JPH09218344A - Focus detecting device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To reduce the influence of a chromatic aberration on focus detection precision as much as possible on the ultraviolet side. SOLUTION: An infrared cutting filter 2 arranged in a focus detection optical system cuts light on a longer wavelength side than about 710nm as infrared-side light and also cuts light on a shorter wavelength side than about 450nm a little longer than the lower limit of specific luminous efficiency on the short- wavelength ultraviolet side. Consequently, the influence of the chromatic aberration of a photographic lens becomes small on both the long-wavelength side and short-wavelength side and the influence of the chromatic aberration is reduced.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a secondary image formation phase difference type focus detection device used in a camera or the like, and an infrared cut filter for cutting light in an infrared region is arranged in a focus detection optical system. The present invention relates to a focus detection device.

[0002]

2. Description of the Related Art Generally, in a focus detection device of a secondary imaging phase difference system, an object image formed by a taking lens is
The first and second secondary imaging lenses cause re-imaging on the first and second line sensors, and the first and second
The focus state of the photographing lens is detected from the relative shift of the secondary object image re-formed on the line sensor.

Here, C used as a line sensor
A photoelectric conversion element such as a CD generally has a peak of spectral sensitivity in a long wavelength region of infrared rays, and cuts light in an infrared region in a focus detection optical system for correction of relative luminous efficiency with human eyes. The filter (infrared cut filter) is required. As this infrared cut filter, a reflection type filter made by coating a glass substrate with a multilayer film is often used. There are various possible places for arranging the infrared cut filter, but it is often arranged in front of the field mask and the field lens near the primary focal plane of the taking lens.

Regarding the spectral characteristic of this infrared cut filter (which wavelength range of light is transmitted), when the subject has low brightness or low contrast, auxiliary light for illuminating the subject for focus detection is emitted. One proposal is made in Japanese Examined Patent Publication No. 7-86582 in relation to the device. Among them, firstly, it is desirable that the spectral sensitivity of the light receiving unit for focus detection is sensitive only to visible light so as not to be affected by the chromatic aberration of the taking lens, as long as it is premised on photographing with visible light. However, it is desirable to use an infrared light region that is out of the visible light region as much as possible for the auxiliary light so that the person who is the subject does not feel dazzling. Above, a wavelength longer than about 650 nm (nanometer) is used for the auxiliary light, and the light receiving unit for focus detection has sensitivity up to about 750 nm where the influence of the chromatic aberration of the photographing lens is allowable. ” FIG. 4 shows the above Japanese Patent Publication No. 7-86582.
FIG. 5 shows the relative spectral sensitivity (spectral transmittance) of the focus detection light receiving unit proposed in Japanese Patent Publication No. Show. Since the wavelength of the light projected as the auxiliary light is on the longer wavelength side than 650 nm due to the auxiliary light filter,
Focus detection with auxiliary light is performed with light having a wavelength between 650 nm and 750 nm.

[0005]

However, there are the following problems in the spectral characteristics of the light receiving portion for focus detection in the above technique. Cut wavelength in long wavelength range (infrared side) = 750
nm is a little too long. No consideration is given to the ultraviolet region, which is a short wavelength.

With respect to the cut wavelength of 750 nm in the long wavelength range, the precision of focus detection using auxiliary light, the focus detectable distance, and the size of the focus detection error due to the chromatic aberration of the photographing lens under artificial illumination are in balance. It is set. Generally, in chromatic aberration correction (so-called achromatism) in optical design of lenses, F line (486 nm) and C line (656 nm)
Design to minimize the difference in aberrations of.
However, with the increasing number of zoom lenses in recent years, in order to reduce the difference in aberration between the F-line and the C-line within the range in which the focal length changes, a short wavelength range per g-line (435.8 nm) and a long wavelength range per 720 nm are required. Aberrations in the wavelength range may become large at a specific focal length. With such a lens, even if there is no practical problem under natural light,
At a focal length where the aberration of light in the short wavelength region / long wavelength region becomes large, the influence of the aberration on the focus detection accuracy becomes large under an artificial light source that contains a large amount of light in the wavelength of such region.

First, in order to reduce the influence of aberration in the long wavelength region, the cut wavelength on the long wavelength side should be shorter than 750 nm. In this case, focus detection with auxiliary light becomes a problem, but light sources such as LEDs used for auxiliary light have recently been developed to have high brightness, such as a high brightness type. Even if the range of wavelengths used is narrow, focus detection has become possible in a practical range. Therefore, at present, even when the focus detection is performed with the auxiliary light, it is customary to set the spectral sensitivity of the focus detection light receiving unit to about 710 nm on the long wavelength side. Further, if focus detection by auxiliary light is not performed, it is preferable to set the thickness to about 680 nm in order to further reduce the influence on the focus detection accuracy such as chromatic aberration in the long wavelength region of the lens.

By the way, if the influence of the chromatic aberration in the long wavelength region is reduced in this way, the wavelength region in the relatively short wavelength region (outer ultraviolet region)
The influence of the chromatic aberration becomes larger. This is the problem mentioned above. As long wavelength range is up to about 750 nm, the focus detection accuracy under the artificial light source is deteriorated because the chromatic aberration in the long wavelength range of the lens is large quantitatively. It doesn't matter much. However, when the influence of chromatic aberration in the long wavelength region is reduced, that is, when the long wavelength side of the spectral sensitivity of the focus detection light receiving unit is shortened, the chromatic aberration per g-line (435.8 nm) in the short wavelength region is reduced. The influence on the focus detection accuracy cannot be ignored. Therefore, in the focus detection light receiving section having a spectral sensitivity from 400 nm or less as shown in FIG. 4, focus detection error under artificial illumination having a wavelength component different from that of natural light poses a problem.

The present invention has been made to solve such a problem, and an object of the present invention is to provide a focus detection apparatus capable of minimizing the influence of chromatic aberration on the focus detection accuracy even in the ultraviolet region. To do.

[0010]

In order to achieve such an object, a first invention (an invention according to claim 1) is a secondary imaging phase difference type focus detecting apparatus, wherein infrared light is An infrared cut filter having a spectral transmittance that cuts and cuts light on the short wavelength side including at least the g-line is arranged in the focus detection optical system. According to the present invention, the infrared cut filter arranged in the focus detection optical system cuts the light on the infrared side and includes at least the g-line which is slightly longer than the lower limit of the relative visibility in the ultraviolet region of the short wavelength. Light on the short wavelength side is cut.

The second invention (the invention according to claim 2) is the first invention.
In the invention, the light on the short wavelength side including at least the g-line that is cut by the infrared cut filter is the light on the shorter wavelength side than about 450 nm. According to this invention, the infrared cut filter arranged in the focus detection optical system cuts the light on the infrared side, and is slightly longer than the lower limit of the relative luminosity in the ultraviolet region of a short wavelength of about 450 nm. Light on the short wavelength side is cut.

The third invention (the invention according to claim 3) is the first
In the invention, the infrared light cut by the infrared cut filter is light having a wavelength longer than about 710 nm. According to the present invention, the infrared cut filter arranged in the focus detection optical system cuts the light on the longer wavelength side of about 710 nm as the light on the infrared side, and at the same time, it compares the light in the ultraviolet region of the short wavelength. Light on the short wavelength side including at least g-line, which is slightly longer than the lower limit of sensitivity, is cut.

A fourth aspect of the invention (the invention according to claim 4) is a secondary imaging phase difference type focus detection device, wherein light on a longer wavelength side than a set wavelength set as a value of 700 nm or less is infrared side. In addition, an infrared cut filter having a spectral transmittance that cuts light having a wavelength shorter than about 450 nm is arranged in the focus detection optical system. According to the present invention, by the infrared cut filter arranged in the focus detection optical system, for example, light on the longer wavelength side of about 680 nm is cut as infrared light, and at the short wavelength ultraviolet side, Light on the shorter wavelength side of about 450 nanometers, which is slightly longer than the lower limit of luminosity, is cut.

The fifth invention (the invention according to claim 5) is the fourth invention.
In the invention, when the infrared cut filter is arranged in the focus detection optical system, the auxiliary light is not used during focus detection. According to the present invention, auxiliary light is not used during focus detection, and light having a wavelength longer than about 680 nm is cut as infrared light by the infrared cut filter disposed in the focus detection optical system. In addition, light on the shorter wavelength side of about 450 nm, which is slightly longer than the lower limit of the relative luminous efficiency in the ultraviolet region of the short wavelength, is cut.

[0015]

DESCRIPTION OF THE PREFERRED EMBODIMENTS The present invention will be described below based on embodiments. [Embodiment 1: Use auxiliary light for focus detection] FIG.
Is the relative spectral sensitivity (spectral transmittance) of the infrared cut filter arranged in the focus detection optical system of the focus detection apparatus according to the present invention.
FIG. In this embodiment, in order to reduce the influence of aberration of light near the g-line (435.8 nm), light on the short wavelength side is cut at about 450 nm. On the long wavelength side, auxiliary light is used at the time of focus detection, and it is set to about 710 nm.

That is, in this embodiment, as the auxiliary light is used for focus detection, the infrared cut filter arranged in the focus detection optical system converts the light on the longer wavelength side from about 710 nm to the infrared light. In addition, the light on the shorter wavelength side of about 450 nm, which is slightly longer than the lower limit of the relative luminous efficiency in the ultraviolet region of the short wavelength, is cut.

According to this embodiment, since the cut wavelength is set so as to reduce the influence of the chromatic aberration of the taking lens on both the long wavelength side and the short wavelength side, the focus detecting device is less susceptible to the chromatic aberration. . In this embodiment, the light on the short wavelength side is cut at about 450 nm, but it is sufficient to cut the light on the short wavelength side including at least the g-line, and the light is not limited to about 450 nm. Absent.

[Second Embodiment: Auxiliary Light is Not Used in Focus Detection] FIG. 2 shows the relative spectral sensitivity (spectral transmittance) of the infrared cut filter arranged in the focus detection optical system of the focus detection apparatus according to the present invention. It is a figure which illustrates. In this embodiment, in order to reduce the influence of aberration of light near the g-line (435.8 nm), light on the short wavelength side is cut at about 450 nm. On the long wavelength side, the set wavelength is set to 680 assuming that auxiliary light is not used during focus detection.
It is set to about nm.

That is, in this embodiment, it is assumed that the auxiliary light is not used at the time of focus detection, and the infrared cut filter arranged in the focus detection optical system is used to provide 680 nm.
The light on the longer wavelength side is cut as the light on the infrared side, and the light on the shorter wavelength side than about 450 nm, which is slightly longer than the lower limit of the relative luminosity in the ultraviolet region of the short wavelength, is cut.

According to this embodiment, since the cut wavelength is set so as to reduce the influence of the chromatic aberration of the taking lens on both the long wavelength side and the short wavelength side, the focus detecting device is less susceptible to the chromatic aberration. . In this embodiment, the light on the short wavelength side is cut at about 450 nm, but it is sufficient to cut the light on the short wavelength side including at least the g-line, and the light is not limited to about 450 nm. Absent.

FIG. 3 shows an example in which the infrared cut filter of the above two examples (Embodiment 1 and Embodiment 2) is incorporated in a focus detection device. An infrared cut filter 2 is arranged immediately behind the field lens 1 (between the field lens 1 and the reflection mirror 3). Of course, infrared cut filter 2
Is not limited to this location, and may be at the position of the cover glass 5 on the front surface of the field lens 1 (in that case, the infrared cut filter also serves as the cover glass), or on the front surface of the secondary imaging lens 4. You may make it arrange | positioned at the etc.

Further, when focus detection is performed in a plurality of areas on the screen, the cut wavelengths on the outer side of the ultraviolet may be different depending on the areas. By doing so, it is possible to reduce the influence of chromatic aberration in the area outside the optical axis where various aberrations are large and the focus detection accuracy tends to be inferior to the center of the screen, and it is possible to improve the focus detection accuracy in the area outside the optical axis.

[0023]

As is apparent from the above description, according to the present invention, the infrared cut filter arranged in the focus detection optical system allows the infrared rays to be at least slightly longer than the lower limit of the relative luminous efficiency in the ultraviolet region of the short wavelength. Light on the short wavelength side including the g-line is cut, and the influence of chromatic aberration on the focus detection accuracy can be minimized even in the ultraviolet region.

[Brief description of drawings]

FIG. 1 is a diagram (first embodiment) illustrating a relative spectral sensitivity (spectral transmittance) of an infrared cut filter arranged in a focus detection optical system of a focus detection device according to the present invention.

FIG. 2 is a diagram (second embodiment) illustrating the relative spectral sensitivity (spectral transmittance) of an infrared cut filter arranged in a focus detection optical system of a focus detection device according to the present invention.

FIG. 3 is a vertical cross-sectional view showing a main part of a focus detection device incorporating an infrared cut filter according to the present invention.

FIG. 4 is a diagram showing a relative spectral sensitivity (spectral transmittance) of a light receiving unit for focus detection in a conventional focus detection device.

FIG. 5 is a diagram showing a relative spectral sensitivity (spectral transmittance) of a filter for auxiliary light in a conventional focus detection device.

[Explanation of symbols]

1 ... Field lens, 2 ... Infrared cut filter, 3 ...
Reflection mirror, 4 ... Secondary imaging lens, 5 ... Cover glass.

Claims (5)

[Claims] 1. An object image formed by a taking lens,
The first and second secondary imaging lenses cause the first and second
Secondary imaging phase difference for refocusing the image on the line sensor and detecting the focus state of the photographing lens from the relative shift between the secondary object images refocused on the first and second line sensors. In the system focus detection device, an infrared cut filter having a spectral transmittance that cuts light on the outside of red and cuts light on the short wavelength side including at least the g-line is arranged in the focus detection optical system. A focus detection device. 2. The infrared cut filter according to claim 1, wherein the short-wavelength side light including at least g-line is 450
A focus detection device that cuts light on the shorter wavelength side of about nanometers. 3. The focus detection device according to claim 1, wherein the infrared cut filter cuts light having a wavelength longer than about 710 nm as infrared light. 4. An object image formed by a taking lens,
The first and second secondary imaging lenses cause the first and second
Secondary imaging phase difference for refocusing the image on the line sensor and detecting the focus state of the photographing lens from the relative shift between the secondary object images refocused on the first and second line sensors. In the system focus detection device, spectral transmission that cuts light on the longer wavelength side than the set wavelength set as a value of 700 nanometers or less as infrared light and cuts light on the shorter wavelength side of about 450 nanometers A focus detection apparatus, wherein an infrared cut filter having a refractive index is arranged in a focus detection optical system. 5. The focus detection device according to claim 4, wherein when the infrared cut filter is arranged in the focus detection optical system, auxiliary light is not used during focus detection.