I got bad electronics on my 550D. When I use it with the 18-135mm the f number randomly jumps around and I can't set it. It's not AE because it happens on manual mode :/
I took the lens to a repair shop but they can't find the problem and I have to bring the camera in too so they can check on it. Sucks
Also the focusing screen is horribly filthy, but they said it doesn't show up in photos and I should live with it. They don't clean focusing screens because there's a very high risk of damaging them and they'd have to replace it if they do. What the hell, they ARE fragile, but new focusing screens cost like $5 at Canon according to Several Forums From The Internet.
Maybe I'll end up doing it myself. I'll get a new one first in case I screw up the old one.
Oh well. Had to vent it out.
I can not for the life of me understand how so much shit accumulated INSIDE the viewfinder of my 850 without me ever changing the lens or exposing it to the elements.
I advice you not to clean it yourself if possible, unless you're very sure of what you're doing.
[writing this from android during math class]
Btw, I have a micro 4/3, so I'm not a big pro in DSLRs, but isn't it possible to blow a bit of compressed air - that you normally use to clean the inside of your PC - onto the mirror, that would go up to the viewfinder? Maybe that would save you the dissembly.
It's really not at all difficult to disassemble it, the focusing screen just pops right out and back in, the only problem with doing so is you need an extremely clean and dust-free room or you're just going to introduce a fuckton more shit into your viewfinder assembly.
To Diso: If you're certain it's the focusing screen instead of the viewfinder assembly, I say go for it. It only takes a couple seconds to remove it and put the new on in so you're really not likely to introduce a lot of dust or dirt unless you're in the worst conditions imaginable.
Lucky you that it only costs 5$, my Rebel G would have a new screen by now but the screens cost 45 fucking dollars. Keeping in mind the Rebel G is cheap consumer shit.
@Crollapse: I'm almost certain it's the focusing screen. And the focusing screen is the only thing I'm cleaning. I am ABSOLUTELY NOT EVER touching the prism for ANY reason. I'd rather ship it to Canon Japan.
$45 for a focusing screen? Could it be out of production or something?