Cam ring, and a zoom lens barrel with the cam ring

1. A zoom lens barrel comprising:

a linear guide ring which is positioned about an optical axis, said linear guide ring including at least one linear guide slot extending parallel to said optical axis;

a cam ring which is coaxially positioned around said linear guide ring, said cam ring including at least one cam groove; and

a movable lens frame which supports a lens group and includes at least one cam follower, said cam follower passes through said linear guide slot to be engaged in said cam groove so that a rotation of one of said cam ring and said linear guide ring relative to the other causes said movable lens frame to move along said optical axis via engagement of said cam follower with said linear guide slot and said cam groove;

wherein said cam ring is provided with a large ring portion, a small ring portion having a smaller diameter than said large ring portion, and a radial flange portion which is positioned between said large ring portion and said small ring portion to connect said large ring portion with said small ring portion; and

wherein said cam groove is formed on both said small ring portion and said radial flange portion so that one end of the cam groove constitutes an open end at said radial flange portion, whereby said cam follower can be inserted into said cam groove through said open end.

2. The zoom lens barrel according to claim 1 , said zoom lens barrel having at least two said movable lens frames, each having said cam follower which is engaged with a corresponding said cam groove,

wherein said cam ring comprises coaxial first, second and third ring portions having different diameters decreasing in the optical axis direction of the zoom lens barrel, a first radial flange portion which connects said first ring portion with said second ring portion and a second radial flange portion which connects said second ring portion with said third ring portion; and

wherein one of said cam grooves is formed on both said second ring portion and the first radial portion, and the other of said cam grooves is formed on both said third ring portion and said second radial portion for inserting and guiding said cam followers provided on each of said two movable lens frames, respectively.

3. The zoom lens barrel according to claim 1 , wherein said cam groove is formed on said cam ring as a through slot radially penetrating through said cam ring.

4. The zoom lens barrel according to claim 1 , wherein said diameter of said cam ring decreases in a rearward direction of said cam ring so that said large ring portion is positioned in front of said small ring portion with said radial flange portion being provided therebetween; and

wherein a front end of said cam groove extends to a front surface of said radial flange portion to be formed as an open end on said front surface of said radial flange portion so that said cam follower can be inserted into said cam groove through said open end from the front of said cam ring.

5. The zoom lens barrel according to claim 1 , wherein said cam follower is formed integral with said movable lens frame.

6. The zoom lens barrel according to claim 1 , wherein said linear guide ring is a stationary member.

7. The zoom lens barrel according to claim 6 , further comprising a mount ring formed at a rear end of said zoom lens barrel, said linear guide ring being formed integral with said mount ring.

8. The zoom lens barrel according to claim 1 , further comprising a zoom ring which is coaxially provided around said cam ring, said cam ring being rotated about said optical axis via rotation of said zoom ring.

9. The zoom lens barrel according to claim 8 , further comprising a stationary barrel which is coaxially provided between said cam ring and said zoom ring in the radial direction, said zoom ring being rotatably supported on said stationary barrel.

10. A zoom lens barrel comprising:

a first movable lens frame which supports a first lens group, and includes at least one first cam follower;

a second movable lens frame which supports a second lens group, and includes at least one second cam follower;

a linear guide ring which is coaxially provided about an optical axis, and includes at least one linear guide slot extending parallel to said optical axis; and

a cam ring which is coaxially provided around said linear guide ring, said cam ring including at least one first cam groove and at least one second cam groove;

wherein said first cam follower and said second cam follower pass through a common said linear guide slot and engage in said first cam groove and said second cam groove, respectively, so that a rotation of one of said cam ring and said linear guide ring relative to the other causes said first movable lens frame and said second movable lens frame to move along said optical axis via engagement of said first cam follower with said linear guide slot and said first cam groove and via engagement of said second cam follower with said linear guide slot and said second cam groove, respectively;

wherein said cam ring is provided with a large ring portion, a middle ring portion having a smaller diameter than said large ring portion, a small ring portion having a smaller diameter than said middle ring portion, a first radial flange portion which is positioned between said large ring portion and said middle ring portion to connect said large ring portion with said middle ring portion, and a second radial flange portion which is positioned between said middle ring portion and said small ring portion to connect said middle ring portion with said small ring portion;

wherein said first cam groove is formed on both said middle ring portion and said first radial flange portion so that one end of said first cam groove constitutes a first open end at said first radial flange portion, whereby said first cam follower can be inserted into said first cam groove through said first open end; and

wherein said second cam groove is formed on both said small ring portion and said second radial flange portion so that one end of said second cam groove constitutes a second open end at said second radial flange portion, whereby said second cam follower can be inserted into said second cam groove through said second open end.

11. The zoom lens barrel according to claim 10 , wherein said diameter of said cam ring decreases in a rearward direction of said cam ring so that said large ring portion is positioned in front of said middle ring portion and said middle ring portion is positioned in front of said small ring portion, with said first radial flange portion being positioned between said large ring portion and said middle ring portion and with said second radial flange portion being positioned between said middle ring portion and said small ring portion;

wherein a front end of said first cam groove extends to a front surface of said first radial flange portion to be formed as said first open end on said front surface of said first radial flange portion, so that said first cam follower can be inserted into said first cam groove through said first open end from front of said cam ring; and

wherein a front end of said second cam groove extends to a front surface of said second radial flange portion to be formed as said second open end on said front surface of said second radial flange portion, so that said second cam follower can be inserted into said second cam groove through said second open end from front of said cam ring.

12. A cam ring including at least one cam groove in which at least one cam follower formed on a linearly-guided movable member is engaged, a rotation of said cam ring causing said linearly-guided movable member to move along an axis of said cam ring by engagement of said cam follower with said cam groove;

wherein said cam ring is provided with a large ring portion, a small ring portion having a smaller diameter than said large ring portion, and a radial flange portion which is positioned between said large ring portion and said small ring portion to connect said large ring portion with said small ring portion;

wherein said cam groove is formed on both said small ring portion and said radial flange portion so that one end of said cam groove constitutes an open end at said radial flange portion, whereby said cam follower can be inserted into said cam groove through said open end.

13. The cam ring according to claim 12 , comprising:

coaxial first, second and third ring portions having different diameters decreasing in the optical axis direction of the zoom lens barrel, a first radial flange portion which connects said first ring portion with said second ring portion and a second radial flange portion which connects said second ring portion with said third ring portion; and

wherein one of said cam grooves is formed on both said second ring portion and the first radial portion, and the other of said cam grooves is formed on both said third ring portion and said second radial portion for inserting and guiding said cam followers provided on each of said two movable lens frames, respectively.