Skewed stars help

[Gerry Casa Christiana]

Hello all

Im just started in imaging and I have to say I'm pleased with the first result BUT on closer inspection I see I have slightly oblong stars. So people know what I've got and done here it is  

http://www.astrobin.com/full/271950/0/?nc=user

I have a baader coma corrector that I'm using set to 55mm from canon sensor and I have tried short exposures and I notice that it's still there in short exposures. Could it be collimation? It's the only thing I didn't do that evening. 

I would appreciate your input! 

Thanks

Gerry

 

[Uranium235]

The distortion seems to be across the whole frame (centre included). A few suggestions:

1) Collimation, make sure its good (or as good as you can get)

2) Make sure the corrector and camera is properly seated in the drawtube (do the thumbscrews up nice and tight) - as any wiggle or slop will be punished with dodgy stars and/or flex.

3) Make sure the focuser has no slop itself - that can be reduced by tweaking the tension screws underneath.

[spaceman_spiff]

I had a similar problem a while ago. It was tilt caused by a gap between the drawtube and the telescope. I wedged two bits of card in there and that fixed the problem.

HTH Dan

[Xplode]

Collimation is definitely a little of and i think it could also partially be caused by vibrtations from the mirror. Have you tried the mirror lock and see if it makes any difference?

[Gerry Casa Christiana]

14 minutes ago, spaceman_spiff said:

I had a similar problem a while ago. It was tilt caused by a gap between the drawtube and the telescope. I wedged two bits of card in there and that fixed the problem.

HTH Dan

By the drawtube do you mean the actual focuser? 

Yes im a newbie. I've also just checked and my coma corrector was at 53mm from the focal plane so it could be that. 

I hope to try tonight even with the moon

Thanks

 

[spaceman_spiff]

1 minute ago, Gerry Casa Christiana said:

By the drawtube do you mean the actual focuser? 

Yes im a newbie. I've also just checked and my coma corrector was at 53mm from the focal plane so it could be that. 

I hope to try tonight even with the moon

Thanks

 

Hi there,

Yes that's where the problem was for me. There was a few millimetres of free movement and the draw tube (the bit that goes in and out) was pushed by the focus locking screw. Check the focuser for any free movement, if there is none then you can rule this problem out and look at collimation.

Dan

[Gerry Casa Christiana]

13 hours ago, spaceman_spiff said:

Hi there,

Yes that's where the problem was for me. There was a few millimetres of free movement and the draw tube (the bit that goes in and out) was pushed by the focus locking screw. Check the focuser for any free movement, if there is none then you can rule this problem out and look at collimation.

Dan

Thanks Dan

Ill check that. Many thanks for the help

Gerry

[alacant]

Hi. Not certain but I think that's caused by the heavy mirror moving as you slew. The clips which hold the mirror have to be firm, but not tight. Maybe you have a loose one? After checking, it's a good time to collimate from zero. Worth a look? HTH.

[Gerry Casa Christiana]

3 hours ago, alacant said:

Hi. Not certain but I think that's caused by the heavy mirror moving as you slew. The clips which hold the mirror have to be firm, but not tight. Maybe you have a loose one? After checking, it's a good time to collimate from zero. Worth a look? HTH.

I will certainly check all these things.

many thanks 

[Gerry Casa Christiana]

On 17/11/2016 at 18:40, Xplode said:

Collimation is definitely a little of and i think it could also partially be caused by vibrtations from the mirror. Have you tried the mirror lock and see if it makes any difference?

I think it's about the only thing I haven't tried. Still have the same problem. I'm beginning to wonder if it's the mirror on the spider vanes that's not correctly set up but is it hard to adjust. I'll try the mirror lock on the camera. It's like the light difused and slightly skewed like through a prism.