Originally posted by SideRaptor Uh, how good there possibly be an optial viewfinder on mirrorless camera...?
As noted above, the same as on any other camera where bracing against the face to steady the camera is desirable. Holding the camera at arms length to take the shot is OK for iPhone or snapshots, but not particularly great otherwise.
There is also the matter of shooting in bright light where you can't see the LCD display or shooting in a club setting or performance where the brightness of the LCD is a distraction to other people present.
In general, the need could be satisfied (at least for primes) with a series of auxiliary finders and Pentax does sell an auxiliary optical viewfinder for the "Q7" that works with the normal lens for that camera. It might also be possible to re-purpose auxiliary finders from other makers.
Steve
(...shoots a lot with rangefinder film cameras...well acquainted with non-ttl finders...)