Help: Is this coma?

[Peje]

I'm noticing that my stars to the left side of the image are trailing off towards the edge. To me, stars in centre and right look fine. Could this be coma?

I have collimated for a different target that I'll be switching to in a couple of hours (assuming the weather holds up) but I suspect this isn't just because the collimation.

Any advice would be greatly appreciated,
Pete

[ronin]

I really would not like to say yay or nay. To me and my eyes are garbage and the screen is not good the left just looks sort of less in focus. The right hand stars just seem more well defined.

At F/4 you would I expect need a coma corrector and if that was without one it is a good result.

The left hand ones seem to almost be 2 star images imperfectly centered on one another, thus giving an "extended" size to them. Not reaqlly a comet like tail. The imperfect centering is sort of at 8 O Clock in the lower left and at 10 O Clock in the upper left. So coma like in that respect of radial.

Haven't helped much have I ?

Maybe check collimation but unless that is out I cannot really add much. Camera tilt would throw the lot out.

Do you not have a coma corrector ?

[Louis D]

If it's only on one side, I'd guess it's out of focus stars (which can mimic comatic stars).  The question would be why are they out of focus on only one side.  I'd have to guess the imager isn't perfectly square on to the image plane.  Something is probably tilted just slightly somewhere.  Might just be droop in the imaging train.  Is the left side up or down in the real world at the focuser?

[Peje]

3 minutes ago, ronin said:

I really would not like to say yay or nay. To me and my eyes are garbage and the screen is not good the left just looks sort of less in focus. The right hand stars just seem more well defined.

At F/4 you would I expect need a coma corrector and if that was without one it is a good result.

The left hand ones seem to almost be 2 star images imperfectly centered on one another, thus giving an "extended" size to them. Not reaqlly a comet like tail. The imperfect centering is sort of at 8 O Clock in the lower left and at 10 O Clock in the upper left. So coma like in that respect of radial.

Haven't helped much have I ?

Maybe check collimation but unless that is out I cannot really add much. Camera tilt would throw the lot out.

Do you not have a coma corrector ?

Yes using a coma corrector, I didn't mention camera tilt but I was thinking about it.

Camera tilt is something that is vexing me a little. I have no idea how I can reliably avoid it since my focuser isn't one of the threaded types.

[Peje]

2 minutes ago, Louis D said:

If it's only on one side, I'd guess it's out of focus stars (which can mimic comatic stars).  The question would be why are they out of focus on only one side.  I'd have to guess the imager isn't perfectly square on to the image plane.  Something is probably tilted just slightly somewhere.  Might just be droop in the imaging train.  Is the left side up or down in the real world at the focuser?

I think left on my image is actually the right side of the camera, it's a newtonian with camera mounted at 0/180 degrees.

[ronin]

Really can only suggest you check out as much as feasible in the time you have and hope that whatever the cause is gets rectified. But at f/4 the scope will need regular and often attention. Just thinking that maybe something has moved without you realising it, or sooner then expected.

Tilt would I expect show on both sides as it is the whole camera that is tilted.

I guess filters are in use are they firmly retained?

Satellite passing through on the left I presume.

[Louis D]

2 minutes ago, ronin said:

Tilt would I expect show on both sides as it is the whole camera that is tilted.

Not if he focuses somewhere between the center and right.  Then, it would be most obvious on the far left due to depth of field hiding defocus in the center and right.  I'd suggest going to live view of the image and magnifying the left side while applying manual torque to the imaging train to see if there is flex.

[Peje]

2 minutes ago, Louis D said:

Not if he focuses somewhere between the center and right.  Then, it would be most obvious on the far left due to depth of field hiding defocus in the center and right.  I'd suggest going to live view of the image and magnifying the left side while applying manual torque to the imaging train to see if there is flex.

I was thinking this myself but looking at the focus output from SGPro it seems fairly balanced.

I guess I'm gonna have to put my mech eng degree to use and figure out a way to get consistent parallelism