CROSS-REFERENCE TO RELATED APPLICATIONS

The present application claims priority under 35 U.S.C. § 119 of Japanese Application No. 2017-202784, filed on Oct. 19, 2017, the disclosure of which is expressly incorporated by reference herein in its entirety.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to a variable focal length lens apparatus.

2. Description of Related Art

As a variable focal length lens apparatus, an apparatus has been developed which uses a liquid lens system (hereafter, simply referred to as lens system) in a principle described in U.S. Patent No. 2010-0177376 specification, for example. The lens system is formed by immersing a cylindrical vibrating member formed by a piezoelectric material in transparent liquid. In the lens system, when an AC voltage is applied to an inner circumferential surface and outer circumferential surface of the vibrating member, the vibrating member expands and contracts in a thickness direction and vibrates the liquid inside the vibrating member. By adjusting a frequency of the applied voltage according to the natural frequency of the liquid, a concentric standing wave is formed in the liquid and a concentric region having a different refractive index centered on a center axis line of the vibrating member is formed. Therefore, in the lens system, when light passes along the center axis line of the vibrating member, the light follows a path of that diffuses or converges in accordance with the refractive index for each concentric region.

The variable focal length lens apparatus is configured such that the lens system noted above and the objective lens (such as normal convex lens or a group of lenses) for focusing are aligned on the same optical axis. When parallel light is emitted at the normal objective lens, the light passing through the lens is focused at a focal position apart by a predetermined focal length. On the other hand, when the parallel light is emitted at the lens system aligned coaxially with the objective lens, the light is diffused or converged by the lens system and the light passing the objective lens is focused at a position shifted further or closer from the original focal position (when there was no lens system). Therefore, in the variable focal length lens apparatus, a drive signal input in the lens system (AC voltage of the frequency which generates the standing wave in the liquid inside) is applied and an amplitude of the drive signal is increased/decreased, and thereby the focal position for the variable focal length lens apparatus can be controlled as desired within a fixed range (predetermined variation range that can be increased/decreased by the lens system using the focal length of the objective lens as a standard reference).

As described above, in the variable focal length lens apparatus using the lens system, the focus position can be changed periodically. When constructing an observation system such as a microscope system by the variable focal length lens apparatus of this type, it is preferred that a magnification dose not fluctuate even with the change in the focal length. In other words, an optical system having the lens system is sought to be arranged in a telecentric optical system so as not to change the total magnification for the microscope system even when lens power of the lens system changes.

The telecentric optical system having the lens system is configured, as shown inFIG. 3, with an objective lens91, an imaging lens92, and a lens system93aligned on an optical axis, for example, on the same optical axis A. Specifically, a telecentric section is formed between the objective lens91and the imaging lens92and the lens system93is arranged therebetween. At this point, a rear side focal position of the objective lens91(focal length fo) is conjugated with a primary point position pp1of the lens system93. In addition, a front side focal position of the imaging lens92(focal length ft) is conjugated with a primary point position pp2of the lens system93. Then, a diaphragm (in other words, telecentric diaphragm) must be arranged at the rear side focal position of the filed lens. However, arranging the diaphragm at the primary point position pp1inside the lens system93causes a physical diaphragm element to be arranged in the liquid inside the lens system93, and thereby preventing the resonance of the liquid inside the lens system93and a function as the lens system93may be damaged.

In response, as shown inFIG. 4, in the telecentric optical system having the objective lens91, imaging lens92, and lens system93, by adding relay lenses94,95(focal length f1, f2) and performing a relay of an exit pupil of the objective lens91(rear side focal position), the position where a diaphragm96is arranged and the position where the lens system93is arranged are separated and the diaphragm96can be taken outside of the lens system93. However, since the relay lenses94and95are added to the variable focal length lens apparatus, optical axis length for the variable focal length lens apparatus is increased, which makes it difficult to use the variable focal length lens apparatus toward the observation system such as the microscope system.

SUMMARY OF THE INVENTION

The present invention provides a variable focal length lens apparatus which is telecentric and compact.

The variable focal length lens apparatus according to the present invention includes a objective lens and an imaging lens that are aligned on the same optical axis; a front side lens system and a rear side lens system that are disposed in a section between the objective lens and the imaging lens on the optical axis, and change a refractive index in accordance with an input drive signal; and a diaphragm disposed in the section between the front side lens system and the rear side lens system on the optical axis.

In the present invention, light from a work piece (measured object) is guided from the objective lens, the front side lens system, the diaphragm, to the rear side lens system and can form an image on an image detection element or the like via the imaging lens. Then, by periodically changing a refractive index of the front side lens system and the rear side lens system in accordance with the input drive signal, a focal length as the variable focal length lens apparatus can be varied. In the present invention, the objective lens and the imaging lens are aligned at a proper position on the optical axis, and thereby the section (where the front side lens system, diaphragm, and rear side lens system are arranged) between the objective lens and the imaging lens can be configured in telecentric. Accordingly, when the focal length of the front side lens system and the rear side lens system varies periodically, a magnification can be prevented from changing. Further, the lens system is divided into two to the front side and the rear side and the diaphragm is disposed in the section therebetween, and therefore, in the telecentric section from the objective lens to the imaging lens, the lens system and the diaphragm can be arranged together creating a compact optical system without adding a relay lens separately.

In the variable focal length lens apparatus of the present invention, the front side lens system and the rear side lens system share the same standard and each lens system is connected to a drive control device which inputs the same drive signal preferably. In the present invention, since the front side lens system and the rear side lens system share the same standard, by inputting the same drive signal from the drive control device, a resonance state of each lens system can accurately and readily be obtained. At this point, as the front side lens system and the rear side lens system, it is preferable to use two lens systems each having ½ lens power required as the lens system (variable focal length element) of the variable focal length lens apparatus.

The present invention provides a variable focal length lens apparatus which is telecentric and compact.

