Patent ID: 11906716
Assignee: NIKON CORPORATION
Field: Optics (Instruments)
Classification: CPC G | IPC G

Claim 10:
11. A zoom optical system comprising a plurality of lens groups, wherein
upon zooming, distances between adjacent lens groups change,
the zoom optical system comprises: a focusing lens group that moves upon focusing; and a cylindrical member to which a driving apparatus for moving the focusing lens group is fixed,
upon zooming, the cylindrical member moves,
the focusing lens group is relatively movable with respect to the cylindrical member by the driving apparatus,
an amount of movement of a lens disposed to an object side or an image side of the focusing lens group upon zooming is different from the amount of movement of the cylindrical member upon zooming,
the focusing lens group comprises a first focusing lens group that moves upon focusing and a second focusing lens group that is disposed closer to an image than the first focusing lens group and moves upon focusing,
the first focusing lends group and the second focusing lens group have positive refractive powers,
the second focusing lens group consists of a single lens, and
the zoom optical system satisfies the following conditional expression:

−1.000<dA/dB<2.000

where dA: an amount of movement of the second focusing lens group with respect to an image surface upon zooming from a wide-angle end state to a telephoto end state, a sign of movement toward an object being assumed to be +, and a sign of movement toward an image being assumed to be −, and
dB: an amount of movement of the cylindrical member with respect to the image surface upon zooming from the wide-angle end state to the telephoto end state, a sign of movement toward the object is assumed to be +, and a sign of movement toward the image is assumed to be −.