The Skywatcher 120/600 refractor is an achromat. As such it has some chromatic aberration that throws blue rings around stars. Not so bad for visual but for photography can be unwanted. ED or APO refractors are best for photography but are more expensive.
There was a thread on the 120mm F5 here.
http://www.iceinspace.com.au/forum/s...d.php?t=117525
My latest toy is a Skywatcher ED100 refractor and it's a great no hassle scope.