a 24 x 24mm sensos is smaller than a 36x24 sensor though...except it is not fullframe. and the hood? canon surely could make bigger/wider hoods hehehe
Look at the rear baffles of a number of lenses too - they're also rectangular. The lenses aren't always corrected symmetrically, especially if they don't have rotating elements.
And look at you guys - you've actually managed to post some pictures with genuine artistic merit (did I just say that?), and have a real photographically-related discussion that's based on truth, not myths. Guess I'm not going to be able to shut the thread down just yet.


APS-C Square sensor. 


