Odd star shapes C11 Edge + 0.7 FR + COAG + ASI071MC Pro

[rodrigol]

Hi,

I recently installed a C11 dew heater in front of the corrector plate. I did this with the telescope in the vertical position and don't think I've overtightened anything.  The issue I see now is that stars look egg-shaped, more on one side than the others. The image attached (not processed nicely but only to show the issue I'm facing) shows this (please zoom in to the corners). What can be causing this? Is this tracking, flex (I use COAG), collimation, corrector plate alignment? Thanks for watching!

 

Edited May 15, 2022 by rodrigol

[newbie alert]

Collimation,spacing possibly

Did you use flats?

[rodrigol]

Nothing in the form of calibration frames- I will do flats and darks next.  Spacing between the FR and the sensor is 147+/- 1mm. Collimation is good in the centre. I don't know how to diagnose this. 

Thanks for replying!

 

[rodrigol]

Here is  the image after processing with calibration frames (darks and flats). Thanks!

 

[AstroMuni]

Beautiful shot. If this was mine, I would be happy and not try to improve it further 🙂

[rodrigol]

Thanks for the kudos(!) I really want to get the most out of the scope and mount. I feel I have learned a lot about processing but what is the poiunt if the kit is not performing 🤗

 

[alacant]

3 hours ago, rodrigol said:

what is the poiunt if the kit is not performing

Hi

Mmm. Our only experience with a sct was an old orange tube c8 and even with excellent seeing, we couldn't get anywhere near this quality; for this type telescope at such a focal length, it's pretty good.

If you want to go further and assuming the collimation checks are OK, there is -very slight- drift. Mount backlash maybe? Seeing not good enough? Guiding aggression?

 

And almost certainly the main culprit, tilt:

 

It could simply be a case of dismantling the camera end and re-threading, tightening with the corrector pointing at the ground and wiggling the parts as you go. Another trick is loosening the reducer lens retaining ring and shaking on a horizontal surface whilst re-tightening until the rattle just disappears.

Is the mirror locking ok? Does the collimation hold as you alter the tube angle?

Worth a try?

Cheers and good luck.

 

Edited May 17, 2022 by alacant

[rodrigol]

Wow! Thank you so much for all the advice above. It all makes perfect sense to me. Please, can I ask how did you measure the tilt onthe image? To me it seems there is a lot of tilt. I hope the main cause is in the imaging train and your advice regarding re-threading eveything carefully helps. 

I really like how people help each other here!

Best wishes and thanks again!

R:)

[alacant]

1 hour ago, rodrigol said:

measure the tilt

We use Siril.

HTH

[rodrigol]

Fantastic - Siril, eh?! Going for it now. Many thanks! Lot's to read and learn now 🙂

[rodrigol]

Many thanks for the advice above. I had the lucky luxury to have clear skies on a Saturday/Sunday night and decided to image the Eagle nebula after having reseated the entire imaging train when the telescope is in a inverted vertical position. The Celestron OAG (which is a great piece of kit but one has to be careful all parts are seated properly flush to one another before tightening all the thumb screws) was probably one of the mayor contributors to the tilt observed above.  Another posible source of tilt is the Celestron heater ring. I reduced the voltage going to it to ~1/3 (don't know exactly how much) of what it was. Siril is an amazing piece of software! Thanks for the tip!!!

Below is an early processed Eagle nebula with the result of SIril's 'tilt' command. There is some way to go but the tilt has been vastly improved!

 

 

Stars are rounder on all corners and I feel the telescope and current imaging train are performing much better. The only possible moving part in the imaging train is the tilt corrector on the ASI091MC Pro, which I'm going to examine as soon as I understand which corner of the image corresponds to each screw. 

I'm very grateful to everyone for their comments and kind help!