JPS63167336A - Zooming system - Google Patents

Abstract

PURPOSE:To attain sure focusing even at the time of zooming by controlling the moving speed of a movable lens in its optical axis direction so that an image forming point based upon a change in a focal distance is changed approximately linearly to zooming time. CONSTITUTION:An image forming point A is changed approximately linearly to the rotationed angle of a cylindrical cam 7 by specifying the shape of a cam groove 8 in the relation between a distance (a) based upon the movement of a movable concave lens L due to the cam groove 8 and the rotational angle thetaof the cam 7. Since a power zooming motor 9 is rotated at a constant speed, the rotational angle theta of the cam 7 is changed at a constant speed and a change at the image forming point A is approxilmately linear to time. Thereby, the change of the image forming point A about the zooming time can be approximately linearly set up so as to pass from a point P1 to a point P2, and when the cam 7 is rotated at the constant speed, the change at the image forming point A of a zoom lens can be set up approximately linearly to the zooming time. Consequently, accurate focusing always following the changed on the image forming point at the time of zooming can be attained.

Description

DETAILED DESCRIPTION OF THE INVENTION (Field of Industrial Application) The present invention relates to a zooming method for a video camera, etc., and particularly to a zooming method in which the change in the imaging point during zooming is approximately linear.

(Prior Art) Conventionally, as shown in FIG. 5, zoom lenses include a fixed convex lens Lr, a movable concave lens L2 . It is generally known that the lens is composed of four groups of lenses: a movable convex lens L3 and a fixed convex lens L4.

In a zoom lens having such a configuration, for example, imaging light 1 from an object at an infinite distance enters the fixed convex lens L1 as parallel light, and the second focal point F of this fixed convex lens L1 is
The light is refracted so as to be converged at 1, and further refracted by the movable concave lens L2 so as to be equivalent to the light emitted from the first focal point F3 of the movable convex lens L3.

Then, Fil refracted by this movable concave lens L2
The light 1 is refracted by the movable convex lens L3 to become parallel light, and is further focused by the fixed convex lens L4 onto the imaging surface 1 located at the second focal point F4 of the fixed convex lens 4. It has become.

In addition, the focal length of each of the above lenses 1 to L4 is r
t, f 2 , f 3 , f 4 Tea')
, the focal length of the conosum lens is to.

In the zoom lens configured as described above, by moving the movable concave lens L2 in the optical axis direction (in the six directions of arrows) and moving the movable convex lens L3 in accordance with the movable concave lens L2, the zoom lens Zooming is performed by appropriately changing the focal path Wil'o without changing the imaging position.

In this case, the positional relationship between the movable concave lens L2 and the movable convex lens L3 is such that the distance between the second focus Fl of the fixed convex lens L1 and the movable concave lens L2 is a, and the distance between the first focus F3 of the movable convex lens L3 and the movable concave lens is a. When the distance from L2 is b, it is determined to satisfy the following formula, and the distance a is varied to move the position of the movable concave lens L2, and along with this movement, the above formula (1) is satisfied. Zooming is performed by varying the distance and moving the movable convex lens L3.

In addition, focusing in the zoom lens described above involves front lens correction in which the fixed convex lens L1 is moved without changing the imaging point A to move the second focal point F1 of the fixed concave lens L, or the fixed convex lens L4 is moved. This is performed by rear lens correction in which the imaging point A is moved to coincide with the imaging surface 1.

(Problems to be Solved by the Invention) In the conventional zoom lens, the movable concave lens L2 and the movable convex lens L3 are moved in the optical axis direction by, for example, a cylindrical cam mechanism, and the position of the movable concave lens L2 is When expressed as the above-mentioned distance @a, this distance a and the rotation angle θ of the cylindrical cam had a linear proportional relationship as shown in FIG.

However, when performing rear lens correction, the position of the imaging point A and the rotation angle θ of the cylindrical cam are linearly proportional to changes in the focal length f of the zoom lens, as shown in FIG. Otherwise, especially when the movable concave lens L2 moves to the long focal point side, the imaging point A will change rapidly as the rotation angle θ changes.

In this case, there is a problem that the correction of the fixed concave lens L4 for focusing cannot follow up completely, and the screen becomes out of focus only during zooming.

(Means for solving the problems) The present invention has been made in view of the above-mentioned circumstances,
An object of the present invention is to provide a zooming method that can perform focusing reliably even during zooming.

In order to achieve this object, the present invention employs a zooming method as shown in FIG. To provide a zooming method characterized in that the speed of movement of the movable lens in the optical axis direction is controlled so that the imaging point A changes approximately linearly with respect to the zooming time as the focal length changes. It is something.

(Function) According to the zooming method as described above, the change in the imaging point A of the zoom lens during zooming becomes approximately linear;
The amount of change per unit time is approximately constant.

Here, if the line representing the above-mentioned imaging point A passes from the middle point P1 to the point P2 in FIG.
The amount of change per unit time, that is, the layer of change of the imaging point A per unit time is the minimum among any curves passing from point P2 to point P2.

Therefore, since this amount of change is minimal, the position of the focusing lens can be corrected at the imaging point A even during zooming.
It is possible to sufficiently follow changes in the image, and prevent out-of-focus conditions from occurring during zooming.

(Embodiments) Hereinafter, preferred embodiments of the present invention will be described in detail with reference to FIGS. 1 to 5.

In this embodiment, four groups of lenses L1 as shown in FIG.
The present invention is applied to a zoom lens constituted by L4, and a cylindrical cam 7 that engages with a pin 6 protruding from a lens barrel 5 housing a movable concave lens L2 constituting this zoom lens. By making the shape of the cam groove 8 into a predetermined curve, when the rotational speed of the cylindrical cam 7, that is, the zoom drive speed is constant, the moving speed of the movable concave lens L2 in the optical axis direction (in the direction of the arrow) can be controlled. This allows the change (amount of change) of the imaging point A per unit time to be approximately constant.

That is, the lens barrel 5 is fitted into the cylindrical cam 7 so as to be freely movable, and the bin 6 protruding from the outer periphery of the lens barrel 5 is connected to the cam formed on the inner periphery of the cylindrical cam 7. It is engaged with the groove 8.

Further, a first gear G1 is carved on the outer peripheral surface of the cylindrical cam 7, and this first gear G1 is rotated by a power zoom motor 9 via a second gear G2. It meshes with No. 3 gear G3.

Then, by rotating the motor 9 at a constant speed and driving the zoom, the cylindrical cam 7 is rotated, whereby the lens barrel 5 is guided by the cam groove 8 together with the movable concave lens L2 and moved in the optical axis direction. It looks like this.

Here, in this embodiment, the planar development shape of the cam groove 8 is the rotation angle θ of the cylindrical cam 7 and the distance a shown in FIG.
The shape is approximately the same as the curve obtained by multiplying the curve representing the relationship by 8 in the θ direction.

When the movable concave lens L2 is moved using such a cam groove 8, the imaging point A of the zoom lens is approximately directly proportional to the rotation angle θ of the cylindrical cam 7, and the imaging point A is approximately Changes linearly.

Therefore, when the rotational speed of the cylindrical cam 7, that is, the zoom driving speed is constant, the imaging point A changes approximately linearly with respect to the zooming time.

The fixed convex lens L4, which is the focus lens in this embodiment, is moved in the optical axis direction as appropriate by a focus drive mechanism (not shown).

Next, the shape of the cam groove 8 will be explained.

First, if the amount of change to the imaging point is Δ, then the case where the imaging point A changes linearly with respect to the rotation angle θ of the cylindrical cam 7 is: 1=kl (constant) (2) This is a case where the expression dθ holds true.

Here, the amount of change Δ is determined.

In FIG. 3, if the distance between the main surface M of the zoom lens and the subject is 1 cm, the distance between the main surface M and the imaging point A is mJ12, and the focal length of the zoom lens is f, then becomes.

Therefore, from this equation (4), becomes.

Here, in this equation (5), since JL+) f O, this equation (5) can be approximated by a2 Δ辷− (6).

Further, when the focal length 111fo in this equation (5) is determined, the following is obtained in FIG. 5: fo=-14 (7).

Here, as is clear from the figure, h:h'-f1:a, l-1:h--
From f 3 :b theal, the above equation (7) becomes.

Also, since it is from the above equation (1), substituting the above equation (8) into the above equation 0 gives the following equation.

Here, in this equation (10), fl, 12°f3.
Since f4 is a constant, the above equation (10) can be written as follows.

Therefore, the above (formula 0 is becomes.

Therefore, by substituting this equation (13) into the above ('2J equation), it becomes as follows.

If the relationship between a and θ that satisfies this equation (15) is found, the amount of change Δ of the imaging point A with respect to the rotation angle θ will be constant.

Therefore, if we solve this equation (15) for a, we get
The relationship between the above a and θ to be determined is, therefore, the distance a based on the movement of the movable concave lens L2 by the cam groove 8, in relation to the rotation angle θ of the cylindrical cam 7, as shown in (16) above.
By specifying the shape of the cam groove 8 so as to satisfy the formula, the change in the imaging point A becomes approximately linear with respect to the rotation angle θ of the cylindrical cam 7.

Further, in this embodiment, since the power zoom motor 9 is rotated at a constant speed, the rotation angle θ of the cylindrical cam 7 changes at a constant speed.

Therefore, the change in the imaging point A is also approximately linear with respect to time.

As described above, according to this embodiment, by setting the shape of the cam groove 8 of the cylindrical cam 7 to satisfy the above formula (16), the change with respect to the zooming time to the above image forming point is shown in FIG. It can be made approximately linear so as to pass from the midpoint P1 to the point P2.

Therefore, when the cylindrical cam 7 is rotated at a constant speed, the change in the imaging point A of the zoom lens according to this embodiment can be made approximately linear with respect to the zooming time.

Here, the line representing the imaging point A has the smallest amount of change per unit time among the lines passing from point P1 to point P2 in the middle of FIG.

Therefore, even during zooming, the fixed convex lens 4, which is a focus lens, can be made to follow changes in the image forming point A, thereby achieving reliable focusing.

In addition, in this embodiment, the power zoom motor 9
Although the cylindrical cam 7 is rotated at a constant speed using the cylindrical cam 7, the same effect can be obtained even when the cylindrical cam 7 is rotated manually and driven for zooming, as long as the rotation speed is constant.

By the way, in the above embodiment, the movable concave lens L is rotated at a constant speed by the power zoom motor 9, and the cam groove 8 of the cylindrical cam 7 is formed into a predetermined curved shape.
The moving speed of the movable concave lens L2 in the optical axis direction is varied according to the position of the movable concave lens L2. The rotational speed of the motor may be varied depending on the position of the movable concave lens L2.

An example in this case will be described below.

In this embodiment, the lens barrel 10 housing the movable concave lens L2 is fitted into the cylindrical cam 11 so as to be slidable only in the optical axis direction, and the cylindrical cam 11 is similar to the previous embodiment. First to third gear G1. It is designed to be rotated by pulse motors 12 for G2, G3 and power zoom.

Furthermore, a linear cam groove 13 is formed on the inner circumference of the cylindrical cam 11.
is formed, and a pin 14 protruding from the outer periphery of the lens barrel 1o is engaged with this cam groove 73.

Roughly speaking, a fourth gear G4 meshes with the first gear G1, and this fourth gear G4 is connected to the rotary encoder 1.
It is attached to the rotation shaft 16 of No. 5. Thereby, this rotary encoder 15 outputs a position information signal S1 representing the position of the movable concave lens L2.

Then, this position information signal S1 is supplied to a control circuit 17, and this control circuit 17 supplies a pulse signal of a predetermined frequency to the pulse motor 12 as a motor drive signal S2 based on this position information signal S1. There is.

Here, the control circuit 17 detects the distance a in the equation (16) based on the position information signal S1, and sets the rotation speed of the pulse motor 12 based on this distance a.

That is, the above equation (16) can be expressed as follows by replacing the rotation angle θ in equation (16) with the zooming time t.

Then, the control circuit 17 sets the rotation speed of the pulse motor 12 so that the distance a and the zooming time t satisfy equation (17).

Therefore, in this embodiment, the above (1
7) The rotational speed of the pulse motor 12 is set and controlled so as to satisfy the formula, and the moving speed of the movable concave lens L2 in the optical axis direction is variably controlled, thereby zooming the imaging point A of the zoom lens in this embodiment. It can be changed approximately linearly with respect to time.

(Effects of the Invention) As is clear from the above description, the present invention configures the zoom lens so that the image forming point changes approximately linearly with the zooming time as the focal length of the zoom lens changes. By controlling the speed of movement of the movable lens in the optical axis direction, the amount of change per unit time can be minimized, which allows accurate focusing that always follows changes in the imaging point during zooming. It can be made possible.

[Brief explanation of the drawing]

Figure 1 is a graph showing the relationship between the rotation angle of the cylindrical cam and the imaging point and the distance # (position) of the movable lens in the present invention.
The figure is a cross-sectional view showing the main part of the embodiment according to the present invention, FIG. 5 is a diagram schematically showing the optical system of a general zoom lens, and FIG. 6 is a diagram showing the rotation angle of a conventional cylindrical cam and the distance between the imaging point and the movable lens ( It is a graph showing the relationship with the position [). 7... Cylindrical cam, 8... Cam groove, 11... Cylindrical cam, 12... Pulse motor, 13... Cam groove, A.
...Image point, f, ...Focal length, L2...Movable lens (movable concave lens). 100 (Figure 2 Figure 4 Figure 6 Figure 6

Claims (1)

[Claims] A zooming method that changes the focal length of the zoom lens by moving a movable lens constituting the zoom lens in the optical axis direction using a zoom drive, A zooming method characterized in that the moving speed of the movable lens in the optical axis direction is controlled so that the imaging point changes approximately linearly with respect to the zooming time.