I'm not sure, but in the past, when I've done mirror work I've always used a camera with manual focus to avoid the mirroring fooling an auto focus. I also use aperture priority so that I can set a high f-stop number for maximum depth of field and as much in focus as possible.
Lastly, don't use flash as it will bounce off the mirror. If there's not enough light to hand hold the camera either use a tripod or even prop the camera up on such as a stack of books. If you use the delay timer (usually of around 10 seconds or so) with either method it will help minimise any blurring through camera vibration, especially important if you are using books.
Good luck!
TonyW.
