JPH0124285B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a variable focus optical system, and in particular, when an object moves relative to a certain reference position, the focal length is changed according to this movement, so that the bundle of rays from the object is always transformed into parallel rays. The present invention relates to a variable focus optical system that has a function of emitting light as a bundle.

In order to accurately measure the moving distance of an object relative 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 perform 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) are performed. For lenses with particularly high precision, two movable parts of the lens system for zooming are used.
Most require more than one group. As described above, conventional general variable focus optical systems have drawbacks such as a complicated mechanism and large lens system due to the large number of movable parts, and it has been difficult to reduce the price.

An object of the present invention is to obtain a variable focus optical system for measurement that has few movable parts for changing the focal length, 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 approximately equal to each other. The lens group that is farthest from the object is movably provided among the lens groups. Then, the one lens group is moved according to the object distance to emit a beam of light from the object as a parallel beam of light.

In other words, as shown in Fig. 1, suppose that two lens groups, the first lens group _G1 and the second lens group _G2 , are arranged with an interval d from the object side, and the refractive power of each lens group is Principal plane spacing d as K ₁ and K ₂
When combining the two groups, the refractive power K of the lens system combining the two groups and the amount of deviation Δ of the principal plane H on the object side of the combined lens system from the position of the principal plane of the first lens group G ₁ are respectively K=K ₁ +K ₂ −dK ₁ K ₂ Δ=K ₂ /Kd. K ₁ and K ₂ can be considered constants. The composite refractive power K is changed by changing d by zooming, but now by eliminating d from both equations, Δ
Find Δ=K ₁ +K ₂ −K/KK _1Here , if we set K ₁ =−K ₂ , we get Δ=−1/K _1.If we move the second lens group G ₂ , which is farther away from the object, we can synthesize it. The principal plane position is fixed regardless of magnification.

In this way, K ₁ = -K ₂ In other words, the refractive powers of the two lens groups have opposite signs and are equal in absolute value. In other words, |K ₁ |= |K ₂ | In other words, the absolute values of the refractive powers are equal. It is composed of a convergent lens group and a diverging lens group, and by moving the lens group 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 an embodiment of the present invention, in which a converging lens group _G1 is fixedly installed on the object side, and a diverging lens group _G2 that is movable along the optical axis is behind it.
It has been established. Object O and principal plane H of the composite system
Diverging lens group _G2 moves on the optical axis according to the change in distance from
The main plane H of the composite system is kept at a constant position. Here, if the refractive power of the converging lens group G ₁ is K ₁ and the distance between the object O and the principal plane H of the synthesis system is L, then the amount of movement y of this lens group is approximately y = 1/K ₁ ²・1 /L, and a relatively simple cam mechanism generally expressed as y=1/x may be used. Furthermore, in the present invention, the two lens groups have positive and negative refractive powers, and the absolute values thereof are approximately equal to each other, so the Petzval sum of the entire lens system is approximately zero, resulting in a wide angle of view lens system. It has the advantage of being easy to use.

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, and the converging lens group may be moved.

FIGS. 3A and 3B 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 always enters a condensing lens system 3. For example, an imaging device 5 using a CCD (charge-coupled device) using a condensing lens system 3
The distance to the target object is calculated by forming an image of the target object on top and measuring the size of this image. It is clear that in such a device it is necessary that the reference point for distance measurement does not move due to movement of the focal point (variation of magnification), and for this purpose it is necessary It is extremely effective to use a focusing optical system. In this case, the third A
As shown in the figure, the distance between the principal point H of the variable focus optical system 2 and the object 1 is _L1 , and the object 1 has a known height h.
If the height of the object image measured by the imaging device 5 is h _{1 '} , then the focal length of the variable focus optical system 2 is f ₁ , and the condenser lens system 3
If the focal length of is f ₃ , then L ₁ tanθ ₁ = h at all times, but when the object is in focus, L ₁ = f ₁ . At this time, h=f ₁ tan θ ₁ h ₁ ′=f ₃ tan θ ₁ holds, and from both equations, f ₁ =L ₁ =h/h ₁ ′f ₃ . Here, since the height h of the object 1 and the focal length f ₃ of the condenser lens system 3 are known, by simply measuring the image height h ₁ ' on the imaging device 5, the object distance L can be calculated from the above equation. It is possible to find ₁ .

As shown in Fig. 3B, even if the object distance changes to L ₂ , the focal length of the variable focus optical system 2 can be changed to f ₂ by moving the lens group farther from the object and the focus can be adjusted. L ₂ = f ₂ , and at this time, h = f ₂ tan θ ₂ h ₂ ′ = f ₃ tan θ ₂ (h ₂ ′ is the image height), and from both equations, f ₂ = L ₂ = h/h ₂ ′ It becomes f ₃ . Therefore, in this case as well, it is possible to determine the object distance L ₂ from the above equation by simply measuring the image height h ₂ ′.

In this way, the object distance can be determined simply by measuring the image height of the object image on the imaging device 5 when focusing is performed.

By the way, in the object distance measuring device shown in FIGS. 3A and 3B, if the focal length of the variable focus optical system 2 is directly read from the amount of movement of the movable lens group, the movable lens necessary for focusing It is possible to immediately detect the object distance (=synthetic focal length) from the amount of movement of the group.

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=f tan θ, which simplifies lens design.

The variable focus optical system according to the present invention can not only be 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 a known object size as a reference. It is also possible to use

[Brief explanation of drawings]

Fig. 1 is a diagram explaining the principle of the present invention, Fig. 2 is a schematic configuration diagram showing an embodiment of the present invention, Fig. 3A, Fig. 3B
The figure shows an 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], G ₁ ... convergent lens group, G ₂ ... diverging lens group, H ... both lens groups G ₁ ,
Composite principal plane of G ₂ .

Claims (1)

[Claims] 1. 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. and the refractive power of both lens groups is
When K ₁ and K ₂ , approximately satisfy the relationship |K ₁ |= |K ₂ A variable focus optical system characterized by moving a lens group and always emitting a bundle of rays from an object as a bundle of parallel rays.