JPH0365524B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a focus correction device for an autofocus camera, and more specifically, the present invention relates to a focus correction device for an autofocus camera, and more specifically, to a camera equipped with a distance measurement device using triangulation apart from a photographic optical system. This invention relates to a camera focus correction device that corrects out-of-focus that occurs when an after-focus converter is attached.

FIG. 1 shows a light projection type distance measuring device using a triangular distance measurement method in a general camera.

In the figure, reference numeral 1 denotes a light source, and an image of the light source 1 is projected onto a subject 3 by a projection lens 2. Subject 3
The spot image of the light source 1 projected above is formed on the optical position detection element 5 by the light receiving lens 4. At this time, the position of the spot image on the optical position detection element 5 changes depending on the distance to the subject 3. From the light emitting lens 2 and light receiving lens 4, which are distance measuring optical systems, to the subject 3
The following relationship holds true between the distance u to the object and the amount of deviation Δs of the spot image from the reference position. Expressing this in a formula, Δs=f·L/u (1) In this formula (1), f is the focal length of the light projecting lens 2 and the light receiving lens 4, and L is the base line length.

On the other hand, the following relationship holds true between the amount of extension Δt of the photographing lens (not shown) of the camera and the subject distance u. Let f′ be the focal length of the photographing lens,
Expressing this in a formula, Δt=f' ² /u−f' (2) In formula (2), if u≫f', formula (2) becomes as follows.

Δt≒f′ ² /u ...(3) Therefore, from equations (1) and (3), the amount of deviation of the spot image Δs and the amount of extension of the photographing lens Δt are both reciprocals of the subject distance u, and the amount of extension of the spot image Δs It can be seen that the amount Δt is proportional to the spot image shift amount Δs. Therefore,
By detecting the amount of deviation Δs of the spot image by the optical position detection element 5, the amount of extension Δt of the photographic lens can be determined.

FIG. 2 shows a conventional autofocus camera focus correction device using the distance measuring device shown in FIG.

This focus correction device is designed to perform focus correction when an afocal converter for photography is attached to a photography lens.

In the figures, parts or members that are the same or equivalent to those of the distance measuring device shown in FIG. 1 are given the same reference numerals and redundant explanations will be omitted.

In this conventional example, a thin prism 6 is attached to the light receiving lens 4 on the subject 3 side. This thin prism 6 is designed to be able to correct the amount of deviation Δs of the spot image in accordance with the photographing afocal converter attached to the photographing lens.

That is, when a photographing afocal converter with an angular magnification γ is attached to the photographing lens, the composite focal length of the photographing optical system becomes γf'. Therefore, from equation (3), the amount of extension Δt of the photographic lens becomes γ ² f' ² /u, which is γ ² times the amount of extension f' ² /u when no afocal converter is attached.

Therefore, if the amount of deviation Δs of the spot image is multiplied by γ ² , we get
Since the amount of extension Δt of the photographic lens is also γ ² times,
Focus correction will be performed accurately.

Therefore, in this conventional example, as shown in FIG. 2, a thin prism 6 is provided on the subject 3 side of the light receiving lens 4 to change the optical path, and the amount of deviation of the spot image is set to γ ² Δs. Therefore, even if an afocal converter for photographing is attached to the photographic lens, the amount of deviation of the spot image can be adjusted, and focus correction can be performed.

However, in such a conventional camera focus correction device, the amount of the spot image increased by the thin prism 6 does not change even if the object distance u changes, the angle ε at which the optical path of the thin prism 6 changes. Therefore, the object distance u is set at a constant value, for example, 3, so that the amount of deviation of the spot image including the increase due to the thin prism 6 becomes γ ² Δs.
When set to m, focus correction is performed accurately, but as the subject distance u changes, the amount of shift of the spot image that increases due to the thin prism 6 must also change accordingly. Since the amount of deviation of the spot image that increases due to the thin prism 6 is constant, focus correction cannot be performed accurately, and the distance range in which accurate focus can be obtained is narrow. There was a problem that it was over 2m long when used.

This is because, in order to accurately correct the focus, the amount of deviation d of the spot image that increases when the thin prism 6 is attached needs to satisfy the following equation. That is, the total amount of deviation of the spot image including the increase due to the thin prism 6 is γ2Δs= ^γ2・fL/u, and the amount of deviation of the spot image when the thin prism 6 is not attached is Δs=f. - Since L/u, the amount of deviation d of the spot image that increases when the thin prism 6 is attached is expressed by the following equation.

d=γ ²・fL/u−f・L/u=(γ ² −1)f・L/u
...(4) In other words, from this equation (4), d also changes as the subject distance u changes. Therefore, when the object distance u changes, the thin prism 6 changes accordingly.
It is clear that the amount of deviation d of the spot image, which increases with , must also change. However, u
>> When f, d does not change much from equation (4), so the focus correction can be performed almost accurately by providing the thin prism 6.

Furthermore, when a telephoto afocal converter for photographing is attached to a photographing optical system, there is a tendency for atopic to occur because infrared light does not reach the lens at long distances.

This invention was made by focusing on these conventional problems, and it uses an afocal converter for telephoto or wide-angle photography in a camera that has a triangular distance measurement optical system separate from the photographic optical system. SUMMARY OF THE INVENTION It is an object of the present invention to provide a camera focus correction device that, when used in an optical system, has a wide photographable distance range and enables distance measurement with good focusing performance.

In order to achieve such an object, the camera focus correction device of the present invention projects an image of a light source onto a subject using a projection lens, separately from a photographing optical system to which an afocal converter for photographing is attached. In a focus correction device for a camera having a distance measuring optical system using triangular distance measurement, in which a spot image projected on a spot image is formed on an optical position detection element by a light receiving lens, the light emitting lens and the light receiving lens of the distance measuring optical system are Afocal converters for focus correction each having two total reflection surfaces are provided in front of the camera, and the product of the angular magnification of the afocal converters for focus correction and the extension rate of the baseline length is the angular magnification of the afocal converter for photography. It is characterized by being equal to the square of .

The present invention will be explained below based on the drawings.

FIG. 3 is a diagram showing a first embodiment of the present invention. In the drawings, parts or members that are the same or equivalent to those of the conventional example are given the same reference numerals and redundant explanations will be omitted.

This embodiment is a telephoto focus correction device.
Light projecting lens 2 and light receiving lens 4 in the distance measuring optical system
Telephoto afocal converters 9 and 10 each consisting of a single lens are attached to the front surface, which is the side facing the subject 3. This focus correction afocal converter 9 has total reflection surfaces 11 and 12 that are parallel to each other. Further, the focus correction afocal converter 10 also has mutually parallel total reflection surfaces 13 and 14. The optical axis of the light passing between these total reflection surfaces 11 and 12 and between 13 and 14 is parallel to the base line length L. Therefore, the afocal converters 9, 1 for focus correction
By providing 0, the focal length f and base line length L of the light projecting lens 2 and light receiving lens 4 are simultaneously extended.

Since the light source 1 of the distance measuring optical system is a monochromatic infrared ray and is used only near the optical axis, aberrations can be sufficiently corrected even if the focus correcting afocal converters 9 and 10 are single lenses.

In addition, when the telephoto focus correction afocal converters 9 and 10 are used, the effective aperture of the distance measuring optical system increases, so the amount of light incident on the optical position detection element 5 increases, and the distance measuring optical system increases. The maximum possible distance limit is extended.

Next, the effect will be explained.

If, for example, a telephoto afocal converter with an angular magnification γ is attached to the photographing lens of the photographing optical system, the combined focal length of the photographing optical system will be γf'.
Therefore, the amount of extension of the photographic lens is γf′ ² /u
It is clear from the prior art that this is γ ² times the amount of extension f′ ² /u when no afocal converter for photography is attached. If the amount of deviation Δs of the spot image is increased by γ ² times, the amount of extension Δt of the photographing lens will also be increased by γ ² times.

Here, the amount of deviation Δs of the spot image is Δs=f・L/u, as shown in equation (1), and γ ² times that amount is γ ²・Δs=γ ²・f・L/u... (5) This is expressed by equation (5).

From this equation (5), the amount of deviation Δs of the spot image can be increased by γ ² by increasing the focal length f of the distance measuring optical system by γ ² or by increasing the base line length L by γ ² . .

Further, when the angular magnification γ of the distance measuring optical system, that is, the extension rate of the focal length f, is α, and the extension rate of the base length L is β,
The right side of equation (1) is α, β, f, L/u, and the left side is α, β, Δs. Therefore, at this time, α and β
If the relationship ＝γ ² holds true, the amount of deviation of the spot image Δs regardless of the magnitude of the object distance u
can be ^doubled by γ.

Therefore, the product of the extension rate α of the focal length f of the distance measurement optical system and the parsimony rate β of the base line length L is photographed in front of the subject 3 side of the light emitting lens 2 and light receiving lens 4 of the distance measurement optical system. an afocal converter 9 for focus correction equal to the square of the angular magnification γ of the afocal converter for use;
10, two total reflection surfaces 11, 12, and 1 that make the optical axis of the light transmitted inside parallel to the extension of the focal length f of the ranging optical system and the base line length L are provided.
By simultaneously extending the base line length L in steps 3 and 14, the spot image shift amount Δs can be increased by γ2 ^times . This can be detected by the optical position detection element 5 and the amount of extension of the photographing lens can be set to Δt which is γ ² times, so that accurate focus correction can be performed. Since the focus correction afocal converters 9 and 10 simultaneously extend the focal length f of the distance measuring optical system and the base line length L, they are different from those that only extend the focal length f. It is advantageous because it can be small in size, and when the angular magnification γ of the photographing afocal converter attached to the photographing optical system is large, the focus correction afocal converters 9 and 10 attached to the distance measuring optical system are compact. .

This embodiment shows an example in which when a telephoto shooting afocal converter is attached to the photographing optical system, telephoto focus correction afocal converters 9 and 10 are correspondingly provided to the distance measuring optical system. However, it is of course possible to perform similar focus correction by providing a wide-angle photographing afocal converter in the photographing optical system.

As explained above, according to this invention,
In addition to the photographic optical system to which the afocal converter is attached, the image of the light source is projected onto the subject using a light projecting lens, and the light position of the spot image projected onto the subject is detected using a light receiving lens. In a focus correction device for a camera having a distance measuring optical system using triangular distance measurement to form an image on an element, a focus correction device having two total reflection surfaces each in front of a light emitting lens and a light receiving lens of the distance measuring optical system. An afocal converter is provided, and the product of the angular magnification of the afocal converter for focus correction and the extension rate of the base line length is equal to the square of the angular magnification of the afocal converter for photographing, so that the photographing optical system For example, if a telephoto AF focal converter with an angular magnification γ is attached to a telephoto lens, the distance measuring optical system has two total reflection surfaces, and the product of the angular magnification and the extension rate of the base line length is the AF focal length for photography. By providing an afocal converter for focus correction equal to the square of the angular magnification of the focal converter, the focal length f of the ranging optical system and the baseline length are simultaneously extended, and the amount of deviation of the spot image can be reduced. Since Δs can be made ² times γ, the amount of extension of the photographic lens can be made ² times γ, which expands the measurable subject distance range compared to focusing correction using a conventional thin prism, and also allows focusing at long distances. Improves accuracy.

Further, by using a telephoto focus correction afocal converter, the effective aperture of the distance measuring optical system is increased, so the amount of light incident on the optical position detection element is increased, and the maximum distance that can be measured is extended.

Furthermore, since the afocal converter for focus correction has two total reflection surfaces that are parallel to each other, it is possible to simultaneously extend the focal length of the ranging optical system and the base line length. When the angular magnification of the photographic afocal converter attached to the photographic optical system is large, the focus correction afocal converter attached to the distance measuring optical system is compact. This has the effect of making the entire camera smaller.

In addition, when an afocal converter for shooting with a wide angle and an angular magnification γ is attached to the shooting optical system, for example, the distance measuring optical system has two total reflection surfaces parallel to each other, and the angular magnification and the extension rate of the base line length are By providing an afocal converter for wide-angle focus correction whose product is equal to the square of the angular magnification of the afocal converter for photography, the same reason as the afocal converter for telephoto focus correction is provided. Therefore, the range of object distances that can be measured is expanded.

Specifically, when focus correction was performed using a conventional thin prism, the shortest photographing distance was about 2 m, but in this invention, the angular magnification γ of the photographic afocal converter attached to the photographic optical system was is 1.41x for telephoto and 0.71x for wide-angle, and if the shortest shooting distance of the photographic optical system is 0.8m, then when the afocal converter for telephoto focus correction is attached to the distance measuring optical system, The shortest shooting distance is
When a wide-angle focal correction afocal converter is installed, the shortest shooting distance becomes 0.4m to ∞, expanding the range of subject distances.

In addition, when a telephoto focus correction afocal converter is installed, the effective aperture of the distance measuring optical system increases and the amount of incident light from the spot image projected onto the subject increases. You can also measure distances.

[Brief explanation of drawings]

Fig. 1 is a schematic diagram showing the optical system of a conventional light projection type distance measuring device, Fig. 2 is a schematic diagram showing the optical system of a camera focus correction device, and Fig. 3 is a schematic diagram showing the optical system of a camera focus correction device according to the present invention. FIG. 2 is a schematic diagram showing a main part of an optical system in one embodiment. 1... Light source, 2... Light emitting lens, 3... Subject, 4... Light receiving lens, 5... Optical position detection element,
9,10...Focus correction converter, 11,1
2, 13, 14... Total reflection surface.

Claims (1)

[Scope of Claims] 1. An image of a light source is projected onto a subject by a projecting lens, separately from a photographing optical system to which an afocal converter for photographing is attached, and a spot image projected onto the subject is transmitted to a receiving lens. In a focus correction device for a camera having a distance measuring optical system using triangular distance measuring to form an image on an optical position detection element by means of a triangular distance measuring system, the distance measuring optical system includes two total reflection lenses in front of each of a light emitting lens and a light receiving lens of the distance measuring optical system. An afocal converter for focus correction having a surface is provided, and the product of the angular magnification of the afocal converter for focus correction and the extension rate of the base line length is equal to the square of the angular magnification of the afocal converter for photographing. A camera focus correction device featuring: