M31 - Edge stars elongated

[Jerry Barnes]

Like several others I took advantage of the first clear sky for ages.  This is 3 hrs of data on M31, 120s subs.  The stars at the edges are elongated and look terrible but the ones in the centre are ok by comparison.

I have some issues with guiding to sort out and I'm struggling to get the focus working reliably but first things first, any ideas what my issue with the stars is?

Could it be something to do with where the filter is?  Before I got the ASI2600 I was using a Nikon Z6 and the filter was mounted in the flattener, about as far away from the sensor as it could be.  Now its in the filter drawer set up like the attached image.  I seem to remember reading something which might be relevant but I cant find it now.

 

 

EQM-35 Pro

ZenithStar61 plus flattener

Optolong CLS filter

ASI 2600MC pro

Guiding with and ASI120mm mini and William Optics 50mm Slide-base Uniguide scope

ZWO focuser

[scitmon]

Certainly looks like incorrect spacing between your flattener and the camera (should be 55mm), can you describe what you have in between these?

[Jerry Barnes]

I have whats in the diagram, ie

WO flattener for the ZS61 (adjustable, set to about 0.7 in this case,  1/3 of the filter width) +  

M42-M48F-16.5L +

ZWO Filter drawer +

ASI 2600MC

thats 16.5 + 21 + 17.5 = 55mm plus the 0.7

 

 

[alacant]

Hi

We don't see many of these but IIRC (68mm), you need an extra 13mm between the FF and the sensor.

HTH

 

Edited September 8, 2021 by alacant

[Jerry Barnes]

10 hours ago, alacant said:

Hi

We don't see many of these but IIRC (68mm), you need an extra 13mm between the FF and the sensor.

HTH

 

yes it does thank you.  Looking at the manual again I need to adjust the flattener to 12.9 to get the total of 67.9.  Thats what I had before with my Nikon - duh!