Could this be sensor tilt?

[Gumminess8083]

Hmm, interesting observation!

I'll try taking everything apart once again and re-tightening all the parts!

10 hours ago, pipnina said:

Could be the front cell or the focuser aren't quite done up tight? I've had that issues before...

Am I correct in assuming that fixing this would require me to open up my scope?

[Richard_]

When I started imaging with the  QHY268M and filterwheel with my FLT120 back in Summer 2022, I thought I had tilt and back focus issues. After I got the right back focus, it turned out my focus tube was drooping which was causing the tilt. Nipping up the screws on the draw tube resolved the problem and I no longer had tilt issues. 

Back in November, I swapped my telescope out for my Redcat51 and put the QHY268M and filterwheel on. I noticed some issues which looked to be tilt related which was surprising since I don't believe I had major tilt with my FLT120, and prior to this my ASI533 and Mini-EFW with the Redcat produced no tilt issues. 

I haven't had a clear night since then to test on stars, but I'm currently in the process of building a jig per the thread linked below. I want to verify if there's tilt on my camera before adjusting the tilt plate on my Redcat.

• If my sensor is tilted, I will correct it, then set the camera and filterwheel back on the Redcat to check if any tilt remains
• If the sensor is found to be flat, then the tilt is being introduced somewhere between my filterwheel and Redcat (eg spacers, Redcat tilt plate). This tilt could be caused by sagging due to the extra weight of my camera system compared with ASI533 and mini-EFW. Or perhaps one or more of my spacers are not perfectly flat, in which case adjusting the tilt plate on the Redcat could alleviate this

Sorry I don't have an answer, but I'm going through a similar scenario with regards to tilt and looking to resolve. 

 

[pipnina]

1 hour ago, Gumminess8083 said:

Hmm, interesting observation!

I'll try taking everything apart once again and re-tightening all the parts!

Am I correct in assuming that fixing this would require me to open up my scope?

In my case it meant tightening the flathead grubscrews that held the focuser onto the scope. These have always been external screws for me so I could just take a screwdriver to them and tighten them to remove the slop. Only my current focuser is tilt-adjustable though.

[Richard_]

On 18/01/2023 at 09:38, Richard_ said:

When I started imaging with the  QHY268M and filterwheel with my FLT120 back in Summer 2022, I thought I had tilt and back focus issues. After I got the right back focus, it turned out my focus tube was drooping which was causing the tilt. Nipping up the screws on the draw tube resolved the problem and I no longer had tilt issues. 

Back in November, I swapped my telescope out for my Redcat51 and put the QHY268M and filterwheel on. I noticed some issues which looked to be tilt related which was surprising since I don't believe I had major tilt with my FLT120, and prior to this my ASI533 and Mini-EFW with the Redcat produced no tilt issues. 

I haven't had a clear night since then to test on stars, but I'm currently in the process of building a jig per the thread linked below. I want to verify if there's tilt on my camera before adjusting the tilt plate on my Redcat.

• If my sensor is tilted, I will correct it, then set the camera and filterwheel back on the Redcat to check if any tilt remains
• If the sensor is found to be flat, then the tilt is being introduced somewhere between my filterwheel and Redcat (eg spacers, Redcat tilt plate). This tilt could be caused by sagging due to the extra weight of my camera system compared with ASI533 and mini-EFW. Or perhaps one or more of my spacers are not perfectly flat, in which case adjusting the tilt plate on the Redcat could alleviate this

Sorry I don't have an answer, but I'm going through a similar scenario with regards to tilt and looking to resolve. 

 

Replying to my own post as a follow up. Here's a summary of my findings, which may be helpful for others:

• Tilt was not attributed to my camera -> source of tilt was likely due to the tilt plate on the Redcat not being perfectly flat from factory
• After tilt was eliminated, my images with Redcat51 appear to show slight coma or astigmatism around perhipary of image
• Deconvolution tools (like BlurXterminator) may help fix star shapes

Camera Tilt Analysis

I got around to making a rig to determine if my camera had any tilt. In short, the camera appeared to be virtually free of tilt from the factory without further adjustments needed. I've provided a link to my test rig in the SGL cross-post below. This makes sense since my images were tilt free with one telescope but appeared to have tilt with the other (Redcat51). So it looks like the source of tilt is not from the camera.

 

Tilt Analysis and Corner Inspection

Below, I have provided some pre-tilt analysis images of my FLT120 and Redcat51 when analysed using ASTAP. The FLT120 is perfectly tilt free whilst the Redcat51 showed signs of tilt in the upper right corner. This is what lead me to performing the tilt test as mentioned above. In order to do this test, I needed to remove my camera from the Redcat51 and unbolt the camera from the filterwheel. Upon completion of my tests, before I put the camera back onto the Redcat I loosened the push/pull screws on the Redcat tilt plate and flattened it against the rotator, then tightened the screws back in. This puts the tilt plate back to square and offers a good starting point. I then put the camera, filter wheel and adapters back onto the Redcat ensuring that everything was nice and snug.

I took some more images using the Redcat51 and repeated the analysis in ASTAP. Now, the images appear to be flat and the tilt in the upper right corner has been removed. My best guess is that either the tilt plate for the Redcat wasn't "flat" from factory setting or my imaging train wasn't screwed tight enough onto the Redcat which would allow a bit of drooping.

I looked closer at the corner stars in the "post tilt" images, and I can now see what looks to be slight coma or astigmatism since the stars aren't perfectly round. It can't be back focal distance as the Redcat is of petzval design and is insensitive to it (also, my back focus was 56mm which is pretty standard) and images were shot whilst in focus. I've attached the Aberation Inspector results of my M45 master Luminance showing the corner stars. I gave it a blast of BlurXterminator (deconvolution tool) and the star shapes are much better. I'm going to leave this system as is without further changes, knowing that the star shapes can be minimised/corrected in post processing.

 

Before doing tilt analysis:  QHY268M with FLT120 (No tilt)

 

Before doing tilt analysis:  QHY268M and Redcat51 (tilt in upper right corner, look at the star shapes)

 

After doing tilt analysis:  QHY268M and Redcat51 (no tilt)

 

After doing tilt analysis:  QHY268M and Redcat51 (no tilt)

 

M45 master Luminance aberation inspector (pre-BlurXterminator deconvolution)

 

M45 master Luminance aberation inspector (post-BlurXterminator deconvolution)