JP2775484B2 - Zoom lens barrel and its flange back adjustment method - Google Patents

Description

Description: BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a zoom lens, and more particularly to a method of adjusting a flange back when a zoom lens is incorporated in a camera.

(Prior Art) In recent years, the widespread use of zoom lenses has led to a demand for high-magnification zoom lenses even in lens shutter cameras, and the number of movable lens groups for zooming is increasing. .

Conventionally, in general, adjustment (FC adjustment) to match the imaging point position by the zoom position from the short focus side to the long focus side is performed with the most advanced lens group of the zoom lens system, and flange back adjustment (Ff adjustment) is performed by moving and adjusting all the lens units in the optical axis direction, and a mechanism for that is provided separately.

If a mechanical method in which the FC adjustment and the ff adjustment are separated in this manner is used, the mechanism is complicated and the number of parts increases, which has been one of the factors that cause an increase in cost.

In the case of multi-group zoom lenses, if FC adjustment is performed with the most advanced lens group, it is necessary to increase the amount of movement for adjustment, and inevitably to secure the peripheral light amount on the short focal length side The outer diameter of the state-of-the-art lens group had to be large, resulting in a lack of compactness.

(Problems to be Solved by the Invention) The present invention aims to obtain a compact and inexpensive zoom lens mechanism which does not include the above-mentioned problems, despite being a multi-group movable zoom lens system. is there.

(Means for Solving the Problem) The method for adjusting the flange back of a zoom lens barrel according to the present invention is directed to a lens barrel for a zoom lens optical system having at least four movable lens groups.
A mechanism for fitting the sliding frame for the third lens group and the sliding frame for the fourth lens group, and for moving the second lens group frame in the optical axis direction in the sliding frames for the first to third lens groups. The cam barrel, which is loosely fitted to the fixed barrel and engages with the cam followers of the two sliding frames, is movable in the optical axis direction by an adjustment ring disposed outside the fixed barrel. In the lens barrel, the flange focal length adjustment on the short focal length side is performed by moving the whole lens unit together by adjusting the optical axis direction of the cam barrel. It is characterized by being moved.

The moving mechanism of the second lens group is operated from outside using a motor, and the moving mechanism for zooming and the moving mechanism for focusing are shared.

(Examples) Hereinafter, the present invention will be described in detail by examples with reference to the drawings.

FIG. 1 shows an outline of a zoom lens optical system having four movable groups. I, II, III, and IV are first, second, third, and fourth movable lens groups, respectively, and zooming is short. As shown, each lens group moves toward the object side from the focal point side to the long focal point side. In the present invention, the movement of the first movable lens group and the third movable lens group by zooming is the same.

The solid line indicating the movement locus of the second movable lens group indicates the position moved during zooming. Focusing is performed by moving from this base point to the position indicated by the dotted line.
At this time, the amount of movement for the same object distance differs according to the difference in focal length due to zooming, as indicated by the optical axis direction arrow.

FIG. 2 is a schematic view of the mechanism of the lens barrel of the present invention, where 1 is a fixed barrel,
2 is a cam cylinder, 3 is a sliding frame for the first to third lens groups, 3 'is a sliding frame for the second lens group, 4 is a sliding frame for the fourth lens group, 5
Is a movable diaphragm, 6 is a second lens group guiding pole, and 7 is a second lens group guiding pole.
A lens group driving screw shaft, 8 is a second lens group driving AF motor (AFM), 9 and 10 are zooming driving cam followers, 11 is a flange back adjustment ring, and 12 is a cam cylinder holding ring.

When the cam barrel 1 is rotated by a motor (not shown), zooming is performed in the lens group sliding frame 3 shown in FIGS.
A predetermined movement is given to the cam followers 9 and 10 implanted in the fourth lens group sliding frame 4 via the cam groove of the cam barrel 1 and the guide groove (not shown) of the fixed body,
A predetermined movement of the first lens group, the third lens group, and the fourth lens group is performed. At this time, in association with the rotation of the cam barrel 1, the screw shaft 7 is rotated by the AF motor 8 via the zoom encoder ZE and the microcomputer CPU via a reduction gear (not shown), and the second lens group frame 3 is rotated. ′, The frame 3 ′ is moved in the optical axis direction within the sliding frame 3 by the difference between the moving amount of the sliding frame 3 and the moving amount of the second lens group.

In focusing, a distance measurement signal from a distance measurement mechanism (not shown) enters the CPU, the focal length at that time is read from the zoom encoder ZE, a focusing movement amount is calculated by the CPU, and a reduction gear (not shown) is calculated by the AF motor 8. The rotation is given to the screw shaft 7 through the above, and a predetermined movement is given to the second lens group frame 3 'to achieve focusing.

The lens barrel of the present invention uses the ff
When the adjustment ring 11 is rotated, the ff adjustment ring 11 and the cam cylinder 2
The cam screw 2 is moved in the optical axis direction by the engaging screw. The movement of the cam cylinder 2 also causes the first to third lens group sliding frames 3 and the fourth lens group sliding frame 4 to move back and forth integrally via the cam floors 9 and 10, so that all the groups are integrated. Adjustment in the optical axis direction becomes possible.

In the lens barrel of the present invention, the cam barrel 2 can be adjusted in the optical axis direction, and the ff adjustment on the short focal length side is moved in the optical axis direction by rotating the adjustment ring 11, that is, the entire lens system is integrated. Is used to adjust the movement in the optical axis direction, and for other FC adjustments using the zoom position, a method is adopted in which only the second lens group is moved and adjusted. In other words, in the FC adjustment by other zoom positions, if the adjustment amount at that position is measured at about three points including the long focal point, the other positions are automatically controlled by the software in the CPU. This can be done by giving a quantity.

If the adjustment by the second lens group is performed at all positions, assuming that the flange back adjustment amount is 0.5, in the lens system of this embodiment, the adjustment amount of the second lens group is about 0.3 on the short focal length side, and about 0.3 on the long focal length side. The adjustment amount of the second lens group is significantly different from the adjustment amount of about 0.03. Significantly degrades performance. Therefore, even if the short focus side is adjusted by moving the entire unit together, the amount of movement is small, so that the performance degradation is small. Also,
If the short focus side is adjusted by moving the entire group first at other zoom positions, the correction amount by the second lens group will also decrease in the vicinity of the long focus where a large amount of movement is required.

(Effect of the Invention) According to the flange back adjustment method of the present invention, 1. FC amount is adjusted by adjusting the movement amount of the second lens (lens group movable with respect to the sliding cylinder controlled by the cam cylinder) during zooming. No adjustment is required, the zoom movement mechanism and the focus movement mechanism can be shared, and ff adjustment can be performed with the cam barrel, reducing the number of mechanical parts and eliminating the complexity of the mechanism, enabling the supply of a compact and inexpensive zoom lens barrel. It became.

2. Movement of the focal position due to cam groove machining accuracy error can be corrected, and the cam cylinder machining cost can be reduced.

3. It was possible to always adjust the best position for each product, and the performance of all products could be maintained.

It has a remarkable effect.

[Brief description of the drawings]

FIG. 1 is an optical layout diagram of a zoom lens having four possible groups for implementing the adjustment method of the present invention, and FIG. 2 is a schematic view of a mechanism of an embodiment of a lens barrel structure therefor. In the figure, reference numerals I, II, III, and IV denote first, second, third, and fourth movable lens groups, respectively, 1 is a fixed body, 2 is a cam barrel, and 3 is a first to third lens groups. 3 'is a sliding frame for the second lens group, 4 is a sliding frame for the fourth lens group, 5 is a movable diaphragm, 6 is a pole for guiding the second lens group, and 7 is a drive for the second lens group. Screw shaft, 8 is AF for driving the second lens group
Motors 9, 9 are cam followers for zooming drive, 11
Denotes a flange back adjustment ring, and 12 denotes a cam cylinder holding ring.

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Claims (3)

(57) [Claims] 1. A lens barrel for a zoom lens optical system having at least four movable lens groups, wherein a sliding frame for the first to third lens groups and a sliding frame for the fourth lens group are fitted in a fixed barrel. A mechanism for moving the second lens group frame in the optical axis direction is provided in the first to third lens group sliding frames, and the cam followers of the two sliding frames are loosely fitted to the fixed barrel. The cam barrel to be fitted can be moved in the optical axis direction by an adjustment ring arranged outside the fixed barrel, and the lens barrel having the above-described structure can adjust the short focal length of the flange back by adjusting the optical axis of the cam barrel. A flange back adjustment method for a zoom lens barrel, characterized in that the whole lens group is moved and adjusted by a direction adjustment, and the flange back adjustment of other zoom positions is performed by moving only the second lens group frame in the optical axis direction. 2. The zoom lens barrel according to claim 1, wherein said second lens group frame moving mechanism shares a moving mechanism during zooming and a moving mechanism during focusing. Method 3. A lens barrel for a zoom lens optical system having at least four movable lens groups, wherein a sliding frame for the first to third lens groups and a sliding frame for the fourth lens group are fitted in a fixed barrel. A mechanism for moving the second lens group frame in the optical axis direction is provided in the first to third lens group sliding frames, and the cam followers of the two sliding frames are loosely fitted to the fixed barrel. The cam barrel to be fitted can be moved in the optical axis direction by an adjustment ring disposed outside the fixed barrel.