Originally posted by Clavius And they are not? OVF shows nothing during video recording. Doesn't show live DOF preview, no WB settings, no focus zooming, no peaking, no histogram, etc. OVFs are darker. The size of OVF is dependant on the sensor/mirror format while EVF is not. OVF and its sub-parts requires much manual calibration, and thus makes the camera much more expensive. All in all, a camera with an EVF immerges me more in the act of taking a photo or video, then an SLR. It doesn't only let me look through the lens and its characteristics, but also "through" the sensor and its own characteristics.
OVFs - I don't have a problem with anybody who wants to buy a camera with OVFs - go for it! But from an intellectual weighing of pros and cons, i don't see that they stack up well against todays EVFs.
Even besides the pros listed ably by Clavius, there's a couple more.
Weight - One can throw out the pentaprism and the mirror mechanism. that should save weight, esp considering there needs to be less body volume for the pentaprism.
Reliability - less mechanical mechanism to wear out and fail.
Liveview doesn't measure up to an EVF. Liveviews are clunky, noisy and can't be held up against the eye like an EVF.
OVFs are dim - a couple months ago, i sat down in a coffee shop with a friend to look at his A7R/S. Then i looked at my K3 OVF again, and it was just dim - i thought there was something wrong with it. Then i realized, i just got used to it being dim, esp indoors. With an EVF, one can dial up whatever brightness one wants or doesn't want - not with an OVF.
What you see is what you get - with an EVF, i don't have to remember to look at the exposure meter - the EVF view is what i'll get.
Again - enjoy your OVFs if you want or own one. I own OVFs as well - i just enjoy the EVFs more.