Hans
Never had a problem with my ONAG. There's no image degradation at all. If you're thinking of putting it on a newt then you will need a lot of back focus to cope unless you have an oddball home brew focuser like mine (
http://www.iceinspace.com.au/forum/a...e.php?a=140489)
Most people put it on SCTs where the back focus is less of a problem. Adjusting two focusers at the same time can be a bit of a pain and the guide scope focuser adjustment is awkward but you get used to it.
Cheers
Stephen