Is my Redcat faulty.

[Thorney]

Below is a full frame shot with a Redcat 51, asi2600mc and optolong l extreme filter. 
 

I’ve only just recently noticed that the star shapes in the corners of these images seem off and I have read a few things online from people saying they had to return the Redcat due to coma issues.
 

My question is do I have this problem? Is it down to poor focus? or am I just being over fussy/ paranoid?

Any help will be much appreciated. 
 

[almcl]

Don't think it's coma so much as tilt.  Here's what ASTAP measures (28%):

[Laurin Dave]

I would suspect the most likely culprit is the camera chip rather than the scope,  several have reported tilt issues with the ASI2600.  I'd have a go at adjusting the tilt screws on the face, probably just a fraction of a turn  required to fix. 

[Thorney]

30 minutes ago, almcl said:

Don't think it's coma so much as tilt.  Here's what ASTAP measures (28%):

Thank you for looking at this and highlighting the issue. I’ve seen a few people use these graphs but they are a bit complex for me. I guess I need to do my research and do some more learning as it proves to be rather helpful. 

[Thorney]

19 minutes ago, Laurin Dave said:

I would suspect the most likely culprit is the camera chip rather than the scope,  several have reported tilt issues with the ASI2600.  I'd have a go at adjusting the tilt screws on the face, probably just a fraction of a turn  required to fix. 

Thank you for the reply. I’ll have a look into this and see if I’ll be able to fix it. Hopefully it is just a minor tweak. 

[Laurin Dave]

I'd think so based on my own ASI2600mc which had much worse tilt than yours and it was just a fraction of turn to correct .. 

How_to_clean_ASI_camera_and_redry_the_desiccant (3).pdf

[Adam J]

Sure you have tilt but I honestly do  i see a little coma in the centre of the field and that should not be the case as the result of tilt alone. 

Best thing to do is a star test to examine the optical alignment of the scope. Centre a bright star in the FOV and then de-focus it until you have about 5 rings visible. Do this either side of focus blow it up and post the result and i will be able to say for sure if there is a problem. 

I use one of these at about 10metres to do this without having to wait for good seeing / clear skys. 

https://www.firstlightoptics.com/other-collimation-tools/hubble-optics-5-star-artificial-star.html

Adam

[Thorney]

5 hours ago, Adam J said:

Sure you have tilt but I honestly do  i see a little coma in the centre of the field and that should not be the case as the result of tilt alone. 

Best thing to do is a star test to examine the optical alignment of the scope. Centre a bright star in the FOV and then de-focus it until you have about 5 rings visible. Do this either side of focus blow it up and post the result and i will be able to say for sure if there is a problem. 

I use one of these at about 10metres to do this without having to wait for good seeing / clear skys. 

https://www.firstlightoptics.com/other-collimation-tools/hubble-optics-5-star-artificial-star.html

Adam

Thank you for the reply. It’s showing a couple of clear nights this week so I’ll have a go and post my results. Appreciate your time. 

[rnobleeddy]

5 hours ago, Adam J said:

Sure you have tilt but I honestly do  i see a little coma in the centre of the field and that should not be the case as the result of tilt alone. 

Best thing to do is a star test to examine the optical alignment of the scope. Centre a bright star in the FOV and then de-focus it until you have about 5 rings visible. Do this either side of focus blow it up and post the result and i will be able to say for sure if there is a problem. 

I use one of these at about 10metres to do this without having to wait for good seeing / clear skys. 

https://www.firstlightoptics.com/other-collimation-tools/hubble-optics-5-star-artificial-star.html

Adam

Does this work for setting back focus for flattener/reducers etc?  I can't think of any reason why not.

[Adam J]

3 hours ago, rnobleeddy said:

Does this work for setting back focus for flattener/reducers etc?  I can't think of any reason why not.

Back focus is something best judged by looking at the in focus corner stars in my opinion as out of focus stars will result in the corrector being in the wrong position. With a flattener reducer the image is only ever optimally corrected when in focused.

If you mean with a in focus artificial star then even in this case the optimal back focus may change with for focus distances shorter than infinity although it will get better as you increase the distance to the artificial star.

Adam

Edited January 10, 2022 by Adam J