>I am amazed at your comment about F3's finder. Sharp it is. Bright ?
>15% or so of the light goes through the mirror to the metering cell at
>the bottom. (rest deleted)

Hmmm.... 15% loss represents what percentage of a stop? If you want to
see how meaningful 15% loss is, stop a lens down one whole stop from wide-open (using the DOF preview button) - a whopping 50% loss is
pretty subtle, I think, let alone 15% - which can be more than compensated for using different screen designs, prism improvements, etc.
And, yes, an F3 viewfinder IS the model for the state-of-the-art
bright, sharp, undistorted, accurate, easy to see SLR finder, IM(NS)HO.
Hope this helps.