Dpreview.com are reporting today the iPhone 5 does indeed have a different image sensor to the iPhone 4S. ”Close examination shows the iPhone 5 is using a 4.1 mm lens to give a 33 mm equivalent field of view, rather than the 4S’s 4.3 mm lens, which gave a 35 mm equivalent view’. They have determined this information by looking at the EXIF data of two images, one of their own taken with the iPhone 4S and the other from Apple taken with the iPhone 5. In tests the iPhone 4S selected ISO 64 whilst the iPhone 5 dropped down to ISO 50, inferring ‘the newer model has a lower minimum sensitivity’.
Effectively what this means is that the new sensor in the iPhone 5 is just a tiny fraction larger.