JPH03174129A - Camera - Google Patents

Abstract

PURPOSE:To perform autofocusing in a TTL system without imparing the merit of a compact camera which is small-sized and low-priced by providing a half prism between the backmost position of a photographing lens and a shutter. CONSTITUTION:A luminous flux for range-finding which is transmitted through a photographing lens 1 is bent before it is transmitted through the shutter 4, that is, on the objective side of the shutter 4, by the half prism 3. Then, it does not pass the shutter 4 but bypasses it to be guided to a focus detecting device 2. In such a case, the luminous flux is allowed to reach a film surface because the half prism 3 transmits the photographing luminous flux. Even though the TTL system is adopted in spite of a lens shutter type camera, the action of the shutter combined with a diaphragm in the case of autofocusing is made unnecessary and a mechanism for performing the above action is also made unnecessary, thereby miniaturizing the camera itself and simplifying the mechanism.

Description

[Detailed description of the invention] [Industrial application field]

The present invention relates to a camera, and more particularly to a lens-shutter type camera equipped with a TTL focus detection device.

[Conventional technology]

Many examples of single-lens reflex cameras that are equipped with a focus detection device and perform autofocus are already known. - Focusing of an eye reflex camera has traditionally required high precision, and a so-called TTL type focus detection device has been adopted in which detection is performed using light that has passed through a photographic lens. On the other hand, there is a strong demand for compact cameras that employ lens shutters, which are generally referred to as compact cameras, to be smaller and lower in price. Therefore, TTL focus detection devices are not used, and external light-type distance measuring devices are used instead. It was common to use zone focusing. However, in recent years, even compact cameras have become expensive. As the demand for higher focusing accuracy increases, lenses that employ the TTL method are appearing even though they are lens shutter types.

[Problem to be solved by the invention]

By the way, as mentioned above, in order to employ the TTL method even though it is a lens shutter type, conventionally, a reflecting mirror that guides light for distance measurement to a focus detection device is installed behind the shutter. Therefore, the shutter is opened to perform focus detection even when not photographing, and therefore a separate light-shielding plate is required to block exposure of the film. In conventional cameras of this type, the shutter is once closed when photographing, then the light shielding plate is opened, and the shutter is opened again to expose the photograph. Also, when the exposure is complete,
An extremely complex operation is performed in which the shutter is closed, the light shielding plate is closed, and then the shutter is opened again. In order to perform such complex operations, the mechanism itself has to become complex and large, which results in the loss of the original advantages of compact cameras, such as compactness and low cost, in conventional cameras of this type. Was. The present invention has been devised in view of the above-mentioned conventional technical problems and to effectively solve them. SUMMARY OF THE INVENTION Therefore, an object of the present invention is to provide a camera that can perform TTL autofocus without sacrificing the original advantages of a compact camera, such as being small and inexpensive due to a simplified mechanism.

[Means to solve the problem]

The camera according to the present invention solves the conventional technical problems as described above, and is configured as follows in order to achieve the object. That is, in a camera having a lens barrel installed behind the rearmost position of the photographic lens, a half prism is used that allows the photographing light beam to reach the film surface and guides the distance measuring light beam to the focus detection device by bypassing the shutter. mosquito,
It is provided between the rearmost position of the photographic lens and the shutter. (Although the present invention employs a configuration that detects the focusing state of the photographic lens, in the following description, this is also referred to as distance measurement.)

[Effect]

In the camera according to the present invention, 1. The distance measuring light beam that has passed through the photographic lens is bent by a half prism before passing through the shutter, that is, on the object side of the shutter. Due to this, the light flux for distance measurement is sharp. Instead of passing through the light, it bypasses it and is guided to the focus detection device. Since the half prism transmits the photographing light flux, this light flux is allowed to reach the film surface. Furthermore, since the number of optical members passing through after the optical path is divided by the half prism is reduced, distance measurement errors caused by errors in these optical members are also reduced. In particular, in a camera having a bifocal optical system, an auxiliary lens group that enters and exits the optical system to configure the photographing optical system at each focal point is located at the center of the above-mentioned half prism. Since the auxiliary lens group moves in and out of the position on the subject side, the accuracy of distance measurement does not deteriorate compared to the case where the auxiliary lens group moves in and out after the shutter.

【Example】

A preferred embodiment of the present invention will be described below with reference to FIGS. 1 to 10. FIG. 1 is a diagram showing a photographing optical system and a focusing optical system of an embodiment of a camera according to the present invention, viewed from the longitudinal cross-sectional direction of the camera. still,
Here, the focusing optical system refers to an optical system that guides a distance measuring light beam to a focus detection device. In the figure, 1 is a photographic lens group of a photographic optical system, and 2 is a focus detection device. Reference numeral 3 denotes a half prism, which has a semi-transparent surface 5 for bending the distance measuring light beam that has passed through the photographic lens group 1 and guiding it to the focus detection device 2 . 4 is a shutter that also serves as an aperture, and 6 is a total reflection mirror that forms a pair with the semi-transparent surface of the half prism 3 and guides the distance measuring light beam to the focus detection device 2. To give an overview of the operation of the camera according to the present invention, first, the amount of depression of the release button is divided into two levels, and when the release button is depressed one level, the switch of the first level is turned on. This first stage switch is a switch that starts photometry and focusing of the camera, and when it is turned on, preparation for photographing is automatically completed. Then, in this state, the operating state of the second stage switch is determined. The second stage switch is turned on by pressing the release button one more step, opening and closing the shutter 4, which also serves as an aperture, for accurate exposure, and then winding the film after the exposure is complete to start the next shot. Prepare as much as possible. The series of exposure operations is thus completed. FIG. 2 is a diagram showing the optical system of the focus detection device (AF element) 2 and the photographing optical system developed along the optical axis and viewed from above the camera. In FIG. 2, a mirror 6 is arranged with an inclination of 45° in front of the intended imaging plane (F), which is located at a position equivalent to the film plane with respect to the photographing lens 1'. A rectangular opening 6a is formed to define a field of view for detection. A condenser lens L0 is arranged behind the intended image plane (F), and further behind that a pair of re-imaging lenses L, , L, are arranged on the optical axis (C) of the photographic lens 1'. arranged symmetrically. These pair of re-imaging lenses L, , L, are the photographing lens 1
'Thus, the image formed on the planned imaging plane (F) is re-imaged. A mirror Ml is arranged with an inclination of 45° between the condenser lens L0 and both re-imaging lenses L+, Lt. is further bent by 90 degrees to make it perpendicular to the optical axis (12) (see Figure 3).The arrows indicated by (A), (B), and (C) in Figure 2 indicate the direction of the photographing lens l. The front-focus image, the focused image, and the rear-focus image formed by (C
): (A , ), (A t), (
B , ), (B ri, (C, ). (C2) are formed as the first image and second image, respectively. Here, (A), (B), and (C) are indicated by upward arrows in the figure. When the images are formed as shown, the corresponding first images are formed.
．． The second image is formed as an image indicated by both downward arrows, and the first... The interval between the second images changes depending on the focus adjustment state of the photographing lens 1'. Therefore, the reimaging lenses L, ,L
With respect to 1' focus adjustment state can be detected. Furthermore, M
,,M. is an aperture mask placed in front of the re-imaging lens L, ,L. The part indicated by 7 in FIG. 3 represents the area through which the distance-measuring light flux passes on the semi-transparent mirror surface. FIG. 4 is a diagram showing an embodiment of the camera of the present invention having a bifocal photographing optical system, as seen from the longitudinal cross-sectional direction of the camera. Figure 4 (
Fig. 4(b) shows a configuration in which a wide-angle photographing optical system is formed, in which a main lens group 1'', a half prism 3, and an aperture shutter 4 are arranged in this order. Fig. 4(b)
2 shows a configuration in which a photographing optical system on the telephoto side is formed, in which a main lens group 1'', an auxiliary lens group 8, a half prism 3, and an aperture shutter 4 are arranged in order. Auxiliary lens group 8 is placed between the ″ and half prism 3.
is inserted perpendicular to the optical axis. In other words, no matter which focal length the photographing optical system is configured, the half prism 3 is located at the rearmost position of all the photographing lens groups and in front of the shutter 4. When inserting the auxiliary lens group 8 to this position, the main lens group 1'' moves toward the subject on the optical axis, and the auxiliary lens group 8 is inserted into the space formed between the main lens group l'' and the half prism 3. Just insert l! 5t, it is possible to prevent errors in the auxiliary lens group 8 when forming the telephoto side photographing optical system from remaining as distance measurement errors in the focusing optical system. In other words, in a conventional lens-shutter type camera with a bifocal optical system, an auxiliary lens group is inserted on the image side of the diaphragm-shutter. When inserting the group 8, if the same configuration as before is adopted and it is inserted on the image side of the shutter 4, the distance measuring light beam will not pass through the auxiliary lens group 8 but will be guided to the focus detection device 2. Therefore, it becomes impossible to measure the distance at the shooting focal length. Distance measurement at the photographing focal length is possible by providing a dedicated auxiliary lens in the distance-measuring light beam, but optical errors may occur between the auxiliary lens group 8 and the auxiliary lens in the distance-measuring light beam. Since this is unavoidable, autofocus accuracy will be reduced. In addition, since the distance-measuring light flux guided to the focus detection device 2 is guided to the focus detection device 2 with the width of the light flux passing through the main lens group 1'' unchanged, the distance-measuring light flux is equivalent to the telephoto side optical system. An unbalance will occur where the width is either too large or too small compared to the f5 aperture.In the embodiment shown in Fig. 4, a negative power rear converter is inserted as the auxiliary lens group 8 Although we have shown an example in which the auxiliary lens group 8 forms a photographing optical system on the telephoto side, it is also possible to construct a photographing optical system on the wide-angle side by inserting a rear converter with positive power. is also possible, and
It is also possible to form a more telephoto or wider-angle photographing optical system by combining positive and negative lenses and placing the auxiliary lens group 8, which has almost no power as a whole, in front of the main lens group 1'', that is, on the subject side. 1 and Table 2 show specific numerical examples of the above-mentioned bifocal optical system. A case is shown in which a rear converter 8 as an auxiliary lens group is inserted between them. f is focal length, FNo is F
number, 2ω is the angle of view, rl and R, are the main lens group 1"
In the rear converter 8, the radius of curvature of the first lens surface counted from the subject side, di and ri, are the axial distances, n and N are the refractive indexes, and ν and T1 are the Abbe numbers. Furthermore, surfaces marked with an asterisk (*) indicate that they are aspherical surfaces. Its shape has an X coordinate in the optical axis direction,
If the y-axis is taken in the direction perpendicular to this and the paraxial radius of curvature is R1, it is expressed as follows. Here, a+ t)+ C+ d+ e+
... are aspheric coefficients, and are as follows. a=0.0 b=o, 48936xlo-5 c=-0, 17436X10-" d=o, 60940X10" e=o, 37639X10-" (hereinafter blank) 1 35 7 93 Table refractive index (Nd) 1. 78560 1.67339 1.71700 1.63980 Arahe number (νd) ν, 42.81 ν, 29.25 ν347.86 T134.55 1.63980 1.85000 T, 34.55 T, 40.04 1. 51680 ν, 64.20 Fig. 5 is a diagram showing the cross-sectional shapes of the main lens group 1'', half prism 3, and shutter 4, and Fig. 6 is an aberration diagram of the main lens group 1'', and (a) is the sine condition. and spherical aberration, (b) shows astigmatism, and (c) distortion. Figure 7 shows the cross section of each part when the rear converter 8 is inserted between the main lens group 1'' and the half prism 3. Figure 8 shows the aberration diagram, where (a) shows the sine condition and spherical aberration, and (b)
) shows astigmatism, and (c) distortion, respectively. FIG. 9 is a perspective view of the half prism 3. Semi-transparent surface 5
In this configuration, for example, only the shaded area in the figure may be used as a semi-transparent mirror, but if the nof prism 3 is placed at the rearmost position of the photographic lens group, the semi-transparent mirror will be placed above the film surface. It is predicted that this will be printed as "vignetting" and will be undesirable in terms of drawing. Therefore, it is possible to deal with this by making the entire slope a semi-transparent mirror, or by applying semi-transparent processing to surfaces other than the slope of the half prism 3. FIGS. 10(4) and 10(5) show a method for creating a half prism. (1) The a and b sides of a flat plate-like transparent material, such as glass, are polished and cut and polished so as to form an inclined surface approximately in the center thereof. (2) Perform semi-transparent treatment on the slope C. (3) Glue the slope C and repolish surfaces a and b. The semi-transparent processing performed here is performed on the a-plane and slope C of the upper half of the block, and the b-plane of the lower half of the block. Possible treatments include forming a multilayer dielectric film, performing partial vapor deposition of aluminum, or forming a thin film of silver. Normally, when the slope C is constructed of a multilayer film, it is constructed taking into consideration the oblique incidence characteristics of 45°, but the a-plane of the upper half block and the b-plane of the lower half block are sloped in consideration of the normal incidence characteristics. It is also conceivable to have a film structure with characteristics different from those of C. By configuring the focusing optical system in the camera of the present invention as described above, the distance measuring light beam is guided to the light receiving element array of the focus detection device without passing through the shutter 4.
Autofocusing using the TTL method can be performed at all times regardless of the operation of the shutter 4. Therefore, the shutter 4 only needs to be opened and closed for exposure, and the mechanism for this purpose can be made smaller and simpler than a conventional compact camera.

【Effect of the invention】

As is clear from the above description, the present invention provides the following excellent effects. In other words, even if a lens-shutter type TTL method is adopted, the operation of the shutter that also serves as an aperture is unnecessary when performing autofocus, and the mechanism for this is also unnecessary, making it possible to downsize the camera itself and improve its mechanism. Simplification is achieved.

[Brief explanation of the drawing]

FIG. 1 is a diagram showing the photographing optical system and focusing optical system of an embodiment of the camera according to the present invention, viewed from the vertical cross-sectional direction of the camera, and FIG. 2 shows the photographing lens and the focusing optical system. Figure 3 shows the expanded view from above the camera.
FIG. 2 is a perspective view showing the photographing lens and focusing optical system shown in the figure. Fourth
The figure is a diagram showing a photographing optical system and a focusing optical system when the camera according to the present invention has a bifocal optical system, as viewed from the longitudinal cross-sectional direction of the camera. FIG. 5 is a diagram showing cross-sectional shapes of the main lens group, half prism, and shutter in FIG. 4. FIG. 6 is an aberration diagram of the main lens group. Figure 7 shows the rear lens between the main lens group and the half prism.
A diagram showing the cross-sectional shape of each part when the converter is inserted,
FIG. 8 is an aberration diagram of the photographing optical system shown in FIG. 7. FIG. 9 is a perspective view of the half prism. FIG. 10 is a diagram showing a method for creating a half prism. 1... Shooting lens group, lo... Shooting lens, 1".
...Main lens group, 2...Focus detection device, 3...Half prism, 4...Shutter, 5...Semi-transparent surface of half prism, 6...Mirror, 7...Semi-transparent Passage area of the distance measuring light beam on the mirror surface, 8... Auxiliary lens group, e... Optical axis of the photographing lens, F... Planned image forming plane, L
Q... Condenser lens, L l + L 1... Re-imaging lens, Ml... Mirror, M,, M 1... Aperture mask patent Applicant Minolta Camera Co., Ltd. Agent Patent attorney Blue lily ( Figure 3x Figure 5 1# (0) FNO3,5 (b) W word 318° Spherical aberration Sine condition 31-point aberration (C) wlI318@ Distortion% Figure 7 Figure 8 (0) lb ) Spherical aberration Sine condition Astigmatism (C) Distortion 7.

Claims (1)

[Claims] (1) In a camera that has a lens shutter (4) installed behind the rearmost position of the photographic lens (1, 1', 1''), it allows the photographing light flux to reach the film surface and is used for distance measurement. The light flux is bypassed by the shutter (4) and the focus detection device (
The half prism (3) that leads to the photographing lens (1,
1', 1'') and the shutter (4).