SharpCap Forums

Hi Robin,

Do you know what is causing this odd alignment?

Thanks,

Robert

Hi Robert,

yes, I suspect that you are using an Alt/Az mount, which means that as time passes and the mount moves to track the stars the image appears to rotate in the field of view of the camera (this is called field rotation). SharpCap can deal with this happening during the stacking process by rotating each new image to match the orientation of the stacked image, but that means that some areas of the stack stop getting new data, so they become darker compared to the core of the stack which is still getting new data added from every frame.

This looks like quite a severe case of rotation - that might indicate that you were capturing the image with the telescope pointing quite high up in the sky (where field rotation for Alt/Az mounts) is the fastest.

This does not affect images taken with equatorial mounts (the camera orientation stays the same relative to the sky as the mount follows the sky's movement for an equatorial mount). It can also be counteracted by a fairly expensive piece of kit called a rotator, which can be set up to turn the camera relative to the telescope at a rate that counteracts the effect. In general though it's probably easiest just to crop the image down to exclude the affected parts!

cheers,

Robin

Hi Robin,

I am using a equatorial mount (CGEM II).
I also run into some other problems, maybe they are related;
The center coordinates are too far from the real center.
And the image is inverted.

Thanks,

Robert

Hi Robert,

ok, with rotation showing on an equatorial mount, coupled with co-ordinates being wrong, the most likely cause is quite bad polar alignment, so that is worth checking carefully (fortunately SharpCap has a tool for that !)

Image orientation is related to the orientation of the camera in the telescope focuser, so if you want a target to appear a particular way around, you need to rotate the camera. This is typically a fiddly process that probably requires re-focusing afterwards, so best to do it as little as possible.

cheers,

Robin