Nikon D3100 Rumours Start

"Rumors about a new entry level DSLR between the Nikon D3000 and the D5000 started few months ago. This new camera will not be called D4000 as previously expected, but Nikon D3100."

Well, that'd make sense; Nikon switched to a 4 digit convention to avoid numbering congestion in this day of 2 year or less product cycles. What's interesting about the rumours (Photokina is 2 months away) is that Nikon appears to be following up on its announcement of coming up with some surprises. In this case the rumours are hinting that the new camera will support continuous AF in live view and video mode, something like the micro Four Thirds cameras.

If patent applications are to believed, Nikon has been working on this a while, and among the several patent diagrams shown, the interesting one is this:

In case you can't figure it out, it's a live view sensor with a separate AF sensor. I'm very curious to see if Nikon will implement a main pellicle mirrior (last seen in the Canon EOS 1n RS) in in a live view camera to cope with the AF issues in contrast detection AF methods. Problem with pellicle mirrors is that it robs light, as essentially you share some light with the other sensor.

Normally, even in a standard SLR, part of the main reflex mirror is partially slivered to allow some light to hit the secondary mirror behind the main mirror. This is to deflect light to the AF sensor that is at the bottom of the camera, like in the figure above. The secondary mirror is smaller than the main mirror; after all, your AF sensor does not cover the entire frame. In this case though, having a permanent pellicle mirror is an all or nothing solution since having 1/3 the image area being a little less bright will look weird. My line of thinking is that the solution is either going to be software-based by brightening or darkening the appropriate areas, or that mirror is going to flip out of the way when the photo is being taken. The latter will negate the advantage of not having mirror slap in a mirrorless camera though.