Hi,
My original post got hijacked and turned into a post on Mosaics so I am reposting this in the hope that someone can help.
I am having problems with the image rotating after a meridian flip.
It is as if the camera has rotated, which it hasn’t, so the image taken after the flip is several degrees rotated compared to the image after the flip (this is after rotating the image 180 degrees to get both the same way up).
It’s not usually much of an issue as I crop the overlap out but I’m imaging chip filling targets at the moment and I can’t use the flip which is hitting my imaging time.
Jon, just to be sure, are you saying that this happens even if you’re not moving to a different pane in a mosaic? Ie, you’re staying on the same target? If so, I’ve noticed this as well, and don’t know what’s causing it. I don’t do mosaics, so it’s way down low on my troubleshooting list and I haven’t tried to figure it out. What rotator are you using? I use an Optec Pyxis 2" with Andy Galasso’s driver.
Yes, I also haven’t yet done Mosaics, I also don’t have a Rotator, the camera is in a fixed position which is why the rotation is odd.
Obviously something is out of kilter but I don’t know what, or how to go about working it out.
I have noticed that with the mount Polaris aligned my imaging camera does not have Polaris centered - even after allowing for the required offset.
Or to put it another way the camera is not quite polar aligned when parked even though the mount is.
So something, perhaps the shoe on the telescope or the mounting point on the mount is slightly off. Not sure if tis could cause the flip issue but its all I can think of.
Presuming you’re guiding, do you see field rotation from frame to frame irrespective of the flip? I.E. if you take 20 frames before the flip, is #20 rotated from #1?
Hi,
No, I see no rotation in frames taken before the flip, there is the usual displacement due to dithering but nothing else.
I also don’t see any relative rotation in frames taken after the flip.
The rotation is only between the pre-flip batch of frames and the post-flip batch of frames.
My camera is fixed, no rotator, so that’s not the issue, it must be something else that is misaligned, I’m wondering if its the Telescope to mount shoe?
This is, most probably, due to some cone error. After the flip, the centering process must compensate for it and this produces the deviation from the expected 180°. Anothe cause might be some flex in your optical path.
You may want to have a look at the amount of centering movements after the flip.
Hi Horia, thanks for replying.
I will look into the cone error, that sounds like a good lead, but can you let me know a little more about the centering, I’m not sure what you mean?
Although this isn’t ideal, might I suggest trying APT (https://www.ideiki.com/astro/Default.aspx) with your setup and see if the rotation occurs after the meridian flip with it? If it doesn’t, then it’s not your hardware, but a SGP issue.
I saw your other thread and people don’t seem to read and comprehend very well these days. Not once did you mention mosaic in your original post.
It is highly unlikely that SGP is the issue. SGP is either telling the mount to flip or slew depending on the mount. In either case, the mount is responsible for executing the flip. I suspect some type of cone error is the problem.
Obtaining another imaging program and setting it up and testing it is no small task when the chance of SGP being the issue is very remote. Concentrate on things that are more likely.
SGP seems to be working ok and centering as it should. I suspect Cone error is the problem. It would be a big job to learn new software, We get so few clear nights I struggle to remember what I already know between sessions
