Originally posted by eddie1960 If it could be done efficiently then Hassy would have already done it
Maybe I should make myself clear. No reason to argue by analogy.
A square sensor does make sense
if the image circle is fully contained on the sensor, i.e., if the sensor width equals the image circle. This is 43.3x43.3mm^2 ! Only possible with mirrorless because as has being said of the required mirror clearance. This sensor has 1872 mm^2 surface!
This is 29% more surface than the sensor in the 645D has (and 117% more surface than 24x36). Clearly not an option as long as sensor surface is a cost factor, and requires mirrorless. But if sensor surface isn't a cost factor anymore, then we'll see lens modules with embedded sensor (such like the GXR modules).
So, such a square 43.3mm sensor (~5x the surface of APSC) will come at some point in the future and will allow to shoot (with FF glass):
39.8 x 16.9 mm^2 (cinemascope 2.35:1)
37.7 x 21.2 mm^2 (HD 16:9)
36.0 x 24.0 mm^2 (photo 3:2)
34.6 x 26.0 mm^2 (compact & MF 4:3)
30.6 x 30.6 mm^2 (square)
26.0 x 34.6 mm^2 (compact & MF portrait 3:4)
24.0 x 36.0 mm^2 (photo portrait 2:3)
(So, if cinemascope if the widest which is ever shot, the 43mm square sensor may actually become 36x40mm^2 which is still the surface of the 645D sensor.)
BTW, the cinemascope mode would make a 12.0mm FF lens usable as a 10.9mm movie lens. This is a case for a 24x40mm sensor rather than a square sensor actually
Sensor cost is already almost no factor in P&S cameras which is why we see the 16:9 to 4:3 variable image formats never reaching the sensor corner. Even the Nokia 808 does this with its huge (for a P&S) sensor.
However, as long as sensor cost
is a factor, the sensor should be fully contained within the image circle, i.e., the sensor diagonal equals the image circle.
And with a FF glass circle, this allows for the following sensor formats:
30.6 x 30.6 mm^2 (-> 20.4 x 30.6 or crop 1.18 for 3:2)
34.6 x 26.0 mm^2 (-> 23.1 x 34.6 or crop 1.04 for 3:2)
36.0 x 24.0 mm^2 (-> 24.0 x 36.0 or crop 1.00 for 3:2)
So, with sensor cost playing a rôle, a 3:2 sensor is the best option for most situations.
If increasing the sensor, it is better invested into a linear scale than a square sensor with lots of cropped area in most of the images.
With sensor cost playing no rôle, a lens-module based camera would be best and then, a 43mm square sensor may be used for FF optics.