Hi,
The latency is from shutter finger pressed until shutter opens. The rapid response depends that no mirror needs to be moved out of the optical path. The A77 shots also over ten fps for the same reason.
There is probably a significant lag in the viewfinder. A77 does not have contrast AF. It uses a semi transparent mirror for AF. The exposure is made trough the mirror, so the camera looses some ISO.
The advantages I see:
1) The viewfinder image is the actual image
2) There will not be any alignment problem lens to sensor at the focus point. It's as good as it can be.
3) Viewfinder image can be at actual pixels
4) No vibration from the mirror, possible to shoot vibration free without mirror lock up if remote release is used.
5) No dust on sensor as it sticks to the mirror instead, further away not really visible at least normally
6) Flipping mirror cause air in the mirror chamber to circulate and redistribute dust, this effect will be eliminated.
7) Possible to use viewfinder enhancements like histogram, blinking highlights, peaking and virtual horison. Not all of this implemented on all cameras.
For me, live view focusing is the most crucial. I cannot focus reliably by eyesight. LV focus at actual pixels is dead accurate.
Best regards
Erik
Yes, I was thinking about the latency from scene to eye, not from scene to flash card (but interesting that it is so low).
Perhaps they could have been "better" in some ways if LV/video was not offered? (At least cooler).
Perhaps they will be worse in some ways if 120fps readout for improved contrast AF is implemented?
-h