weird shape stars

[cbbella]

hi, i have a canon 70d attached to a skywatcher ST80 sitting on sw star adventurer pro with the L-bracket.  i levelled my tripod and polar aligned.  i switched to liveview and zoomed in on a bright star (Arcturus) and used a bahtinov mask to focus.  i then took a test shot at 30secs at iso1600 and the stars look a weird shape.  does anyone know what is the cause of this

original RAW file attached

 

 

_MG_0336.CR2

Edited July 24, 2020 by cbbella

[MarkAR]

Looking at the direction of the smudging in the stars, most of it is diagonal bottom left to top right. Except for the bottom right corner of the image where it is bottom right to top left. 

Difficult to judge but it might be image tilt, possibly from the focus tube.

[cbbella]

I have to have my focus tube fully extended to obtain focus and then locked in position with the screw.  i do notice a little movement of the focus tube especially with the heavy DSLR attached so it may well be image tilt as you suggest, thanks

[MarkAR]

Might be worth using a screw in extension and moving the focus tube in.

[cbbella]

i think i have one somewhere, i'll give that a go. thanks