Coma

[Jpr78]

I recently collimated my 10” SN. I bought a laser but I don’t believe they are accurate unless you spend good money. So i used the secondary adjustment first method making sure the secondary was rotated to face the focuser and the tilt was proper. Here i used a laser and measured from the laser as it comes out of the focuser to the edge of the OTA tube and where the laser hits the other side to the edge of the tube as well. I then used a pinhole cap to get all 3 circles concentric through the pinhole (focuser tube end, pinhole and end of the OTA tube). I then adjusted to primary to bring the center donut into the center of everything. After this method I checked collimation with the laserr and it was off center on the primary by half an inch. I trust my manual method much more and chalked it up to bad laser collimation. My issue is with Coma on all of my images. Perhaps someone could shed some light as to whether my oblong stars are a result of coma or bad collimation. It is frustrating because it completely ruined what could have been a great image in my eyes.

Edited July 25, 2020 by Jpr78

[michael8554]

Does look like coma, the centre stars are round and the elongations all point away from the centre of the image.

SN's have less coma than many designs but presumably aren't perfect.

However this looks to be a Stack which may include stacking artefacts, so you should check your subs too.

Michael

 

[RayD]

Are you using a coma corrector, reducer or flattener of some sorts?  If so, I would check the spacing from that to your camera sensor.

[Jpr78]

I am not using any flatterers or CCs. I went through all of my subs. I had to trash about 15 of them. That stack is only 6 subs.

[michael8554]

38 minutes ago, Jpr78 said:

I had to trash about 15 of them.

For what reason ?

Michael

[Jpr78]

15 hours ago, michael8554 said:

For what reason ?

Michael

A few were satellites and others the coma was much worse almost looking like double stars.

[michael8554]

Satellites trails will be removed if you choose Kappa-Sigma stacking.

Double stars sounds like guiding problems.

Michael

[vlaiv]

This is 10" Schmidt Newtonian?

That is something like 1000mm of focal length or so? I presume camera is full frame sensor in order to get that sort of FOV?

No way you will have fully corrected full frame circle on that scope. Best you can hope for would be 4/3 or similar?

Guiding problems will manifest across whole frame equally - all stars will have same issues - not only corner ones.