JPH01123209A - Large-aperture lens - Google Patents

Abstract

PURPOSE:To shorten the axial thickness and overall lens length of a lens by specifying the band-shaped step parts which constitute the boundaries between the refracting surfaces of central parts and the refracting surfaces of peripheral parts. CONSTITUTION:The two front and rear refracting surfaces in the optical axis direction of a piece of the lens made of a synthetic resin consist of respectively of the refracting surfaces A1, A2 of the central parts and the refracting surfaces B1, B2 of the peripheral parts. These surfaces are so connected that the refracting surface A1 is recessed with respect to the refracting surface B1 and the refracting surface A2 is recessed with respect to the refracting surface B2 respectively in the band-shaped step part constituting the boundary between the refracting surfaces A1 and B1 and the band-shaped step part constituting the boundary between the refracting surfaces A2 and B2. The lens having the small axial thickness and the overall lens length is thereby obtd. while the sufficient aperture ratio and imaging performance as light projecting and receiving lenses are maintained.

Description

DETAILED DESCRIPTION OF THE INVENTION (Field of Industrial Application) The present invention relates to a large-diameter lens used as a light projecting and light receiving lens of a distance measuring device of a camera.

(Conventional technology) Autofocus camera, etc.'lr! In distance equipment.

A large diameter single lens made of synthetic resin is generally used for the light emitting and light receiving lenses. First, we will give an overview of the distance measuring optical system.
In FIG. 5, 1 is a floodlight source such as an infrared LED,
The light beam emitted from the light source 1 is focused by the projection lens 2,
The light is emitted towards the subject. This light beam is reflected by the object and is focused on the light receiving surface of the photoelectric conversion means 4 by the light receiving lens 3 which is spaced from the light projecting optical system by the base line length. The output of No. 4 is used as a ranging signal.

In such an optical system, in order to obtain sufficient ranging distance or sufficient ranging accuracy, the aperture ratio of the light emitting lens must be large and the amount of irradiated light must be large, and the receiving lens must have a large aperture to receive light. It is necessary to have a large amount of light. Because the focal length of the light-receiving lens cannot be increased due to restrictions on the size of the light-receiving element and the compactness of the light-receiving lens, it is necessary to increase the aperture ratio in order to increase the diameter of the light-receiving lens.

(Problems to be Solved by the Invention) As mentioned above, it is desirable that both the light emitting and light receiving lenses be bright lenses, but in order to obtain brightness below Fl, 0, the axial lens thickness becomes large. As a result, the following drawbacks occur.

1. Since the total length of the lens, that is, the length from the tip of the lens to the light emitting and light receiving elements is long, the layout of the camera is greatly restricted and the compactness is impaired.

2. The manufacturing time during molding becomes longer, resulting in higher costs. Conventionally, by using an aspheric surface.

Although these drawbacks have been improved along with improved imaging performance, it has not been sufficient.

The purpose of the present invention is to improve the above-mentioned drawbacks of light projecting and light receiving lenses, and to obtain a lens that has a small axial thickness and a small overall lens length while maintaining sufficient aperture ratio and imaging performance as a light projecting and light receiving lens. It is.

(Means for solving this problem) The lens of the present invention is a single lens made of synthetic resin, and the two refractive surfaces in the optical axis direction are the refractive surfaces A0 and A2 in the center and the peripheral portion. It consists of refractive surfaces B1 and B2,
The refracting surface A1 is recessed with respect to the refractive surface B1 in the band-shaped step portion that forms the boundary between the refractive surfaces A1 and 81 and the band-shaped step portion that forms the boundary between the refractive surfaces A2 and B2, and It is characterized in that the refracting surfaces A2 are each connected to the refracting surface B2 so as to be recessed.

Furthermore, among these refractive surfaces, it is desirable that the peripheral refractive surface on the side with a longer conjugate distance be an aspheric surface such that the point of intersection with the optical axis is farther away from the lens as the normal line is further away from the optical axis.

(effect) The operation of this invention will be explained based on examples.

FIG. 1 is a sectional view showing the shape of an embodiment of the light projecting and light receiving lens of the present invention. Further, FIG. 2 is a cross-sectional view of a conventional light emitting/receiving lens whose peripheral portion has the same shape as the peripheral portion in FIG. 1.

In Fig. 1, paraxial characteristics such as focal length and principal point position are shown for the peripheral area consisting of refractive surfaces B0 and B2.

It will be expressed by the same paraxial characteristics as the conventional lens shown in FIG. Now, the position of the principal point on the shorter side of the optical axis, focal length, and conjugate distance of the peripheral portion consisting of the refractive surfaces B1 and B2 represented in this way, and the refractive surface A1. If the central optical axis, focal length, and principal point position on the shorter conjugate distance side of This means that the image and the image formed by the center are formed at approximately the same position. Due to this effect, the lens of the present invention shown in FIG. 1 can have substantially the same imaging effect paraxially as the conventional lens shown in FIG. 2.

On the other hand, the position of the principal point on the side with the longer conjugate distance does not need to be the same between the peripheral part and the center in practical terms. On the other hand, it can be arranged in a positional relationship where it collapses at the boundary. At this time, since the distance between the principal points at the center is shortened, the refracting surface A2 is concave at the boundary with respect to the eight refractive surfaces even on the side where the conjugate distance is short. In this way, the lens of the present invention can have a shorter axial thickness than conventional lenses. Of course, the total length of the lens is also shortened at this time.

In addition, in the lens of this invention, spherical aberration is corrected by making the refractive surface at the periphery on the side with a longer conjugate distance an aspheric surface whose intersection with the optical axis is farther away from the lens as the normal line at a position farther from the optical axis. At the same time, since the sag in the optical axis direction is reduced, it is possible to further reduce the axial thickness of the lens.

In addition, in order to reduce the loss of light amount due to the one-step difference, the light flux passing through the refraction surface A1 and the light flux passing through the refraction surface A2 are made to almost match with respect to the object point at infinity on the axis on the side where the conjugate distance is longer. It is desirable that the positions of the front and rear two step portions are aligned so that the light flux passing through the refraction surface B1 and the light flux passing through the refraction surface B2 are substantially the same.

Note that the front shape of the stepped portion may be circular or rectangular and may be 1° (Example) Examples of the present invention will be described below. Although the cross-sectional shape diagram is shown in FIG. 1, lens data and aberration curve diagrams are described separately for the center and peripheral parts.

Center surface number r d n (A') 1 m
55.689 32.48 1.483002
-294.874 Aspheric coefficient of the first surface K = -1,82620 A1 = 6.99737X10-' PL = 4.
0O00A2=-6,83777xlO-” p2=
6.0000A 3 = -1,87582X10-14
P 3 = 8.0OOO peripheral part number r d n (A') 1 umbrella
60.884 59.83 1.483002
-158.896 Aspheric coefficient of the first surface = -L47396 A1= 3.37236X10-' P1=
4.000OA2=-3,60750X10-11
P2=6.0OOOA3=-7,36196
X10-" P 3 = 8.0000 Aspherical coefficient of the second surface =: -7,87890X 10 Al: 4.82969X10" 11P1 = 4.00
0OA2=-2,27867X10-” P2:6.
0000A 3 =-1,32426XlO-1sP
3 = a, ooo.

The skewer mark in the front is an aspherical surface. When the apex of the aspheric surface is set as the origin of coordinates, and the X axis is in the direction of the optical axis, the X axis is in the direction perpendicular to the optical axis, and the Y axis is in the direction perpendicular to the optical axis, the shape of the aspheric surface is expressed by the following equation.

(i=1.2...) °In the above lens data, the first surface is the refractive surface with the longer conjugate distance, and the apex of the first surface of the center and peripheral portions is 14 .4 connected apart. At this time, the principal point on the side with the shorter conjugate distance is the same in the center and the periphery.

In addition, the center part is Fl, the peripheral part of area 1 darker than 5 is Fl,
Areas brighter than 2 are respectively considered effective areas.

FIGS. 3 and 4 respectively show aberration curve diagrams around the center.

(Effects of the Invention) The lens of this invention is thinner and has a shorter overall lens length, so it contributes to making the camera more compact than conventional rangefinder floodlight lenses, and also reduces the shot time when making 112. Since it can be shortened, costs are also reduced. Furthermore, compared to Fresnel lenses, it is easier to manufacture a mold, there is less disruption of the sign condition, and the imaging performance is superior.

[Brief explanation of the drawing]

Fig. 1 is a cross-sectional view of an example of the lens of the present invention, Fig. 2 is a cross-sectional view of an example of a conventional distance measuring light emitting and receiving lens, and Figs. 3 and 4 are examples of the above-mentioned embodiment. each center of
The peripheral aberration curve diagram, FIG. 5, is a diagram showing an outline of the distance measuring optical system of the camera. Figure 2 Figure 3 Spherical aberration Astigmatism Figure 4

Claims (1)

[Claims] 1. A single lens made of synthetic resin, and the two front and rear refractive surfaces in the optical axis direction are refractive surfaces A_1 and A_2 at the center, respectively.
and peripheral refractive surfaces B_1 and B_2, and in the band-shaped step part that forms the boundary between A_1 and B_1 and the band-shaped step part that forms the boundary between A_2 and B_2, A_1 becomes B_1.
A_1 and B_1, A_2 and B_
A large-diameter lens characterized in that two are connected to each other. 2. A large-diameter lens that satisfies claim 1, wherein the refractive surface of the peripheral portion on the side with a longer conjugate distance is an aspherical surface whose intersection with the optical axis is farther away from the lens as the normal line is further away from the optical axis.