JPH0150891B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION TECHNICAL FIELD The present invention relates to a finder device used in a single-lens reflex camera, a camera having a virtual image finder with a daylight bright frame, a single-lens spotmeter, and the like.

PRIOR ART In general, in a finder device having a daylight-type bright frame, a single-lens reflex camera is configured to perform photometry, etc. in order to direct the viewing frame display light flux and the finder light flux in the same direction, and behind a movable mirror. It is known that a half mirror is used in order to separate a light beam for photometry and a light beam for finder use.
Conventionally, such a half mirror has a flat plate made of a transparent material such as glass that is coated with a light semi-transparent film to make it a light semi-transparent surface. A ghost of the normally formed image occurs due to the reflection of light at
It has the disadvantage that observation using a finder becomes difficult. This ghost occurs both when the normal image is formed by light reflected by the light semi-transparent surface and when the normal image is formed by light transmitted through the light semi-transparent surface. It appears adjacent to the regular image and is particularly noticeable when the image is of high brightness. Moreover, since it is difficult to make the spectral reflectance characteristics of the half mirror completely flat over the entire visible wavelength range, the ghost may have a color different from that of the normal image and be particularly noticeable.

Purpose The present invention has been made in view of the conventional drawbacks as described above, and its purpose is to provide a finder device in which the ghost generated by the half mirror does not hinder observation. .

Embodiments Hereinafter, embodiments of the present invention will be described in detail based on the drawings.

FIG. 1 shows an inverted Galilean finder device having a daylight bright frame according to an embodiment of the present invention. In the figure, 2 is an objective lens, 4 is an eyepiece lens, and these constitute an inverted Galilean finder optical system. are doing. Reference numeral 6 represents a viewing frame for displaying the photographing range, 8 represents a total reflection mirror, and 10 represents a half mirror disposed between the objective lens 2 and the eyepiece lens 4. The half mirror 10 has a semi-transparent film coated on one surface of a substrate 10a made of a transparent material such as glass, and has a semi-transparent surface 10b.
Furthermore, the opposing surface 10c of the light semi-transmissive surface 10b is inclined at an angle α with respect to the light semi-transmissive surface 10b. This angle α is such that a ghost generated by reflection of light on the opposing surface 10c of the half mirror 10 is superimposed on the normal image.

Such angle α is analytically determined using FIG. Figure 2 shows the half mirror 1 in this embodiment.
FIG. 2a is a longitudinal sectional side view of the half mirror 10, and FIG.
Figure 2b is a diagram for determining the half mirror 1.
These diagrams are for finding the angle α for superimposing the ghost on the normal image formed by the light ray that passes through 0, and both diagrams show the case where the image point is closer to the field of view than the half mirror 10. ing.

In FIG. 2a, a ray a emitted from an object point F is reflected and refracted at a point 0 on the semi-transparent surface 10b of the half mirror 10, and is divided into a reflected ray a ₁ and a transmitted ray a ₂ . . The reflection angle at this time is θ, and the refraction angle is θ'. Since the reflected ray _a1 travels straight, when viewed from the observation position side, that is, from the direction of arrow A,
A point F' equivalent to the object point F with respect to the half mirror 10 becomes an image point. On the other hand, the transmitted light ray _a2 travels through the substrate 10a and reaches the half mirror 10 from the point P on the opposing surface 10c.
A part of it is reflected at the point P, passes through the light semi-transmissive surface 10b again, and is emitted out of the half mirror 10 from the same side as the reflected light beam _a1 . If the opposing surface 10c is parallel to the semi-transparent surface 10b as shown by the dashed line in _FIG . Reaching point Q, the surface 1
It passes through 0b and becomes a ray of light a ₂ ″, which passes through the half mirror 1.
It is ejected from 0. This ray a ₂ ″ is parallel to the reflected ray a ₁ because the light semi-transmissive surface 10b and the opposing surface 10 c are parallel, and therefore, the ray a ″ ₂ is at the image point F due to the reflected ray a ₁ It does not appear to be emitted from ′, so it forms a ghost.

Therefore, the opposing surface 10
When c is tilted at an angle α, the light ray reflected at the point P on the opposing surface 10c becomes a ray a ₃ and reaches the point Q' on the light semi-transparent surface 10b, and at the point Q' the refraction angle θ'' It is refracted and becomes a light ray a ₃ ′ and is emitted from the half mirror 10, and this ray a ₃ ′ is the reflected light ray.
It appears to be emitted from the image point F′ due to a ₁ . Here, the distance of OF is l (however, l is positive when the image point F' is closer to the observation position than the half mirror 10), the thickness of the half mirror 10 at the point P is d,
The refractive index of the transparent material constituting the substrate 10a is η, and as shown in the figure, ∠QF′O=β, ∠Q′F′O=
Let β′ be the intersection point of a perpendicular line drawn on the straight line containing the ray a ₁ from point Q′ with the straight line, then the triangle
From F′QS, β=tan ^-1 (2dtanθ′cosθ/−l+2dtanθ′sinθ
) - (1) holds true, and from the geometrical relationship shown, θ''=θ+β' - (2) holds.Furthermore, from Snell's law at points 0 and Q', sinθ= The following relationship is found: ηsinθ′ −(3) ηsin(θ′+2α)=sinθ″ −(4) Here, since l is generally sufficiently large compared to d, if we assume ββ', equation (2) becomes θ''θ+β, and equation (4) becomes ηsin (θ'+2α) sin (θ+β). Therefore, α1/2 [sin ^-1 {sin (θ+β)/η}−θ′]—
(5) However, β＝tan ^-1 (2dtanθ′cosθ／−l＋2dtanθ′sinθ
) θ′=sin ^-1 (sinθ/η). Here, if the incident light beam to the half mirror travels from left to right on the paper as shown, α is positive when measured clockwise. Therefore, the light semi-transparent surface 1 is adjusted by the angle α that satisfies the above equation (5).
By adopting a configuration in which the opposing surface 10c is inclined with respect to 0b, a ghost can be superimposed on the normal image formed by the light beam reflected by the half mirror 10. That is, in the finder device shown in FIG. 1, by adopting a configuration in which the opposing surface 10c is inclined with respect to the light semi-transmissive surface 10b of the half mirror 10 by the angle α determined from above, ghosts in the field frame image can be eliminated. can be superimposed on the regular image of the viewing frame so that the ghost does not obstruct observation even when looking through the viewfinder.

Next, using FIG. 2b, the inclination of the opposing surface 10c for superimposing the ghost on the regular image formed by the light beam transmitted through the half mirror 10 is determined. In FIG. 2b, the light ray b incident on the light semi-transmissive surface 10b of the half mirror 10 is
0b, and is split into a transmitted beam b ₁ and a reflected beam b ₂ . The refraction angle at this time is θ, and the reflection angle is θ'. Since the transmitted light ray _b1 travels straight, when viewed from the observation position side, that is, from the direction of arrow A,
An image point F' formed by the transmitted light beam b ₁ is located on a straight line that includes the transmitted light beam b ₁ . On the other hand, the reflected light beam b ₂ travels through the substrate 10a and is emitted outside the half mirror 10 from a point P' on the opposing surface 10c, but a part of it is reflected at the point P' and passes through the light semi-transparent surface 10b. and is ejected to the outside of the half mirror 10. If the opposing surface 10c is parallel to the semi-transparent surface _10b as shown by the dashed line in FIG.
The ray reaches point R on 0b and passes through the surface 10b.
b ₂ ″ and is emitted from the half mirror 10.
Since the light semi-transparent surface 10b and the opposing surface 10c are parallel, the light beam b ₂ ″ is parallel to the transmitted light beam b ₁ ,
Therefore, the ray b ₂ ″ is the image point of the transmitted ray b ₁
Since it does not appear to be emitted from F′, it forms a ghost.

Therefore, the opposing surface 10
When c is tilted at an angle α', the light ray reflected at the point P' on the opposing surface 10c becomes a ray b ₃ and reaches the point R' on the light semi-transparent surface 10b, and at the point R' the refraction angle θ It is refracted by `` and becomes a ray b ₃ ′, which passes through the half mirror 1.
0, and this ray b ₃ ' is the transmitted ray b ₁
appears to be emitted from image point F′. Here, the distance of O'F' is l' (however, l' is positive when the image point F' is closer to the observation position than the half mirror 10).
The thickness of the half mirror 10 at point P' is d, the refractive index of the transparent material constituting the substrate 10a is η, and as shown in the figure, ∠F′O′=γ, ∠R′F′O′=γ′ Then, γ＝tan ^-1 (2dtanθ′cosθ／−l′＋2dtanθ′sinθ
) − (6) θ″=θ+γ′ −(7) Furthermore, from Snell's law at points O′ and R′, sinθ=ηsinθ′ −(8) ηsin(θ′+2α′ )=sinθ″−(9) The following relationship is obtained. Here, since l′ is generally sufficiently large compared to d, if we set it as γγ′, then equation (7) becomes θ″θ+γ, and equation (9) becomes ηsin(θ′+2α′) sin(θ+γ). .Therefore, α′1/2 [sin ^-1 {sin (θ+γ)/η}−θ′]
―(10) However, γ＝tan ^-1 (2dtanθ′cosθ／−l＋2dtanθ′sinθ
) θ′=sin ^-1 (sinθ/η). Here, if the incident light beam to the half mirror 10 travels from left to right on the paper, α' is positive when measured clockwise. Since equation (10) is exactly the same as equation (5) when using transmitted light, set the angles θ, θ′, θ″ as described above, and set l=l′, β=γ,
When β'=γ', α obtained by equation (5) matches α' obtained by equation (10).

Therefore, when a ghost is superimposed on a normal image formed by a light beam reflected by the half mirror 10, when a ghost is superimposed on a normal image formed by a light beam transmitted through the half mirror 10, Also, α1/2 [sin ^-1 {sin (θ+β)/η}−θ′]—
(11) β＝tan ^-1 (2dtanθ′cosθ／−l＋2dtanθ′sinθ
) θ′=sin ^-1 (sinθ/η). However, here, assuming that the incident light beam to the half mirror travels from left to right on the paper surface as shown in the figure, α is positive when measured clockwise, and η: constitutes the substrate 10a. refractive index of the transparent substance θ; reflection angle or refraction angle of the light ray that is first emitted outside the half mirror 10 from the light semi-transmissive surface 10b; d; Thickness l: Distance from the intersection of the light beam first emitted from the light semi-transmissive surface 10b to the outside of the half mirror 10 with the light semi-transmissive surface 10b to the image point F',
A case where the image point F' is closer to the observation position than the half mirror 10 is defined as positive. This relationship holds true regardless of the angle θ, and also holds true when the image point is closer to the observation position than the half mirror, such as in a single-lens reflex camera or a finder device of a single-lens spotmeter.

In an inverted Galilean finder device having a daylight bright frame as shown in Figure 1, each optical element is set so that the diopter of the viewing frame optical system and the diopter of the finder optical system are approximately equal. Therefore, the light semi-transparent surface 10 is placed so that the ghost is superimposed on the normal image of the viewing frame.
By using the half mirror 10 having the opposing surface 10c tilted by the angle α determined by the above equation (11) with respect to b, the ghost can also be superimposed on the subject image.

FIG. 3 shows the optical system of a single-lens reflex camera according to another embodiment of the present invention, in which 12 is an objective lens, and 14 is a substrate 14a.
One surface is coated with a light semi-transparent film to form a light semi-transparent surface 14b, and the opposing surface 14c is the light semi-transparent surface 1.
Half mirror tilted at an angle α with respect to 4b, 1
6 is a light-receiving element arranged to photometer the light transmitted through the half mirror 14, 18 is a condenser lens, 20 is a pentaprism, and 22 is an eyepiece lens. Here, the angle α is a value that satisfies the above equation (11), and by configuring it in this way, the ghost can be superimposed on the normal image formed by the objective lens 12 on the focal plane. The ghost can be prevented from obstructing observation.

Next, substitute the actual numerical value into the above equation (11) and calculate the angle α.

(i) In the finder optical system of an inverted Galilean finder device with a daylight bright frame, l = -25 mm, d = 1.2 mm, η = 1.515, θ
= π/4, then α=31'.

(ii) In the finder device of a single-lens reflex camera, if l = 20 mm, d = 1.2, η = 1.515, and θ = π/4, then α = -43'. These calculated values almost match the values 30′ and −42′ actually found from the ray tracing results, so by setting the angle α to satisfy equation (11), the normal image can be calculated. It is clear that the ghost can be superimposed on the Furthermore, in the above embodiment, since the angle α is minute, it has almost no effect on aberrations of the finder optical system.

The present invention is not limited to the above-mentioned embodiments, but is also applicable to a finder device of a spotmeter configured to photometer the light transmitted through a half mirror. For example, in such a spotmeter finder device, l = 13 mm, d = 1.2 mm,
Substituting the numerical values η = 1.515 and θ = π/4 into equation (11) gives α = -1゜09', which is the value α = -1゜05' actually obtained from the ray tracing results. Therefore, even in a spotmeter finder device using a half mirror, by using a half mirror whose opposing surface is tilted by an angle α that satisfies equation (11) with respect to the light semi-transmissive surface, By superimposing the ghost on the normal image to be observed, a finder device can be obtained in which the ghost does not interfere with observation. In addition, in this case as well, the angle α
is so small that it has almost no effect on the aberrations of the finder optical system.

Effects As described above, the present invention provides a finder device having a half mirror in which one surface of a flat substrate made of a transparent material is a semi-light-transmitting surface. In order to superimpose the ghost on the image, the opposing surface of the half mirror facing the light semi-transmissive surface is α1/2[sin ^-1 {sin (θ+β)/η}−θ′ ] β=tan ^-1 (2dtanθ′cosθ/−l+2dtanθ′sinθ
) The ghost is superimposed on the normal image formed by reflection or transmission on the half mirror by tilting it by an angle α determined by θ'=sin ^-1 (sinθ/η). With this configuration, it is possible to obtain a finder device that can observe a clear image without the ghost generated by the half mirror interfering with observation. Furthermore, the finder device of the present invention is significantly different from a conventional finder device having a half mirror in which the half mirror is simply replaced with a half mirror whose opposing surface is tilted at the angle α with respect to the light semi-transmissive surface. With this configuration, it is possible to easily prevent the ghost caused by the half mirror from interfering with observation.

[Brief explanation of drawings]

FIG. 1 is a diagram showing a finder device according to one embodiment of the present invention, FIG. 2 is a longitudinal sectional side view of a main part of a half mirror according to the embodiment, and FIG. 3 is a diagram showing another embodiment of the present invention. 10, 14...Half mirror, 10a, 14a...
Substrate, 10b, 14b...light semi-transparent surface, 10c, 1
4c...Opposing surface.

Claims (1)

[Scope of Claims] 1. In a finder device having a half mirror in which one surface of a flat plate-shaped substrate made of a transparent material is a light semi-transmissive surface, an opposing surface opposite to the light semi-transmissive surface of the half mirror is a light semi-transmissive surface. A finder device characterized in that the ghost is superimposed on a normal image formed by reflection or transmission on the half mirror, which is tilted at an angle α shown by the following formula with respect to the surface: α1/2 [sin ^{- 1} {sin(θ+β)/η}−θ′] However, β=tan ^-1 (2dtanθ′cosθ/−l+2dtanθ′sinθ
) θ'=sin ^-1 (sin θ/η) η: refractive index of the transparent substance θ: angle of reflection or refraction of the light beam first emitted from the semi-transparent surface to the outside of the half mirror d: the opposing surface Thickness l of the half mirror at the point where the light ray is first reflected on the semi-transparent surface; Image point from the intersection of the light ray that is first emitted outside the half mirror on the semi-transparent surface with the semi-transparent surface; (positive when the image point is closer to the observation position than the half mirror).