This is going to seem weird, but my eyepiece on my 5DIII seems to be out of focus.
I know what the diopter does and how to use it, and trust me, that is not the problem.
If I manually focus on a target using just the eyepiece, the focus is significantly off. So I set the camera up, use live view or autofocus to focus, and look through the eyepiece, it's blurry. I adjust the diopter to get the sharpest focus, but it's never sharp. If I take the photo, it's tack sharp. Now, if I go back to the eyepiece and adjust focus until it's sharp in the eyepiece, then take the photo, it's completely out of focus. How can this be? I'm spinning the focus dial the equivalent of 8-10 inches of focal distance to get the eyepiece to "look" in focus.
To sum it up, the autofocus and manual focus with the LCD are perfectly fine, but the eyepiece is just off.
I really want to start manually focusing more often but I can't use the eyepiece...
I hope this makes sense. Any advice?