JPS6042728A - Image forming optical system - Google Patents

Abstract

PURPOSE:To obtain high-area magnification in the circumference of a field of view by providing an image forming lens, and a conical mirror which is constituted so that the center axis coincides with the optical axis of the image forming lens, and whose bus consists of a concave curve. CONSTITUTION:A titled system is provided with a conical mirror 14 which is placed in front of an image forming lens 3 so that the center axis coincides with the optical axis of the image forming lens 3, and whose bus consists of a concave curve. Therefore, when main light beams A, B are tracked from an image guide 2 side, they are condensed by the conical mirror 14, and as a result, an interval l2 in the direction parallel to the axis of an intersection point to a pipe wall S of the main light A and B becomes wider than an interval of conventional constitution, therefore, a short part forms an image on the same part on the incident end face of the image guide 2. Accordingly, in comparison with that of conventional constitution, the magnification in the direction parallel to the axis of the pipe wall S becomes high in the circumference of a field of view, and an image whose interval in the diameter direction is wide is obtained in the circumference of a field of view. Therefore, a detailed state of the pipe wall S can be observed.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to an imaging optical system, particularly an imaging optical system for an endoscope for observing the inner wall of a tube.

This type of conventional imaging optical system is, for example, as shown in FIG. German Utility Model No. 7834- basically consists of a lens 3 and a conical mirror 4 arranged in front of the imaging lens 3 such that its axis coincides with the optical axis of the imaging lens 3.
1.80) is the imaging lens 3 which is an endoscope objective lens.
Due to the unique strong negative distortion aberration, the magnification in the direction parallel to one axis of the inner wall S of the tube is small at the periphery of the visual field, and as a result, it is difficult to observe the fine details of the inner wall S of the tube.

That is, if a grid as shown in FIG. 2 is drawn on the tube inner wall S, this observed image will be an image with narrow radial intervals around the visual field as shown in FIG. 3. On the other hand, at the periphery of the visual field, the magnification of the tube inner wall S in the circumferential direction is maximum in the visual field.

Therefore, by increasing the magnification in the direction parallel to the axis of the inner tube wall S in the periphery of the visual field, the maximum area magnification can be obtained in the periphery of the visual field.
As a result, it becomes possible to observe the fine details of the inner wall S of the tube, and so it has been desired to do so.

In view of the above points, the present invention aims to provide an imaging optical system that increases the magnification in the direction parallel to the axis of the inner wall of the tube in the periphery of the field of view. It basically consists of a conical mirror arranged in front of the imaging lens so as to coincide with the optical axis of the imaging lens, and whose generating line is a concave curve. The following description will be made based on the embodiment shown in FIGS. 4 and 5, referring to the same reference numerals for the same members as in the conventional example above. It is a conical mirror that is arranged in front of the imaging lens in a coincident manner and whose generatrix line is a concave curve. Therefore, the incidence of image guide 2! Let's consider the principal rays A and B that form images at two different positions on the 111 plane in comparison with the conventional example shown in Fig. 1 (however, the apex angles θ of the conical mirrors 4 and 14 are assumed to be equal). When principal rays A and B are traced from the image guide 2 side, in the case of the conventional example (Fig. 1), they are diffused by the conical mirror 4, but in the case of the present example (Fig. 4), they are diffused by the conical mirror 4. The light is focused by 14. As a result, the inner wall S of the chief rays A and B
In the conventional example, the interval in the direction parallel to the axis of the intersection with e,
In this example, lV2 is 11'2<'
Becomes I. Therefore, as in the present embodiment, the short portion is imaged on the same portion of the incident end surface of the image guide 20 as in the conventional example, so that the inner wall S of the tube in the periphery of the field of view is better in this embodiment than in the conventional example. The magnification in the direction parallel to the axis is increased, and images with wide radial spacing around the field of view are obtained as shown in FIG. Thus, according to the proposed imaging optical system, a high area magnification can be obtained around the field of view, and as a result, the inner wall S of the tube can be
You will be able to observe the details of

FIG. 6(d) shows a second embodiment, in which the generatrix of the conical mirror 14 is brought into focus at the entrance pupil 15 of the imaging lens 3.
It is matched with a part of a parabola having . Further, FIG. 7 shows a third embodiment, in which the generatrix of the conical mirror 14 is set to two focal points O7,0□ on the same side off the optical axis.
This corresponds to a part of the circumference of an ellipse with . In this case, since the curvature of the generatrix of the circular mirror 14 becomes more curved as the distance from the optical axis increases, the magnification in the direction parallel to the axis of the tube inner wall S increases as the periphery of the visual field increases.

In any of the above cases, the light beam traced back near the center of the field of view is diffused at the apex of the conical mirror 14 and no image is formed. The generatrix of the part may be made of a concave curve.

FIG. 9 shows a fourth embodiment, which uses not only the conical mirror 14 in the observation optical system but also the illumination optical system 16.
It is also used to reflect the light emitted from the FIG. 10 shows a fifth embodiment, in which a conical mirror 14 is used as an optical system for a camera, and in this case it is possible to photograph a field of view of 3600.

The imaging optical system according to the present invention is not limited to observation of the inner wall of a tube, but can also be applied to a wide-angle endoscope, a rigid scope, a camera, a television camera, an electronic camera, and the like. Further, as a manufacturing method for the conical mirror 14, synthetic resin molding, glass molding, etc. are advantageous in terms of cost.

The imaging optical system according to the present invention has the important advantage that a high area magnification can be obtained at the periphery of the field of view, making it possible to observe fine details.

[Brief explanation of the drawing]

Figure 1 is a diagram showing a conventional imaging optical system for observing the inner wall of a tube, Figure 2 is a diagram showing a grid drawn on the inner wall of a tube, and Figure 3 is a diagram showing the observation field of view according to the conventional example. FIG. 4 is a diagram showing an embodiment of the imaging optical system according to the present invention, FIG. 5 is a diagram showing the observation field according to the embodiment described above, and FIGS. FIG. 8 is a diagram showing another example of a conical mirror, and FIGS. 9 and 10 are diagrams showing a fourth and fifth embodiment, respectively. 3...Imaging lens, 14...Conical mirror. ′:j′ and agent Yasushi Shinohara 1ν1〉, ζ1'4+L7',
, I, 'f 3'1 Fig. 4] 4 Fig. 5 tsu・6 Fig. 1 j'7 Fig. 5 -1 et al. q 18 Fig. 19 Fig. IO Fig.

Claims (1)

[Claims] An imaging optical system comprising an imaging lens and a conical mirror arranged in front of the imaging lens so that its central axis coincides with the optical axis of the imaging lens and whose generating line is a concave curve.