Read what Nikon-guru Thom Hogan wrote yesterday:
“One curious aspect of the D3100 is the sensor. “Nikon developed” appears in the marketing materials, and the sensor is indeed not the same one as in the Sony NEX5 (as originally speculated) in several key ways, one of which is physical size, the other pixel count. The Nikon 14mp sensor has slightly more pixel count in a slightly smaller area than the Sony. Indeed, the area is no longer what I’d call DX. The D5000, D90, and D300 have a sensor area of 23.6 x 15.8 (28.4 diagonal), while the D3100 has a sensor area of 23.1 x 15.4 (27.8 diagonal). This represents a loss of about 2% in image circle coverage needed. We’re now at 1.55x crop as opposed to the old 1.52x. It’s an unusual change, but the bottom line is that the Nikon and Sony 14mp sensors are indeed different in important ways. But I’ll repeat: the proof is in the pudding. We need to test the new sensor on live subjects before making any useful pronouncements about it.
Update: I’ve now heard even more details about the D3100 sensor and from a few sources closer to Nikon Japan. It does indeed appear that Nikon has moved to producing their own sensors. They may be licensing or cooperating on some of the underlying technologies, but it appears that Nikon has decided that Nikon DSLRs will in the future have Nikon-controlled and Nikon-exclusive sensors. That they haven’t chosen to make a bigger deal of this is strange. And some parts of Nikon appear not to have gotten the memo on this, as I’ve seen quotes from Nikon personnel in some subsidiaries that say “Sony sensor.”