(I write this somewhat tongue in cheek. Try not to get too bent out of shape if you are in the wrong camp...).
"I'm sure I would have been a sports photographer and, perhaps a very good one, but I just couldn't bear to grapple with one of the significant shortcomings of the modern DSLR. I'm sure you've experienced it if you've tried tracking a football player with a mirror-encumbered camera. Or perhaps you've lived with the mechanical menace of the DSLR when trying to keep a fast runner well composed.... We all know what the Achille's Heel of generations and generations of DSLR camera is but for some reason we've all chosen to ignore it, or to sweep it under the carpet and make our excuses.
It's the dreaded MIRROR BLACK OUT. Each time we actuate the shutter the mirror leaps up (alarmingly) and blocks our view of the image we are so intent on capturing. Visualus Interruptus.
The image is there, in front of our eye, and then it's gone and replaced with a visual fluttering of blackness, accompanied by some raucous noise and then a decidedly unsettling vibration. Thwack! Bam! Kapow! Oh sure, it's only a few (or a dozen or a hundred) milliseconds but it interrupts our continuous observation of the objects of our (momentary) desire. The faster the frame rate the longer the overall percentage of time blacked out. The slower the shutter speed the longer the overall percentage of time blacked out.
It's been there since we gave up our Leica rangefinders in order to use longer telephoto lenses. It's always been a grave compromise as well as a source of indiscreet noise and interrupted concentration. And anyone who ever shot with a Pentax 6x7 camera (the most egregious of the breed) probably deserves restitution for partial hearing loss from the loud shutter/mirror cacophony and for the sheer amount of time spent waiting for the massive mirror to rise and then smash itself back down again.
I can hear the cheers already from legions of sports photographers, who felt they had no choice but to use Canon 1D series cameras and Nikon Fsomething cameras to capture sports photographs, as the new Sony a9 makes it initial appearance on the market. Imagine, at speeds above 1/125th of a second (the general realm of sports shooters) there is absolutely NO FINDER BLACK OUT AT ALL. NONE. Even at 20 frames per second.
The EVF shows the image continuously, refreshing the finder image 60 times per second (about twice the speed of human perception). Never again will these beleaguered pros face the humiliation of finder blackout. Never again will they feel the ravaging vibration of the slamming mirror assembly thrashing around in their hands. And, if they choose, then never again will they spook a golfer or diver with their klaxon-like shutter noise. In one low key product introduction Sony has saved the hordes of sports shooters from their own self-inflicted mechanical hell. Oh happy days. "
Ah, but just now I am learning that the new a9 is too small and light to be a serious professional sports shooting tool. Too many chiropractors would be forced out of business...