JPH037919A - Back focus adjusting device for vari-focal lens system - Google Patents

Abstract

PURPOSE:To make a back focus adjustment with high accuracy by providing a fixed ring with a back focus adjusting ring which engages a cam ring threadably by a threadable rotation on an optical axis and further fitting the fixed ring with a leaf spring which energizes the cam ring along the optical axis. CONSTITUTION:A cam groove 12 is formed in the cam ring 10 on the side of the fixed side 4 and the driven element part 16 of the lens support frame 14 of a 2nd lens group 2 engages the groove; and a helicoid part 20 is provided on the opposite side from the fixed ring 4 and a helicoid part 22 provided at the outer periphery of the lens support frame 15 of a 1st lens group 1 engages the helicoid part 20 threadably. Here, lens groups 1 are moved in the lens support frames 15 and 14 in the direction of the optical axis O to make a focusing adjustment. Further, a screw 48 is loosened to move a rack 44 to the position where it does not engage the gear part 34 and the back focus adjusting gear 46 is rotated to move the cam ring 10 along the optical axis O to make a back focus adjustment. Further, the fixed ring 4 is fitted with the leaf spring 6 which energizes the cam ring 10 along the optical axis to adjust the gap between an adjusting ring 32 and the ring 10.

Description

DETAILED DESCRIPTION OF THE INVENTION (Industrial Application Field) The present invention provides a fixed ring, a cam ring that has a cam portion and rotates with respect to the fixed ring, and a cam engagement member that engages with the cam portion. The present invention relates to a variable focus lens system including a movable lens holding frame having a section.

(Prior art and its problems) A variable focus lens needs to be focused by adjusting its back focus, ie, adjusting the position of the lens system with respect to a camera body, for example.

An example of a conventional back focus adjustment device is a structure in which a washer is interposed between the camera body and the lens system, and a number of washers with different thicknesses are prepared, and the appropriate one is selected and used. Are known.

However, with this configuration, the lens system must be removed from the camera body in order to replace the washer, which is not only extremely troublesome, but also requires the use of washers of various thicknesses. be.

As another example of a conventional back focus adjustment device, an eccentric bin is pivotally supported on a member integrated with the camera body, an engaging member that engages with the eccentric bin is attached to a holding frame of a lens system, and the eccentric bin is fixed. A configuration is known in which the engaging member and lens system are moved by rotation.

In this configuration, since only one eccentric bin is used,
There was a problem that the lens system was decentered with respect to the optical axis of the camera body.

(Object of the Invention) The present invention has been made in view of the above-mentioned problems of conventional back focus adjustment devices, and has a simple structure that enables reliable and highly accurate focus adjustment without decentering of the lens system. An object of the present invention is to provide a back focus adjustment device.

(Structure of the Invention) The present invention includes a fixed ring, a cam ring having a cam portion and rotating with respect to the fixed ring, and a movable lens holding frame having a cam engaging portion that engages with the cam portion. In the variable focus lens system, a back focus adjustment ring is provided between the fixed ring and the cam ring, and the back focus adjustment ring is rotatably attached to the fixed ring around the optical axis and is threadedly engaged with the cam ring by a spiral around the optical axis. A back focus adjustment device for a variable focus lens system, further comprising a plate spring attached to the fixed ring for biasing the cam ring along the optical axis.

(Example) Embodiments of the present invention will be described below based on the drawings.

As shown in FIGS. 1 and 2, the variable focus lens system includes a second lens system 2 and a second lens system 2 that move along the optical axis 0 and do not rotate about the optical axis 0.

A plate spring 6 is interposed at the front end of the fixed i14 to hold it m.
8 is installed. A front cover 7 that covers the entire lens is attached to the front end of the holder i18. Fixed II4
and the retaining ring 8 slidably support the cam ring IO therein.

The cam ring IO is provided with a cam groove 12 on the side of the fixed ring 4, in which the follower part 16 of the lens support frame 14 of the second lens group 2 is engaged, and a helicoid 920 is provided on the opposite side of the fixed ring 4. A helicoid holder 22 provided on the outer periphery of the lens support frame 15 of the lens group 1 is screwed thereto. The cam ring IO also has a flange-like protrusion 24 on its central outer circumference and a gear ring 26 integral with the flange-like protrusion 24. The gear 1i26 is engaged with a drive motor (not shown) for rotating the cam ring 10.

As shown in FIG. 1, the leaf spring 6 has a substantially square outer shape, and has three approximately T-shaped suppressing portions 30 that protrude inward around a central circular hole. The suppressing portion 30 is fixed [displaced toward the 4th side].

A back focus adjustment ring 32 is arranged between the leaf spring 6 and the holding m8 without a gap in the optical axis direction. The back focus adjustment ring 32 has a gear part 34 on the outer circumference for manually rotating the back focus adjustment ring 32, and has a screw thread on the inner circumference that engages with a threaded part 36 provided on the outer circumference of the cam ring 10. It has 840. The suppressing portion 30 of the leaf spring 6 urges the protrusion 24 of the cam ring IO toward the fixed ring 4.

As shown in FIG. 3, a rack 44 and a back focus adjustment gear 46 are engaged with the gear portion 34.

The rack 44 can be attached to the gear part 3 by loosening the screw 48.
4 can be moved to a position where it is no longer engaged.

In the above configuration, focus adjustment is performed by moving the lens group l in the optical axis 0 direction with respect to the lens support frames 15 and 14, respectively. Furthermore, loosen the screw 48, move the rack 44 to a position where it does not engage with the gear part 34, rotate the back focus adjustment gear 46, and move the cam ring IO to the optical axis 0.
to adjust the back focus. At this time, a drive motor (not shown) serves to prevent the cam ring 10 from rotating. Thereafter, each of the lens groups 1 is moved relative to the lens support frame 15 to perform focus adjustment.

In the above embodiment, the leaf spring 6 is provided, but the leaf spring 6 may be omitted if the gap between the threaded portion between the cam ring 10 and the back focus adjustment ring 32 is within an allowable range.

(Effects of the Invention) According to the present invention, since the entire lens system can be precisely moved in the optical axis direction using a spiral structure, a reliable and highly accurate back focus can be achieved with a simple structure without eccentricity of the lens system. It has the advantage of being adjustable.

Also, when the cam ring rotates, the entire lens system moves in the optical axis direction using the screw on the back focus adjustment ring.
It also has the advantage that the length of the cam groove of the cam ring and the helicoid portion in the optical axis direction can be made shorter than the conventional one.

[Brief explanation of the drawing]

FIG. 1 is an exploded perspective view of a back focus adjustment device for a variable focus lens system according to an embodiment of the present invention, FIG. 2 is a vertical sectional view of the back focus adjustment device along the optical axis, and FIG. FIG. 3 is a partial cross-sectional view along a plane perpendicular to the optical axis of the adjustment device. ...Second lens system...Second lens system...Fixed ring...Plate spring 0...Cam ring 4.15...Support frame 6...Gear ring 0...Suppression part 2 ... Focus adjustment ring 4 ... Gear part

Claims (2)

[Claims] (1) A variable focus lens system that includes a fixed ring, a cam ring that has a cam portion and rotates with respect to the fixed ring, and a movable lens holding frame that has a cam engagement portion that engages with the cam portion. A back focus adjustment ring is interposed between the fixed ring and the cam ring, and is attached to the fixed ring so as to be rotatable about the optical axis and is threadedly engaged with the cam ring by a spiral about the optical axis, and further, A back focus adjustment device for a variable focus lens system, characterized in that a leaf spring for biasing the cam ring along the optical axis is attached to the fixed ring. (2) The back focus adjusting device for a variable focus lens system according to claim 1, wherein the back focus adjusting ring has a gear portion, and the fixed ring has a releasable locking member that engages with the gear portion.