JP2545524B2 - Space filtering lens system - Google Patents

Description

The present invention relates to a spatial filtering lens system in which a spatial filter is arranged on a focal plane of a lens to limit a pass band in a Fourier-transformed spatial frequency domain. Regarding

[Description of the Related Art] Spatial filters of various shapes are arranged on the focal plane of the lens, a specific frequency component is blocked in the Fourier-transformed spatial frequency domain, and other frequency component light is passed through, and only the component light is used. The principle of spatial filtering for obtaining an image is widely known in the field of optics.

As the Fourier transform lens used in the above spatial filtering processing, a spherical lens having a plurality of lenses is usually used, and as the spatial filter, a metal film is formed on a glass plate by a film forming means such as vacuum deposition to obtain a predetermined filter. What is formed in a pattern is used.

[Problems to be Solved by the Invention] When configuring the spatial filtering lens system as described above, it is necessary to adjust a plurality of lenses and spatial filters to the frame body and adjust and fix the optical axes.

In particular, if a minute optical system having a lens diameter of several mm or less is to be constructed, polishing and manufacturing of a small-diameter lens will cause a significant increase in cost with significant difficulty.

[Means for Solving Problems] A lens system having at least two lenses, which is composed of a gradient index medium whose refractive index changes in the radial direction in a cross section, has a specific spatial frequency range on a focal plane of an object side lens. A spatial filter was placed to block light and allow light in other frequency ranges to pass.

[Operation and effect] In the gradient index lens in which the refractive index changes in the radial direction in the cross section perpendicular to the optical axis, the lens medium itself has a refractive power, so that both end surfaces (entrance / emission surface) of the lens are It has the same image-forming effect as a spherical lens in a flat state, is easy to polish, and has a spherical aberration equivalent to that of an aspherical lens using a homogeneous medium by selecting the shape of the refractive index distribution appropriately. Correction is possible.

Therefore, according to the spatial filtering lens system of the present invention, by selecting the length of the object-side lens as the length with the end surface as the focal plane, it is possible to precisely adjust the spatial filter by closely arranging it on the flat lens surface. Spatial filtering processing can be performed.

[Examples] The present invention will be described below in detail based on the examples shown in the drawings.

In FIG. 1, 1 is a first lens, 2 is a second lens, and both lenses 1 and 2 have a maximum refractive index on the optical axis 3 in the plane orthogonal to the optical axis 3 toward the outer periphery. A graded refractive index distribution is given. Then, the lens 1 and the lens 2 are arranged so that the optical axes 3 thereof coincide with each other, and both lenses 1 and 2 are arranged.
The surfaces 1B and 2A facing each other are bonded and joined with the spatial filter plate 4 interposed. Then, the object side end surface of the first lens 1
Curvature radius R1 of 1A, curvature radius R2 of image-side end surface 1B, curvature radius R3 of object-side end surface 2A of second lens 2, curvature radius of other end surface 2B
In the illustrated example, each of R4 is infinity, that is, a plane. Then, the first lens 1 is, for example, 1/1 so that the focal plane 5 coincides with one lens end surface 1B as shown in FIG.
There are 4 pitch lengths.

As shown in FIG. 2, the filter plate 4 has an outer diameter of lenses 1, 2
A light-shielding portion 7 having a small diameter is formed in the center of the transparent disc 6 which is the same as the above, using a well-known pattern forming means such as vapor deposition and printing.
A group of light rays emitted from the object 9 and incident on the lens 1 in parallel or at a small angle with respect to the optical axis 3 is blocked by the light shielding portion 7 at the end surface 1B (focal plane 5) and does not enter the lens 2. On the other hand, as shown in FIG. 4, a light beam 10 which is emitted from the object 9 and enters the lens 1 at a relatively large angle with respect to the optical axis 3 is condensed at a position apart from the optical axis at the other end surface 1B. Then, after passing through an annular light-transmitting portion 8 provided around the light-shielding portion 7 of the filter plate 4, the light enters the lens 2 and forms an image 11 at a point a certain distance from the surface 2B of the lens 2. .

That is, in the illustrated example, high-pass spatial frequency pass filtering is performed in which only light rays having an angle of a certain value or more with respect to the optical axis are passed.

In addition to the above, by changing the shape of the light-shielding portion 7 of the filter plate 4 in general, light rays emitted from an object are shielded from components in a specific spatial frequency range, and images are formed only with light rays having other frequency components. Therefore, image processing such as formation of a differential image can be performed.

In the illustrated example, the lens end surfaces 1A and 2B of both lenses 1 and 2 other than the surface in contact with the spatial filter plate 4 are also flat,
These surfaces may be curved. However, if all the surfaces of the lenses 1 and 2 are made flat as in the illustrated example, it is advantageous because the lens surface processing is easiest.

Next, another structural example of the spatial filter in the present invention will be shown.

FIG. 5 shows the emission surface of the first lens 1 instead of providing a spatial filter on a transparent plate separate from the lens as in the above-mentioned example.
A light-shielding portion 7 of the spatial filter is directly formed as a coating on 1B by vapor deposition, printing or the like, and the lens surface left around this partial light-shielding coating 7 is used as a light-transmitting portion 8 of the spatial filter. In the example of FIG. 6, a plurality of spatial filters having different characteristics, that is, a set of a light-shielding portion 7 and a light-transmitting portion 8 having different shapes are provided on one substrate, and the filter plate 4 is arranged in a direction crossing the lens optical axis. By moving the image to a specific spatial frequency component light, it is possible to quickly switch to an image of another component.

In the example shown in FIG. 7, the spatial filter is switched without using any mechanically movable part. The filter plate 4 is composed of a liquid crystal element, for example, a small area part 4A near the center.
It is divided into two independently controllable sections, the outer peripheral section 4B surrounding this and the sections to be applied, and the voltage applied to both sections is changed by the switches 12 and 13, so that the light-shielding section and the light-transmitting section are divided into the central section and the outer section. I am trying to switch to and. As a spatial filter for non-mechanically switching between the light-shielding portion and the light-transmitting portion, in addition to liquid crystal, a general display element whose optical transmittance changes by changing an electrical or magnetic input, an element such as an optical shutter Can be used.

EFFECTS OF THE INVENTION According to the present invention, it is possible to easily configure a minute spatial filtering optical system without using a frame.

That is, since the gradient index medium is used, the lens focal plane on which the spatial filter should be placed can be aligned with the lens end surface, and this surface can be made flat, so that the filter can be aligned by simply placing it closely on the lens surface. Is performed automatically, and therefore is extremely easy to assemble and suitable for mass production.

[Brief description of drawings]

1 is a side sectional view showing a first embodiment of the present invention, FIG. 2 is a front view of a spatial filter plate, and FIGS. 3 and 4 are examples of FIG. 1 showing a space for light having different spatial frequencies. FIG. 5 is a side sectional view showing each action of the filter, FIG. 5 is a perspective view showing a second embodiment of the present invention, and FIG. 6 is a perspective view showing a third embodiment of the present invention.
FIG. 7 is a perspective view showing a fourth embodiment of the present invention. 1,2 ... Gradient index type lens, 3 ... Optical axis 4 ... Spatial filter plate, 5 ... Focal plane 7 ... Shading portion, 8 ... Translucent portion, 9 ... Object 11 ... Image, 12,13 …… Switch

Claims (2)

(57) [Claims] 1. A lens system having at least two lenses composed of a gradient index medium in which the refractive index changes in the radial direction,
The object side lens of the lens system has a lens length such that at least the second surface of the lens is a flat surface, and the focal plane of the lens is the second surface, A spatial filter that blocks light and allows passage of light in other frequency ranges is provided in contact with or directly on the second surface of the lens, and at least the first surface of the image side lens of the lens system is a flat surface, The spatial filtering lens system, wherein the object side lens and the image side lens are cemented via the spatial filter. 2. The spatial filtering lens system according to claim 1, wherein the spatial filter has a variable shape of a light shielding portion or a light transmitting portion.