ELONGATED STARS in one corner only

[carastro]

Been imaging for ages but don't quite understand this.

I was imaging with a dual rig, and the problem is not in both cameras, so I don't think it can be guiding.

On my ED80 which has a Baader click lock, so I don't think it can be tilt, I am getting elongated stars in one corner only, but the elongation is not away from the centre, but almost as if there is field rotation, i.e. in a rotational direction.  But as I say only in one corner.

If the stars had been elongated pointing away from the middle then I would have thought it was spacing , which I must admit I did very sloppily (i.e. from memory rather than measurement).  But surely if the spacing was wrong I would have the same in all four corners.

Any experts out there who can offer a solution?

Many thanks in anticipation, and here is hoping I will be able to rectify it.

Carole 

 

 

[parallaxerr]

It is an odd one. Field rotation type elongation suggests flattener spacing is too far from the sensor, but only in one corner does suggest tilt is the cause. Can't imagine what else it could be?

 

P.S. I had tilt even with a baader click-lock. In the end I bought 2" nosepiece extensions to fit to my flattener so it extended further in to the focuser tube bore, keeping everything better aligned.

[carastro]

Thanks for your reply.  

Previously when I have used the Baader click lock, the stars have been round in all corners.

What I am getting is what is showing in your second image but only in the bottom right corner.

I am also scratching my head. 

Polar-aligned "spot on" with Polemaster. 

Carole 

 

[carastro]

No other ideas?

Well if no more ideas are forthcoming, I will double double check my spacing next time out, but it's really puzzling.

Carole 

[michael8554]

Hi Carole

You're thinking that if it were tilt then top left AND bottom right would be out ?

So top left as Jon's first image, bottom right as Jon's second image ?

Try rotating the camera 90 degrees and see where the problem is then.

Michael

[symmetal]

If the centre of the sensor was not perfectly on axis with respect to the field flattener but was shifted along one of the sensor diagonals then one corner of the sensor would then be further away' from the flattener's central axis compared to the other three corners. If the flattener/sensor spacing was also slightly too far the 'radial' elongated stars would only show in that one corner.

Try moving the sensor slightly closer to the flattener or perhaps just rotating the camera by 180 will shift the sensor to be more on axis.

[carastro]

Thanks Guys, I will check the spacing is accurate in the first instance, its all packed away in the van at the moment, (went to camp last week and going back again tomorrow and its too deeply packed inside to retrieve.  I have two cameras and two FRs and I "think" this camera was on the one with the Baader variable spacer and I had previously used it on a CCD/Camera lens set up, so its possible the spacing was slightly incorrect, but didn't have a measure with me.  I have packed one for this trip.  

Having a dual rig I need to orientate the cameras the same way.  180 degrees won't be a great step because the filterwheel will be sticking upwards and getting caught up on the scope cover when I put it on and off which is not ideal.  But maybe changing the length of the Baader variable spacer will do the trick. 

Carole 

 

[symmetal]

4 hours ago, carastro said:

Having a dual rig I need to orientate the cameras the same way.  180 degrees won't be a great step because the filterwheel will be sticking upwards and getting caught up on the scope cover when I put it on and off which is not ideal.

Ahh! I only mentioned it as I 'cured' a slight tilt error by rotating the camera 180 but as it was an Atik One with the built in filter wheel the orientation of the camera didn't affect anything. ? Good luck with getting your problem fixed. 

[carastro]

If I continue to get the same problem it will be worth rotating 180 degrees when I get home and can do it in the obsy as a diagnostic aid.

Carole