JPH0323896B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a focusing plate for focus detection used in a single-lens reflex camera, and more particularly to an improvement in an image split type distance measuring section.

An image split type distance measuring section using a prism is often used as a distance measuring section in a focus plate of a single-lens reflex camera. This image split type distance measuring section has good focus detection accuracy (distance measuring accuracy), but when using an interchangeable lens with a large F number, that is, low brightness, the distance measuring section will darken, and the measurement will be difficult. It has the disadvantage of being difficult to track.

The distance measurement accuracy and the shadow of the distance measurement section have an inverse relationship with each other with respect to the prism apex angle of the split prism. That is, by increasing the prism apex angle of the splitting prism, it becomes possible to guide the luminous flux from the peripheral part of the exit pupil of the photographic lens to the eyepiece of the viewfinder, thereby improving distance measurement accuracy.

However, if a split prism with a large prism apex angle is used with a somewhat dark interchangeable lens, the brightness of the distance measuring section will darken, making distance measurement impossible. Conversely, if the prism apex angle is made small, the distance measurement accuracy will decrease, but
Distance measurement is possible even with a fairly dark interchangeable lens with a large F number.

Because of this phenomenon, the prism apex angle is usually kept at around 8 degrees without increasing it to a large value.
This makes it possible to measure distances even with dark interchangeable lenses with an F number of about 5.6, at the expense of some distance measurement accuracy.

The present invention alleviates the relationship between distance measurement accuracy and shadowing of the distance measurement section, which is a problem with the conventional image split type distance measurement section described above, and enables easy and high focusing even when using a dark interchangeable lens. The purpose is to provide a focus plate that can measure distances with precision.

The main feature of the reticle for achieving the object of the present invention is that the reticle has an image splitting prism that forms a separated image during defocusing,
The image splitting prism has a first prism part that forms one of the separated images and a second prism part that forms the other of the separated images, and each of the first and second prism parts has a diffraction grating made up of a large number of microprisms arranged periodically,
Each of the refractive surfaces of the plurality of micro prisms of the first prism section is tilted in the same direction so as to deflect the light beam incident on the first prism section in a plurality of directions, thereby converting the one image into a plurality of images. Consisting of a plurality of slopes having different inclination angles, each refractive surface of the plurality of micro prisms of the second prism section deflects the light beam incident on the second prism section in a plurality of directions to form a plurality of images of the other one. In order to obtain an image of , the first prism part is composed of a plurality of slopes having different inclination angles and tilting in the opposite direction to the plurality of slopes of the first prism part.

As described above, the focusing plate of the present invention has the feature that by utilizing the diffraction effect and refraction effect of the micro prism having the above-described configuration, the defocus state is displayed more clearly, making distance measurement very easy. There is.

Next, embodiments of the present invention will be described.

FIG. 1 is an overall view of one embodiment of the focusing plate of the present invention. In the figure, reference numeral 1 denotes a focus plate, and reference numeral 11 denotes an image splitting prism corresponding to a distance measuring section, which has a first prism section 2 and a second prism section 3.

FIG. 2 is a perspective view of a main part of one of the prism parts, for example, the first prism part 2, of the image splitting prism 11 of this embodiment.

The first prism section 2 (hereinafter referred to as the "prism section") shown in FIG. 2 has, for example, a prism 12 having a prism apex angle of ₂ as shown in FIG. angle
₁ , and corresponds to the shape obtained by removing the diagonal line portions 22. Therefore, this distance measuring section is functionally equivalent to a prism 23 provided with a refraction grating 24 having a fine cut structure, as shown in FIG. 4, and as a result, it has both functions. ing.

As can be seen from the prism structure in FIG. 2, from another perspective, this prism portion 2 is composed of a minute prism 20 having an apex angle _{of 1} and a minute prism ₂₁ having an apex angle of 2. Because of this structure, as shown in FIG. 5A, the light beam 51 that has entered the prism section 2 is deflected by the minute prism 20 at an angle θ ₁ , and a light beam 51a is deflected by the minute prism 21 at an angle θ. It is dispersed into _two light beams 51b. This allows light beams at different angles from the entrance pupil of the photographing lens to be guided to the eyepieces.

Due to this optical action, when the object image is in a defocused state, the prism section 2 separates the image with lateral deviation, and each lateral deviation separated image itself is further separated into double images, and when this double image separation is small, the image becomes blurred. observed as. That is, as shown in FIG. 5B, when the light beam 51 is in focus in the prism section 2, no diffracted waves are generated and the image can be observed without any problem.

However, in the state of defocus, two lights 51 of strong intensity are shown by diagonal lines in FIG. 5B.
a and 51b are generated, and a diffracted wave is generated around them.

In the prism section 2 of this embodiment, the incident light 51 is mainly 2
The light is separated into two lights 51a and 51b, and the intensity of the other lights is weakened. That is, in order to focus on one point on the optical axis, the light beam 51 incident on the prism section 2 is separated into two directions by the prism action of the micro prisms 20 and 21.

Figure 5C shows the two lights 51a and 51b at this time.
shows the intensity distribution of As a result, as shown in FIG. 5D, two images 13 and 14 are formed by the respective light beams 51a and 51b. Therefore, when observing this state through a viewfinder, as shown in FIG. At the same time, the object image is observed in a blurred manner (indicated by straight line double image separation in the figure).

Note that 13' and 14' are images separated by the second prism section 3. If the degree of separation by the diffraction grating is large, the object image will be observed as a double image rather than a blur.

As shown in FIG. 5D, the defocus image in this distance measuring section is such that a double image due to the light from the diffraction grating made of a micro prism is seen in the distance measuring section 52, and the defocus is zero, that is, the object image. When the image correctly matches the focus plate, the image blur caused by the double image disappears, and the upper and lower images match, indicating the in-focus state.

As described above, in this embodiment, the second prism part 3 has a structure as shown in FIG. 6 and has an angle in the opposite direction to that in FIG.
By combining these, a reticle using an image splitting prism that causes lateral shift of the upper and lower images as well as image blurring (double image) is realized.

FIG. 7 is an explanatory diagram showing the appearance of the distance measuring section when a shadow occurs when a photographing lens with a dark F number is attached in this embodiment.

In FIG. 7, 28 and 29 are portions corresponding to the micro prism 20 having a large apex angle φ ₁ .
Since this micro prism 20 becomes dark first, dark lines in a striped pattern appear. In order to prevent this, the period P of the micro prism structure in FIG. 2 is made small, and therefore the width P ₁ of the micro prism 20 is made small so that it cannot be resolved with the naked eye. In a normal single-lens reflex camera, P = about 20μm, P ₁ = 10μ
There is no problem if you keep it below about m.

Conversely, if P = 200 μm and P ₁ = 100 μm, the value of the width P ₁ will be equal to the microprism size, and the action of the two micro prisms 20 and 21 with different prism apex angles will change the grid line direction. A jagged pattern is observed at the edge of the line image that crosses the line image. Furthermore, slight camera shake when holding the camera in the hand can cause image flickering. In addition to the lateral shift of the split image, these phenomena can also be used for focus detection.

In the prism structure shown in FIG. 2, by replacing the basic prism with a Fresnel prism as described above, it is also possible to use a ranging section having a shape as shown in FIGS. 8 and 9. These also have the same functions as those in FIG. One set of micro prisms with apex angles of ₁ and ₂ in FIGS. 8 and 9 corresponds to the prism portion of the image splitting prism.

Although the above description has been made regarding an image splitting prism that is divided into upper and lower parts, the present invention can be similarly applied to an image splitting prism of a type that generates horizontally shifted images in the upper, lower, left, and right directions as shown in FIG. Can be applied.

FIG. 10 is a plan view showing only the distance measuring section. Reference numerals 32 and 33 designate prism portions having the cross-sectional shape described above to cause lateral deviation of the image. Reference numerals 30 and 31 are prism portions having a structure in which 32 and 33 are rotated by 90° about the central axis.

Therefore, when a crosshair on an object is distance-measured using this distance-measuring section, a blurred (double) image as shown in FIG. 11 is observed during defocus.

To manufacture the distance measuring section as described above, a photoresist is applied to each prism that makes up the conventional image splitting prism, a concave-convex structure is created using a photo-etching method, and electroforming technology is applied based on this. For example, a method is used in which a mold is obtained by using a mold, and this mold is used to transfer the uneven structure onto the plastic.

Further, a mold can also be made directly by carving a recess with a diamond cutting tool directly on the mold component constituting the conventional image split type distance measuring section.

As described above, by configuring the first and second prisms constituting the image splitting prism as described above, the present invention achieves new functions not found in conventional image splitting prisms through diffraction and refraction effects. It is possible to obtain a reticle with .

Furthermore, by using the focusing plate of the present invention, for a bright photographing lens with a small F number, not only the image splits but also the respective split images themselves are observed as multiplexed or blurred during defocusing, allowing for more accurate distance measurement. It is possible. Furthermore, distance measurement can be performed without the distance measuring section becoming dark even with a dark lens with a larger F number than a focusing plate using a conventional image splitting prism. Incidentally, the present invention can provide a focus plate useful not only in cameras but also in various optical machines.

[Brief explanation of drawings]

FIG. 1 is a schematic diagram showing a focus plate according to an embodiment of the present invention, FIG. 2 is a perspective view of a main part of a prism-like structure of a prism portion according to the present invention, and FIG. 4 is a functional exploded view of the prism section in FIG. 2, FIGS. 5A to D are explanatory diagrams of the optical action of the prism section according to the present invention, and FIG. 6 is the first prism section in FIG. 2. FIG. 7 is a perspective view of the other second prism section combined with the second prism section, FIG. 7 is an observation view when distance measurement is performed using the focusing plate of the present invention, and FIGS. 8 and 9 are other implementations of the prism section according to the present invention. FIG. 10 is a plan view of a distance measuring section of another embodiment in which diffraction gratings whose grating directions are orthogonal to each other are provided on a prism, and FIG. 11 is a cross-sectional view of the main part of the example. This is a diagram when the crosshairs are observed. In the figure, 1 is a focus plate, 2 is a first prism section, 3 is a second prism section, and 20 and 21 are minute prisms.

Claims (1)

[Claims] 1 A focusing plate having an image splitting prism that forms a separated image during defocusing,
The image splitting prism has a first prism part that forms one of the separated images and a second prism part that forms the other of the separated images, and each of the first and second prism parts has a diffraction grating made up of a large number of microprisms arranged periodically,
Each of the refractive surfaces of the plurality of micro prisms of the first prism section is tilted in the same direction so as to deflect the light beam incident on the first prism section in a plurality of directions to turn the one image into a plurality of images. Consisting of a plurality of slopes having different inclination angles, each refractive surface of the plurality of micro prisms of the second prism section deflects the light beam incident on the second prism section in a plurality of directions to form a plurality of images of the other one. A reticle comprising a plurality of slopes having different inclination angles and tilting in a direction opposite to the plurality of slopes of the first prism portion in order to obtain an image of .