Pellicle mirrors are back, but this time it’s not just to allow higher FPS in continuous shooting [drive] mode. Sony has brought back semi-transparent mirrors to take a portion of the light and direct it towards phase detection AF sensors for use while shooting video. Compared to contrast detection based AF using the image sensor, phase detection is faster and more accurate. This should definitely help address many of the AF concerns found in DSLRs (which use contrast detection AF) when shooting in video mode. Sony’s three new cameras sporting this design are the A33, A55 and A55v (has GPS built in).
The downside as I see it is that you’re stuck using an EVF. I have yet to see an EVF I’m truly impressed with. Perhaps it’s because I spend so much time shooting in the dark, but there is usually a significantly annoying delay or blurring of the viewfinder image compared to an optical viewfinder. Sony’s pellicle doesn’t allow an optical viewfinder and while a rejiggering of such a system could allow for both an optical viewfinder and phase detection AF, you’d find the light coming in to the camera is getting split across more and more systems. OK in bright light but could lead to trouble when it gets darker.
This will be interesting to watch and see how these do and whether they catch on. I’m still under the impression that if you want video from a DSLR that Canon is the way to go, but they don’t have phase detection AF when shooting video. Supposedly they’re working on a new camera that will have a stronger focus on these dual roles and perhaps they’ll do something similar. Or not.
It looks like Sony is aiming for the meat of the affordable midrange with the A55. B&H has it listed currently for $850 with an 18-55 lens. I imagine we might see some other interesting things soon enough with Photokina fast approaching, perhaps another manufacturer will announce their latest and greatest solution to improve video AF.
Check out Sony’s marketing shpiel here if you’re interested.
