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On the mechanical side it might be difficult, as you point out, to set standards for focus smoothness but it ought to be possible to set them for the torque required to rotate the wheel and also for the maximum 'slack' or 'free-play' permissible when changing the direction of rotation.
Lee
That would definitely a great start! But I'm afraid the majority of potential customers could not care less. Unless they would be guided by informed salespersons, of course.