From what we can tell, there is no strategy for keeping dust off the translucent mirror, except to blow the surface gently with air; it cannot be cleaned, and should never be touched. A fingerprint would require replacement at a service center.Fast forward to Kirk Tuck, who has transitioned to using the Sony α77 for the main body of his work. In today's post on his blog where he documents using the Sony's for food photography, he had this to say:
I am happy with the Sony a77 with one exception: While the sensor cleaning works perfectly (vibrates at shut down) nothing is ever cleaning off the fixed mirror. When I shot at f11 I found two big dust spots and was unable to dislodge them from the mirror with puffs of air. I'm taking Sony at their word that we shouldn't use anything to physically touch the mirror surface. But it will bite if I [can't] figure out a way to clean dust spots off, short of sending the bodies back to Sony for periodic cleaning.I would also like to point out that Kirk left a comment on my year-ago post about not worrying so much about the pellicle mirror:
The Nex 7 is superior in this regard.
I owned a Canon RT with the pellicle mirror and one of the selling points was the extremely short shutter lag. Something like 22 ms. I owned the camera for years and at first I was worried about dust on the mirror but it's far enough away from the imaging plane that it was never in focus. A little compressed air was enough for any small trash on the front. Also consider that they may have an IR or other filter in front of the mirror like Kodak did with their 660 and 760 cameras which would block intrusion of dust and allow user cleaning of the outside surface. Win, win, win. I don't think Sony would let this one off the leash without having dealt with a very obvious possible source of customer dissatisfaction. We'll see.This is an example of why it is so important to pay attention to bloggers like Kirk. He buys non-trivial equipment and uses it substantially in the course of his work. This makes it statistically significant that he will find a problem before just about anyone else, and if he does, Kirk will certainly write about it. I've not known Kirk to ever hold back writing about camera gear issues.
Why do I care? Because I live in a rather messy environment, central Florida, and the periodic summer monsoon season. I've written repeatedly about how my cameras would be covered in condensation just walking from an indoor air conditioned environment into the very muggy out of doors. I don't change lenses in such an environment, and it's one reason I have two bodies with lenses firmly attached. In spite of these careful precautions I've still had to clean my sensors on occasion, but at least I could clean them. But I'm not so sure I want a camera that I can't easily service in the field. Logistics is as important an element to consider in any camera as any other feature, perhaps even more so. If it requires lots of trips to the depot to keep a camera working, that's a hidden expense I don't want to incur. Sending a camera in for periodic (yearly) maintenance is normal, or sending it in for a major problem such as physical damage. But getting junk on my mirror? No thanks.
Update 19 August
From a follow-on post from Kirk Tuck:
I grabbed a can of compressed air and a Sensor Brush (and followed the instructions sent by a reader of the blog). I blew the brush with the compressed air to remove dust on both sides. Apparently this also imparts a positive charge to the bristles that helps lift dust off. I did a wipe from top to bottom on one side (left/right, not back/front), flipped the brush over and then did the same to the adjacent half of the mirror.
Being fearful of destroying my mirror I shot test frames and blew them up on the monitor. Dust is gone and no ill effects followed on.