Double stars on Light frames.

[senzala]

All I find that several of my light frames have double stars. I'm a bit confused as to why this happens.

There are no trails, so assume that it is not guiding, which was under a second.

The pictures is 3 min exposure with a 183mm pro camera, Zwo filter wheel. The telescope is a 6" Classic Cassegrain on an EQ5 pro mount controlled by ASIAIR pro.
Everything is carefully balanced.

There was a lot of moonlight? Could this be the cause?

Thanks in advance!

[Stickey]

Puzzling. Possibilities are: mount got knocked during an exposure,  or mount is sticking occasionally, or the guiding is having a problem,  or there's a reflection sometimes happening within the optical train,  although not sure why only sometimes.

Mike

[Elp]

I can usually replicate this when I'm setting up a second lens on one rig whilst the first is imaging. Something's moved the setup, whether it be environmental or physical.

[The Lazy Astronomer]

As the others have suggested, the mount has moved a relatively large distance suddenly. If you figure out your camera orientation relative to the mount, then you work out which axis is causing the problem.

As to why, the fact it affects several lights would imply it's probably more likely to be a tracking issue, rather than the mount being knocked. 

[almcl]

Don't think moonlight has anything to do with it.

As others have said, the scope has moved by a noticeable amount in Dec (your image below overlaid with RA/Dec axes) and the doubling is pretty  much aligned with the long red arrow (Dec)

This should show up in the guide log for the time of the relevant sub, are you able to see a corresponding jump on the Dec trace?

If so there are several possibilities, temporary cable snag or drag being one such.

[david_taurus83]

Don't be fooled by the guiding numbers in ASIAir app as they are very optimistic..

Do the jumps happen at frequent intervals? Have you set to dither after a set number of frames? It could be the next image in the sequence has started before the mount has had time to recover from the dither. A large amount of backlash would have the effect of the mount not moving despite guide pulses so the size of the pulse increases and increases and you suddenly get a large movement which can cause it to jump and overshoot.