JP2000088642A - Optical system for measuring light of single lens reflex camera - Google Patents

Abstract

PROBLEM TO BE SOLVED: To accurately measure the light in a field to be photographed by contg. an infrared-absorptive material in the material of a condenser lens and meeting the conditions of a specified equation about the lens thickness on the optical axis of the condenser lens and the lens thickness at its effective part's most peripheral edge. SOLUTION: A light from an object passes through a photograph lens 1, reflects upward on a main mirror 2 to form an image of the object on a pint plate 4 set at a position equivalent to a film surface 3, and the image is observed through a penta-prism 5 and an eyepiece 6. Part of the light forming the image on a pint plate 4 is condensed by a condenser lens 7 through the penta-prism 5 and guided to a photo detector 9 to measure the light at the object side. The condenser lens 1 is made of a material contg. an infrared- absorptive material so as to meet 0.5<Ds/Dc<1.0 where Dc is the lens thickness on the optical axis of the condenser lens 7 and Ds is the lens thickness at its effective part's most peripheral edge. Thus, a light measuring optical system of a single lens reflex camera can be easily constituted.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a photometric optical system for a single-lens reflex camera, and more particularly to a pentaprism for changing an optical path when a light beam from an object field is guided to a light receiving surface for photometry. The present invention relates to a photometric optical system of a single-lens reflex camera for photometrically measuring an object field by efficiently arranging a condenser lens and a light receiving means behind the exit surface.

[0002]

2. Description of the Related Art Conventionally, in the photometric optical system of a single-lens reflex camera (single-lens reflex camera), various photometric optical systems have been proposed for performing photometry by arranging a condenser lens and a light receiving means behind an exit surface of a pentaprism. Have been.

In such a photometric optical system, a sensor is used as a light receiving means. In general, there is a large difference between the spectral sensitivity of the sensor and the relative luminosity of the eyes of a human (photographer), and the sensor has a large sensitivity distribution especially in an infrared region where the relative luminosity is low. Therefore, in the case of photographing with illumination having a large light energy in the infrared region such as sunlight, the photometry of the object scene may be largely shifted.

In order to cope with this, conventionally, an infrared cut filter is arranged behind or behind the prism, in front of or behind the condenser lens to cut off the infrared light, and the spectral characteristics are compared with the relative luminous efficiency or the film sensitivity. Was approaching.

[0005] The infrared cut filter is generally made of a flat plate having a surface coated with a high reflection characteristic in the infrared region or an optical member in which a coloring material absorbing infrared light is mixed in a medium. I have.

FIG. 3 is a schematic view of a main part of a photometric optical system of a conventional single-lens reflex camera. In FIG. 1, a light beam from the object transmitted through the photographic lens 1 is reflected upward by the main mirror 2 and forms an image on the film surface 3 and on a focus plate 4 placed at a transparent position. A part of the light beam on the focus plate 4 and from the image is condensed on the light receiving element 9 by the condensing lens 7 provided above the eyepiece 6 through the pentaprism 5. At this time, the infrared cut filter 8 was arranged between the condenser lens 7 and the light receiving element.

[0007]

However, the provision of the infrared cut filter as a separate member complicates the entire apparatus, and is not only undesirable, but also causes unnecessary ghosts due to reflection on each surface. In particular, when a point light source is present in the screen, a malfunction may occur in divided photometry.

Therefore, it is conceivable to reduce the number of parts and cost by providing the function of an infrared cut filter by using the above-mentioned condensing lens, and also to reduce ghost.

As the method, there are two methods: a method using an infrared-reflection coating on the condenser lens and a method using a medium to which a coloring material that absorbs the infrared region is added.
One can be considered.

In a method of applying an infrared reflection coating to a condenser lens, the coating is used on a surface having a curvature, and the incident angle of each light beam greatly differs depending on the incident position of the lens. In general, the characteristics of the coating depend on the incident angle of the light beam, so that there is a difference in the spectral characteristics of each light beam, and a good infrared cut effect cannot be obtained.

On the other hand, in the method of molding using a condensing lens medium to which a coloring material that absorbs the infrared region is added, the thickness of the lens differs between the central part and the peripheral part of the condensing lens. However, there is a problem that a sufficient spectral characteristic cannot be obtained in the peripheral portion of the condenser lens.

According to the present invention, when a converging lens and a light receiving means are arranged behind an exit surface of a prism for changing the direction of an optical path to measure a subject field, the configuration of the converging lens is appropriately set. Accordingly, an object of the present invention is to provide a photometric optical system of a single-lens reflex camera, which can accurately measure an object field while simplifying the entire apparatus.

[0013]

The photometric optical system of a single-lens reflex camera according to the present invention comprises: (1-1) a light-collecting lens and a light-receiving means disposed behind an exit surface of a prism for changing an optical path direction. In a photometric optical system of a single-lens reflex camera for receiving a light beam other than an effective light beam for finder image observation that has passed through the prism and measuring the field of view, the condenser lens contains an infrared absorbing material in its material. When the lens thickness on the optical axis of the condenser lens is Dc and the lens thickness at the outermost periphery of the effective portion of the condenser lens is Ds, 0.5 <Ds / Dc <1.0 (1) ) Is satisfied.

In particular, (1-1-1) wavelength 700n on the optical axis of the condenser lens
When the internal transmittance at m is τa and the internal transmittance at a wavelength of 550 nm on the optical axis of the condenser lens is τb, 0.0 <τa <0.1 ‥‥‥ (2) 0.7 <τb <1.0 ‥‥‥ (3) must be satisfied.

(1-1-2) When the effective diameter of the condenser lens is H, 0.8 <Dc / H <1.5 (4). And so on.

(1-2) A light beam other than the effective light beam for finder image observation, which has passed through the prism, is condensed by using a light-collecting lens and light-receiving means disposed behind the exit surface of the prism for changing the optical path direction. In a photometric optical system of a single-lens reflex camera that receives light and measures the field of view, the focusing lens contains an infrared absorbing material in its material, and the thickness of the focusing lens on the optical axis is Dc. When the thickness of the lens at 70% of the effective portion in the peripheral direction from the optical axis of the optical lens is Dm, 0.5 <Dm / Dc <1.0ｍ (5) is satisfied.

In particular, (1-2-1) wavelength 700n on the optical axis of the condenser lens
When the internal transmittance at m is τa and the internal transmittance at a wavelength of 550 nm on the optical axis of the condenser lens is τb, 0.0 <τa <0.1 ‥‥‥ (2) 0.7 <τb <1.0 ‥‥‥ (3) must be satisfied.

(1-2-2) When the effective diameter of the condenser lens is H, 0.8 <Dc / H <1.5 (4). And so on.

(1-3) A light beam other than an effective light beam for observing a finder image, which has passed through the prism, is condensed by using a light-collecting lens and a light receiving means disposed behind the exit surface of the prism for changing the optical path direction. In a photometric optical system of a single-lens reflex camera that receives light and measures the field of view, the light-collecting lens contains an infrared absorbing material in its material, and the infrared-absorbing material has a concentration in the periphery of the light-collecting lens. The transmittance is made substantially uniform over the entire effective surface by increasing the density as the number of times increases.

(1-4) A light beam other than an effective light beam for finder image observation, which has passed through the prism, is condensed by using a condenser lens and light receiving means arranged behind the exit surface of the prism for changing the optical path direction. In a photometric optical system of a single-lens reflex camera for receiving light and measuring the field of view, the condensing lens has a plurality of lenses, at least one of which contains an infrared absorbing material in its material. When the lens thickness on the optical axis of the lens Rx containing the material is Dc, and the lens thickness at the outermost periphery of the effective portion of the lens Rx is Ds, 0.5 <Ds / Dc <1.5 (6) Is satisfied.

In particular, (1-4-1) When the internal transmittance at 700 nm wavelength on the optical axis of the lens Rx is τa, and the internal transmittance at 550 nm on the optical axis of the lens Rx is τb. 0 <τa <0.1 ‥‥‥ (2) 0.7 <τb <1.0 ‥‥‥ (3)

[0022]

DESCRIPTION OF THE PREFERRED EMBODIMENTS FIG. 1 is a schematic view of a main part of a first embodiment of the present invention. In FIG. 1, a light beam from a subject (not shown) transmitted through a photographing lens 1 is reflected upward by a main mirror 2, and is then transferred to a focus plate 4 located at a position equivalent to a film surface (photosensitive surface) 3. An image is formed, and the image is observed through an eyepiece 6 through a pentaprism 5. A part of the light beam from the subject image formed on the focus plate 4 is condensed by a condensing lens 7 provided above an eyepiece 6 through a pentaprism 5 and guided to a light receiving element 9. The photometry on the object side is performed based on the signal obtained by the light receiving element 9.

A feature of the photometric optical system of the single-lens reflex camera of the present invention is that the condensing lens 7 is made of a material containing an infrared absorbing material, and each element such as thickness and transmittance is specified.

FIG. 2 is a schematic view of a main part of a second embodiment of the present invention. This embodiment is different from the first embodiment in FIG. 1 only in that an inner mirror is provided inside the condenser lens 7 to bend the optical path, and the other configuration is the same. At this time, the shape of the condenser lens 7 may be handled in a state where the optical path is expanded without bending the optical path by the inner mirror.

Next, the features of each embodiment will be described.

(A-1) FIG. 4 is a lens sectional view of the condenser lens 7 according to the first and second embodiments of the present invention. As shown in the figure, the lens thickness on the optical axis of the condenser lens 7 is D
c, when the lens thickness at the outermost periphery of the effective portion of the condenser lens 7 is Ds, Dc = 3.0 Ds = 1.73. The above-mentioned conditional expression (1) is as follows: Ds / Dc = 0.58.

The wavelength 70 on the optical axis of the condenser lens
When the internal transmittance at 0 nm is τa and the internal transmittance at a wavelength of 550 nm on the optical axis of the condenser lens is τb, τa <0.1 0.7 <τb.

That is, the spectral transmittance characteristic on the optical axis of the condenser lens 7 is set so as to satisfy the conditional expressions (2) and (3).

(A-2) FIG. 5 is a sectional view of a condensing lens 7 according to an embodiment of the present invention. As shown in the figure, the lens thickness on the optical axis of the condenser lens 7 is D
c, Dc = 3.5 Dm = 2.63 where Dm is the lens thickness at 70% of the effective portion in the outermost peripheral direction from the optical axis of the condenser lens 7. The conditional expression (5) above is Dm / Dc = 0.75.

The wavelength 70 on the optical axis of the condenser lens
When the internal transmittance at 0 nm is τa and the internal transmittance at a wavelength of 550 nm on the optical axis of the condenser lens is τb, τa <0.1 0.7 <τb.

That is, the spectral transmittance characteristic on the optical axis of the condenser lens 7 is set so as to satisfy the conditional expressions (2) and (3).

(A-3) FIG. 6 is a sectional view of a condenser lens 7 according to an embodiment of the present invention. As shown in the figure, the lens thickness on the optical axis of the condenser lens 7 is D
c, where Ds is the lens thickness at the outermost periphery of the effective portion of the condenser lens 7, Dc = 4.0 Ds = 2.4. The above-mentioned conditional expression (1) is Ds / Dc = 0.6.

The wavelength 70 on the optical axis of the condenser lens
When the internal transmittance at 0 nm is τa and the internal transmittance at a wavelength of 550 nm on the optical axis of the condenser lens is τb, τa <0.1 0.7 <τb.

That is, the spectral transmittance characteristic on the optical axis of the condenser lens 7 is set so as to satisfy the conditional expressions (2) and (3).

When the effective diameter of the condenser lens 7 is H, conditional expression (4) satisfies Dc / H = 1.14 from H = 3.5.

(A-4) When the material of the condenser lens contains an infrared absorbing material, the concentration of the infrared absorbing material is made higher as it goes to the periphery of the condenser lens 7. As a result, the spectral transmittance over the entire effective surface of the condenser lens 7 is made substantially uniform.

(A-5) FIGS. 7 and 8 are lens cross-sectional views of the condenser lens 7 according to the eighth and ninth embodiments of the present invention. In this embodiment, the condenser lens 7 is composed of a positive lens 7a and a negative lens 7b.
And two lenses.

One of the lenses (the lens 7b in FIG. 7, the lens 7a in FIG. 8) contains an infrared absorbing material. Assuming that the lens thickness on the optical axis of the lens Rx containing the infrared absorbing material is Dc and the lens thickness at the outermost periphery of the effective portion of the lens Rx is Ds, in FIG. 7, Dc = 0.9 Ds = 1.2 It is. In the above-mentioned conditional expression (6), Ds / Dc = 1.33. In FIG. 8, Dc = 1.4 Ds = 1.0. The conditional expression (6) above is Ds / Dc = 0.714.

A wavelength 70 on the optical axis of the lens Rx
When the internal transmittance at 0 nm is τa and the internal transmittance at a wavelength of 550 nm on the optical axis of the lens Rx is τb, τa <0.1 0.7 <τb.

That is, the spectral transmittance characteristic on the optical axis of the condenser lens 7 is set so as to satisfy the conditional expressions (2) and (3).

Next, the technical meaning of each of the above conditional expressions will be described. Conditional expression (1) defines the thickness ratio between the center (on the optical axis) and the periphery of the condenser lens. When the ratio of the thickness at the periphery to the center of the condenser lens becomes smaller than the lower limit in the conditional expression, the difference in thickness between the center and the periphery increases, and the difference between the internal transmittances increases. The tendency is particularly remarkable in the infrared section to be shielded,
Not preferred.

The upper limit of the conditional expression means that the condenser lens has a convex shape. The conditional expressions (2) and (3)
Respectively define the internal transmittance at the transmission wavelength and the absorption wavelength for performing the optical function as the infrared cut filter. If the transmittance τa is larger than the upper limit of the conditional expression (2), the infrared cut filter is not suitable because the effect of absorbing infrared light cannot be expected.

On the other hand, the transmittance τ is smaller than the lower limit of the conditional expression (3).
As b decreases, the amount of light reaching the light receiving sensor decreases,
It is not preferable because characteristics at low luminance are deteriorated.

Conditional expression (4) defines the ratio of the thickness at the center of the condenser lens to the effective diameter of the condenser lens. The condenser lens requires a relatively bright F-number lens, but in that case, the opening angle on each surface becomes large,
The amount of change in the optical axis direction of the peripheral part with respect to the central part becomes large.

If the ratio of the thickness at the center of the condenser lens to the effective diameter of the condenser lens becomes smaller than the lower limit of the conditional expression (4), it becomes impossible to secure a sufficient F-number.

On the other hand, when the value exceeds the upper limit, not only is it difficult to secure a space for arrangement, but also the moldability of the condenser lens deteriorates, which is not preferable.

This conditional expression (5) defines the ratio of the lens thickness at 70% of the center of the condenser lens and the outermost peripheral direction of the effective ray portion. In general, it is preferable that the difference in the internal transmittance is small in all the luminous fluxes. However, in a photometric optical system having a relatively large numerical aperture, it is sufficient that the change in the internal transmittance is small in the average of all the luminous fluxes.

Therefore, the light beam at the 70% position in the outermost peripheral direction of the effective ray portion is considered as a representative value, and the ratio of the thickness of the 70% effective light portion in the outermost direction to the center of the condenser lens is a condition. When the value is smaller than the lower limit of the equation, the difference in thickness between the central portion and the peripheral portion increases, and the difference in internal transmittance between the central portion and the peripheral portion increases.

This tendency is particularly remarkable in an infrared portion to be shielded from light, which is not preferable. The upper limit of the conditional expression means that the condenser lens has a convex shape.

Conditional expression (6) defines the shape of the lens Rx containing an infrared absorbing material when the condenser lens is composed of a plurality of lenses. Lens R
When the ratio of the thickness at the periphery to the center of x becomes smaller than the lower limit of the conditional expression (6), the difference in thickness between the center and the periphery increases, and the difference between the internal transmittances increases. . This tendency is particularly remarkable in an infrared portion to be shielded from light, which is not preferable.

Similarly, when the ratio of the thickness at the periphery to the center of the lens Rx exceeds the upper limit of the conditional expression (6),
The difference in thickness between the central portion and the peripheral portion increases, and the difference in internal transmittance increases, which is not preferable.

Next, numerical examples of the condenser lens will be described.

[0053]

[Outside 1]

[0054]

As described above, according to the present invention, when a converging lens and a light receiving means are arranged behind the exit surface of a prism for changing the optical path direction to measure the field, the converging lens is used. By appropriately setting the configuration of (1), it is possible to achieve a photometric optical system of a single-lens reflex camera capable of accurately measuring the field of view while simplifying the entire apparatus.

In particular, according to the present invention, as described above, the shape of the condenser lens containing the infrared absorbing material is satisfied by satisfying at least one of the conditional expressions (1) to (6). There is an effect that the photometric optical system of the single-lens reflex camera can be realized with a simple configuration, in which the amount of infrared absorption is almost constant irrespective of the position of the lens and the spectral transmission characteristics are good.

[Brief description of the drawings]

FIG. 1 is a schematic diagram of a main part of a first embodiment of the present invention.

FIG. 2 is a schematic view of a main part of a second embodiment of the present invention.

FIG. 3 is a schematic diagram of a photometric optical system of a conventional single-lens reflex camera.

FIG. 4 is an explanatory view of a condenser lens according to the present invention.

FIG. 5 is an explanatory view of a condenser lens according to the present invention.

FIG. 6 is an explanatory view of a condenser lens according to the present invention.

FIG. 7 is an explanatory view of a condenser lens according to the present invention.

FIG. 8 is an explanatory view of a condenser lens according to the present invention.

FIG. 9 is a graph of a change in spectral transmittance between the center and the periphery of the condenser lens according to the present invention.

FIG. 10 is a graph showing a change in spectral transmittance between the center and 70% of the periphery of the condenser lens according to the present invention.

[Explanation of symbols]

 REFERENCE SIGNS LIST 1 photographing lens 2 main mirror 3 film surface 4 focus plate 5 pentaprism 6 eyepiece 7 photometric condenser lens 7 a condenser lens 1 7 b condenser lens 2 8 infrared cut filter 9 light receiving element

Continued on the front page F-term (reference) 2G065 AA15 AB02 AB04 BA01 BB06 BB10 BB26 CA03 DA18 2H002 DB00 DB07 HA24 JA02 2H087 KA02 LA27 PA01 PA02 PB01 PB02 QA02 QA07 QA12 QA13 QA14 QA22 QA37 QA41 RA05 RA01 9

Claims (9)

[Claims] 1. A light beam other than an effective light beam for finder image observation, which has passed through the prism, is received by using a condensing lens and a light receiving means disposed behind an exit surface of a prism for changing the optical path direction. In a photometric optical system of a single-lens reflex camera for photometry of an object field, the condensing lens contains an infrared absorbing material in its material, the lens thickness on the optical axis of the condensing lens is Dc, and the A photometric optical system for a single-lens reflex camera, characterized by satisfying 0.5 <Ds / Dc <1.0, where Ds is the lens thickness at the outermost periphery of the effective portion. 2. A wavelength 7 on the optical axis of the condenser lens.
Assuming that the internal transmittance at 00 nm is τa and the internal transmittance at the wavelength of 550 nm on the optical axis of the condenser lens is τb, 0.0 <τa <0.1 0.7 <τb <1.0 is satisfied. 2. A photometric optical system for a single-lens reflex camera according to claim 1, wherein: 3. The photometric optical system of a single-lens reflex camera according to claim 2, wherein 0.8 <Dc / H <1.5 when the effective diameter of said condenser lens is H. 4. A light beam other than an effective light beam for finder image observation, which has passed through the prism, is received by using a light-collecting lens and a light-receiving means disposed behind the exit surface of the prism for changing the optical path direction. In a photometric optical system of a single-lens reflex camera for photometry of an object field, the condensing lens contains an infrared absorbing material in its material, the lens thickness on the optical axis of the condensing lens is Dc, and the A photometric optical system for a single-lens reflex camera, characterized by satisfying the following condition: 0.5 <Dm / Dc <1.0, where Dm is the lens thickness at 70% of the effective portion in the outermost peripheral direction from the optical axis. 5. A wavelength 7 on the optical axis of the condenser lens.
Assuming that the internal transmittance at 00 nm is τa and the internal transmittance at the wavelength of 550 nm on the optical axis of the condenser lens is τb, 0.0 <τa <0.1 0.7 <τb <1.0 is satisfied. 5. A photometric optical system for a single-lens reflex camera according to claim 4, wherein: 6. The photometric optical system for a single-lens reflex camera according to claim 5, wherein when the effective diameter of said condenser lens is H, 0.8 <Dc / H <1.5 is satisfied. 7. A luminous flux other than an effective luminous flux for finder image observation, which has passed through the prism, is received by using a condenser lens and a light receiving means disposed behind the exit surface of the prism for changing the optical path direction. In a photometric optical system of a single-lens reflex camera for photometry of an object scene, the converging lens contains an infrared absorbing material in its material, and the infrared absorbing material has a concentration as it goes to the periphery of the converging lens. A photometric optical system for a single-lens reflex camera, characterized in that the light is darkened so that the transmittance over the entire effective surface is substantially uniform. 8. A luminous flux other than an effective luminous flux for finder image observation, which has passed through said prism, is received by using a condenser lens and a light receiving means disposed behind the exit surface of the prism for changing the optical path direction. In a photometric optical system of a single-lens reflex camera for photometry of an object scene, the condenser lens has a plurality of lenses, at least one of the lenses contains an infrared absorbing material in its material, and contains an infrared absorbing material. The lens thickness on the optical axis of the obtained lens Rx is Dc,
A photometric optical system for a single-lens reflex camera, characterized by satisfying 0.5 <Ds / Dc <1.5, where Ds is the lens thickness at the outermost periphery of the effective portion of the lens Rx. 9. A wavelength 700 on the optical axis of the lens Rx.
0.0 <τa <0.1 0.7 <τb <1.0, where τa is the internal transmittance at 550 nm and τb is the internal transmittance at a wavelength of 550 nm on the optical axis of the lens Rx. The photometric optical system for a single-lens reflex camera according to claim 1, wherein: