JP2006139188A - Photometric system of camera - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a photometric system correcting a photometric value according to the characteristics of a mounted focusing screen in a camera with the interchangeable focusing screen. <P>SOLUTION: In the SLR camera of a focusing glass interchangeable type, the identification of the mounted focusing screen is performed by using a photometric system. A photometric correction value is switched by the kind of the identified focusing screen. The SLR camera is provided with a focusing screen identification mode and discriminates the diffusion characteristics of the mounted focusing screen from the ratio of a photometric sensor output in two prescribed aperture values. <P>COPYRIGHT: (C)2006,JPO&NCIPI

Description

  The present invention relates to a photometric device for a camera capable of exchanging a focus plate.

  In general, in a single-lens reflex camera, a subject image formed by a photographing lens is formed on a focusing plate disposed at an equivalent position to the imaging surface, and the subject image on the focusing plate is corrected through a pentaprism and an eyepiece lens. It has a viewfinder device that magnifies and observes as a real image. Generally, a focusing plate has a diffusing surface on the eyepiece lens side, and a Fresnel lens is formed on the photographing lens side. In order to determine the exposure amount according to the brightness of the subject, a metering sensor and a metering sensor are placed near the exit part of the pentaprism and the eyepiece lens, and the subject image on the focus plate is re-imaged on the light receiving surface of the metering sensor. Thus, the subject brightness is measured based on the output of the photometric sensor corresponding to the subject image.

  Various focusing plates having different diffusion characteristics according to the open Fno of the photographic lens to be mounted and the exit pupil distance have been developed. When a bright lens of Fno is attached to the camera, it is easy to confirm the in-focus state by attaching a focusing plate having a large diffusion characteristic, that is, a large light distribution angle, and a relatively dark lens of Fno is attached to the camera. When attached, a subject image can be observed brighter by attaching a focusing plate having a small diffusion characteristic.

For example, see Patent Document 1.
Japanese Patent Laid-Open No. 11-237657

  However, in a camera that can be mounted by replacing an arbitrary focusing plate from among such various focusing plates, the state of the subject luminous flux that passes through the focusing plate, the amount of transmitted light, etc., due to the diffusion characteristics of the mounted focusing plate Is different. For this reason, if the focus plate is different, the state of the subject luminous flux incident on the photometric sensor, the amount of light, and the like also change, and accurate photometry may not be possible.

  An object of the present invention is to provide a photometric device capable of correcting a photometric value in accordance with the characteristics of a mounted focus plate in a camera capable of exchanging the focus plate.

  The invention according to claim 1, which achieves this object, includes photometric means for receiving subject light flux that has passed through the focus plate and measuring subject brightness, and focus plate holding means for detachably holding the focus plate. The camera has a focus plate identification operation mode for identifying the type of the focus plate, and in this focus plate identification mode, the photometric value is changed by performing a plurality of photometric operations continuously while changing the aperture of the lens. From this, the diffusion characteristics of the focus plate and the Fresnel lens power are identified, and the type of the focus plate is specified. It has control means that selectively uses the correction value corresponding to the identified focus plate, and it is possible to calculate the necessary correction value by photometric operation while changing the aperture even for unknown focus plates of unknown type This is a photometric device for a camera having the above characteristics.

  As described above, in the present invention, it is possible to determine the characteristics of the focus plate mounted using the existing photometry device, and based on the determination result, the photometric correction value corresponding to the diffusion characteristic is used, so that an accurate photometry operation can be performed. It becomes possible.

  The present invention will be described below with reference to the drawings. FIG. 1 is a schematic sectional view showing a configuration around a photometric device of a single-lens reflex camera to which the present invention is applied. A subject luminous flux incident from a photographing lens (not shown) is reflected by the main mirror 6 and is incident on the focus plate 1 and the penta roof prism 2 arranged at a position equivalent to the imaging surface 7. The light beam reflected in the penta roof prism 2 and emitted near the center of the optical axis of the subject light beam passes through the eyepiece lens group 3 and enters the photographer's eyes.

  On the upper side of the eyepiece lens, a photometric lens 4 and a divided photometric sensor 5 constituting a photometric system are arranged. The light beam emitted from the penta roof prism is formed on the split photometric sensor 5 as an image of the focusing plate by the photometric lens 4.

  As shown in FIG. 2, the divided photometric sensor 5 is composed of photoelectric elements divided into 5 × 3, and can divide the area on the focusing plate in a corresponding manner to perform photometry. The brightness of the subject is measured according to the output value of each divided part of the photometric sensor 5, and the necessary exposure amount is determined. Even if the same Fno lens is mounted, the output value of the photometric sensor differs depending on the light distribution characteristic of the focus plate. For the discrimination of the focus plate, the output of the sensor corresponding to the center of the screen indicated by 51 is used. By using the sensor at the center of the screen, the output change due to the pupil position of the photographing lens does not occur, and the subsequent focus plate discrimination operation can be stably performed.

  FIG. 3 shows a main part of the control circuit of this camera. In the illustrated embodiment, the control unit is provided with a control CPU 101 and an LPU 102 that is installed on the photographic lens side and controls the lens as a whole. The LPU on the lens side is connected to and controlled by the diaphragm device 103 and transmits the information in the EEPROM 104 storing the lens specific information to the camera side CPU 101.

  On the other hand, the CPU 101 is connected to an EEPROM 105 as storage means in which data relating to the photometry mode corresponding to the type of the focus plate, exposure correction values, etc. are written, and as a switch means, a main switch 106 for controlling on / off of the power source, A release switch 107 and the like are connected, and operation switches 108 and 109 for changing an aperture value, a shutter speed, and the like, and a photometric sensor 5 are connected. Further, the CPU 101 is connected to a shutter device 110 which is a main function of the camera, and a display device 111 which displays photographing information such as an aperture value and a shutter speed. Further, the mode changeover switch 112 is connected to the CPU 101, and the focus changeover operation mode can be set by operating the mode changeover switch 112. The type of the focus plate identified in the focus plate identification mode is stored in the EEP-ROM 105, and the photometric operation is performed using the photometric correction information unique to the identified focus plate during the photometric operation. The focus plate identifying operation will be described with reference to the flowchart of FIG. The camera operator switches the focus plate of the camera or operates the mode switching device at any time to set the focus plate discrimination mode (step 201), and the camera displays on the display device 111 that the focus plate discrimination mode is set. (Step 202) The camera confirms that the lens is mounted, performs the first photometric operation with the aperture set to the first predetermined value, and stores the first photometric value (step 203). At this time, when a lens capable of determining the lens is not attached and when a brightness higher than a predetermined photometric value cannot be obtained, the process returns to step 202 to confirm with the operator that it is in the determination mode. If an output greater than or equal to the predetermined value is obtained in step 203, the second photometric operation is immediately performed with the aperture set to the second predetermined value, and the second photometric value is stored (step 204). The first photometric value and the second photometric value are compared to determine the mounted focus plate. The determined focus plate type is stored in the EEP-ROM 105.

  Next, the principle of discrimination will be described. The photometric optical system optical axis 9 in FIG. 1 is installed with a predetermined angle with respect to the finder optical axis 8. FIG. 5 schematically shows the viewfinder optical axis with respect to the focus plate and the optical axis of the photometric optical system. Reference numeral 1 denotes a focusing plate, 8 denotes a finder optical axis, 9 denotes an optical axis of the photometric optical system, and forms an angle α with respect to the finder optical axis 8. Reference numeral 10 denotes a light beam incident on the focus plate 1 at an incident angle of 0. The light beam 10 is diffused in the direction of the arrow indicated by a maximum of 12 due to the diffusion characteristic of the focusing screen 1 and forms an angle of β with the finder optical axis 8. On the other hand, when the focusing characteristic of the focusing plate 1 is large, it diffuses in the direction of the arrow indicated by 13 at the maximum and diffuses to the angle of the finder optical axis 8 and β ′. Since α <β ′, the sensor output value corresponding to the center of the screen can be obtained even if the lens Fno is small and no matter how thin rays enter the center of the focus plate. When α> β, when Fno is small and a thin light beam is incident, there is no incident light beam to the photometry system and no output can be obtained. In an actual photographing lens, a light beam incident on the focusing plate is incident not only on an incident angle of 0 but also on a lens plate corresponding to Fno. If the angle between the lens 13 and the finder optical axis is γ, the angle emitted from the focus plate is γ + β due to the diffusion property of the focus plate, and β varies depending on the diffusion property. When γ + β is smaller than the angle α formed with the finder optical axis 8 of the photometric optical system, the light beam incident on the photometric system disappears and the output of the photometric sensor becomes extremely small. Therefore, it is possible to determine the value of β by changing Fno, that is, γ using the lens diaphragm mechanism and searching for γ where the output of the photometric sensor is small (assuming that α is already known). FIG. 6 shows the γ characteristic of the photometric output according to the characteristics of the focus plate. The angle is α = 8 °, β = 5 ° or β = 10 °. When β = 5 °, the output gradually decreases until γ is about 5 °. However, when γ is made smaller than that at 5 °, the output sharply decreases, and when γ = 3 °, the output is almost zero. Become. On the other hand, when β = 10 °, the sensor output value gradually decreases as γ decreases. By comparing the photometric sensor output when γ = 5 ° and the photometric sensor output value when γ = 2 °, it is possible to determine whether the diffusion angle of the mounted focus plate is 5 ° or 10 °. When γ = 5 °, the photometric sensor output is E1, and when γ = 2 °, the photometric sensor output is E2. If E2 / E1≈0, a focus plate of β = 5 ° is mounted. If E2 / E1≈0.2, it can be determined that a focus plate of β = 10 ° is attached.

  The curve shown in FIG. 6 varies depending on the characteristics of the focus plate. If the sensor output corresponding to γ, that is, Fno is measured in advance and the value of E2 / E1 is stored, it is possible to discriminate the focus plate having a plurality of characteristics. .

The figure showing the structure of 1st Example of this invention. The figure showing the photometric sensor which comprises this invention. The figure which shows the control circuit principal part which this invention comprises. The flowchart of a focus board discrimination | determination. The figure which shows the relationship between the optical axis of a photometry optical system, and a focus board diffusion characteristic. The graph which shows the relationship between the photometry output according to an aperture value, and a focus board diffusion characteristic.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Focus plate 2 Penta prism 3 Eyepiece 4 Photometric lens 5 Photometric sensor 6 Main mirror 7 Imaging surface 8 Viewfinder optical axis 9 Photometric optical system optical axis

Claims (1)

  Photometric means for measuring the luminance of the subject by receiving the luminous flux of the subject that has passed through the focus plate and a holding member that allows the focus plate to be attached and detached. The photometric means detects the characteristics of the mounted focus plate, and sets the photometric correction parameters. A camera photometric device comprising parameter determining means for determining based on a focus plate characteristic detection result of the photometric means.

Images