JPS5854311A - Variable focus optical system - Google Patents

Abstract

PURPOSE:To reduce movable parts for changing the focal length and to simplify the mechanism to make it compact, by fixing a lens group in the object side out of two, convergent and divergent lens groups and making the lens group distant from the object movable in the direction of the optical axis. CONSTITUTION:The first group lens G1 and the second lens group G2 are arranged at an interval (d) in order from the object side, and refracting powers of these lens groups are denoted as K1 and K2, respectively, and two lens groups are constituted of a convergent lens group and a divergent lens group so that refracting powers K1 and K2 have signs opposite to each other and the same absolute value. For example, the convergent lens group G1 is fixed in the object side, and the divergent lens group G2 is provided in the rear of the lens group G1 movably along the optical axis, and the divergent lens group G2 is moved on the optical axis in accordance with the change of the length between an object O and a principal plane H of the synthetic system, and thus, a parallel luminous flux is always emitted, and the principal plane H of the synthetic system is held in a fixed position.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a variable focus optical system, in which when an object moves relative to a reference position (%Kj), the focal length is changed according to this movement, so that the beam of light from the object is always parallel. The present invention relates to a variable focus optical system that has the function of emitting a beam of light.

In order to accurately measure the moving distance of an object with respect to a certain reference position using this type of optical system, when the focus of the optical system is set on the moving object, a fixed Requires points. It is necessary to use this fixed point as a measurement reference point and at the same time correct various aberrations of the lens system accordingly. Conventionally, many zoom lenses, which are representative of variable focus optical systems, have been designed that have undergone two types of corrections (for example, in camera lenses, aberration correction due to changes in focal length and correction to keep the rear focal position constant) have been made. Ori,
%, most lenses require two or more groups as movable parts of the lens system for zooming.

As described above, conventional general variable focus optical systems have drawbacks such as a complicated rounding mechanism with many moving parts and a large lens system, and it has been difficult to reduce the price. .

The present invention has fewer rounded movable parts that change the focal length,
The objective is to obtain a variable focus optical system for measurement that is mechanically simple, has a compact lens system, and is inexpensive.

The variable focus optical system according to the present invention maintains the position of the principal point unchanged during zooming, and consists of two groups, a convergent lens group and a diverging lens group, whose absolute values of refractive power are almost mutually strong. The lens group farther from the object is movably provided than the other lens groups. Then, one lens group is moved according to the object distance 111 to emit a beam of light from the object as a parallel beam of light.

In other words, as shown in Figure 1, from the object side, the 11th
Assuming that two lens groups, the 21st group (G1) and the 2nd lens detail (Gl), are arranged with a spacing of d, and if the refractive power of each lens group is 1sKt, and the principal plane spacing is d, then the 2nd lens group 1 and the 1121st group of the principal plane (H) on the object side of the combined lens system (
The amount of deviation Δ from the principal plane position of Gl) is given by K = K1 +, -dK, and Δ = -d, respectively. K, , can be considered as a constant. By zooming, we change 9d to change the composite refractive power K. Now, if we eliminate d from both equations and find , we get K K.

Here, if we set = - to 1, if we move the second lens group (Gm) that is far from the object, the position of the synthesized principal plane will be fixed regardless of the magnification change K.

In other words, the refractive powers of the two lens groups have opposite signs and the same absolute value. In other words, lK, 1-IK = 1, that is, the convergent lens has the same absolute value of refractive power. It consists of a lens group and a diverging lens group, and by moving the lens group that is farther from the object, the focal length can be changed while keeping the principal point position of the composite system unchanged.

FIG. 2 is a schematic configuration diagram showing one embodiment of the present invention.
A converging lens group (G1) is fixedly provided on the object side, and a diverging lens group (G1) movable along the optical axis is provided behind it.

The diverging lens group (at) moves on the optical axis according to the change in the distance between the object (0) and the main plane (H) of the synthesis system, and always emits a parallel light beam, while also ) is kept in a constant position. Here, if the refractive power of the converging lens group (G1) is 1, and the distance between the object (0) and the main plane (H) of the composite system is L, then the amount of movement y of this lens group is approximately 1 y'' - A relatively simple cam mechanism generally expressed as y=- may be used for "L" and "-".Furthermore, in the present invention, the refractive power of the two lens groups is different from positive to negative. Since the optical system has almost the same absolute value, the Veravar sum of the entire lens system becomes almost zero, which has the advantage of making it easy to create a lens system with a wide angle of view.

Further, in this embodiment, the converging lens group is arranged on the object side and the rear diverging lens group is movable, but the arrangement may be reversed, or a configuration in which the converging lens group is moved may be used.

FIG. 3(4) and Φ) show an example in which the variable focus optical system according to the present invention is applied to a distance measuring device. In this device, when a target object 1 whose height is accurately known changes its distance, the optical system 2 of the present invention focuses on this target object, and a parallel beam 4 is always incident on the condensing lens system 3. Then, using the condenser lens system 3, for example, using a C0D (charge-coupled device), a target object is placed on the camera, and the size of this image is measured. It calculates distance.

It is clear that in the case of such a device, the reference point for rounding for distance measurement must not move due to focus movement (variation of magnification). It is extremely effective to use a focusing optical system.

In this case, as shown in FIG. 3(A), the variable focus optical system 2
Divide the distance between the principal point (H) and the object 1, and calculate the angle of the object 1 with a known height h.

When the height of the object image measured by the imaging device 5 is denoted by ', and the focal length of the variable focus optical system 2 at this time is f, then hl' = fltan #1 tan #1 = - shame. Therefore, the object distance is given by L,=-・fl 1 , and similarly, as shown in FIG. If the image height of the measured object image is I, and the focal length of the variable focus optical system 2 is f, then it is given by: Therefore, if we have a mechanism that can output the movement of the movable lens as the focal length of the composite lens system, h* hl's fl *
k+lkl'+ft+... is known, and the distance Li at any point can be measured.

As described above, according to the present invention, the structure is simple with two groups and only one movable part, and the movable lens group can be moved by a relatively simple cam, and the lens barrel structure is also simple. Further, the present invention is particularly useful as a variable power optical system for relatively long distances from several meters to several tens of meters, and a variable power ratio of up to about 20 is sufficiently possible. Furthermore, since the reference point is the main plane of the composite system, distortion can be corrected using the same equation as in a normal lens system: y==ftan#, making lens design easier.

The variable focus optical system according to the present invention is not only used to measure distance, but if the distance is accurately measured, it can be used to test the performance of an imaging lens system using a known distance and known object size as a reference. It is also possible to use

[Brief explanation of the drawing]

FIG. 1 is an explanatory diagram of the principle of the present invention, and FIG. 2 is a schematic configuration diagram showing an embodiment of the present invention. 3rd: B, = tuff U This is a precedent example in which the variable focus optical system according to the present invention is applied to a distance measuring device. [Explanation of symbols of main parts] G1...Convergent lens group Gt...Divergent lens group H...Synthetic principal plane of both lens groups (Gt, as) Fig. 1 Δ Section 2

Claims (1)

[Claims] Consists of two groups: a convergent lens group and a diverging lens group, of which the lens group on the object side is fixed, and the lens group far from the object side is movable in the optical axis direction. , when the refractive powers of both lens groups are respectively Kl * x, #1
While satisfying the relationship: IK11=IK・1 and keeping the combined principal plane of both lens groups at a constant position, one of the movable lens groups is moved according to the object distance, and the ray flux from the object is A variable focus optical system that always emits a parallel beam of light.