Argh! This is doing my head in now .....

[Black Knight]

Well, here's the next episode in my long-running badly-shaped star saga. 'Tis truly an epic!

Yesterday I re-collimated the focuser on my Quattro for the second time. The first time I did it, it did improve things somewhat, but now, although things are no worse, they ain't no better either .

This is a stacked image from last night of M101. I haven't done any processing on it, this was simply to test how the re-collimation of the focuser went.

It looks a bit like rotation, but according to DSS, the rotation angle from 12 * 5 minute subs amounted to 0.01 degree. Guiding was particularly good, no problems at all.

I don't know where to look next, to be honest: I'm stumped. I feel pretty much like throwing in the towel on this one. I've been battling with this issue ever since I got my Quattro. Maybe I just got a bad one, I don't know ...

So I'd be grateful for any suggestions where I can go from here.... the pub probably!

First pic is the complete image

Second pic is the top left

Third pic is the top right

Fourth pic is bottom left

Fifth pic is bottom right

Sixth pic is the central area

[Shibby]

Andy, I'm not 100% certain but all the stars seem to be elongated in the same direction. Have you tried taking very short subs to see if the problem is still present - this would confirm that it's an optical problem and nothing to do with guiding.

If you're already collimating the focuser, I assume you've probably checked and rechecked the mirror collimation many times? Secondary tilt?

[Starlight 1]

flex issue, or your guide star is over saturated.

[kookoo_gr]

check the colimation of your scope by using a bright star and a bahtinov mask. place the star at the center of the FOV and focus. then move that star with the mask on the scope at each corner of the scope and see if the focus is perfect (do not change the focus at this step), also rotate the mask 90 degrees to see the focus on both the x and y axes. if the collimation is fine then at each corner you should have the same focus of the star. if the collimation ia at your satisfaction i would check for flexure and my thoughts are that if you have a vixen style puck then that it will introduce flex. if you change it to an adm saddle i think that your problems will go away.

[Black Knight]

flex issue, or your guide star is over saturated.

I don't think it's that. I tried 3 different targets, in different areas of the sky. I imaged M3, using shorter 2 and 3 minute subs which show the same problem .

[Black Knight]

Andy, I'm not 100% certain but all the stars seem to be elongated in the same direction. Have you tried taking very short subs to see if the problem is still present - this would confirm that it's an optical problem and nothing to do with guiding.

If you're already collimating the focuser, I assume you've probably checked and rechecked the mirror collimation many times? Secondary tilt?

Yeah, I've re-collimated so many times I've lost count! I had to remove the spider to collimate the focuser, so that's been done from the ground up, too .

[Black Knight]

check the colimation of your scope by using a bright star and a bahtinov mask. place the star at the center of the FOV and focus. then move that star with the mask on the scope at each corner of the scope and see if the focus is perfect (do not change the focus at this step), also rotate the mask 90 degrees to see the focus on both the x and y axes. if the collimation is fine then at each corner you should have the same focus of the star. if the collimation ia at your satisfaction i would check for flexure and my thoughts are that if you have a vixen style puck then that it will introduce flex. if you change it to an adm saddle i think that your problems will go away.

I'll try this next time I'm out. I have an ADM dual mounting bar with ADM Vixen saddles, fitted onto a normal Skywatcher Vixen puck - If you see what I mean! . I'd love to test an ADM puck. Do you think someone would lend me one to test, lol! .