JPH01287511A - Focus detecting device - Google Patents

Abstract

PURPOSE:To increase the probability that focus detection becomes possible and to shorten the lens driving time up to focusing after focus detection by setting the position of a lens after a low-contrast research scan to a specific stop position, and setting this specific stop position to a position where the lens is used normally at high frequency. CONSTITUTION:When the focus detection by a focus detecting means 2 is disabled, this state is decided by a disabled detection deciding means 4. In this case, a focus detecting means 2 performs focus detection while the lens 1 is driven by a lens driving means 3 under the control of a lens scan control means 5 to make a lens scan (low-contrast research scan) for searching for a lens position where the focus detection is impossible. This lens scan is made between the terminal positions of the lens 1 or in a narrower range. When the lens position where the focus detection is possible is not found, the lens driving means 3 is so controlled under the control of a control means 7 as to drive the lens 1 to a specific stop position Ns determined by a lens position determining means 6. Consequently, the time up to focusing is shortened.

Description

DETAILED DESCRIPTION OF THE INVENTION [Industrial Field of Application] The present invention relates to a focus detection device used in a single-lens reflex camera equipped with an automatic focus adjustment device.

[Prior Art] Conventionally, in an automatic focus adjustment device that detects the focus state of a lens for photographing and drives the lens to the in-focus position, when focus detection is impossible, it is possible to detect focus while driving the lens. It has been proposed to perform an operation to search for the lens position (so-called low contrast scan) (Japanese Patent Laid-Open No. 59-18
Publication No. 2411).

In addition, in the above publication, it is detected that the lens has reached either the closest end position or the infinity end position, and when one end position is reached for the first time, the driving direction of the lens is reversed, and then the other end position is reversed. It has been proposed to stop the lens drive when the end position of the lens is reached.

[Problems to be Solved by the Invention] In the above-mentioned conventional technology, if a lens position that allows focus detection cannot be found even after performing a low contrast scan,
The lens drive is stopped at either the closest end position or the infinity end position, and an indication that the focus cannot be detected is displayed. Therefore, in a state where focus cannot be detected after low-contrast scanning, the lens position is biased toward either the closest end position or the infinity end position. If the photographer shakes the camera in this state, or if a subject appears in the area where the photographer is holding the camera, the lens position will be biased and the focus will often not be detected. Even if detection becomes possible, the lens must be driven from a biased lens position to the in-focus position, so there is a problem that it takes a long time to focus, and there is a risk of missing a valuable photo opportunity.

For example, if a contrasting subject (wild bird) appears in a bright background (blue sky) with little contrast and you are trying to detect the focus while following it as it moves quickly, the lens position may be biased. , even if the subject enters the focus detection area, focus may not be detected, and even if focus can be detected, the subject may disappear while the lens is being driven from the biased lens position to the in-focus position.
You will miss a valuable photo opportunity.

The present invention has been made in view of these points, and its purpose is to provide a focus detection device that has a high probability of being able to detect focus after low contrast scanning and that takes a short time to focus. It is in.

[Means for Solving the Problems] In order to solve the above problems, in the focus detection device according to the present invention, as shown in FIG.
1), a focus detection means (2) for detecting the focus state of the lens (1), and a lens drive means (2) for driving the lens (1).
3), a focus detection impossibility determining means (4) for determining whether focus detection by the focus detecting means (2) is impossible, and when it is determined that the focus cannot be detected by the focus detecting impossibility determining means (4), A lens scanning control means (5) for driving the lens (1) by the lens drive means (3) and performing a focus detection operation by the focus detection means (2), and determining a predetermined stop position Ns of the lens (1). Lens position determining means (6)
When a lens position where the focus can be detected cannot be found by the lens scanning by the lens scanning control means (5),
A control means (7) for controlling the lens drive means (3) to drive the lens (1) to a predetermined stop position Ns determined by the lens position determination means (6). It is something to do.

However, FIG. 1 is an explanatory diagram showing the configuration of the present invention in functional blocks, and in the embodiments described later, the main part of the above configuration is realized by a microcomputer program.

[Effect] Hereinafter, the operation of the present invention will be explained with reference to FIG.

A photographic lens (1) forms an image of light from a subject.

The focus detection means (2) detects the focus state of the lens (1). The focus state of the lens (1) is usually detected as the amount of defocus (defocus amount) from the in-focus position, and the front focus and the back focus are distinguished by the sign thereof. During normal focus detection, the lens (1) is driven toward the in-focus position based on the focus detection result of the focus detection means (2).

The lens (1) is driven by a lens driving means (3).

By the way, if the current position of the lens (1) is far away from the in-focus position, focus detection by the focus detection means (2) may become impossible. This state is determined by the focus detection failure determining means (4).

If it is determined that focus detection is impossible, focus detection is performed by the focus detection means (2) while driving the lens (1) by the lens drive means (3) under the control of the lens scanning control means (5). Accordingly, a lens scan (low contrast scan) is performed to search for a lens position where focus can be detected. This lens scanning is performed between the end positions of the lens (1) or within a slightly narrower range.

If a lens position where the focus can be detected cannot be found by this lens scanning, under the control of the control means (7),
The lens driving means (3) is controlled to drive the lens (1) to a predetermined stop position it N s determined by the lens position determining means (6).

[Embodiment] FIG. 2 is a block circuit diagram showing the circuit configuration of a camera as an embodiment of the present invention. However, illustrations of parts not directly related to the focus detection operation are omitted. <
μC) is a microcomputer that performs calculations and sequence control for focus adjustment. (LEC) is a lens circuit provided in the interchangeable lens, which transmits information specific to the interchangeable lens to the microcomputer (μC). (A.F.C.
) is a focus detection circuit that photoelectrically converts the subject light that has passed through the lens and outputs focus detection data.
μC). (DSP) is a display circuit that displays the focus of the lens and indicates that focus cannot be detected. (ILM) is an auxiliary light emitting device that irradiates the subject with auxiliary light for focus detection. (M) is a motor for driving the focusing lens of the interchangeable lens, and the lens drive circuit (L
The lens drive circuit (LDC), which extends and edges the lens under the control of the DC), receives motor drive speed signals, motor drive direction signals, and motor stop signals from a microcomputer (μC). Input the control signal,
Based on this, the motor (M) is driven. (ENC)
is an encoder that detects the amount of rotation of the motor (M) and outputs pulses to the microcomputer (μC) according to a predetermined amount of rotation of the motor (M).

Here, the microcomputer (μC) uses a lens position counter N to know the amount of lens extension from the infinity position, which is the most retracted state, as an absolute amount.
It has a built-in L. This lens position counter NL is reset to NL=0 by an internal command when the lens is retracted to the infinite position, and when the lens is extended, the encoder (ENC) is reset by an internal command.
When the lens is retracted, it is counted down according to pulses from the encoder (ENC) according to an internal command. When the lens is extended to the closest position, the value of the lens position counter NL is N1. =Nmax. This maximum extension amount N ax differs depending on the lens, and is read from the lens circuit (LEC) into the microcomputer (μC) as lens-specific information.

(BAT) is a power supply battery, and a microcomputer (
μC) and other circuits. Power battery (BA
A time constant circuit consisting of a series circuit of a resistor (R1) and a capacitor (C1) is connected to both ends of the resistor (T).
The connection point between R1) and the capacitor (C1) is connected to the power-on reset terminal (RES) of the microcomputer (μC). When the power battery (BAT) is connected, a power supply voltage is applied between the power terminal (Vcc) and the ground terminal (GND) of the microcomputer (μC), and the microcomputer (μC) becomes active.
Until the charging voltage of the capacitor (C1), that is, the voltage applied to the reset terminal (RES) of the microcomputer (μC) reaches a predetermined voltage, the microcomputer (
When the voltage of the capacitor (C1) exceeds a predetermined voltage, the microcomputer (μC) is reset and starts operating from step #l (see FIG. 3), which will be described later.

(SR) is a reset switch, and this switch is OFF.
When N is pressed, the lens is reset to the initial position. (S
oo) is an infinity position detection switch, which is turned on when the lens is retracted to the infinity position. (SM) is a main switch, which is turned on when using the camera. (
SL) is a photographing preparation switch, which is normally turned on by the first stroke of a release button (not shown). (SAF
) is the AF mode switch, and this switch (SAF
) is ON, the autofocus mode is selected to drive the lens to the focus position based on the focus detection result, and when the switch (SAF) is OFF, the autofocus mode is selected based on the focus detection result. A manual focus mode is selected in which only the image is displayed and the lens is not driven. (SMZ) is a macro zone switch, which is opened when the zoom ring is set to the macro zone in a zoom lens with a macro mechanism. When set to macro zone,
Since the autofocus mode is disabled, in order to notify the microcomputer (μC) of this, the lens circuit (LEC) outputs a signal SMZ indicating the macro zone to the microcomputer (μC).

Next, the focus adjustment operation of the camera will be explained with reference to a flowchart. First, when the battery is installed and a power-on reset is performed, the microcomputer (μC) executes the programs starting from #1 shown in FIG. first,
#1 resets all flags. However, only the lens not installed flag LENOF (described later) should be set to 1, #
In step 2, input lens data from the lens circuit (LEC). From the lens circuit (LEC), the lens attachment signal ICP, macro zone signal SMZ, macro lens attachment signal LCPR1, maximum extension amount N IIax, open The aperture value A Vo, focal length information ZFZ, conversion coefficients, AF enable signal AFE, AF coupler signal AFCP, etc. are input to a microcomputer (μC). Here, the focal length information ZFZ is the focal length f(
am) is logarithmically transformed, and in this embodiment, it is assumed to be expressed by the following equation.

ZFZ=8X(2fogz(f/6.25)+11-■
Further, the conversion coefficient is a coefficient for converting the defocus amount DF into the lens drive amount ΔN. AF possible signal AF
E is a signal indicating that the interchangeable lens is a focus detectable lens. The AF coupler signal AFCP is a signal indicating that the interchangeable lens is equipped with a power transmission mechanism (AF coupler) for automatic focus adjustment.

In #3, the presence or absence of the lens attachment signal ICP is determined. If the lens is attached, the lens circuit (LEC) supplies the lens attachment signal ICP to the microcomputer (μC), but if the lens is not attached, the lens attachment signal ICP is not supplied, so the microcomputer (μC) determines whether the lens is attached by checking the presence or absence of the lens attachment signal ICP. If there is no lens attachment signal in #3, it is determined that the lens is not attached, and in #8 the lens not attached flag LENOF is set to 1, and the process proceeds to #10 (Fig. 4). Also, in #3, the lens attachment signal is output. If there is, it is determined that the lens is attached, and #
4, it is determined whether the flag LENOF is 1. If LENOF=1 in #4, it is determined that the lens is attached from the state where the lens is not attached, and the lens not attached flag L is set in #5.
Set ENOF to 0 and proceed to #6, 500 m5 in #6
After waiting for the time ec to elapse, the ω renormalization subroutine (FIG. 10) is executed in #7. Then, in #10, it is determined whether the main switch (SM) is ON. #
If the main switch (SN) is not ON at 10, #2
Returning to step 1, the presence or absence of the lens attachment signal is determined. Therefore, when the battery is attached and processing starts from #1, and when the lens is attached during the loop from #2 to #10, the subroutine for renormalization is executed after waiting for 500 n5ec. It turns out.

Here, to explain the reason for waiting for 5001 Isec, the photographer often holds the lens in his hand when attaching the battery or lens. If you start retracting the lens immediately, the drive system will be overloaded and
Lens retraction may stop midway, damage the lens or camera drive system, or the photographer may become surprised and drop the camera. To prevent this, 5
After waiting for a time of 0.005 seconds, lens retraction is started when the photographer takes his hand off the lens.

Next, if the main switch (SM) is ON in #10, the lens initial position calculation subroutine (Fig. 9) is executed in #15, and (1) renormalization subroutine (Fig. 9) is executed in #20.
After executing the lens initial position setting subroutine (FIG. 11) in #25, it is determined in #30 whether the main switch (SM) is OFF. If the main switch (SM) is OFF, the renormalization subroutine at #35 is executed and the process returns to #2 (FIG. 3). #30
If the main switch (SM) is not OFF, #45
Proceed to.

FIG. 9 is a flowchart showing the contents of a subroutine for calculating the lens initial position. When this subroutine is called, first, in #1000, lens data is input from the lens circuit (LEC).

In #1005, the macro lens attachment signal LCP
Determine the presence or absence of R. If the macro lens of equal or larger magnification is attached in #1005, the defocus amount DFs for setting the lens initial position is set to DFm/2 in #1040, and the process returns to the step in which the subroutine was called. Here, DFa is the maximum defocus amount that covers the range from the closest position to the infinity position of the lens. #100
If a macro lens of 100% magnification or higher is not attached in 5, #
The defocus amount DFs is determined from 1010 to #1.030. In #1010, it is determined whether the focal length information ZFZ is 40 or less, and if ZFZ≦40, in #1020
Then, return with DFs=O. ZFZ for $1010
If >40, the defocus amount DFs corresponding to the lens initial position Ns is calculated based on the focal length information ZFZ in #1030, and the process returns.

Here, the meaning of the algorithm for determining the initial lens position shown in #1010 to #1030 will be explained.

In this algorithm, the defocus amount DFs (μm) from the infinity position to the initial lens position Ns is calculated using the calculation formula % (where ZFZ>40) expressed as a linear function of the focal length information ZFZ. Using the above formula (■), the focal length f is from 24MIII to 800+*
Figure 14 shows the results of calculating the defocus amount DFs at the initial lens position Ns and calculating the imaging magnification β = DFs/f for the case of m.As can be seen from Figure 14, the above equation 0 is The focal length used is f (35m
The defocus amount DFs at the initial lens position Ns is determined so that a frequently used photographic magnification β (1/80 to 1/40) can be obtained for a lens with an angle of +m to 300 am. If the focal pressure 1r is handled in millimeters within the camera body, then simply DFs=β×r×
It would be fine to set it to 1000 [μ ring], but in reality, within the camera body, the focal length "is treated as information ZFZ logarithmically compressed using the above formula 0. In this case,
Although it is not easy to obtain the defocus amount DFs (μ plow) as a linear function of the focal length information ZFZ so that the condition of 1/80≦β≦1/40 is satisfied, the above 0
The formula is the realization of this. When the imaging magnification β(f) is calculated using the above formula 0, β([)octIn(f
) -Zn(6,25X 4 ))/r. dβ/
If we find the maximum value from the condition of df=0, we get (1/β)=46 when r-68.

In addition, r = 33 mm) knee < 1713 ) = 8
0.5, when r-300+u+, (1/β)=81.
It becomes 7.

Moreover, in the above formula 0, the multiplication coefficient is 64 = 2', so after subtracting the constant 40 from the focal length information ZFZ, the defocus of the lens initial position Ns can be obtained by simply shifting the lens six times to the left. s can be found. Therefore, the defocus amount DFs at the lens initial position Ns can be easily calculated from the focal length information ZFZ read from the lens circuit (LEC).
The calculation time can be shortened, and the storage capacity of the calculation program can be reduced. In addition, the defocus amount DFs of the lens initial position WNs is determined according to various focal lengths f.
Compared to a method in which the information is stored in advance, the storage capacity of the ROM can be reduced.

(Left below) Table 1 However, in the above table, * means 28~135-1 when the zoom lens is at 135-, and t means 70-210~ when the zoom lens is at 210 m.
5, the data is when the customer's 75-300mm zoom lens is at 300mm.

Table 1 shows commonly used photographic magnification β and maximum defocus amount DF for lenses with various focal lengths.
It shows a. In a wide-angle lens with a focal length f of less than 35 mg+, the maximum defocus amount DFm is small, and it is considered that focus can be detected no matter where the lens position is.

Therefore, it is considered that the lens should be stopped at an infinity position so as to obtain the commonly used photographic magnification of 110o. Therefore, in this example, 1624 mm (ZFZ≦40
), DFs=O. On the other hand, lenses with a commonly used focal length (35-30C) + m),
The commonly used photographic magnifications range from 1/40 to 1/60. The range of photographic magnifications in which focus detection is possible is thought to be slightly wider than this, and focus detection is possible if the initial stop position of the lens is determined so that a photographic magnification within the range of 1/4o to 1/80 is obtained. It is thought that the probability that this will occur will be high. Therefore, in this embodiment, f>24 mm (ZFZ>
40)+7), using the above formula 0, 1/80≦
The defocus amount DFs of the lens initial position Ns such that β≦1/40 is calculated.

FIG. 10 is a flowchart showing the contents of the ω renormalization subroutine. When this subroutine is called, a subroutine for lens condition determination is executed in #1100. Here, the lens condition determination subroutine is
An example will be explained in FIGS. (a) and (b).

In FIG. 12(a), first, in #2000, the presence or absence of the lens attachment signal ICP is determined. If there is a lens attachment signal in #2000, the open aperture value of the lens is determined in #2010.
It is determined whether o is smaller than a predetermined value AFAV. Here, the predetermined value AFAV is the size of the AF pupil through which the focus detection light beam passes, expressed as an aperture value. Open aperture value AV
If o is smaller than the predetermined value AFAV, the focus detection light beam passing through AF@ will not be eclipsed by the lens.

If AVo<AFAV in #2010, the presence or absence of the AF enable signal AFE is determined in #2020. #A in 2020
If the F enable signal AFE is present, it is determined that a focus detectable lens is attached, and the process returns with the lens condition flag LOKF set to 1 in #2030. If there is no lens attachment signal in #2000, lens renormalization cannot be performed, so the process returns with the lens condition flag LOKF' set to 0 in #2040. If AVo≧AFAV in #2010, the focus detection light flux passing through the AF pupil is vignetted by the lens, so it is determined that accurate focus detection cannot be performed, and the process returns with the lens condition flag LOKF set to O in #2040. do. If there is no AF enable signal AFE in #2020, it is determined that a lens that cannot detect focus, such as a reflective telephoto lens or a shift lens, is attached.
In #2040, the lens condition flag LOKF is set to 0 and the process returns.

12th rI! I(b) is another example of lens condition determination, and after determining the presence or absence of the ICP attachment signal in #2000, I
If there is a CP attachment signal, the presence or absence of the AF coupler signal AFCP is determined in #2025.

If AF coupler signal AFCP is present in #2025, AF
It is determined that a lens equipped with a coupler, that is, a lens that can be driven for focusing by the motor of the camera body, is attached, and the lens condition flag is set at #2030.
Return with F set to 1.

If there is no AF coupler signal AFCP in #2025, A
It is determined that the lens does not have an F coupler and a lens is attached, and the process returns with the lens condition flag LOKF set to 0 in #2040.

If the lens conditions shown in FIG. 12 (,) or (b) are satisfied, the lens condition flag LOKF becomes 1, and if the lens conditions are not satisfied, the lens condition flag LOKF becomes 0. Returning to the flow in Figure 10, #
In step 1102, the lens condition flag LOKF is determined. $
If 1102 is LOKF-〇, #1104 to #11
Skip step 15 and return. #110
If LOKF=1 in 2, lens renormalization is started in #1104. After starting lens drive in #1104,
In #1105, it is determined whether the infinite position detection switch (S■) is ON. # 1. Switch at 105 (S■
) is not ON, the judgment operation in #1105 is repeated until the switch (Sω) is turned ON. If the lens is retracted to the infinity position in #1105 and the switch (SCO) is turned ON, then in #1110 Stop lens renormalization,
In #1115, the lens position counter NL is reset and the subroutine returns to the called step.

FIG. 11 is a flowchart showing the contents of the subroutine for setting the lens initial position. When this subroutine is called, the lens condition determination subroutine is executed in #1200, and the lens condition flag LOKF is determined in #1202. If LOKF=O"l' in #1202, #
Skip steps 1204 to #1215 and return. If LOKF=1 in #1202, #120
In step 4, the defocus amount DFs for setting the lens initial position is multiplied by the conversion coefficient K to calculate the lens drive amount ΔN=DFsXK from the infinity position, and in step #1205, lens extension is started. In #1210, it is determined whether the lens drive amount has reached ΔN. Lens drive amount is ΔN with #1210
If the lens drive amount has not reached ΔN, the determination operation in #1210 is repeated until the lens drive amount reaches ΔN. If the lens drive amount reaches ΔN in #1210, the lens drive is stopped in #1215, and the subroutine is called. Return to step.

Returning to the flow of FIG. 4, in #45, it is determined whether the AF mode switch (SAF) is ON.

If the AF mode switch (SAF) is not ON in #45, set the flag MF indicating manual focus mode to 1 in #50, and proceed to #80.
If the P mode switch (SAF) is ON, it is determined in #55 whether the flag MF is 1. #55 MP=1
If so, it means that the switch (SAF) has just been turned on, and in #60, set the flag MF to 0 and proceed to #65. In #65 to #75, the above-mentioned lens initial position calculation,
■Execute each subroutine of renormalization and lens initial position setting to set the lens initial position, and then #1
Proceed to #45. If MP = 1 in #55, it means that the switch (SAF) has been ON before, #
Proceed to 80.

In #80, the presence or absence of the lens attachment signal ICP is determined.

If the lens is not attached in #80, the flag LENOF indicating that the lens is not attached is set to 1 in #100, and #1054. : Progress tr, if the photographing lens is attached at #80, it is determined whether the flag LENOP is 1 at #90. If LENOF = 1 in #90, it means that the lens has just been attached, so in #95 the flag LENOF is set to 0, in #96 wait until the time of 500+5see has passed, and in #65 to #75 the lens initial After setting the position, proceed to #145, LENO at #90
If F=1, it means that the lens has been attached before, and the process proceeds to #105.

At #105, the macro zone switch (SMZ) is turned on.
In other words, it is determined whether the zoom lens is in the macro zone. Macro zone switch (SM) with #105
Z) is not ON, that is, if it is in the macro zone,
In #110, the flag SMZOFF indicating that the macro zone switch (SMZ) is OFF is set to 1, and in #125
Proceed to #105, macro zone switch (SI4z)
If it is ON, it is determined in #115 whether the flag SMZOFF is 1. If SMZOFF=1 in #115, it means that the macro zone switch (SMZ) has just been turned on, and the 7-lag SMZOFF is set to 0 in #120.
After setting the lens initial position in #65 to #75, proceed to #145. #115t'SMZOFF=
If it is not 1, the macro zone switch (SM2
) has been turned on, and the process advances to #125.

In #125, it is determined whether the reset switch (SR) is ON. If the reset switch (SR) is not ON in #125, the reset switch (SR) is turned on in #130.
The flag 5ROFF indicating that is OFF is set to 1,
Proceed to #145, reset switch (SR) at #125
If it is ON, it is determined in #135 whether the flag 5ROFF is 1.

If 5ROFF=1 in #135, it means that the reset switch (SR) has just been turned on, and #140
After setting flag 5ROFF to O and setting the lens initial position in #65 to #75, proceed to #145, #135
If 5ROFF = 1, it means that the reset switch (SR) has been turned on before, and the lens has already been set to the initial position, so #65 to #7
The process proceeds to #145 without performing the lens initial position setting in step 5.

Therefore, after setting the lens initial position (#15 to #25) immediately after turning on the main switch (SR),
Immediately after the F mode switch (SAF) is turned on, immediately after the lens is attached, or the macro zone switch (SMZ)
) is turned on, or the reset switch (SR
) is turned ON, or when the focus cannot be detected even after performing the low contrast scan described below (#25).
The lens initial position is set only in cases (see 2); in other cases, the lens initial position is not set. Therefore, when shooting similar scenes or when shooting multiple pictures in succession When the probability of focusing near the previous lens position is high, as in the case of the previous lens position, the initial lens position is not set, and power consumption is lower than when the lens initial position is set every time the focus is detected. , and the time required for focus adjustment is shortened.

In #145, it is determined whether the photographing preparation switch (Sl) is ON. If the photographing preparation switch (Sl) is not turned on, the entire display is turned off in #40 and the process returns to #30. Below, #30, #45, #80, #105, #125
, and #145, check the status of the main switch (SM), AF mode switch (SAF), lens attachment signal ICP, macro zone switch (SMZ), reset switch (SR), and shooting preparation switch (Sl). Monitor.

In the middle of this loop, the main switch (SM) is turned off.
When it is, as mentioned above, ■ Renormalization (#35)
and go through the loop #2 to #10 again until the lens is attached or the main switch (SM) is turned on.
Wait until N. Also, in the middle of the loop from #30 to #145, switches (sAF), (SMZ), (SR
) is turned on, or when a lens is attached, the lens initial position set (#65~
#75) In this way, the camera is waiting for the shooting preparation switch (Sl) to be turned on, but #14
If the photographing preparation switch (Sl) is turned ON in step 5, the process proceeds to #175 (FIG. 5) to start focus detection.

Focus detection is performed in #175, and it is determined in #180 whether focus detection is impossible. If focus cannot be detected in #180, proceed to #290 (Figure 7) to perform focus determination.
If the focus cannot be detected in #180, it is determined in #185 whether the brightness is low. If the brightness is low in #185, proceed to #330 (Fig. 8) to emit the auxiliary light. If the brightness is not low in #185, proceed to $190 (Fig. 8) to find a lens position where contrast can be obtained. Proceeding to Fig. 6), a low-contrast scan is performed, but by limiting the range of the low-contrast scan to the narrowest possible range, an effort is made to shorten the time required for the low-contrast scan. In other words, in the focus detection device, the range in which focus detection is possible is determined, and from the current lens position to the rear bin side +DFa,
Assuming that focus detection is possible within the defocus amount range of -DFa on the front focus side, focus detection is possible within the range of ±DFa from the current lens position without changing the lens position. It is within. Therefore, #190
(Fig. 6), the scanning amount in the feeding direction is ΔN=N
Calculate as max-NL-DFaXK. This allows the DF to be extended even if it is not extended to the maximum extension position N wax.
This is because if the aXK is extended to the front position, the maximum extended position Nmax will also be within the focus detectable range 2DFa.0 Next, in order to know the scan direction, it is determined in #200 whether the flag FOWF is 1. . This flag F
OWF is a flag indicating that scanning is to be performed in the forward (FOWarcl) direction. When performing a low contrast scan for the first time, the flag FOWF has been reset, so FOWF is not 1. Therefore, first, proceed to #205, set FOWF-1 at #205, and set #2 to #2.
Proceed to #20, lens drive (feeding direction) in #220
Outputs a signal to the lens drive circuit (LDC) to perform
After focus detection is performed in #225, it is determined in #230 whether focus detection is impossible. If the focus cannot be detected in #230, the flag FOWF is reset in #233, and the process proceeds to #290 (Fig. 7) to determine focus. If the focus cannot be detected in #230, the lens is adjusted in #235. Drive amount is ΔN
Determine whether it has been reached. Lens drive amount is ΔN in #235
If the focus has not been reached, the process returns to #225, and it is determined whether the focus cannot be detected while continuing to drive the lens in the extending direction. If the lens drive amount has reached ΔN in #235, the lens drive is stopped in #240, and the flag F is set in #245.
Determine whether OWF is 1. F'0WF with #245
If =1, this means that a lens position where the focus can be detected was not found even though scanning was performed in the extending direction, so the process returns to #200 to perform scanning in the extending direction. If FOWF=1 at $200, it means that the scanning in the feeding direction has already been completed, so in #210, the scanning amount in the feeding direction is changed to Δ
Let N=Nshoax. This is to reset the counter by carrying it out to the end. In #215, the flag FO is set to indicate that the scan is in the renormalization direction.
Set WF to 0 and proceed to #220. In #220, the lens drive circuit (L D
A signal is output to C), and the process returns to #245 via #225 to #240. This time, since FOWF = 1, it does not return to #200 and proceeds to #250. In other words, when FOWF = 1 in #245, both the scanning in the feeding direction and the scanning in the renormalization direction are performed. , it means that no lens position where the focus can be detected was found, so in preparation for the next focus detection, a subroutine for calculating the initial lens position is executed in #250, and in #252
After executing the lens initial position set subroutine,
In step #255 (FIG. 7), a focus detection failure display is performed. If focus detection becomes possible in #230 during scanning in the border direction, flag FOWF is set in #233.
#290 (Figure 7) to reset and perform focus judgment
Proceed to.

When displaying focus detection failure in #255 (Fig. 7), #2
At 60, set the low contrast scan end flag LSENDF to 1
shall be. This flag is a flag to indicate that a lens position where the focus can be detected was not found even though low contrast scanning was performed.Next, after returning the flag FOWF indicating the scan direction to 0 in #265, # At step 270, it is determined whether the photographing preparation switch (Sl) is ON. #27
If the shooting preparation switch (Sl) is not ON at 0, #4
Clear all display with 0 and return to #30. If the photographing preparation switch (Sl) is ON in #270, focus detection is performed in #275, and it is determined in #280 whether focus cannot be detected. If the focus cannot be detected in #280, the process returns to #270.

If the focus is not detectable in #280, the low contrast scan end flag LSENDF is set to 0 in #290, and #29
5 to determine whether the image is in focus. If it is determined in #295 that the layer is not in focus, the process proceeds to #300, where the in-focus and focus detection failure indications are erased, and in #305, the lens drive amount ΔN=DFXK is calculated based on the defocus amount DF, and in #310 to start driving the lens. In #311, it is determined whether the lens drive amount has reached ΔN. If the lens drive amount has not reached ΔN in #311, the determination operation in #311 is repeated until the lens drive amount reaches ΔN. If the lens drive amount reaches ΔN in #311, the lens drive is stopped in #312. , return to #270. Press #270 to turn on the shooting preparation switch (S
If l) remains ON, focus is detected in #275, followed by steps #280 to #290, and again in #295 to determine focus.The lens is focused in steps #305 and #310 described above. Since the lens is being driven toward a certain position, there is a high possibility that it will be in focus here.

If it is in focus at #295, the focus is displayed at #315,
In #320, it is determined whether the photographing preparation switch (Sl) is ON. At #320, the shooting preparation switch (Sl) is turned on.
If so, the determination operation of #320 is repeated until the photographing preparation switch (Sl) is no longer ON, and a so-called focus lock state is established. Although unrelated to the present invention, in a camera in focus priority mode, release is permitted in this focus lock state, and when the release button (not shown) is pushed to the second stroke, the camera releases. It is something that performs an action. If the photographing preparation switch (Sl) is no longer ON in #320, the display is turned off in #40 and the process returns to #3o. In other words.

When the photographing preparation switch (Sl) is turned off, the focus lock state described above is released.

Next, when passing through #330 in Figure 8, it is determined that the brightness is low and focus cannot be detected in #185 and #180 (Figure 5), so auxiliary light emission is necessary. However, there are cases where it is useless to emit the auxiliary light, so #3
The determination is made in steps 30 and #335. Here, the auxiliary light emitting device (ILM) shown in FIG. On the other hand, the focus detection circuit (AFC") includes a focus detection optical system using a TTL phase difference detection method, and its optical axis is aligned with the photographic lens. Coincides with the optical axis.Therefore, there is a parallax between the light flux range of the optical system for auxiliary light projection and the light flux range for focus detection, and the light flux range is
(changes depending on the angle of view), the light flux range for focus detection is completely included in the light flux range of the optical system for flashing the filler light. This is the lower limit of the range that can be illuminated, and it is useless to emit filler light for objects closer than this. Also, if a long focal length lens is attached to the camera,
Since the auxiliary light is vignetted by the lens barrel, the auxiliary light does not illuminate the subject, and even if the auxiliary light is emitted, it may be wasted. Note that the lower limit of the range in which the subject can be illuminated to enable focus detection with fill-in light can be reduced by adopting a TTL fill-in light system, but the upper limit of the range in which focus detection is possible with fill-in light irradiation can be made larger. Since the reach distance of the auxiliary light is about 10+ at most, we cannot expect much.Therefore, in #330, it is determined whether the focal length f of the lens is 2501 or more, and in #330, f≧2.
If it is 50, it is determined that the auxiliary light may be blurry due to the long lens length or large lens diameter, so proceed to #190 (Figure 6) without emitting the auxiliary light, and set the low control light. Perform a scan.

In addition, when shooting with a long focal length lens, there are many long-distance shots where the auxiliary light does not reach, so there is not much problem with disabling the auxiliary light.If it is #330 and f≧250, then #3
At step 35, it is determined whether there is a macro lens attachment signal LCPR of equal or greater magnification. If a macro lens of equal or larger magnification is attached in #335, it is determined that the shooting is at close range, which is closer than the lower limit of the range where focus detection is possible with auxiliary light irradiation, and the auxiliary light is not emitted. Proceed to #190 (Fig. 6) and perform a low-contrast scan.If a macro lens of 100% magnification or higher is not attached in #335, emit an auxiliary light in #340, perform focus detection in #345, and # At 350, it is determined whether focus detection is impossible. The auxiliary light is emitted only for a predetermined period of time for each focus detection.

If the focus is not detected in #350, proceed to #395.
If focus cannot be detected in #350, perform ■ renormalization in #355 to reset the counter, and #
At 370, auxiliary light is emitted, at #375 focus detection is performed, and at #380 it is determined whether focus detection is impossible. #38
If the focus is not detected at 0, proceed to #395, #38
If the focus cannot be detected with 0, it is determined whether the lens is at the initial position in #381, and if the lens is not in the initial position, the lens initial position is set in #382, and #3
In step 83, a flag indicating that the lens is at the initial position is set, and if focus detection is not possible even in the 0th focus detection, the process proceeds to #390, and the process proceeds from #381 to #385 to display a focus detection failure display. Press #390 to turn on the shooting preparation switch (Sl).
) is ON. If the photographing preparation switch (Sl) is ON in #390, the process returns to #375. #39
If the shooting preparation switch (Sl) is not ON at 0, #4
Clear the display with 0 and return to #30.

In #395, the focus detection failure display is erased, and in #400, it is determined whether focus is achieved. If the focus is #400, #4
20 indicates the focus, and #425 sets the shooting preparation switch (
SL) is ON. If the shooting preparation switch (Sl) is ON in #425, the shooting preparation switch (Sl) is turned on.
The determination in #425 is repeated until the photographing preparation switch (Sl) is no longer ON in #425, the display is turned off in #40, and the process returns to #30. #40
If the value is 0 and the focus is not in focus, the lens drive amount ΔN=DFXK is calculated from the defocus amount DF in #405, and lens drive is started in #410. In #412, the lens drive amount is Δ
Determine whether N has been reached. With #412, the lens drive amount is Δ
If the lens drive amount has not reached ΔN, the determination operation in #412 is repeated until the lens drive amount reaches ΔN. If the lens drive amount reaches ΔN in #412, the lens drive is stopped in #413, and the photograph is taken in #415. It is determined whether the preparation switch (Sl) is ON. At #415, the shooting preparation switch (Sl) is set to O.
If it is N, the process returns to #370, and if it is not ON, the display is turned off in #40 and the process returns to #30.

Determination of defocus amount DFs (#1010 to #10) in the lens position calculation subroutine (Fig. 9) described above
In the algorithm 30), focal length information ZF
Depending on Z, the defocus amount DF of the lens initial position Ns
s is being calculated.

FIG. 13 is a flowchart showing a modification of this algorithm, which can be used in place of steps #1010 to $1030. In #1500,
It is determined whether the focal length f is 28- or less (ZFZ≦a). If #1500 is “≦28-seagull, then #1510
Set 0 as the shooting magnification β in , and proceed to #1570.
At $1500, it is determined whether r>28I@lI tear lever, and at $1520, it is determined whether the focal length r is 210 mm or less (Z F Z ≦b). #1520, if f≦210mm, #
Set (1/40) as the imaging magnification β at 1530, and #
Proceed to 1570. If r>210-1 in #1520, focus pressure 1r is 600s+m or less (Z F
It is determined whether Z≦C). #1540 and f≦60
If it is 01, use #1550 as the shooting double true β (1/6
0) and proceed to #1570, #1540
If you have 600m + Te, set the photographing magnification β to #1560 (
1/100) and proceed to #1570, #1570
Now, by multiplying the photographic magnification β by the focal length information ZFZ, we can obtain the lens extension amount D from the infinity position to the lens position Nb.
Calculate Fs. In the algorithm shown in FIG. 13, when the focal length r is, for example, 35 rings to 105 rings, the defocus amount DFs, which is the focal length f multiplied by the imaging magnification β=(1/40), is selected. In other words, always (1/4
The lens is initially set at a position where an imaging magnification of 0) can be obtained.

[Effects of the Invention] As described above, the present invention makes it possible to set the lens position after low contrast scanning to a predetermined stop position. This has the effect of increasing the probability that focus can be detected and shortening the time required for driving the lens from focus detection to in-focus.

[Brief explanation of the drawing]

FIG. 1 is a block diagram showing the basic configuration of the present invention, FIG. 2 is a block circuit diagram of an embodiment of the present invention, and FIGS.
The figure is a flowchart showing the same operation as above, and FIG. 14 is an explanatory diagram of the same operation. (1) is a lens, (2) is a focus detection means, (3) is a lens drive means, (4) is a focus detection impossible determination means, (5) is a lens scanning control means, (6) is a lens position determination means, (
7) is a control means.

Claims (1)

[Claims] (1) A photographic lens, a focus detection means for detecting the focus state of the lens, and a lens drive means for driving the lens;
a focus detectability determining means for determining whether focus detection by the focus detecting means is impossible; and a lens driving means to drive the lens and a focus detecting means to A lens scanning control means for performing a focus detection operation, a lens position determining means for determining a predetermined stopping position of the lens, and a lens position determining means for determining the lens position when a lens position where the focus can be detected cannot be found by the lens scanning by the lens scanning control means. 1. A focus detection device comprising: control means for controlling a lens drive means to drive the lens to a predetermined stop position determined by the determination means.