Elongated stars at the bottom left of image

[konstantinos75]

Hi

I send you this 5 minutes image of Castor I have captured with my setup.

https://www.dropbox.com/s/ytxhkswloufx3rq/castor-5min.jpg?dl=0

As you can see at the bottom left the stars are not round, but in the other parts of the image the stars are round.

My thought is that this is not a collimation issue because if that was the case I would expect elongated stars all over the image.

Any ideas what makes the elongated stars at the bottom left will be appreciated.

My setup:

Vixen VC200L f/6.4, sbig st2000xm CFW9

Imaging and guiding with sbig st2000xm

Thank you

Konstantinos

 

[pyrasanth]

The error may be caused by the field not being completely flat or tilted. The image analysis in CCDInspector has revealed a field curvature of 23% & a tilt of 15%- this might be enough to cause this issue. Try a field flattening lens & see if this helps. The test suggests your collimation is also out slightly but I don't think this will cause the effect you are seeing.

[ollypenrice]

While we might reasonably expect mis-collimation to be uniform across the image I recently found that it wasn't. (This was on a Meade ACF.) The defects from mis-collimation were, in fact , worse and worse in the direction of just one corner. I can't account for this.

Olly

[konstantinos75]

^Hello

^{Thank you both for your reply to my issue. I have loaded the 5 minutes FIT image of Castor to the CCDInspector.}

^{The result shows that my field when the CCD camera is attached to the focal reducer is not flat and comes with a 18.7% curvature.}

^{Also the CCD camera optics are not aligned with the telescope optics and there’s a 14% total tilt at the bottom left direction.}

^{The CCD camera with the filter wheel are attached to the focal reducer of the telescope using this Baader adapter.}

^{Baader Adapter from M68 and M60 to 2" - length only 12mm -  BA2458196}

^{But Vixen suggests the following adapter}

^{Use the optional Vixen Direct Wide Photo Adapter 60 and the proper T-Ring or the Vixen Camera Adapter 43 and proper T-Ring if you'd like to mount your camera to the Focal Reducer.}

^{So I don’t know if it’s the spacing distance between the focal reducer and the CCD camera sensor which produces the field curvature in my case. The tilt can be justified with the camera not adjusted firmly or a focuser tilt.}

Konstantinos