The coarse focusing knob of most microscopes is equipped with a friction adjustment ring.
If this ring nut is rotated to loosen the correct clutch, the microscope stage loses focus because the weight of the stage alone is sufficient to bring down the whole group by simple effect of gravity.
In this case it is sufficient to rotate the ring nut in the opposite direction to the direction of rotation applied when the clutch is loosened, to reset the microscope.
Note that too high a clutch may cause malfunction due to excessive friction between the pinion and rack of the focusing assembly.

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