Whats wrong? Collimation, Tracking, Focus?

[Stian]

Hi,

Autumn is here in Norway which means I can start using my scope again. My setup: Nexstar 6SE on a wedge with a Canon 100D connected.

I never seem to get my images right. There are always some strange looking stars and I am trying to figure out if this is related to Collimation, Tracking, Focus or something else.

Focus: (Vega)

30sec Exposure of Vega:

As you can see Vega looks OK, but all surrounding stars seems to be having some issues. Is there a clear indication based on Your expertise on where my problem might be?

50sec exposure of M57 (Ring Nebula)

Thanks.

Stian

 

 

[Dave S]

Hi Stan

My first question is are you using the Alt-Az Goto mount that the 6E normally comes with?  I ask this because I've had similar issues with Alt-Az Goto's as it seems (to me) that the tracking motors don't seem to operate together but in turn, so you get this funny L shaped tadpole effect on stars.  Unfortunately Alt-Az mounts aren't really very good for imaging.  Saying that.  top marks for getting a really good image of the ring nebula if indeed you are using Alt-Az.

 

As the 6E is of the cassegrain type of scope I don't think collimation is the issue.  as the distortion is off axis I would suspect it is coma distortion which can be corrected with a suitable coma correcter.  I would also consider making or buying a wedge to make the mount behave more like an equitorial mount so only one motor has to drive the tracking.

 

Anyone out there who has more experience would be better placed to advise you on this so feel free people to correct me.

 

Dave...

 

[Dave S]

Many apologies

I misread your name.  sorry Stian (not Stan. Doh!)

Dave...

[Victor Boesen]

47 minutes ago, Dave S said:

As the 6E is of the cassegrain type of scope I don't think collimation is the issue

Agree, i found this picture on the internet, which indicates how stars look with and without a Baader Rowe coma corrector, and as you can see the star on the left looks really identical to the stars you have on your picture.

But if you haven't had this issue before, then i don't know what it is.

Clear skies!

Victor Boesen

[MattJenko]

Being slightly pedantic, that image of Vega through the mask doesn't look spot on either in terms of focus, although I think that the main issue is the aberrations from the uncorrected SCT itself.

[MattJenko]

Also, as the aberrations look worse on the left hand side and get progressively more so, I think there is also some tilt in your imaging train somewhere, almost certainly a focuser sagging with the weight of the camera.