Originally posted by RioRico But a 36mm square sensor would allow 36x24mm (either way, portrait or landscape) or 30x30mm or various other sizes at different aspects, all within a 43.26mm PK-mount image circle. Selecting the aspect in-camera is enticing. Professional? No. Fun? Yes.
Well you are forgetting the round sensor with 43,26mm diameter wich can do everything you want. You can go far with K-mount.
Actually there was one camera that has a sensor that keeps the diagonal the same and uses a different part of the sensor for square, 16:9, 4:3 or 3:2 picture style. (I think Panasonic, but don't know wich camera anymore).
This camera (from the sketch) should have an EVF in the pointing part. In that way you could use it for small lenses like the Polaroid and using the top screen for video or tripod use.