Why this Field Rotation???

[avandonk]

Ken here is an image of your eight images stacked with RegiStar then levels and curves in PS.
Would be better with original images. I did a median combine with RegiStar after registration this removes hot pixels as
the field was rotating.
Absolutely accurate polar aligning is essential for wide fields to not get rotation. When autoguiding the guide camera and imaging camera have to be very well aligned. In fact if both are well aligned any rotation tells you polar alignment is off.
This does not matter with RegiStar as it uses all the stars to align.

bert

[Doug]

Ken, how sure of the lens quality? or how sure are you that the mount/adapter has it square to the web cam?
I've aligned combined the 8 images in MaxDslr and it looks a bit more like a lens issue to me.

[ballaratdragons (Ken)]

Originally Posted by avandonk

Absolutely accurate polar aligning is essential for wide fields to not get rotation. When autoguiding the guide camera and imaging camera have to be very well aligned. In fact if both are well aligned any rotation tells you polar alignment is off.
This does not matter with RegiStar as it uses all the stars to align.

bert

Thanks Bert, you've done a good job.

The Scope and Guidescope are aligned, and polar alignment is spot on. But this image was taken with a 6-60mm zoom lens attached to the Toucam and then held onto the guidescope with rubber bands. No guiding was used. I just relied on the mounts tracking. I've done this a few times before but this is the 1st time I have had field rotation.

Originally Posted by Doug

Ken, how sure of the lens quality? or how sure are you that the mount/adapter has it square to the web cam?
I've aligned combined the 8 images in MaxDslr and it looks a bit more like a lens issue to me.

The lens is good quality, but I can't be 100% sure of its squarness to the chip. It is a slap-up job. But would that cause field rotation?

[Doug]

Ken, I think your rubber bands might have a bit of explaining to do.
I was just looking at a single frame that you posted and noticed a sort of embossed effect. So I am wondering if you have applied any flat fields to the individual frames?
Granted it looks somewhat like rotation, but then again not really.
If I apply a mild amount of offset filter to the a/c image I posted I get nice round stars in the foreground with a stipple textured background.
It might be worthwhile going back to your original frames from the web cam (avi?) and redoing them. If you are calibrating, you might try stacking them without calibration to see if there is a difference. The amount of field rotation across those 8 frames is not beyond the alignment capabilities of s/w so I think you need to look at other things.

[ballaratdragons (Ken)]

Originally Posted by Doug

So I am wondering if you have applied any flat fields to the individual frames?
Granted it looks somewhat like rotation, but then again not really.
If I apply a mild amount of offset filter to the a/c image I posted I get nice round stars in the foreground with a stipple textured background.
It might be worthwhile going back to your original frames from the web cam (avi?) and redoing them. If you are calibrating, you might try stacking them without calibration to see if there is a difference. The amount of field rotation across those 8 frames is not beyond the alignment capabilities of s/w so I think you need to look at other things.

Nope, no Flats used. I never do.

Sorry to be a pain Doug, but can you say all that again but in English this time

Practically none of that made sense to me

[Doug]

I don't think you are a pain Ken, we just didn't communicate well.
I have seen sub frames that look something like what I am seeing here. In that case the problem was the use of flat frames that had somehow been created with light coming from a different angle. This gave similar effects to what I have attempted to highlight in the first attached image.
In that image, notice how there is a shadow effect on the brighter stars and also the general background texture looks a bit like a lunar landscape.
For what it is worth, I believe this is the reason for the bazaar results you are getting when you try to stack the images.
It seems to me that there is an underlying corruption taking place when your S/W is handling the images. Either something has gone wrong as the files have been downloaded from your web cam or they are being corrupted when you begin processing somehow.

The second image has the stars rounded a bit. But note the streaky background. Surely if the problem was simple rotation all of the image would be effected in the same way, instead of just the background.
The second image is the A/C image; Aligned/Combined.
I'd try taking another shot at imaging with this setup again; its gotta be file corruption..

[ballaratdragons (Ken)]

No Doug, it isn't file coruption. I saw the image rotate on the screen I was capturing on. Every time the exposure time ran out and the resulting image appeared, it had rotated slightly. I was hoping it was just lateral movement, but stacking proved it to be rotation.

There are no Darks, Flats or any other added frames. Just the raw frames.

I will make an animation of the frames to double check. I just hope the finished animation will fit in here.

[ballaratdragons (Ken)]

Here is the animation, yep, it's Field Rotaton. The Centroid is in the upper right corner about a 1/3 the way in from the right.

[h0ughy (David)]

maybe for some reason one of the axis was jammed or bumped on the mount?

[ballaratdragons (Ken)]

Originally Posted by h0ughy

maybe for some reason one of the axis was jammed or bumped on the mount?

Dunno Houghy,

I am going to repeat the whole imaging procedure and see if I can find out what is going wrong! But in the daylight so I can see what is happening. I won't image, just watch the mount and camera and look for anomolies. (sound like I'm on Star Trek )

[ballaratdragons (Ken)]

Something else I have just noticed in the animation!!!!!!

The rotation is backwards to real time rotation??????????????????????

Which means that it wasn't a 'stopped mount with natural rotation'!!!

Hmmmm. more investigation needed here.