Forum ate my post! Gah!  Second try: Even ones in the 80s never
had 1:1 zoom. They have at best 0.97x zoom or something close.
The only way to get full 1:1 zoom would be to have no viewfinder
at all -- like one of those glass plate cameras from the 1800s.
Otherwise, any diversion of the light stream is going to cost
some small margin of viewing area just because of the framework
of the mirrors and the reflexive prisms in the viewfinder.