Siril isn't correctly registering image sequences with field rotation

Software Siril
#1

I’m used to doing equatorial-mounted astrophotography in the past, but I got rid of a lot of my gear so I’ve been stuck with a defective alt-az LX90 for all of the recent astro opportunities. I have been trying to learn how to post-process on some of the recent stuff I’ve shot - practicing on the moon, along with the Jupiter / Saturn conjunction. I use Mac, so I’ve tried most of what’s out there for it and it seems that Siril is one of the better apps that has kept up with the recent OS upgrades and security changes.

Longer sequences of the moon (>a minute or two) have field rotation due to the alt-az scope mounting and aren’t being registered correctly. They spin around the center. I’m using the “Enhanced Correlation Coefficient” mode. I’ve tried the other planetary option - “Image Pattern Alignment”, but it only looks at the reference image and then stops.

What am I doing wrong?

#2

Nothing. But this kind of algorithm don’t take into account for rotation.
The only one doing this is the global star registration.
I don’t know one planetary stacking program taking into account rotation field.
Winjupos can fix it before using a stacking software, but not for moon I believe.

#3

Lock042 - Thanks for your response! I’m so surprised that this is the case. So many scopes are being sold with just alt-az mounts these days I was sure that part of the reason was that the s/w was able to account for the field rotation.

Sad to find this out, but at least glad to know to stop banging my head against this issue.

I have a equatorial wedge for the LX90, but it is missing a few pieces. Time to either complete that or buy better gear.

Thanks again for your help!

#4

And this is not a big issue for stellar images (even if you loose a bit of field) .
But for planetary…

#5

maybe we could do something simple that will help a lot: provide a way to automatically rotate images from a sequence based only on their time of capture relative to the reference image? But I’m not sure the centre of rotation is the centre of the image…

#6

No that is really not that simple.
For me, the best way to do is like Winjupos do. And… that’s not easy at all :).

#7

I’m playing with a few other options. One thing that struck me as I was smarting from the reality that my expectations in the astrophotography app realm were set too high was that they were based on my experience with regular photo apps. So I’ve run my moon shots through a few of them and seeing which can handle both the directional and rotational inter-frame movements. So far Photoshop of course can, albeit extremely slowly. A couple of others that I was sure could haven’t come through, but I haven’t given up yet.