>This is normal and the same with every DSLR. There is an LCD
>screen between the focus screen and the prism. That LCD needs
>power to work, without power it will dim and diffuse the light
>going thru. So you can focus the image and it will be sharp on
>the focus screen in the mirror chamber, but you won't be able
>to see that sharp image since the dim LCD is in the path to
>the prism/viewfinder.

Ah, thank you for the explanation. That makes sense. By the way, you accidentally wrote "every DSLR", but this issue actually only affects cameras that have an LCD screen in the optical path of the OVF. My Canon 5D2, 5D, and 20D did not have one and so they work normally even without a battery.