Internal focusing zoom lens
View Patent ↗An internal focusing zoom lens includes a stationary barrel including a focus-guide cam groove; a zoom cam ring including a focus-shift cam groove and rotated about an optical axis during zooming; a focus cam ring including a focus cam groove and rotated about the optical axis and moved in the optical axis direction to move a focusing lens group during focusing; and a focus correction ring for moving the focus cam ring in the optical axis direction by rotation of the zoom cam ring. The focus correction ring includes a focus correction cam-follower engaged in the focus-shift cam groove, the focus cam groove and the focus-guide cam groove. A position of the focus correction cam-follower in the focus cam groove changes via the focus-shift cam groove and the focus-guide cam groove in accordance with the rotation of the zoom cam ring during zooming.
1. An internal focusing zoom lens comprising:
a stationary barrel including a focus-guide cam groove;
a zoom cam ring including a focus-shift cam groove, said zoom cam ring being rotated about an optical axis when a zooming operation is performed;
a focus cam ring including a focus cam groove, said focus cam ring being rotated about said optical axis and moved in said optical axis direction to move a focusing lens group in said optical axis direction when a focusing operation is performed; and
a focus correction ring for moving said focus cam ring in said optical axis direction by rotation of said zoom cam ring,
wherein said focus correction ring includes a focus correction cam-follower engaged in said focus-shift cam groove, said focus cam groove and said focus-guide cam groove, and
wherein a position of said focus correction cam-follower in said focus cam groove changes via said focus-shift cam groove and said focus-guide cam groove in accordance with said rotation of said zoom cam ring when said zooming operation is performed.
2. The internal focusing zoom lens according to claim 1 , wherein said focus correction ring is configured to vary a position of engagement of said focus correction cam-follower with said focus cam groove in accordance with a variation in rotation position of said zoom cam ring when said focus correction ring is rotated.
3. The internal focusing zoom lens according to claim 1 , wherein said focus-shift cam groove comprises a profile via which a position of said focus correction cam-follower is varied in a rotation direction thereof in said focus cam groove in accordance with a variation in rotation position of said zoom cam ring.
4. The internal focusing zoom lens according to claim 1 , wherein said focus-guide cam groove comprises a profile which limits an angle of rotation of said focus correction cam-follower when said zoom cam ring is rotated between a long-focal-length position and a short-focal-length position.
5. The internal focusing zoom lens according to claim 1 , wherein said focus cam groove comprises a profile via which an amount of movement of said focus correction cam-follower is varied in said optical axis direction per every predetermined amount of rotation of said focus cam ring.
6. The internal focusing zoom lens according to claim 1 , wherein said focus cam ring, said stationary barrel and said zoom cam ring are concentrically arranged closely to one another in that order from a radially inner side to a radially outer side, and
wherein said focus correction ring is positioned radially inside said focus cam ring.