RASA11 (V1) - Strange severe tilt

Rainer Ehlert · Dec 3, 2025, 05:05 PM

Hi,

Reading that analysis for me that is not tilt.

Just imagine take a paper and lift it on the two opposite corners.

Is that a stacked image or a single one?

Is this a telescope where the camera is where normally a secondary mirror is?

I am trying to find an explanation for that…

Please post a full size image in order to look at the star shape.

Hi,

It is a stacked image

The telescope is a RASA11 - the camera is in the primary focus, no secondary mirror

full size imge - 300MB, not possible, here is a screenshot

📷 image.pngthe upper left and the lower right corners are similar - the stars are donuts, the lower left and the upper right corner - the stars are more or less in focus and round

Another thing I was thinking is perhaps a slight field rotation and PixInsight did not Align correctly the images.

This has happened lately a few time in my images.

I am just throwing ideas onto the table …

I am not an expert at all but have analysed a lot of images with the help of some friends here in Mexico

Uuh, that does not look good. Never ever seen something like that. I had also a strange pattern but that was 3 corners quite similar and one completely off.

Have you checked all frames? I know that is cumbersome but would shed some light on it.

Do you have another camera to make some tests and so we can rule out the camera?

Is there a way to rotate the camera in front of that scope and so we could see if this pattern rotates too which would mean it is the scope. If it does not rotate it is the camera.

andrea tasselli · Dec 3, 2025, 06:30 PM

I can't see much but looks like the camera is tilted along the diagonal, nothing too uncommon. One corner is too near and the other too far.

Very good point. Did not think about that. That happens when one corner is in front of the focus plane and the other corner is behind the focus plane which gives us unfocused stars. Shame on me.

But that must be a hell of a tilt.

Had the same thing happen recently with a 2600MC. My 2600MM worked great with my Rasa 11 V1 w/ UFC right out of the box but when I went to put on a second 2600MC, I had this diagonal tilt. I spent no less than 2 hours working with the 2600MC’s tilt adapter trying to find the right combination. After approx 30 tries, I got it lol. If you don’t already know, small adjustments go a long way.

Only could read this very quickly, so I may be off-base. But would it not be best to assess this sort of issue with individual subs? And as such, you might generate a separate imaging session to pick a field that has stars that are bright, so that you can take very short subs, to minimize seeing issues, etc.

Edit: Stacked data will likely cover up any true optical defects and may well make non-optical problems even worse. So single subs need to be studied. And that is how Hocus Focus works, not on stacked data.

My being off-based aside, then if you have an issue that is unresolvable with processing, as a former RASA owner, I have the similar experience of this sort of thing and the solution is likely going to be sending it back to Celestron for them to realign everything. If you want to do a collimation yourself, be prepared and be skilled. At best, you may just get the amount of improvement you need, even if not perfect. Worst case, you send it back to Celestron.

Alan Brunelle · Dec 3, 2025, 11:56 PM

Only could read this very quickly, so I may be off-base. But would it not be best to assess this sort of issue with individual subs? And as such, you might generate a separate imaging session to pick a field that has stars that are bright, so that you can take very short subs, to minimize seeing issues, etc.

Edit: Stacked data will likely cover up any true optical defects and may well make non-optical problems even worse. So single subs need to be studied. And that is how Hocus Focus works, not on stacked data.

My being off-based aside, then if you have an issue that is unresolvable with processing, as a former RASA owner, I have the similar experience of this sort of thing and the solution is likely going to be sending it back to Celestron for them to realign everything. If you want to do a collimation yourself, be prepared and be skilled. At best, you may just get the amount of improvement you need, even if not perfect. Worst case, you send it back to Celestron.

Alan, you are absolutely right - see one of my previous posts. I checked the tilt in single subs as well - before and after the flip and the reverse. That means, it is a strong one-sided tilt which is summed up to a double-sided one in the stacked image, the one, which I posted initially.

George,

You need to understand that tilt analysis is using HFD as a proxy for measuring tilt. There are several factors that influence the HFD measurement of a field, focus being chief among them. When performing tilt analysis with a single frame, and comparing that to another single frame you are assuming that both frames are at perfect focus. I’m talking about microns of focus position here, especially with fast systems like RASA where your CFZ is very small. So any focus shift that makes your focus a few microns away from perfect, such as thermal changes to your system, or mirror shift, will amplify or possibly invert your tilt analysis. You also have the compounding effect of field curvature on tilt analysis due to backspacing error (or optical system limitations on field correction). The only real way to perform a robust analysis of system tilt is to analyze a focus bracket run using ASTAP Hyperbolic Curve Analysis, or NINA Hocus Focus. You may find this information helpful as you navigate the topic of tilt and spacing. https://www.dropbox.com/scl/fi/dotyh2gzmojmy75p5kvby/2025-09-12-3nd-Revision-A-guide-to-fixing-tilt-and-spacing-with-objective-analysis-Chris-White.pdf?rlkey=ek4ys23120p9hujidi9xjfnh9&st=r3t9vd3f&dl=0