Canon 50D

I find my Canon 50D difficult to focus manually. When I look through the view finder at the sky, the entire frame has a "frosted" appearance which is uniform throughout the frame. This seems to create a slightly blurred appearance when focusing manually so that the subject never appears to be in clear focus. I have checked all glass and filters and changed filter and lenses and these are not the problem. I have cleaned the eyepiece and carefully adjusted the optics for my vision. The problem seems to worsen when I use a Polarized filter. Canon Co. says that "this the way the camera is made". Could there be a problem with the prism? Can anyone advise me if there is a anything that can be done about this? Does anyone who has a 50D noticed this? Any comments or suggestions would be appreciated.

I'd take the camera to a local reputable dealer/repair store and have them take a look at it, how old is the camera ? I assume its still under warranty right ?

It could be problem with the prism. However, I never focus manually through the viewfinder, the viewfinders on DSLRs just aren't designed for manual focus like old manual focus cameras were and I can never get good results through the viewfinder. The split circle prisms of manual focus cameras have been replaced with autofocus points because most people only auto-focus these days. I still manual focus a lot of the time because I don't trust auto-focus to get it 100% right. The way I do it is I put my camera on a tripod and activate live view and zoom in 10x to the part of the screen I want to focus (usually the hyper focal distance). Using 10x zoom in live view gets you up close to the fine details of the scene and allows you to focus precisely. If you prefer to do it the old way of doing it through the view finder then I would suggest you get a katz eye split prism focusing screen.http://www.katzeyeoptics.com/item--Canon-40D-50D-Focusing-Screen--prod_40D.html
Its just like the split prism on old manual focus cameras. However, I think live view works great.