Blurred Images

I've owned my trusty Meade 6" Schmidt-Newtonian for about a year, but recently I noticed a new problem. It seems as if whenever I try to use the telescope with either my higher powered eyepiece (9mm as opposed to 26) or insert a filter (in this case, UHC), the image seems to blur up a bit. Stars seem to have clouds around them, and objects cant be resolved as well. I didnt notice this problem when i first had the scope, and I believe that I'm collimating it properly. Any advice would be greatly appreciated. And the sooner the better, since I only have 6 days left of enjoying dark skies in New Hampshire.

Thanks a lot,

Matt Schenker

This sounds like scatter, have you looked at the EPs and filters to see if they are dirty? How about the mirror, is it covered in dust?