The old 'egg shaped stars' problem

[edarter]

Hi,

Looking for advice as to why I'm getting egg shaped stars, but mainly in one corner! I'm using a SW 130PDS with a Baader MPC Mk3 and Canon EOS 600D. I've used an old filter ring to get me to the magic 55mm but still I'm getting this same problem. Any advice greatly appreciated.

Single 60 second sub below taken tonight while trying to get the Western Veil Nebula. Bottom right of the image is the worst for egg stars.

Edited November 11, 2019 by edarter

[ebdons]

Hi could be flex or flatness in imaging train, I have this sometimes and it helps to have the focuser hanging down as much as possible and the mount balanced, not sure of the weight on the focuser also on a 130 pds?  you can also use the photoshop star shape fix which does work well. other folks may know more on here. ton

[edarter]

Thank you, did wonder about flex but assumed that I would see it in opposing corners more. Will try rotating the OTA in its rings to position the focuser better.

Is that star shape fix a plug-in? not heard of that before.

Thanks
Ed

[tooth_dr]

It’s been a while since used my DSLR with an MPCC but I thought the EOS M48 adapter got you there exactly?

All the stars looks a little eggy so your spacing isn’t quite right.  What’s the scopes collimation like also?

[Skyline]

Are you sure it's not the mirror being pinched by the clips. It's an easy fix not like refractors 

[alacant]

Hi

You need 58mm from the m48 threads, not 55mm. A 3 to 5mm filter ring will do it. The extra spacing will cure the coma but not the astigmatism visible top right.

Loosen the primary mirror clips about 1/4 turn for each screw.

Cut 10mm or so from the focus barrel, the end which protrudes into the tube.

I think the camera isn't held square. This is almost impossible to do with the supplied sw focuser and the mpcc. One thing which may help is drill and tap another m4 screw at 120º to the existing thumb screws to get purchase on the cc, but make sure they are rounded so that they avoid the undercut on the cc.

Now collimate the telescope.

Or as suggested, just leave it as it is and correct in software.

It sounds a lot but can be done in around an hour.

Cheers and HTH