Takahashi Epsilon spacing / tilt

[tooth_dr]

I've never been entirely happy with the star shapes in the Tak, but until now I've been happy just to shoot with it, and enjoy the speed at which is generates images.

It was pointed out that the diffraction spikes were not aligned the whole way across my image of M31, and on the left side as you look at it, the diffraction spikes are obviously separated compared with the right side of the image.

 

I took at look at the focuser, and to my surprise I noticed the drawtube was actually loose.  I was able to rock it back and forward 1-2mm which was not right.  I tightened up the pressure on the drawtube and the movement was gone.

Late last night I decided to head out, just after midnight, to see if this helped.

I took a few images of Alpheratz, moving it around the frame.  I've attached the images below.  I also took an image of Andromeda with the mask on to help compare the focus of the stars throughout the image.  I dont know if either of these tests prove anything, so if anyone have any input that would be great!

 

 

Analysis of the M31 image from last night yields this in CCDI:

 

Compared with similar M31 image last week prior to tightening the drawtube:

 

Just visually looking at the stars they do appear to have an elongated radial look that suggests my spacing is too far out.  I know that CCDI can yield inaccurate results, and that the results are open to interpretation.

This is an uncropped image from last night 5 x 120s

 

Should I remove some spacing or leave well alone now.

 

TIA

Adam.

 

 

Edited September 1, 2020 by tooth_dr

[Adam J]

If you did make an adjustment it would literally be a fraction of a mm. Personally I would find that result acceptable though and just crack on with imaging. 

Adam

[tooth_dr]

3 hours ago, Adam J said:

If you did make an adjustment it would literally be a fraction of a mm. Personally I would find that result acceptable though and just crack on with imaging. 

Adam

Everything has a low tolerance at F2.8!  I think I might try removing the 0.3mm spacer that I added, I think the sensor is too far away.  I think it's too far rather than too close.

The curvature of several images I have measured from different nights are between 12-18%, which to me seems like a lot?  But then again it may not be.  

 

[tooth_dr]

The ED80 I have is not spaced out enough, and all the stars appear to be pointing to the centre.  I ran that through CCDI, and the curvature is opposite to the above.  I have since added 1mm to it and its better, I think focus wasnt great in that session