A rotary bearing has a pair (32,40) of bearing members, one of which has convex (34) and planar (36) surface portions, and the other of which has concave (42) and planar (44) surface portions. The convex and concave surface portions and the planar surface portions of the two bearing members bear against each other via an interstitial bearing medium of air, with the axial forces between the convex and concave surfaces counteracting the axial forces between the planar surface portions. When incorporated into a drive mechanism, one of the bearing members is connected to a drive shaft via a first torsionally stiff flexible diaphragm (130), and the other bearing member is mounted to a motor (50) (which rotates the drive shaft) via a second torsionally stiff flexible diaphragm. During operation, flexing of the diaphragms (110,130) accommodates eccentricity in the mounting of the motor (50) without transmitting unwanted loads to the bearing.