JPH04212922A - Lens element for infrared radiation - Google Patents

Abstract

PURPOSE:To remove generation of harmful light such as ghost light by providing at the edge part of a lens a notch having a plane which is approximately perpendicular to an optical axis. CONSTITUTION:Light beam 1 from an object to be incident inside a lens through an incidence plane 10 repeats complete reflection between the incident side lens plane 10 and an exit side lens plane 10. The angle of reflection of light gathering at the edge part of the lens is changed by a notched plane 30 which is approximately perpendicular to the axis of the light beam, and the light is discharged out of the lens at an angle which does not reach the inside of the light path of lens. Harmful light gathering at the circumferential edge of the lens is guided by the notched plane 30 out of the light path, and thus can be removed without entering the light path.

Description

[Detailed description of the invention]

0001

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an infrared lens element used in an infrared optical system.

0002

[Prior Art] Infrared lens elements conventionally used in infrared optical systems have a high refractive index (n≧2);
As shown in the figure, part of the infrared rays 2 that entered the lens from the entrance surface 10 undergoes total reflection several times on the lens surface, and then gathers at the edge of the lens and exits from the exit surface 20. There were times when I did. This phenomenon appears prominently in the case of a meniscus shape.

0003

[Problem to be solved by the invention] Such infrared rays 2
When the light exits from the exit surface 20, ghosts and flares occur, significantly degrading the performance of the entire optical system. The present invention takes these conventional problems into consideration and aims to eliminate the generation of harmful light such as ghost light.

0004

[Means for Solving the Problems] In order to solve the above-mentioned problems, the present invention provides a notch having a surface substantially perpendicular to the optical axis at the edge of the lens. It is desirable that the incident light side surface of the peripheral edge of the lens element is cut out.

[0005]

[Operation] With the configuration of the present invention as described above, the entrance surface 1
Harmful light that enters the lens from zero, undergoes repeated total reflection on the lens surface, and collects at the periphery of the lens is guided out of the optical path by a notch at the edge of the lens that has a surface substantially perpendicular to the optical axis. Therefore, it can be removed without entering the optical path.

[0006]

DESCRIPTION OF THE PREFERRED EMBODIMENTS The present invention will be explained below based on embodiments shown in the drawings. FIG. 1 shows how light rays are totally reflected inside the lens in the infrared lens element of the present invention. Incidence surface 1
A light ray 1 from an object that enters the lens from 0 is repeatedly totally reflected on the entrance side lens surface 10 and the exit side lens surface 20, and is concentrated at the edge of the lens. The light rays gathered at the edge of the lens change their reflection angle by the notch surface 30 substantially perpendicular to the optical axis, and the light rays are emitted from the lens at an angle that does not reach the optical path of the lens. Further, it is desirable that the cutout surface substantially perpendicular to the optical axis be a rough surface.

FIG. 2 shows an enlarged sectional view of the cutout portion of the present invention. The light gathered at the notch is scattered light A and reflected light B.
, becomes transmitted light C. Of these lights, reflected light B and scattered light A reach the image plane. Since the reflected light B is guided out of the optical path by the cutout of the present invention, it does not become harmful light. Even if the scattered light A reaches the image plane, the intensity of the light in that case is so small that it does not substantially affect the image.

Further, the depth of the notch of the present invention, that is, the height h of the surface substantially perpendicular to the optical axis, is 80% to 90% of the distance H from the lens edge to the position of the lens effective aperture. It is preferable to do so. If the cutout is made larger than this, the effect of removing harmful light will be reduced, and on the contrary, harmful light will be generated from the cutout surface itself, adversely affecting the image. Furthermore, the actual lens diameter is too large compared to the lens effective aperture, making the entire optical system large. In other words, the effective aperture of the lens is reduced, and the amount of light in the optical system is reduced.

In FIG. 1, a convex surface 40 on the optical axis side is provided as the bottom of the notch, but this is a groove formed during manufacturing and may be a V-shaped groove. Moreover, the planar shape of this notch is an annular shape formed along the periphery of the lens. It goes without saying that the effect will be further enhanced by attaching metal objects to the edge of the effective diameter of the exit surface 20 of the lens, or by painting the corners.

0010

As described above, in the present invention, by providing a cutout surface substantially perpendicular to the optical axis of the lens at the peripheral edge of the lens, harmful light generated by total reflection of light rays inside the lens can be prevented. can remove flare,
Image deterioration due to ghosts can be prevented.

[Brief explanation of the drawing]

FIG. 1 is a cross-sectional view showing the optical path of a lens having a notch according to the present invention.

[Figure 2] Enlarged sectional view of the notch

[Figure 3] Cross-sectional view showing the optical path of a conventional infrared lens

[Explanation of sign]

10 Incident surface 20 Injection surface 30 Notch surface A Scattered light B Reflected light C Transmitted light

Claims (2)

[Claims] 1. An infrared lens element, characterized in that a notch having a surface substantially perpendicular to the optical axis is provided at the edge of the lens. 2. The infrared lens element according to claim 1, wherein the surface substantially perpendicular to the optical axis is formed by cutting out the incident light side surface of the peripheral edge of the lens element.