JPH0664223B2 - Zoom lens with tracking adjustment mechanism - Google Patents

Description

TECHNICAL FIELD OF THE INVENTION The present invention relates to a zoom lens having a tracking adjustment mechanism.

(Background of the Invention) The zoom lens has different temperature characteristics of the back focus movement amount (γ) depending on the zoom state. Figure 2 is 20
An example of the temperature characteristic of the back focus movement amount (γ) in each of the telephoto (T), intermediate (M), and wide angle (W) zoom states of the zoom lens whose back focus is adjusted at ° C is shown.

As is clear from the characteristics shown in FIG. 2, the difference (ε) in the back focus movement amount between the telephoto (T) and the wide angle (W) is generally larger as the zoom ratio is larger. Therefore, for example, in a television camera using a zoom lens with a zoom ratio of 30 or 40, the zoom lens is equipped with a tracking adjustment mechanism, and the tracking lens is manually adjusted in the optical axis direction under the operating environment temperature before shooting. As shown in FIG. 3, by adjusting the back focus at the wide-angle (W) end, the difference (ε) in the back-focus movement amount at the telephoto (T) and the wide-angle (W) ends is made small.

By the way, recently, a high-definition television system has been proposed.
This is a television system for obtaining a reproduced image with high definition and excellent color reproduction by doubling the scanning lines.
The TV camera used for this high-definition TV system is required to have higher performance than ever before. In particular, a zoom lens for a high-definition television camera is required to have a large zoom ratio and strict chromatic aberration correction. Therefore, good chromatic aberration correction and telephoto (T),
A special optical material such as fluorite or high-refractive-index low-dispersion glass is used in order to reduce the difference (ε) in the amount of back focus movement at both ends of the wide angle (W). However, the special optical material has a larger variation in the refractive index due to temperature and a larger coefficient of expansion than ordinary optical materials. Therefore, the back focus movement amount (γ) due to the temperature is large, and for example, in the case of continuous outdoor shooting for a long time, even when the back focus is adjusted on the wide angle (W) side when the early morning air temperature is low prior to shooting, the air temperature changes with time. When it rises, the back focus moves, so there is a difference between the distance scale and the actual subject distance, and if the difference increases further, it will be outside the depth of focus even if the distance scale is adjusted to infinity. A case comes out and interferes with the shooting. Especially, the possibility becomes a big problem on the telephoto (T) side of the long focus lens. Therefore, if the back focus is adjusted by moving the tracking lens for each temperature and each zoom state, the above problem is solved, but tracking for each temperature is complicated, and zooming is performed while continuously performing normal shooting. Since it is often operated, it is actually impossible to perform the tracking adjustment operation at the same time as the zooming operation.

(Object of the Invention) The present invention has been made in view of the above points, and an object of the present invention is to obtain a zoom lens that automatically corrects the movement of the back focus due to temperature and focal length.

(Outline of the Invention) The present invention calculates the amount of movement of the tracking lens from the outputs of the temperature detection means and the focal length detection means, and automatically moves the tracking lens in the optical axis direction to move the image plane due to temperature and zooming. The technical point is to compensate.

(Embodiment) FIG. 1 is a partial cross-sectional view showing a main part of a zoom lens according to the present invention, in which a fixed lens barrel 1a integrated with a mount is used to match the image formation of the lens with the image pickup surface of the camera. An adjustable so-called tracking lens 2 is provided, and the rectilinear barrel 3 that holds the lens 2 is moved in the optical axis direction by the guide of the rectilinear key 5 by the rotation operation of the rotary helicoid ring 4. Reference numeral 6 denotes a tracking adjustment ring, which is provided with an internal gear 6a on its inner circumference, and the internal gear 6a is an intermediate gear 8 axially supported by a correction ring 7 which is rotatably engaged with the lens barrel 1b. Is meshing with. The intermediate gear 8 also meshes with external teeth 4a formed on the outer circumference of the rotary helicoid ring 4. The other end of the correction ring 7 is provided with a crown gear 7a that meshes with the worm gear 10 of the rotary shaft of the tracking adjustment motor 9.

When the rotation of the motor 9 is stopped, when the tracking adjustment ring 6 is rotated, the rotating helicoid ring 4 is rotated via the intermediate gear 8 and the tracking lens 2 is moved in the optical axis direction to move the focus position. Can be changed. On the other hand, even if the tracking motor 9 is driven with the tracking adjustment ring 6 fixed by the clamp screw 6b, the worm gear 10 rotates the correction ring 7 to rotate the intermediate gear 8 and the internal gear 6a of the adjustment ring 6. The outer tooth 4a of the helicoid ring 4 differentially rotates the rotating helicoid ring 4 to move the tracking lens 2 in the optical axis direction to change the focus position. Reference numeral 11 is a temperature sensor, which is arranged at a position most representative of the temperature state of the optical system and the mechanical system.

As described above, FIG. 2 shows a back focus movement amount due to the temperature of the lens with the focal length as a parameter, and a state in which there is no focus movement at 20 ° C. FIG. 3 shows the amount of focus shift due to temperature at the intermediate and telephoto focal lengths when the lens of FIG. 2 is subjected to tracking adjustment so that the focus is matched at the wide-angle side focal length. In any case, you can see that it is out of focus by zooming.

FIG. 4 is a block diagram of one embodiment, and FIG. 5 is a flow chart of its operation. In FIG. 4, 11 is a temperature sensor for detecting the temperature of the lens, 12 is an amplifier for the sensor, 15b
Is the temperature signal that is A / D converted by the A / D converter
Entered in 16. Reference numeral 13 is a zooming operation member, and the focal length is detected by the potentiometer 14 and A / D converter 15
The zooming signal A / D converted by a is the microcomputer 16
Entered in. 17 is a fully automatic / semi-automatic changeover switch, 18 is an automatic correction switch, 19 is a D / A converter, 20 is an amplifier, 9
Reference numeral 21 is a motor incorporating an encoder, and 21 is a tracking lens moving mechanism including the linearly moving barrel 3, the rotating helicoid ring 4, the outer teeth 4a and the like.

Next, the fully automatic / semi-automatic changeover switch 17 will be described.

Adjusting the tracking of the camera and lens is not so frequent unless you change to another lens. In such a case, in the present invention, the switch is set on the side where the tracking adjustment is fully automatic. The amount of back focus movement due to temperature in this case is as shown in FIG. Next, semi-automatic means that tracking adjustment is performed immediately before in order to ensure reliable focus when there is a large temperature change such as a change in cold regions, warm regions, or changes from early morning to midday. In this case, since the tracking adjustment is manually performed at the wide-angle side focal length according to the fluctuation of the environmental temperature, the state of FIG. 2 is represented as shown in FIG.

The microcomputer 16 incorporates two ROM tables that store the correction values based on the graphs shown in FIGS. 2 and 3, and the changeover switch 1
Reference numeral 7 makes it possible to manually select one of the ROM tables. The calculation result of the microcomputer 16 is the D / A converter 19
The tracking lens is moved by driving the motor 9 which is D / A-converted by and is amplified by the amplifier 20 and whose position is controlled by the built-in encoder.

The operation of the embodiment shown in FIG. 4 will be described with reference to the flowchart of FIG.

After mounting the lens on the camera, select full-automatic or semi-automatic. In the case of semi-automatic, first, the tracking adjustment is performed as needed in the environmental condition at that time. The focal position matches on the wide-angle side, but the focus is off on the middle and telephoto sides. (Actually, every time zooming is performed, the focus will be in focus.) The amount of deviation is stored in the first ROM table of the microcomputer, and when the automatic correction switch 18 is turned on, zooming is performed after the on operation. If the position information is stored in the microcomputer 16 via the potentiometer 14 and the A / D conversion circuit 15a,
Is input to and calculated, D / A converted, the motor is driven through an amplifier, and automatic tracking adjustment is performed. When fully automatic, the tracking adjustment is performed on the wide-angle side at room temperature and the automatic correction switch 18 is turned on. The amount of focus shift due to the subsequent zooming and the temperature characteristic of the amount of shift are stored in the second ROM table of the microcomputer.
The tracking lens is automatically corrected based on the ROM table.

(Effects of the Invention) As described above, according to the present invention, there is an advantage that the focus movement caused by the temperature change is prevented in advance and the focus movement does not occur even by the zooming, and the user arbitrarily adjusts the tracking manually. It is also possible to do. Also, by remotely controlling the tracking motor, it is possible to perform tracking adjustment on a monitor with a large screen other than the viewfinder of the camera.

[Brief description of drawings]

FIG. 1 is a partial cross-sectional view of an embodiment, FIG. 2 is a diagram showing a relationship between a lens temperature and a back focus movement amount with a focal length as a parameter, and FIG. 3 is a case where the back focus is adjusted on the wide angle side. FIG. 4 is a diagram showing the relationship between the lens temperature and the back focus movement amount with the focal length as a parameter, FIG. 4 is a block diagram showing an embodiment of the present invention, and FIG. 5 is a description of the operation of the embodiment shown in FIG. It is a flowchart to do. (Explanation of symbols of main parts) 2 ... Tracking lens 7 ... Correction ring 9 ... Tracking motor 11 ... Temperature sensor

Continuation of the front page (51) Int.Cl. ⁵ Identification code Office reference number FI Technical display area H04N 5/232 E

Claims (1)

[Claims] 1. A temperature detecting means, a focal length detecting means, a selecting means for selecting whether to perform automatic tracking adjustment at either an ambient temperature or a room temperature, and a temperature difference of a zoom lens which is previously subjected to tracking adjustment at an ambient temperature. Has a first storage means for storing the back focus movement amount according to the above and a second storage means for storing the back focus movement amount due to the temperature difference of the zoom lens at room temperature, and when the selection means selects the environmental temperature, The temperature detecting means, the focus detecting means,
And a calculation means for calculating the tracking correction amount based on the storage of the first storage means based on the output from the selection means, and a calculation means based on the storage of the second storage means when the normal temperature is selected; A zoom lens having a tracking adjustment mechanism, the zoom lens having a control unit that controls the movement of the tracking lens according to the output of the zoom lens.