JPH01187519A - Focus detector - Google Patents

Abstract

PURPOSE:To shorten a time required until focus detecting impossible display is performed by inhibiting low contrast scanning and directly performing the focus detecting impossible display when focus detecting is not possible even in case of performing low contrast scanning. CONSTITUTION:When a focus detection impossibility decision means 4 decides that focus detecting is impossible and lens scanning is not inhibited, the lens scanning (low contrast scanning) that the position of a lens where focus detecting is possible is seeked under the control of a lens scanning control means 9 is performed. When defocusing quantity is within defocusing quantity DFa in which focus detecting is possible by a focus detecting means 2, a lens scanning inhibiting decision means 8 decides that the lens scanning is inhibited. In such a case, the lens scanning by the lens scanning control means 9 is not performed and the focus detecting impossible display by a display means 10 is performed. Thus, useless lens scanning is omitted and the focus detecting impossible display is swiftly performed.

Description

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

[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). Furthermore, it has been proposed not to perform low contrast scanning when the maximum defocus amount of the lens is smaller than a predetermined value (see Japanese Patent Laid-Open No. 133411/1982). However, the above publication does not disclose how to specifically set the predetermined value, and merely mentions that the predetermined value changes depending on the brightness. The predetermined value that changes depending on the brightness is considered to be a value related to the reliability level, and is completely unrelated to the focus detectable range of the focus detection means. Furthermore, in the above publication, the maximum differential lens amount compared with a predetermined value is a fixed value unique to the lens read from the lens ROM, and is not a variable amount that changes depending on the current position of the lens. do not have.

“Problem to be Solved by the Invention” In the above-mentioned conventional technology, the necessity of low contrast scanning is simply determined by comparing the maximum defocus amount of the lens with a predetermined value that changes depending on the brightness. Since the current position of the lens and the focus detectable range are not taken into account at all, there is a problem in that it is not possible to correctly determine the necessity of low contrast scanning.

For example, when the lens is stopped at one end position, if the other end position is not included in the focus detectable range, it is necessary to perform a low contrast scan toward the other end position. However, when the same lens is stopped at a position other than the terminal position, there is no need to perform low contrast scanning if the far terminal position is included in the focus detectable range. In other words, even if the maximum defocus amount of the lens degree read from the lens ROM is the same, the necessity of low contrast scanning may change depending on the current position of the lens. In the above-mentioned conventional technology, it is not possible to determine whether the need for low contrast scanning changes depending on the current position of the lens.

The present invention has been made in view of these points, and its purpose is to provide a focus detection device that can correctly determine the necessity of low-contrast scanning in consideration of the current position of the lens. It's about doing.

[Means for Solving the Problems] In order to achieve the above object, the focus detection device according to the present invention includes an exchangeable photographing lens (1) as shown in FIG. A focus detection means (2) for detecting the focus state of the lens (1), a lens drive means (3) for driving the lens (1), and a determination as to whether or not focus detection by the focus detection means (2) is impossible. A focus detection impossible determination means (4), a first output means (5) for outputting information regarding the terminal end position Nmax of the lens (1), and information regarding the defocus amount DFa that can be detected by the focus detection means (2). a second output means (6) that outputs the current position N of the lens (1), a lens position detection means (7) that detects the current position N of the lens (1), and a defocus amount from the current position NL of the lens (1) to the final position. Lens scanning prohibition determining means (8) that determines that lens scanning is prohibited when (Nmax - N L) / K, N L / K is within the defocus i D Fa that allows focus detection; and a focus detection impossible determining means When it is determined by (4) that focus detection is not possible and the lens scanning prohibition determining means (8) determines that lens scanning is not prohibited, the lens driving means (3) drives the lens (1) and the focus detecting means ( 2), the lens scanning control means (9) performs the focus detection operation, the focus detection impossible determination means (4) determines that the focus cannot be detected, and the lens scanning prohibition determination means (8) determines that lens scanning is prohibited. It is characterized in that it sometimes comprises a display means (10) for displaying that focus cannot be detected.

Note that when the lens scanning prohibition determining means (8) determines that lens scanning is not prohibited, the defocus amount (N+nax/
2 K) is the defocus amount D Fa that allows focus detection
intermediate position determining means (11) for determining whether the
When the intermediate position determining means (11) determines that the defocus amount is within the defocus amount DFa that allows focus detection, the lens driving means (3) moves the lens (1) to the intermediate position (N max / 2 ). An intermediate position setting means (12) may be added to control the position.

However, FIG. 1 is an explanatory diagram showing the configuration of the present invention in mechanical 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 front focus and back focus are distinguished by the sign. 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).

When it is determined that focus detection is impossible and lens scanning is not prohibited, the focus detection means ( By performing focus detection in step 2), 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.

Information regarding the end position of the lens (1) is lens-specific information and is output from the first output means (5). On the other hand, the defocus amount DFa that can be detected by the focus detection means (2) is determined by the configuration of the focus detection means (2), and is output from the second output means (6). Lens (1)
The current position NL of is detected by the lens position detection means (7). The current position NL of the lens (1) is usually detected as the amount of lens extension from the infinity position, and in this case, since the lens extension amount at the infinity position is 0, the first output means (5) It is sufficient to output only the lens extension JiN+nax at the contact position. From the current position NL of the lens (1) based on the information regarding the terminal position N max output from the first output means (5) and the information on the lens position ffNL detected by the lens position detection means (7) Defocus amount to the nearest position (Nma
x - NL)/K, and the defocus amount (NL/K) from the current position WNL to the infinite position is determined.

Here, I is a constant. Lens scanning prohibition determination means (
8) are these defocus amounts (Nmax-NL)/
When K and (NL/K) are within the defocus amount DFa that can be detected by the focus detection means (2), it is determined that lens scanning is prohibited. This is because in such a case, even if lens scanning is performed, a lens position at which focus can be detected cannot be found.

When the lens scanning prohibition determining means (8) determines that lens scanning is prohibited, the lens scanning control means (9) does not perform lens scanning, and the display means (10) displays an indication that focus detection is impossible. By the above-described operation, unnecessary lens scanning can be omitted, and it is possible to quickly display that the focus cannot be detected.

By the way, at the lens position illustrated in FIG. 1, the defocus amount (N
max -N L)/K is within the focus detectable defocus iDPa, but the defocus amount (NL/K) from the current position N to the infinite position is within the focus detectable defocus amount DFa Even if the value is larger than , it is not determined that lens scanning is prohibited. In this case, the intermediate position determining means (11) determines whether the defocus amount (Nmax/2K) from the intermediate position to the final position of the lens (1) is within the defocus JI D Fa that allows focus detection. Ru. If it is determined that (N max / 2 K )≦DFa, the lens scanning by the lens scanning control means (9) is prohibited, and the lens (1) is moved to the intermediate position under the control of the intermediate position setting means (12). Move to position (Nmax/2). In the example shown in FIG. 1, when the lens (1) is at the intermediate position, the entire focus range of the lens (1) is included in the focus detectable range 2DFa, so the lens is only moved to the intermediate position. No lens scanning is performed.

[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 within the interchangeable lens, and transmits information specific to the interchangeable lens to the microcomputer (μC). (A
FC) is a focus detection circuit that photoelectrically converts the subject light that has passed through the lens and outputs focus detection data, which converts the focus detection data into a digital signal and outputs it to a microcomputer (μC). (DSP) is a display circuit,
Indicates whether the lens is in focus or if focus cannot be detected. (I
LM) is an auxiliary light emitting device for irradiating a subject with auxiliary light for focus detection. (M) is a motor for driving the focusing lens of the interchangeable lens, and extends and retracts the lens under the control of a lens drive circuit (LDC). The lens drive circuit (LDC) receives a motor drive speed signal, a motor drive direction signal, and a motor stop control signal from the microcomputer (μC), and drives the motor (M) based on these signals. . (E
The encoder (NC) detects the amount of rotation of the motor (M) and outputs pulses to the microcomputer (μC) in accordance with a predetermined amount of rotation of the motor (M).

Here, the microcomputer (μC) uses a lens position counter N to know as an absolute amount the amount of lens extension from the infinity position, which is the most retracted state of the lens.
It has a built-in L. This lens position counter NL is reset to NL=O by an internal command when the lens is retracted to the infinite position, and when the lens is extended, the encoder (E N C
) is counted up in response to pulses from the encoder (ENC), and when the lens is retracted, it is counted down in response to pulses from the encoder (ENC) by an internal command. When the lens is extended to the closest position, the value of the lens position counter N becomes NL=N+nax.

This maximum extension amount N max differs depending on the lens, and is read into the microcomputer (μC) from the lens circuit (LEC) 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 reaches a predetermined voltage, the microcomputer (μC)
doesn't work. When the voltage of the capacitor (C1) exceeds a predetermined voltage, the microcomputer (μC) is reset and starts operation from step #5 (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
cc+) 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). (SA
F) is the AF mode switch, and this switch (SA
When F) is ON, an autofocus mode is selected that drives the lens to the in-focus position based on the focus detection result, and when the switch (SAF) is OFF,
A manual focus mode is selected in which only in-focus or out-of-focus is displayed based on the focus detection result and no lens driving is performed. (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 all structure.

In the zoom lens with a macro mechanism used in this example, autofocus mode is disabled when the zoom ring is set to the macro zone.
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. When the power-on reset is performed, the microcomputer (μC) executes the programs starting from #5 shown in FIG. First, all flags are reset in #5. Next, turn on the main switch (SM) with #10.
Determine whether

If the main switch (SM) is not turned on, the determination in #10 is repeated until it is turned on. Main switch (SM
) is ON, the lens initial position calculation subroutine (Figure 9) is executed in #15, the ω renormalization subroutine (Figure 10) is executed in #2°, and the lens initial position set is executed in #25. After executing the subroutine (Figure 11),
At #30, it is determined 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 #10. #
If the main switch (SM) is not OFF at 30, #
Proceed to step 45.

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).

From the lens circuit (LEC), the lens attachment signal IC
P, the macro zone signal SMZ, the same magnification upper macro lens mounting signal LCPR1, the maximum extension amount N max, the focal length r, the conversion coefficient, etc. are input to the microcomputer (μC). Here, the conversion coefficient includes the defocus amount DF
This is a coefficient for converting ΔN into a lens drive amount ΔN. #1
In step 005, it is determined whether or not the same magnification macro lens attachment signal LCPR is present.

If the same magnification macro lens is attached in #1005, the defocus amount DFs for setting the lens initial position is set to DF+n/2 in #1040, and the process returns to the step in which the subroutine was called. Here, DF+^ is the maximum defocus amount that covers the range from the closest position to the infinity position of the lens. If the macro lens is not attached at the same magnification level in #1005, the 'defocus amount DPI) is determined in #1008. This defocus amount DF
b is the amount of defocus from the infinite position to the lens position Nb determined according to the photographing magnification β. In this example, based on the information on the focal length f, the commonly used photographic magnification β
The information of the lens position Nb, which is set in advance in consideration of
Reading from the table.

Table 1 shows commonly used photographic magnification β and lens position N determined accordingly for lenses with various focal lengths.
The defocus amount DFb corresponding to b and the maximum defocus JL D F m of the lens are shown. Note that DFa is a defocus amount that allows focus detection and is determined by the configuration of the focus detection circuit (AFC), and the focus detection range is 2DFa, which is twice that amount.

In #1010, it is determined whether DFb>DFa.

If DFb>DFa in #1010, the defocus amount DFs for setting the lens initial position is set to DFa in #1030.
Then, in #1060, the lens position set flag 5ETF is set to 1, and the process returns to the step where the subroutine was called. #, if DFb≦DFa in 1010, #
1020 is the defocus amount D for setting the lens initial position.
Fs is set to DFb, the lens position set flag 5ETF is set to 1 in #1050, and the process returns to the step where the subroutine was called.

In Table 1, in the above table, when the 28-135 mm zoom lens is at 135 mm, t is 70-210 mm, and the 28-135 mm zoom lens is at 2.
When at 10mm, the book is data when a 75-300mm zoom lens is at 300mm.

FIG. 12 is a diagram for explaining the meaning of steps #1010 to #1030. Figure (a) shows a case where the defocus 1DFb from the lens position Nb to the infinity position determined according to the imaging magnification β is larger than the defocus amount DFa that allows focus detection. is set as DFs=DFa. Therefore, at the initial lens position 1Ns=DFsXK, the infinity position is included in the focus detectable range 2DFa, and if the focus cannot be detected, it is only necessary to scan in the direction in which the lens is extended. The same figure (b) shows the case where the defocus amount DFb from the lens position Nb to the infinity position determined according to the imaging magnification β is less than or equal to the focus detectable def] - the amount of waste DFa, In this case, DFs=DFb. In this case as well, lens initial position N5=DFs
In XI, the infinity position is the focus detectable range 2D.
If the focus cannot be detected, it is sufficient to scan only in the direction in which the lens is extended.

FIG. 10 is a flowchart showing the contents of the ω renormalization subroutine. When this subroutine is called, lens renormalization starts at #1100, and #1 ],
05, it is determined whether the infinite position detection switch (Sω) is ON. #1105 If the switch (Sω) is not ON, the switch (S(1)) will be ON.
05 is repeated. When the lens is retracted to the infinity position in #11.05 and the switch (S■) is turned on, the lens retraction is stopped in #1110, and the lens is retracted in #11.
At step 15, 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 defocus amount DFs for setting the lens initial position is multiplied by the conversion coefficient K in #1200 to calculate the lens drive amount ΔN=DFsXI from the infinity position, and #
At 1205, lens extension is started. In #1210, it is determined whether the lens drive amount has reached ΔN. #121
If the lens drive amount has not reached ΔN at 0, the determination operation in #1210 is repeated until the lens drive amount reaches ΔN. If the lens drive amount reaches ΔN in #1210, #1
At step 215, lens driving is stopped and the process returns to the step from which the subroutine was called.

Returning to the flow of FIG. 3, in #45, it is determined whether the AP mode switch (SAF) is ON.

If the AF motor switch (SAF) is not ON in #45, the flag MF indicating manual focus mode is set to 1 in #50, and the process proceeds to #80. If AF mode switch (SAF) is ON in #45, #5
5, it is determined whether the flag MF is 1 or not. MP with #55
If = 1, it means that the switch (SAF) has just been turned on, and the flag MF is set to 0 in #60 and #6
Proceed to step 5. In #65 to #75, the above-described subroutines of lens initial position calculation, co renormalization, and lens initial position setting are executed to set the lens initial position, and then the process proceeds to #145. If MF=1 is not found in #55, it means that the switch (SAF) has been on for some time, and the process proceeds 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 the process proceeds to #105. If the photographing lens is attached at #80, it is determined whether the flag LENOF is 1 at #90. If LENOF=1 in #90, it means that the lens has just been attached, and the flag LENOF is set in #95.
After setting F to 0 and setting the lens initial position in #65 to #75, the process proceeds to #145. If LENOF is not 1 in #90, 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. If the macro zone switch (SMZ) is ON in #105, it is determined in #115 whether the flag SMZOFF is 1. #1] If SMZOFF = 1 in 5, it means that the macro zone switch (SMZ) has just been turned on, so in #120, set the flag SMZOFF to 0, and set the initial lens position in #65 to #75. After that, proceed to #145. #115 If TSMZOFF=1, it means that the macro zone switch (SMZ) has been turned on before, and the process proceeds to #125.

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

If #135 and 5ROFF = 1, it means that the reset switch (SR) has just been turned on, and #140
After setting the flag 5ROFF to 0 and performing the lens initial position setting in #65 to #75, the process proceeds to #145. #135
If it is not 5ROFF-4, 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 (SM),
Immediately after the F mode switch (SAF) is turned on or the lens is attached, the macro zone switch (SMZ
) is turned on, or switch to reset 1 (S
R) is turned ON, or if the focus cannot be detected even after performing the low-contrast scan described later and the camera is turned ON again after turning off the shooting preparation switch (Sl) (#
(see #155), lens initial position cell l'(#65
~ #75) is performed, and in other cases, lens initial position setting is not performed. Therefore, when the probability of focusing near the previous lens position is high, such as when photographing a similar scene or when shooting multiple frames in succession, the initial lens position is not set and the focus is Compared to the case where the lens initial position is set every time detection is performed, power consumption is reduced and the time required for focus adjustment is reduced.

In #145, it is determined whether the photographing preparation switch (Sl) is ON. If the photographing preparation switch (Sl) is not turned on, press #40 to turn off all displays and return to #30. Below, #30, #45, #80, #105, #125
, while going around the loop passing through #145, check the status of the main switch (SM), AP mode switch (SAF), lens attachment signal ICP, macro zone switch (SMZ), reset switch (SR), and shooting preparation switch (31>). Monitor.

In the middle of this loop, the main switch (SM) is turned off.
When it is, as mentioned above, ■ Renormalization (#35)
and waits until the main switch (SM) is turned on again (#10). Also, in the middle of the loop, one of the switches (SAF), (SMZ), and (SR) is turned ON.
or when the lens is attached, perform lens initial position setting 1 to (#65 to #75) each time.

In this way, the camera waits for the shooting preparation switch (Sl) to be turned on. When the shooting preparation switch (Sl) is turned on in #145, the camera waits for the shooting preparation switch (Sl) to be turned on in #155 (step #155) to start focus detection. Proceed to Figure 4).

In #155, it is determined whether a low contrast scan end flag LSENDF, which will be described later, is 1.

Initially, since LSENDF=O, focus detection is performed in #175, and it is determined in #180 whether focus detection is impossible. If the focus cannot be detected in #180, the process proceeds to #285 (FIG. 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 (Figure 8). If the brightness is not low in #185, then in #190 and #191 (Figure 5), (N max NL)/K > D Fa or NL/K > D It is determined whether F a . However, the fact that the focus cannot be detected means that there is no way that the focus can be detected even if you perform a low contrast scan (detecting the focus while driving the lens and searching for a position where the focus can be detected). It is wasteful to perform the con scan.Therefore, the process proceeds to #255 (see FIG. 7) without performing the low con scan, and a focus detection failure display is performed.

If condition ■ is satisfied in #190 or #191, #
192, it is determined whether N max/2 K≦DFa...■ is satisfied. Here, Nmax/2
K is the amount of defocus from the intermediate position to the final position of the photographing lens (that is, D F m/2 >, which is determined depending on the attached lens. As mentioned above, 2DFa is the amount of defocus from the intermediate position to the final position of the photographic lens. ) is the amount of defocus that allows focus detection, determined by the configuration of Since Nmax/K is included in the focus detectable range 2DFa, there is no need to perform a low contrast scan.Therefore, in order to move the lens to the intermediate position Nmax/2, in #193, the lens drive amount ΔN = Nmax/
2-N is calculated, and lens driving is started in #1941. In #1942, it is determined whether the lens drive amount has reached ΔN. If the lens drive amount has not reached ΔN in #1942, continue #194 until the lens drive amount reaches ΔN.
Repeat the judgment operation in step 2.

# ], if the lens drive amount reaches ΔN in 942, #
After stopping the lens drive in 1943 and performing focus detection in #195, it is determined in #196 whether focus detection is impossible. If the focus cannot be detected in #196, there is no way that the focus can be detected even if the low contrast scan is performed, and it is wasteful to perform the low contrast scan. Therefore, the process proceeds to #255 (FIG. 7) without performing the low contrast scan, and displays that the focus cannot be detected. If the focus cannot be detected, the process proceeds to #285 (FIG. 7) to make a focus determination.

-41=28- If condition #192 is not satisfied, the total focus range of the lens is Nmax/no matter where you change the lens position.
K cannot be covered within the focus detectable range 2DFa. Therefore, in this case, a low-contrast scan is unavoidably performed, but we devised a way to shorten the time required for a low-contrast scan by limiting the range of the low-contrast scan to as narrow a range as possible. ing. That is, in #198 (FIG. 6), the scanning amount in the feeding direction is calculated as ΔN=Nmax-NL-DFaXK.

This is because even if the lens is not extended to the maximum extension position N max, if it is extended to a position DFaXK in front of the user, the maximum extension position N max will also fall within the focus detectable range 2DFa. Next, in order to know the scanning direction, it is determined in #200 whether the flag FOWF is 1.

This flag FOWF is a flag indicating that scanning is to be performed in the direction (FOWard). When a low contrast scan is performed for the first time, the flag FOWF is reset to 1, so FOWF=1 is not set. Therefore, the process first proceeds to #205, sets FOWF=1 in #205, and proceeds to #220. In #220, a signal is output to the lens drive circuit (1-DC) to drive the lens (in the extending direction), and after focus detection is performed in #225, the signal is output in #230.
Determine whether focus detection is impossible. If focus detection is not possible in #230, the flag FOWF is reset in #233, and the process proceeds to #285 (FIG. 7) to perform focus determination. If the focus cannot be detected in #230, it is determined in #235 whether the lens drive amount has reached ΔN. If the lens drive amount has not reached ΔN in #235, return to #225,
While continuing to drive the lens in the extending direction, it is determined whether the focus cannot be detected. If the lens drive amount has reached ΔN in #235, the lens drive is stopped in #240, and in #24
5, it is determined whether the lens position set flag 5ETF is 1 or not. If 5ETF = 1 in #245, it is determined that focus cannot be detected over the entire focus range of the lens without scanning in the renormalization direction.
In order to display that the focus cannot be detected, the process advances to #255 (FIG. 7). If 5ETF is not equal to 1 in #245, it is determined in #250 whether the flag FOWF is 1.

If FOWP=1 in #250, this means that the lens position where focus detection was possible was not found even though scanning was performed in the extending direction, so next scan in the retracting direction. return. If FOWF=1 in #200, it means that the scan in the feed-out direction has already been completed, so in #210, the scan amount in the renormalization direction is ΔN = D Fa X K-N
Calculated as t-. This means that even if you do not renormalize to the infinite position, if you renormalize only the position in front of DFa×,
This is because the infinite position also falls within the focus detectable range 2DFa.

In #215, the flag FOWF is set to 0 to indicate that the scan is in the renormalization direction, and the process proceeds to #220. #
220 outputs a signal to the lens drive circuit (LDC) to drive the lens (in the retraction direction), and #225 to #2
After passing through 45, it reaches #250 again. This time, FOWF=
Since it is not 1, it does not return to #200, but #255
Proceed to (Figure 7). In other words, if FOWF is not 1 in #250, it means that both the scanning in the extending direction and the scanning in the retracting direction were performed, but no lens position where the focus could be detected was found, so the focus cannot be detected in #255. It performs display.

If focus detection becomes possible in #230 during scanning in the retraction direction, the flag FOWF is reset to 1 in #233, and the process proceeds to #285 (FIG. 7) to perform focus determination.

#255 (Fig. 7) When displaying focus detection failure, #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 the low contrast scan was performed. Note that if the focus cannot be detected even though the entire focus range of the lens is included in the focus detection range 2DFa (specifically, #191 or #19
6 to #255), the flag LSE is set in #260 even if low contrast scan is not actually performed.
Let NDF be 1. This is because even if a low contrast scan is performed, it is impossible to find a lens position where the focus can be detected. Next, #265 is the flag F indicating the scanning direction.
After returning OWF to 0, press #27o to turn the shooting preparation switch (
SL) is ON. If the photographing preparation switch (Sl) is not ON in #270, the entire display is turned off in #40 and the process returns to #30. Press #270 to turn on the shooting preparation switch (
Sl) is ON, performs focus detection in #275 and #
In step 280, it is determined whether focus detection is impossible. If the focus cannot be detected in #280, the process returns to #270. If the focus cannot be detected in #280, the lens position set flag 5ETF is set to 0 in #285, the low contrast scan end flag LSENDF is set to O in #290, and it is determined whether focus is achieved in #295.

If it is determined that the focus is not in focus in #295, the process proceeds to #300, where the in-focus and focus detection failure display is erased, and the lens drive amount ΔN=DFX is determined based on the defocus amount DF in #305.
, K are calculated, and lens driving is started in #310. #3
In step 11, it is determined whether the lens drive amount has reached ΔN.

If the lens driving amount has not reached ΔN in #311, the determination operation in #311 is repeated until the lens driving amount reaches ΔN. #311 When the lens drive amount reaches ΔN, #
At 312, the lens drive is stopped and the process returns to #270.

If the shooting preparation switch (Sl) remains ON in #270, focus detection is performed in #275, and then in #280 to #290
After that, focus determination is performed again in #295. #30 mentioned above
Since the lens is driven toward the in-focus position in steps #5 and #310, there is a high possibility that the focus will be achieved here. If the camera is in focus in #295, the focus is displayed in #315, and it is determined in #320 whether the photographing preparation switch (Sl) is ON. #320 and the shooting preparation switch (Sl) is set to O.
If N is selected, the determination operation of #320 is repeated until the photographing preparation switch (Sl) is no longer ON, resulting in a so-called focus lock state. Note that in a camera unrelated to the present invention or in a focus priority mode, release is permitted in this focus locked state, and when the release button (not shown) is pushed to the second stroke,
A camera performs a release operation. If the photographing preparation switch (Sl) is no longer ON in #320, the display is turned off in #40 and the process returns to #30. That is, by turning off the photographing preparation switch (Sl), the above-mentioned focus lock state is released.

After the shooting preparation switch (Sl) is turned off, it is turned on again.
If so, it may be determined as LSENDF-1 in #155. This was previously set as the shooting preparation switch (S).
I turned on l) and performed focus detection, but the focus could not be detected.
This is a case where a lens position where focus detection is possible cannot be found even after performing a low contrast scan, or a case where a lens position where focus detection is possible cannot be found even after performing a low contrast scan. In this case, #157 flag LS
Return ENDF to 0, set the lens initial position in #65 to #75, and proceed to #145. Note that when proceeding to #157, the photographing preparation switch (Sl) must be turned OFF and then ON.

The reason for setting the initial lens position at this time is that when the low-contrast scan end flag t, S E N D F is set, the probability that the subject you want to photograph exists near the current lens position is low; This is because, especially when a low contrast scan is actually performed, the lens position will be biased toward infinity or near the closest position, so it is necessary to return it to an appropriate position.

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 4), 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. The auxiliary light emitting device (ILM) shown in Fig. 2 is usually a combination of a light emitting diode and a light emitting optical system mounted externally above the photographic lens of the camera, or installed on the front of the camera body. including the system. 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 coincides with the optical axis of the photographing lens. Therefore, the luminous flux range of the optical system for auxiliary light projection and the luminous flux range for focus detection have a disparity, and from a predetermined distance in front of the photographing lens (197 = 136 = varies depending on the angle of view) On the other side, the light flux range for focus detection is completely included in the light flux range of the optical system for projecting the auxiliary light. This distance is the lower limit of the range in which the subject can be irradiated with the auxiliary light to enable focus detection, and it is useless to emit the auxiliary light for a subject that is closer than this distance. Further, when a long focal length lens is attached to the camera, the auxiliary light is vignetted by the lens barrel, so the auxiliary light does not hit 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 the auxiliary light is TT.
Although it can be made smaller by adopting the L-type auxiliary light system,
Increasing the upper limit of the range in which focus detection is possible by irradiating the auxiliary light means that the reachable distance of the auxiliary light is at most 10+n.
So I can't expect much from it. Therefore, #330
Determine whether the focal length f of the lens is 250 mm or more, and if f≧250 in #330, it is determined that the auxiliary light may be vignetted due to the long lens length, and the auxiliary light is emitted. Instead, the process proceeds to #190 (FIG. 5), where it is determined whether a low contrast scan is necessary. In addition, when shooting with a long focal length lens, there are many cases where the auxiliary light does not reach the subject.
There is no problem even if the auxiliary light emission is prohibited. If f≧250 is not determined in #330, it is determined in #335 whether or not there is a macro lens attachment signal LCPR of equal or larger magnification. #335 If a macro lens with a magnification of 100% or higher is attached, the camera determines that the shooting is at close range, which is closer than the lower limit of the range where focus detection can be performed using fill-in light, and does not emit fill-in light. #19
0 (FIG. 5), it is determined whether a low contrast scan is necessary. If in #335 a macro lens of equal or larger magnification is not attached, an auxiliary light is emitted in #340, focus detection is performed in #345, and it is determined in #350 whether focus cannot be detected. The auxiliary light is emitted only for a predetermined period of time for each focus detection. If the focus cannot be detected in #350, the process proceeds to #395. #350 If the focus cannot be detected, adjust the lens position to an intermediate distance (for example, 4 m) where focus detection using the auxiliary light is possible, or to a distance where there are relatively many shooting scenes (for example, 3 m). Lens drive amount ΔN- with #355
(f2/Do)xK-N is calculated, and lens driving is started in #360. In #361, the lens drive amount is Δ
Determine whether N has been reached.

If the lens driving amount has not reached ΔN in #361, the determination operation in #361 is repeated until the lens driving amount reaches ΔN. If the lens drive amount reaches ΔN in #361, #
At 362, lens driving is stopped. Then, in #370, the auxiliary light is emitted, in #375, the focus is detected, and in #380, the focus is detected.
Determine whether focus detection is impossible. If the focus cannot be detected in #380, the process proceeds to #395. If the focus cannot be detected in #38o, the focus is not detected in #385, and
In #390, it is determined whether the photographing preparation switch (Sl) is ON. #390 Shooting preparation switch (Sl) is turned on
If so, return to #375. If the shooting preparation switch (Sl) is not ON in #390, turn off the display in #40,
Return to #30.

At #395, the display that focus cannot be detected is erased, and at #4°O, it is determined whether focus is achieved. If the focus is #400, #4
20 to display the focus, and #425 to press the shooting preparation switch (
SL) is ON. #425 If the shooting preparation switch (Sl) is ON, the shooting preparation switch (Sl) is turned on.
The determination in #425 is repeated until Sl) is no longer ON. If 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 0 is not in focus, #405 is the defocus amount DF.
Then, the lens drive amount ΔN=DFXK is calculated, and lens drive is started in #410. In #412, it is determined whether the lens drive amount has reached ΔN. #4] If the lens driving amount has not reached ΔN in step 2, the determination operation in #412 is repeated until the lens driving amount reaches ΔN. If the lens drive amount reaches ΔN in #412, the lens drive is stopped in #413, and it is determined in #415 whether the photographing preparation switch (Sl) is ON. If the photographing preparation switch (Sl) is ON in #415, the process returns to #370; if it is not ON, the display is turned off in #40 and the process returns to #30.

Finally, the correspondence between the basic configuration of the present invention shown in FIG. 1 and the embodiment shown in FIG. 2 will be explained. The lens circuit (L E C) of FIG. 2 is included in the lens (1) and includes a first output means (5).

Further, the focus detection circuit (AFC) includes focus detection means (2
) is supported. The defocus amount DFa that can be detected by the focus detection circuit (AFC) is fixedly stored in the memory in the microcomputer (μC), and this memory is There is. The lens drive circuit (LDC) is a lens drive means (3)
It corresponds to Step #180 in FIG. 4 corresponds to the focus detection failure determining means (4). The encoder (ENC) shown in Fig. 2 and the lens position counter N that counts its output pulses are lens position detection means (7).
It corresponds to

Steps #190 and #191 in FIG. 5 correspond to the lens scanning prohibition determining means (8). The program shown in FIG. 6 corresponds to the lens scanning control means (9). The display circuit (DSP) shown in FIG. 2 corresponds to the display means (10). Step #192 in FIG. 5 corresponds to intermediate position determining means (11), and steps #193 and #194 correspond to intermediate position setting means (12).

[Effects of the Invention] As described above, the present invention prohibits the low contrast scan and immediately displays the focus detection failure display when the focus cannot be detected even if the low contrast scan is performed. This has the advantage that there is no significant power consumption, and the time until the focus detection failure display is displayed can be shortened. In addition, particularly in the present invention, the current position of the lens is detected, and when the defocus amount from the current position of the lens to the end position is within the defocus amount that allows focus detection, low contrast scanning is prohibited. This makes it possible to accurately determine changes in the need for low-contrast scanning due to changes in the current position of the lens, and reduces the chances of low-contrast scanning when the lens is stopped near an intermediate position. It has the effect of making you feel better.

In addition, when it is determined that low contrast scanning is not prohibited, if the defocus amount from the intermediate position to the end position of the lens is within the defocus amount that allows focus detection, the lens is moved to the intermediate position and focus detection is performed. If you do this, you can further reduce the chances of low contrast scanning.

[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. 12 is an explanatory diagram of the same operation. (1) is the lens, (2) is the focus detection means, (3) is the lens drive means, (4) is the focus detection failure determination means, (5) is the first output means, and (6) is the second output. (7) is a lens position detection means; (8) is a lens scanning prohibition determination means;
(9) is lens scanning control means, (10) is display means, (
11) is intermediate position determining means, and (12) is intermediate position setting means.

Claims (3)

[Claims] (1) An interchangeable photographic lens, a focus detection means for detecting the focus state of the lens, a lens drive means for driving the lens, and an inability to detect focus for determining whether focus detection by the focus detection means is impossible. a determining means, a first outputting means for outputting information regarding the end position of the lens, a second outputting means for outputting information regarding the amount of defocus that can be detected by the focus detection means, and detecting the current position of the lens. A lens position detection means, a lens scanning prohibition determination means that determines that lens scanning is prohibited when the defocus amount from the current position of the lens to the end position is within the defocus amount that allows focus detection, and a focus detection impossible determination means. a lens scanning control means for driving a lens by a lens driving means and causing a focus detecting means to perform a focus detection operation when it is determined that focus detection is impossible and a lens scanning prohibition determining means determines that lens scanning is not prohibited; A focus detection device comprising: display means for displaying that focus cannot be detected when it is determined that focus detection is not possible by detection failure determination means and when lens scanning is determined to be prohibited by lens scanning prohibition determination means. (2) When the lens scanning prohibition determining means determines that lens scanning is not prohibited, intermediate position determination determines whether the defocus amount from the intermediate position to the final position of the lens is within the defocus amount that allows focus detection. and an intermediate position setting means for controlling the lens driving means to move the lens to an intermediate position when the intermediate position determining means determines that the defocus amount is within a defocus amount that allows focus detection. The focus detection device according to claim (1). (3) A control means is added that prohibits the operation of the lens drive means and causes the display means to display that the focus cannot be detected when a lens position where the focus can be detected cannot be found by the lens scanning by the lens scanning control means. The focus detection device according to claim 1, characterized in that: