Camera Having an Auto-Focusing Device

1. Field of the Invention

The present invention relates to a single-lens reflex type camera having an auto-focusing device.

2. Related Background Art

A single-lens reflex type camera having an auto-wind mechanism for a film to enable continuous photographing and an auto-focusing device of a TTL focus detection system has been known. In the continuous photographing, exposure to a film and one-frame winding-up of the film are continuously repeated while a release button is depressed. In order to reduce an interval between photographing operations, a photographing lens is stopped at a position set by the auto-focusing device at a time of first frame of photographing and kept at the stopped position until the subsequent photographing operations are completed. In this type of camera, if the release button is depressed in a defocused state at the initial photographing operation, all photographs in the subsequent photographing operations are defocused.

It is an object of the present invention to provide a camera having an auto-focusing device which assures an in-focus state of a photographing lens during a continuous photographing mode.

In order to achieve the above object, in accordance with the present invention, drive of a lens is discontinued prior to an exposure operation in the continuous photographing mode, and the drive of the lens is resumed upon termination of the exposure operation.

The camera of the present invention can inhibit the drive of the lens. In the continuous photographing mode, an interval between the exposure operations when the drive of the lens is inhibited is shorter than an interval between the exposure operations when the drive of the lens is permitted.

FIG. 1 shows a block diagram of an embodiment of the present invention, and

FIGS. 2, 3, 4, 5A and 5B illustrate operations of the embodiment of the present invention.

As shown in FIG. 1, a camera contains a microcomputer (MC) 1 by which auto-exposure (AE) and auto-focus (AF) operations are carried out. The MC 1 usually carries out the AE operation and the AF operation in parallel.

The AF operation is first explained. The MC 1 determines by a signal from a lens detector 6 whether a photographing lens L is an auto-focusing (AF) lens or not, and if it is the auto-focusing lens, a charge storage type charge coupled device (CCD) 2 senses light reflected from an object and an output signal thereof is applied to an A/D converter 3 to convert it to digital data, which is stored in a memory (RAM) in the MC 1. A plurality of photo-diodes are arranged in a line on the CCD sensor 2. The MC 1 processes the object signal stored in the RAM by an appropriate algorithm, for example, by a known in-focus state detection algorithm to detect a defocus distance of the photographing lens to an in-focus position and stores it in a memory Ml. In accordance with the stored defocus distance, an AF lens control unit 5 of the camera drives the photographing lens L to the in-focus position. The in-focus state of the photographing lens is displayed by a display unit 4 in a finder of the camera.

The AE operation is now explained. The MC 1 receives an ISO sensitivity signal from an ISO setting unit 7 of the camera, an open aperture value signal from an open aperture value detector 8 which detects an open aperture value of the photographing lens L, and an object brightness signal from a light metering unit 9. An exposure mode selector 10 selects one of an auto-exposure control mode (shutter time priority mode, aperture priority mode or program mode) and a manual exposure control mode and corresponding signals are applied to the MC 1 from a shutter time setting unit 11 and an aperture value detector 12 which detects the set aperture value of the photographing lens L so that the MC 1 carries out the exposure operation. The result of the exposure operation is displayed by the display unit 4. A release signal of a release circuit 13 which is coupled to a release button is applied to the MC 1 and an exposure control unit 14 in the camera controls the aperture of the lens L and a shutter 19. In the present camera, the operation of the release button is divided into a first stroke and a second stroke.

The display unit 4 drives display device such as LED or liquid crystal. The camera has a film windup device 16, which selects one of a continuous photographing mode and a one-frame photographing made. In response to the depression of the release button in the second stroke, the release circuit 13 generates a release signal for a period in which the release button is depressed. In the one-frame photographing mode, the exposure to the film and one-frame wind-up of the film are carried out at one time in response to the depression of the release button in the second stroke.

An encoder 18 generates a pulse in response to rotation of a motor contained in the AF control unit 5 to drive the lens L. A focus lock circuit 15 generates a focus lock signal while a focus lock button (not shown) is depressed.

A normal photographing sequence of the camera is now explained with reference to FIG. 2. In a step S21, when the release button of the camera is depressed in the first stroke, power is turned on and the camera is initialized and all circuits in the camera start the operation. In a step S22, whether the photographing lens mounted on the camera is the AF lens or not is checked. If it is the AF lens, the AF signal is supplied from the lens detector 6 to the MC 1, and if it is not the AF lens, the process proceeds to a step S23 where the AF control unit 5 is disabled ln a step S24, whether the release button has been depressed in the second stroke or not is checked. lf the decision is NO, the process returns to the step S22. In a step S25, an interrupt is inhibited. In a step S26, the film is exposed in accordance with a result of an AE operation determined in an AE interrupt prior to the step S25 and the exposed film is wound up and the inhibition of interrupt is released. In a step S27, whether the wind-up of the film has been completed or not is checked, and if it has been completed, the process proceeds to a step S28. In the step S28, whether the selected mode is the continuous photographing mode or the one-frame photographing mode is checked, and if it is the one-frame photographing mode, the process proceeds to a step S29. In the step S29, whether the release signal exists or not is checked in the same manner as that in the step S24, and when the release signal terminates, the process goes to the step S22. If it is detected that the AF lens is mounted in the step S22, the process proceeds to a step S31 where the AF control shown in FIG. 3 is carried out.

Referring to FIG. 3, a sub-routine of the AF control is explained. In step S41, the CCD 2 is reset and it discharges the stored charges. In a step S42, the CCD 2 receives a light from the object and starts to store charges. When a sum of the charges stored in the photo-diodes reaches a predetermined level, the store of the charges in the CCD 2 is completed. In a step S43, the interrupt is temporarily inhibited. In a step S44, the charges stored in the CCD 2 are supplied to the A/D converter 3 which supplies digital data to the MC 1. In a step S45, the AF operation is carried out, and in a step S46, operation data derived from the AF operation is stored in the memory Ml. In a step S47, the interrupt is permitted. In a step S48, the in-focus state is displayed by the display unit 4. In a step S49, whether the focus lock circuit generates the focus lock signal or not is checked. If it is not generated, the AF control unit 5 is activated in a step S50 to drive the lens L so that the object image is focused on the film plane. The encoder 18 generates pulses as the lens L is driven. In a step S51, a counter Cl in the MC 1 counts the pulses supplied from the encoder 18. In a step S52, the defocus distance represented by the data stored in the memory Ml is compared with the drive distance of the lens L represented by the count of the counter Cl, and in a step S53, whether the lens L has been driven by the defocus distance represented by the data in the memory M1 is detemined. If the lens L has been driven by the defocus distance, the process proceeds to a step S54, and if it has not, the process proceeds to the step S52. In the step S54, the AF control unit 5 stops the drive of the lens L, and in a step S55, the counter C1 is reset.

What is calculated by the AF operation are the defocus distance and the defocus direction. The AF lens is driven in the defocus direction determined in the step S50.

The AE interrupt and the AF interrupt in FIGS. 4, 5A and 5B are interrupt routines which are periodically performed in the routine shown in FIG. 2.

In FIG. 4, the AE operation is performed in a step S32 and the result of the AE operation is displayed in a step S33.

In FIGS. 5A and 5B, whether the AF len is mounted or not is checked by the output of the lens detector 6 in a step S60. In a step S61, whether the release button has been depressed to the second stroke or not is checked by the output of the release circuit 13. If it has been depressed, the process proceeds to a step S62.

In the single-lens reflex type camera of the present invention, the motor to drive the AF lens is contained in the AF control device 5 of the camera body. An IC device is mounted in the AF lens, and no IC device is mounted in a lens other than the AF lens. The lens detector 6 exchanges signals with the IC of the AF lens to detect whether the AF lens has been mounted on the camera body or not and generates the detection signal.

In a step S62, whether a timer Tl in the MC 1 is activated or not is checked. If it is not activated, the process proceeds to a step S63. In the step S63, whether the focus lock signal has been generated or not is checked. If it has not been generated, the process proceeds to a step S64 where the AF control unit 5 stop the drive of the lens, and if the focus lock signal has been generated, the process proceeds to a step S65 where the exposure control unit 14 exposes the film. In a step S66, after the exposure to the film is completed, one frame of film is wound up by the film wind-up unit 16. In a step S67, the decision similar to that of the step S63 is made, and if the focus lock signal has not been generated, the process proceeds to a step S68 where the drive of the AF lens is controlled in the same manner as that in the steps S50 to S54. The AF lens is driven in the film wind-up period. The AF lens is driven in the step S68 only when the AF interrupt has occurred during the steps S50 to S53 of FIG. 3. If the AF interrupt occurs before the data in the memory Ml coincides with the content of the counter Cl, the AF lens is stopped in the step S64, and since the counter C1 is not reset, the drive of the AF lens is resumed in a step S68. If the AF interrupt occurs immediately after the end of drive of the AF lens, the lens is not driven in the step S68.

Steps S69, S70 and S73 corresponds to the steps S27, S28 and S29 of FIG. 2, respectively. If the continuous photographing mode is detected in the step S70, the process proceeds to the step S71. In the step S71, the same decision as that in the step S63 is made, and if the focus lock signal has not been generated, the timer Tl is reset in the step S72 and the timer Tl is started and the process returns to the main routine of FIG. 2. The timer Tl is activated for a predetermined time and the MC 1 does not carry out the steps S63 to S72 while the timer Tl is activated. The drive of the AF lens in the step S68 may be continued even in the steps S69 and S70. The process does not proceed to the step S63 during the activation period of the timer Tl.

In the camera which carries out the AF control for each frame in the continuous photographing mode, the film is wound up (in several hundreds of milliseconds) after the film has been exposed and then the charges are stored in the CCD for the AF control (for example, in several hundreds of milliseconds to one second although it varies with the brightness of the object), the AD conversion is done (in several milliseconds to several tens of milliseconds) and the AF operation is carried out (in several tens of milliseconds to several hundreds of milliseconds). The time of the timer T1 is set to be longer than the sum of those times less the film wind-up time. Alternatively, a focal distance of the AF lens may be detected to change the time of the timer T1 in accordance with the focal distance.

Where a moving object is photographed in the continuous photographing mode, the shutter button may be released without perfect in-focus state being attained. Since the movement of the object usually has directivity, the AF control is done in accordance with the defocus distance stored at the beginning of the release operation so that the AF control can well follow the movement of the object.

If the focus is locked in the continuous photographing mode, high speed continuous photographing is attained.

While the timer Tl is started after the film has been wound up in the above embodiment, it may be started after the exposure to the film. In this case, the film wind-up time is to be added to the time of the timer T1.