Image rotation with focussing

[Sylvester111]

Hi all, 

Just a quick question that I can’t quite get my head around.  When I rotate the scope end to focus on stars for guiding, the image on SharpCap rotates as well. I don’t really understand how this can happen? The camera sensor doesn’t rotate and surely the lens is just being a lens, so it can’t twist the light through it?

It doesn’t matter too much, but if I use PHD2 for focussing help, I have to click on the same star each time I try to focus, as it’s moved and PHD2 doesn’t know where it is any more. 

Kit is ASI120MM-S and ASI mini guide scope.  
 

Cheers

[Waldemar]

Does it really rotate in sync with focusing, or does it just move a little?
The latter maybe due to bad collimation...

But once focused the problem is gone. Only have to do that once, for guiding is not critical on focusing. Slightly off focus even works better.

 

[Sylvester111]

I need to experiment more, but bad collimation may be the answer. 
and you are right, now it’s dialled in, hopefully I don’t need to touch it again

Thanks!