last subs should show substantial rotation between them.. do you have that?

Derek

[spanky]

If it's image rotation then the first and last subs should show substantial rotation between them.. do you have that?

Derek

No, a bit of drift from left to right, but no rotation

I'm all set up again now and still the same, seems worse on the left corners than on the right.

I get a perfect doughnut defocused star in the centre then when I slew it so it's in teh corner it's all pear-shaped.

Ah well, gonna take some subs anyways and crop the worst bits off. I'll have a proper go at collimating when it goes cloudy again. DOn't want to waste valuable practice time when it's clear!

[rfdesigner]

That does sound more like collimation, I just wondered about alignment as you'd mentioned adding the syscan... wondered if you'd assumed that a computer would totally correct poor alignment. (and it would be free to fix so would be worth checking first)

RE collimation, I've managed to get mine done with a home made cheshire collimator... and I needed to collimate everything...

Derek