It is possible for the mirror assembly to become misaligned in SLR cameras so what you see in the viewfinder isn't "exactly" what the lens is seeing.
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First, let me apologize if my first reply seemed sarcastic, but sometimes the solution is that simple and people do forget about relative motions between objects. I have both telescopes and binoculars and the telescopes have clock drives with four different speeds for the different objects observed, sun, moon, and two different rates for deep sky objects (either one can be used(?)), and you care share the view with others for several minutes. On the other hand, I mount the binoculars on a tripod and move them with the object, if you turn away to call someone else to take a peek, at the moon for instance, it may be gone when you get back. Oh, and be extremely careful looking at the Sun.
Here is a shot through an astronomical solar filter on an 8" telescope, I forget now which eyepiece or magnification I was using:
[a href=\"http://www.pbase.com/bill_in_wv/image/30977842.jpg]http://www.pbase.com/bill_in_wv/image/30977842.jpg[/url]
Now to your last question, anything is possible but I personally would consider highly unlikely if everything is still working and you are not hearing unusual noises coming from the mirror housing, but here I am not an expert by any means. It just seems like the tolerences would be too close for that to be happening. I would guess it more likely, because I wear glasses and do this to myself all the time, is not aligning the eye with the finder the same way each time. I find that sometimes I get involved with composition, looking at some particular item in the finder but when I check the LCD after the shot, it's off to one side or the other or the alignment has changed from what I thought it was when I pressed the release. I also find it doesn't happen as often if I remove my glasses and get closer to the finder. Maybe that's why so many people try to use the LCD for composing with P&Ss and forego the optical viewfinder, I still prefer to look through my camera instead of at it.
That's enough of a ramble for today, again, my apologies if my first reply sounded smarta$$ed, it was not my intent.
Bill in WV