JPH0139089B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a focus plate for focus detection used in single-lens reflex cameras, etc., and in particular, when an object image formed on the focus plate surface is defocused, double images colored in different colors are generated. The present invention relates to a focus plate suitable for double image matching type focus detection to be observed.

Generally, a split image method using a wedge-shaped prism is often used as a focus detection method for single-lens reflex cameras. However, for those who are accustomed to the dual image matching method of focus detection using the rangefinder of intermediate-level cameras, the split image method may be unfamiliar and strange. Therefore, there has been a desire for a highly accurate double image matching type focus detection method that can be applied to single-lens reflex cameras and the like.

Traditionally, for example, Special Publication No. 9474 (1974) and Special Publication No. 54 (1973)
A focus plate using a diffraction grating is known in Publication No. 12817 (the principle of distance measurement is explained therein), and in these focus plates, double images are colored due to the dispersion of the diffraction grating during defocusing. It is stated that.

However, in the focusing plates proposed in these publications, coloring due to dispersion only occurs slightly at the periphery of each image incidentally during double image separation, and the entire image is not colored. Coloring does not substantially contribute to improving focus accuracy.

The present invention provides a system in which a diffraction grating is provided on a focusing plate to perform focus detection using a double image matching method, in which each of the double images generated when defocusing has a different color (preferably a color that is complementary to each other). )
It is an object of the present invention to provide a focusing plate which performs highly accurate focus detection by coloring and, in an in-focus state, double images coincide with each other and the coloring also disappears.

That is, an object of the present invention is to provide a high-precision reticle in which coloring and separation of an image is actively displayed during defocusing.

The reticle of the present invention, as explained in detail below, includes:
In a focus plate having a diffraction grating formed by periodically arranging uneven parts having first and second slopes facing in different directions, most of the first wavelength component of the incident light beam is diffracted to a predetermined order. in the vicinity of the diffraction grating so that most of the second wavelength component different from the first wavelength component exits the focus plate as light and exits from the focus plate as diffracted light of an order different from the predetermined order. First and second color filters having different wavelength characteristics are arranged periodically, so that the first color filter corresponds to the first slope of the uneven portion, and the first color filter corresponds to the second slope of the uneven portion. It is characterized by a second color filter.

Embodiments of the present invention will be described below with reference to the drawings.

FIG. 1 is a schematic cross-sectional view of an embodiment of the focusing plate of the present invention applied to a single-lens reflex camera. In the figure, 1 is a photographing lens, 2 is an aperture, 3 is a quick return mirror, 4 is a light shielding frame, 5 is a photographic film, 6 is a focus plate, 7 is a condenser lens,
8 is a pentaprism, 9 is an eyepiece, and 10 is an observer's eye. 6 is a focusing plate of the present invention;
It has the above-mentioned diffraction grating structure 11 for distance measurement in its center (although the fine structure is not shown).

FIG. 2 is a cross-sectional view of the diffraction grating structure of the focusing plate of the first embodiment. In FIG. 44 is an optically transparent member for the cover.

The color filter 38 is provided directly on the relief structure by vapor deposition of dyes or dyed photoresist. Then, a phase distribution is generated as a result of the contribution of both the unevenness of the adhesive layer and the unevenness of the relief structure on the base, a phase diffraction grating structure is formed, and a diffraction effect is generated on the incident light. This color filter has orange filter section 40.
and blue filter portions 41 are alternately arranged in stripes at the same period as the relief structure. This color filter has a transmittance as shown in FIG. Therefore, when a part of the light rays 42 parallel to the optical axis in the light flux incident on the focus plate passes through the blue filter, after the red wavelength portion is absorbed, only the blue light is separated by the relief structure 37, which is oriented θ with respect to the optical axis. Shoot in the direction.

Similarly, another light ray 43 passes through the orange filter and then exits in the -θ direction with respect to the optical axis. The diffraction grating structure, which is a combination of a relief structure and a color filter, emits approximately the same amount of ±1st-order diffracted light.
As the stripe filter used in this embodiment, a dichroic filter using a multilayer dielectric film or a color absorption filter using a dye can be used.

In this way, the diffraction grating structure of this embodiment has a geometrically symmetrical relief structure for diffracting incident light on the optical axis in two symmetrical directions, and a relief structure in which each period is mutually disposed. The optically asymmetric phase diffraction grating structure is constructed by combining color filter sections with different wavelength characteristics with color filters arranged asymmetrically with respect to the symmetry axis of the relief structure, so that different colors can be produced. This produces a double image that is almost uniformly colored.

FIG. 4 shows an out-of-focus image observed during defocusing when a focusing plate having such a diffraction grating structure as a distance measuring section is used.

FIG. 4 is an enlarged view of only the inside of the distance measuring section when looking at a white rectangular object, such as a blank sheet of paper on a wall, from the eyepiece section during defocus.

In FIG. 5, reference numeral 24 denotes a distance measuring section having a diffraction structure, and an image 25 of +1st-order diffracted light and an image 26 of -1st-order diffracted light are visible. These statues are statue 25
appears to be colored blue, and the image 26 appears colored orange, and the portion where the two overlap appears naturally white.

The second method of the present invention using such a diffraction grating structure
FIG. 5 shows a distance measuring section of a focus plate according to an embodiment. In this embodiment, the color filters in the lattice structure as shown in FIG. 2 are arranged so that the color stripes are different from each other above and below the focus plate, that is, the periodic direction is reversed.

FIG. 6 shows the state of the subject image observed when focusing using this distance measuring section. In FIG. 6, 29 indicates the range of the distance measuring section, and 14 indicates the boundary line between the areas 15 and 16 in FIG.

In FIG. 6, a white bar-shaped object 30 is observed in a defocus state, and each diffraction grating structure separates into a double image, an orange image and a blue image, at the boundary line 14 of the ranging section. do. For example, in the upper half area 18, an orange image 32 ₁ and a blue image 32 ₂ are formed, and in the lower half area 19, an orange image 33 ₂ and a blue image 33 ₁ are formed. A double image is observed, and this colored double image disappears as the object is brought into focus, and is not observed at all in the in-focus state, making focusing easier and increasing precision.

In addition to the above-mentioned effects, the distance measuring section of this embodiment has the opposite color shift direction in the upper half and lower half of the distance measuring section within the observation field, for example, the orange image 32 ₁
By creating a color split in the continuous image along the boundary line 14, as shown in the blue image 33 ₁ , and providing the effect similar to a conventional split image prism, it is easy to determine the defocus state, and the focusing is easy and high. This has a great effect on accuracy. Furthermore, in general, in the double image matching method using colored double images using a dichroic mirror, etc., when the subject is a single color such as orange,
The image corresponding to blue disappears, and only a single image appears, making distance measurement impossible. However, in this embodiment, blue images 32 ₁ and 32 ₂ remain, and distance measurement using color split images is possible.

FIG. 7 shows another diffraction grating structure applicable to the present invention. In FIG. 7, 45 is a substrate with a period P of about 10 μm or less and has a chevron-shaped relief structure 46 on its surface, and 47 is a glass substrate having a color stripe filter 48 on its surface. Base 45
is located close to and above 47. Color stripe filter is orange filter part 40
and blue filter portions 41 are arranged alternately and periodically with the diffraction grating. This color filter has a transmittance as shown in FIG. 3 as in the previous embodiment.

In the embodiments described so far, if the periodic structure of the diffraction grating structure is coarse, it will attract the eye and be harmful during focus detection, so it is preferable that the periodic structure be finer than the resolution of the naked eye. This resolution with the naked eye depends on the performance of the camera's viewfinder optical system, but is usually about 10 μm, so the fineness of the diffraction grating structure should be kept below this value.

Further, as a method of manufacturing a diffraction grating having the shape shown in FIGS. 2 and 7, a photo-etching technique using an optical mask and photoresist, which is used in the manufacture of semiconductor electronic devices, may be applied.
Furthermore, if a master mold is made using electroforming technology using the diffraction grating thus obtained as a master plate, copies can be mass-produced at low cost by transferring the uneven structure of this master mold to a plastic member.

Furthermore, the present invention is not limited to still single-lens reflex cameras, but is also effective in cine cameras.
However, in the case of a cine camera, the viewfinder magnification is large, so the period of the diffraction structure must be made finer than in the case of a still single-lens reflex camera.

In the above-described embodiment, as the most preferable example, the divided regions are divided into two, and the periodic direction is reversed. However, the present invention is not limited to this, and the effects of the present invention can still be achieved.

As described above, the reticle of the present invention has an optically asymmetric structure that separates different wavelength components of an incident light beam in different directions as a diffraction grating structure used in the distance measuring section. By forming a colored double image during defocusing, focusing becomes easy. Furthermore, by dividing the ranging section into a plurality of regions and making the periodic direction of the diffraction grating structure different in each region, color splits are produced at the boundaries of each region, and these can be observed simultaneously during defocus. Furthermore, since the light disappears when the light is in focus, easy and highly accurate distance measurement is possible.

[Brief explanation of drawings]

FIG. 1 is a cross-sectional view of a single-lens reflex camera, FIG. 2 is a diagram showing the diffraction grating structure of the focus plate of the first embodiment, and FIG.
The figure shows the transmittance of the color filter, Figure 4 is a viewfinder observation view, Figure 5 is a view showing the distance measuring section of the second embodiment, and Figure 6 is a finder observation view of the focusing plate of the first embodiment. , FIG. 7 is a diagram showing the diffraction grating structure of the focusing plate of the third embodiment. In the figure, 6 is a focus plate, 11 is a diffraction grating structure, 1
5 and 16 are phase diffraction gratings, 24 is a ranging section, 32 ₁ ,
33 ₂ is an orange image, 32 ₂ , 33 ₁ is a blue image,
38 is a color filter, 40 is an orange filter section, and 41 is a blue filter section.

Claims (1)

[Claims] 1. In a focusing plate having a diffraction grating formed by periodically arranging concavo-convex portions having first and second slopes facing in different directions, most of the first wavelength component of the incident light beam is of a predetermined order. near the diffraction grating so that most of the second wavelength component different from the first wavelength component that is emitted from the focusing plate as diffracted light is emitted from the focusing plate as diffracted light of an order different from the predetermined order. first and second color filters having different wavelength characteristics are arranged periodically, and the first color filter corresponds to the first slope of the uneven portion, and the second color filter corresponds to the second slope of the uneven portion. A focusing plate characterized in that the second color filter is made to correspond to the second color filter.