JPS6214132A - Reticle having fresnel lens surface - Google Patents

Abstract

PURPOSE:To omit the replacement of a reticle by providing alternately surfaces having at least two different kinds of angles on a Fresnel lens surface. CONSTITUTION:Lens surfaces FR1 having a radius R1 of curvature set up so that the focus is positioned on a point P1 and lens surfaces FR2 having a radius R2 of curvature set up so that the focus is positioned on a point P2 are alternately formed on the Fresnel lens surface FLS and these surfaces act as a lens surface having two radiuses R1, R2 of curvature by reducing pitches P. Even if lenses are replaced over a wide range, a visual field can be observed only by one reticle without replacing the reticle FL in accordance with the replacement of lenses or zooming.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a focus plate for a single-lens reflex camera with interchangeable lenses, and more specifically, to a focus plate having a Fresnel lens surface. Regarding the χ plate.

Obedience! In the past, clear type focus plates without matte surfaces have been widely used because they are bright and the image can be seen clearly without having to extend the lens. When using such a focusing plate, the light rays passing through the photographing lens are refracted by a certain amount by the Fresnel lens surface of the clear type focusing plate, and then head toward the eye without being diffused. However, here, It depends on the focal length and F number of the photographic lens! In some cases, the rays of light that have passed through the rays and alpha plates do not reach the eyes, and even if they do, they may not completely enter the clothing.

This will be explained in detail using FIG. 3.

In FIG. 3, (L,) (L2) indicate lenses that are replaced and attached to the camera body, respectively.

(FP) is a focusing plate having a Fresnel lens surface (FS). The focal length of the Fresnel lens surface (FS) is the focal length 2 at the exit pupil position U when the lens (L,) is attached.
It is set so that α is located. This focus plate (F'
An enlarged view of P) is shown in Figure 4. Returning to Figure 3, (PP
) indicates a pentaprism, and (EP) indicates an eyepiece.

With this configuration, the light flux in the shaded area in the figure enters the eye, so the exit pupil is located at the point where the light flux entering the box intersects the optical axis (P, H, that is, the point conjugate with the eye). If you wear the positioning lens r(L+), you can see the entire field of view. However, when a lens (L2) whose exit pupil is located at a point (R2) far from the point (Pl) is attached, the part indicated by the broken line becomes the boundary, so the luminous flux is limited only to the area inside the boundary. As a result, the periphery will be cut off.

Therefore, conventionally, a plurality of types of focal and α plates having different 7-Resnel characteristics (focality and α distance of the Fresnel lens surface) are prepared, and the focal and α plates are exchanged depending on the lens.

However, if the focus plate is replaced depending on the photographic lens, it is extremely difficult to use, and when zooming with a zoom lens with a large zoom ratio, the luminous flux will be reduced. The 7-eye image becomes dark due to vignetting.
! [There is a problem.

SUMMARY OF THE INVENTION An object of the present invention is to solve these problems and provide a focus plate that does not need to be replaced even when lenses are replaced or zoomed.

In order to achieve the above object, the present invention provides a focus plate having a Fresnel lens surface used in a single-lens reflex camera with interchangeable lenses, in which the Fresnel lens surface has the following features:
It is characterized by alternately having surfaces with at least two different angles.

Therefore, according to the present invention, since one focusing plate has a Fresnel lens surface having a plurality of focal lengths, the transmitted light can be guided to a limit across a wide range of interchangeable lenses. There is no longer a need to change the focus plate when changing lenses or zooming.

FIG. 14 ptS1 is a sectional view showing a focusing plate according to an embodiment of the present invention. In Fig. 1, (FL) is a focusing plate, and the focusing plate (
FL) has a Fresnel lens surface (FLS) formed on the negative surface, and the opposite surface facing it is a flat surface.

The Fresnel lens surface (F L S ) has a lens surface (FR,) with a radius of curvature R1 set so that the focal point is located at a point (P,), and a lens surface (FR,) set so that the focal point is located at a point (R2). The lens surfaces (FR2) with the radius of curvature R2 are formed alternately, and by reducing the contact P, the lens surfaces (FR2) with the radius of curvature R2 (i.e., 2
It acts like a lens surface with a focal distance of 1.

Here, the cross sections of both lens surfaces (FR1) and (FR2) are actually not curved (straight) due to manufacturing problems, and the angle becomes gentler toward the center.

FIG. 2 is a developed view showing the optical path of a single-lens reflex camera using this focal plate (FL). In Figure 2,
! Similar to Figure #3, (L,) (L2) are selectively attached lenses, (PP) is a pentaprism, and (E
P) shows the eyepiece.

With this configuration, when the lens (Ll) is attached, the entire field of view can be seen as in the conventional case shown in FIG. On the other hand, when the lens (L2) is attached, the light flux in part (A) reaches the eye without being vignetted, but part of the light flux in part (B) fi is affected by the F number of the lens (L2) (i.e., However, as in the conventional case in Figure t143, the area outside the dashed line is not completely invisible, and the lens surface with radius of curvature R2 (FRY )
The area outside the dashed line can also be seen because the rays of light reach the eye.

With this configuration, even if a wide range of lenses are used interchangeably, it is possible to view the field of view with one focusing plate without having to replace the focusing plate in response to lens exchange or zooming.

Furthermore, in the above embodiment, a Fresnel lens surface having two types of radii of curvature was used, but the present invention is not limited to this, and it is possible to use a Fresnel lens surface having three or more types of radii of curvature. It may be configured so that it has. However, if there are too many types, the repetition period of the 7-renel wire becomes too large, and the image jumps too much, making it impractical.

The effect of this reticle is best exhibited by a transparent type reticle without a matte surface, but the present invention is not limited to this, and the focus plate is a transparent type reticle that does not have a matte surface. It is also effective for sigma and sigma plates.

FIGS. 5(-), 5(b), and 5(c) are enlarged sectional views showing embodiments of focusing plates according to the present invention, respectively. Figure 5 (,)
This example is an enlarged view of the Fresnel lens surface of the embodiment shown in FIG. 1, in which two slopes (FR, ) (FL2) having different angles are arranged alternately as the Fresnel lens surface. Here, when the angle of one slope (FR) is 01 and the angle of the other slope (FL2) is 02, θ1>θ2 within one pitch. In the example shown in FIG. 5(b), one protrusion has two slopes (F
R, ) (FL2). One slope (
When the angle of FR, ) is θ3 and the angle of the other slope (FL2) is 02, within one pitch θ1>θ
It is 2. In the example of FIG. 5(c), one protrusion has three different angles (FR,) (FL2) (
FRY). Here, three slopes (
FR, ) (FL2) (FR:, ) angles are respectively θ1
, θ2, θ.

Then, within one pitch, θ1〉θ2〉
θ. Comparing the examples in Figure 5 (a), (b), and (c), we can see that although the pitch is P in all of them, the appearance of the line ring is because the height of the Fresnel peak is low, so in Figure 5 (,), The example case is a little difficult to see. Furthermore, in the example of FIG. 5(a), the wire ring also enters the position P/2, making the wire ring less noticeable. However, in the example shown in FIG. 5(a), the wavefront is greatly disturbed and is therefore susceptible to the effects of diffraction. Figure 5 (b
), the influence of diffraction is small and the image appears clear.

When the charcoal plate of the present invention is used, the fining image appears bright, but if the amount of defocus of the photographic lens is large, the image becomes multiple and blurred. Therefore, when using the focusing plate of the present invention,
It is better to make the distance between the focal plane of the photographing lens and the Fresnel lens surface of the focusing plate as close as possible.Furthermore, as is clear from Figures 1 and 3, in the center near the optical axis, the Fresnel lens surface is slightly distorted. The image can be seen even if the focal point of the lens does not match the exit pupil of the lens, so the central part of the Fresnel lens surface has only one type of radius of curvature between R1 and R2, and the peripheral part only radius of curvature R1
The lens surface (FR,) and the lens surface (FL,) with the radius of curvature R2
2) may be formed alternately.

1 As detailed above, the present invention provides a focus plate having a Fresnel lens surface for use in a single-lens, 7-lens camera with interchangeable lenses, in which the Fresnel lens surface has at least two types of lenses different from each other. It is characterized by having surfaces at alternating angles, and by configuring it in this way, one focusing plate has Fresnel lens surfaces having multiple focal lengths, so it is possible to focus a wide range of lenses. 5α
The transmitted light can be guided to the eye over a distance, eliminating the need to change the focus plate when changing lenses or zooming.

[Brief explanation of the drawing]

FIG. 1 is a sectional view showing a focusing plate according to an embodiment of the present invention, fjS2
The figure is a developed diagram showing the optical path of a single-lens reflex camera using the focusing plate, Figure 3 is a developed diagram showing the optical path of a single-lens reflex camera using a conventional focusing plate, and Figure 4 is the focal point. It is a sectional view showing a board. FIGS. 5(a), 5(b), and 5(e) are enlarged sectional views showing focusing plates having a Fresnel lens surface according to the above embodiment and a modification thereof, respectively. (FP) (FL); focus, α plate, (FS) (FL S); Fresnel lens surface. Applicant Minolta Camera Co., Ltd. 114 Figure 1 Figure 2 Shoulder view (a) 11I TIA (b) View (C)

Claims (1)

[Claims] 1. A focus plate having a Fresnel lens surface used in a single-lens reflex camera with interchangeable lenses, characterized in that the Fresnel lens surface alternately has surfaces having at least two different angles. A reticle with a Fresnel lens. 2. A focusing plate having a Fresnel lens surface as set forth in claim 1, wherein the surface of the focusing plate opposite to the Fresnel lens surface is a flat surface. 3. A focusing plate having a Fresnel lens surface according to claim 1, wherein surfaces having two or more types of angles are alternately formed only in the peripheral portion of the Fresnel lens surface.