JPS581109A - Automatic focus detection controller - Google Patents

Abstract

PURPOSE:To prevent distance measurement from being carried out while an image on a sensor has deficient contrast, by forcibly driving an optical system when the image on the sensor does not have enough contrast for the distance measurement. CONSTITUTION:Sensors S1 and S2 are arranged in front of and behind the reference focal plane of a lens in a camera, etc., and an object image to be picked up is projected upon them through the lens. When a power source is turned on, an initial resetting signal resets flip-flps FF1 and FF2. The flip-flop FF1 and FF2 count clock pulses to generate two kind of pulses, and a flip-flop 6 is set by the output pulse of flip-flop FF3. An arithmetic circuit OPU processes the output signals of the sensors S1 and S2 to perform front focus/rear focus decision depending upon which sensor's object image to be picked up has greater contrast, and then outputs a lens turning-in/turning-out or a focusing signal. On the basis of the outputs of the sensors S1 and S2, deficient contrast detecting circuits CLD1 and CLD2 detect whether the object images to be picked up on the sensors S1 and S2 are deficient in contrast for the decision of the lens position of the arithmetic circuit OPU.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to an automatic focus detection control device for an optical device such as a camera.

In order to determine the lens position by detecting the contrast of the subject image in an automatic focus detection control device such as a camera, two sensors are placed on the optical axis at different distances from the lens, and which sensor captures the subject image. A common method is to determine front focus, rear focus, and focus by detecting whether the contrast is large.
It is known as No. 0032.

However, with this method, if the focus is extremely blurred or the subject itself does not have much contrast, the contrast of the subject image on the sensor will be very low, leading to incorrect judgments of front focus, back focus, and focus. There is a fear.

SUMMARY OF THE INVENTION It is an object of the present invention to provide an automatic focus detection control device that eliminates the above-mentioned drawbacks and can prevent incorrect lens position determination due to insufficient contrast of an image on a sensor.

The present invention will be described below by way of examples with reference to the drawings.

The figure shows an embodiment of the invention. Sensors S, , S, are arranged in front and behind the reference focal plane of a lens in a camera, etc., and a subject image is projected through the lens. First, when the power is turned on, the initial reset signal causes the flip-flops FF, ~FF
I. is reset. Fri7'7ClffF'F+
-FF'l Counts clock pulses and generates two types of pulses, and outputs pulses from flip-flop 7' FF to flip-flop FF.

is set. The arithmetic circuit OPU has sensors S+, St
The output signal is calculated and the front focus, rear focus,
It determines focus and outputs a lens retraction/extension signal or a focus signal. Contrast deficiency detection circuit CLD+
, CLDt is the sensor S1. S! From the output (or the signal from the arithmetic circuit OPU), it is detected whether the contrast of the subject image on the sensors St, St is insufficient for the lens position determination by the arithmetic circuit OPU. When the contrast of the subject image on the sensor S+ and St is insufficient for determining the lens position and distance measurement is possible, the outputs of the contrast deficiency detection circuit CLD+ and CLD are both H (high level) and the NOR circuit NOR, The output becomes L (low level). If the lens is not in the focused position, the focus signal from the arithmetic circuit OPU becomes L, the output of the NOR circuit NOR1 becomes H, and the analog switch A
S is turned on and analog switch AS is turned on.

Therefore, the lens retraction/extension signal from the arithmetic circuit OPU passes through the analog switch ASI and is sent as a lens drive signal to the lens drive unit, thereby driving the lens to the in-focus position. When the lens reaches the in-focus position, the focus signal from the arithmetic circuit OPU becomes H, the output of the NOR circuit NO& becomes L, and the analog switch A5. is turned off and analog switch Ass is turned on.

Furthermore, the output of inverter N becomes L, and AND circuit A
, , the output of At becomes L, and the analog switch AS
.

is turned off and analog switch AS4 is turned on. Therefore, the lens drive stop signal at a predetermined level is the analog switch A.
S4. AS! The light is sent to the lens drive unit through the lens, and the lens is stopped.

The lens signal is a signal that is inverted to H and L when the lens reaches the maximum retracted position and maximum extended position and is detected by the detection means. Now, if the lens signal is H, the contrast of the object image on the sensor -81, 8m is insufficient for determining the lens position and distance measurement becomes impossible, the contrast deficiency detection circuit CLD+,
The outputs of CLDt both become L and the NOR circuit No. R1
The output of NOR circuit N0R2 becomes H, the output of NOR circuit N0R2 becomes LK, the analog switch ASI turns off, and the analog switch A turns off.
SW turns on. Further, the output of the inverter N2 becomes L, the output of the OR EI circuit ot'tt becomes L, and the flip-flop F F't becomes L.

The reset of FF8 is released. Here, D flip-flop FF4. FF8 latches the lens signal by the pulse output of the flip-flop FFI, and the NOR circuit N
The rising edge of the output of 0RI is the D flip-flop FF.
FF. and AND circuit A, the output of AND circuit A4 becomes H, and flip-flop F is detected.
F, , is set, and the output of AND circuit A becomes H. Therefore, the output of the OR circuit OR becomes H, the analog switch ASj is turned on, and the analog switch AS4 is turned off. Operational amplifier OP is a lens drive stop signal between H and L and AND circuit A.

The H output of is input and the output is HK, and the H output of analog switch As,, AS! The lens is fed through the lens drive unit and the lens is fed out.

When the lens reaches its maximum extended position and the lens signal becomes L, the rising edge of the signal is applied to the D flip-flops FF, FF.
, and is detected by the exclusive OR circuit EO, and a pulse is output from the AND circuit A, and this pulse is sent to the D flip-flop FF? , FF, is counted by a counter consisting of
, , is inverted. Therefore, the output of the AND circuit A becomes H, the output of the AND circuit A becomes LK, and the output of the operational amplifier OP becomes L while the analog switch AS remains on.
Then, the L output is sent to the lens driving section, and the retraction of the lens is started.

After that, when the lens reaches the maximum retraction position and the lens signal becomes H, the rising edge is the D flip-flop FF.
It is detected by FF and the exclusive-orial path EO, and a pulse is output from the AND circuit A6. This pulse is counted by a counter consisting of flip-flops FFq and FFs, and its output becomes L, and the output of the AND circuit AI+At becomes L, turning off the analog switch AS and turning on the analog switch AS4. Therefore, the lens drive stop signal is sent to the analog switches A S 4 and A S t
The light is sent to the lens drive unit through the lens, and the lens is stopped.

When distance measurement becomes impossible when the lens signal is L, the lens is retracted, then extended, and then stopped, contrary to the above-described operation. At this time, the L lens signal is initially latched by the flip 70-tube FF, and the output of the inverter N4 is H, so the rise of the output of the NOR circuit NOR is caused by the flip-flops F'Fs, FF+a and the AND circuit A1. When detected, the output of AND circuit A6 becomes H.
Then, 7 lip flop FF ++ is set.

Therefore, the output of the operational amplifier OP becomes L and is sent to the lens driving section, and the lens is retracted. Thereafter, when the lens signal reaches the maximum retracting position and the lens signal becomes H, the flip-flops FF, .

When the lens reaches its maximum extended position and the lens signal becomes L, the counter FF? , FFδ becomes L, the outputs of AND circuits A, , A, become L, and a lens drive stop signal is sent to the lens drive section to stop the lens.

In this way, when distance measurement becomes impossible, the lens is driven only once over the entire lens drive range and then stopped, but if distance measurement becomes possible while the lens is being driven, the lack of contrast detection circuit CL D+ , at least one of the outputs of CLD* becomes H and the NOR circuit No R.

The output becomes L, and focusing is performed as described above.

In the above embodiment, the lens was driven using a lens signal, but a clock pulse with a sufficiently long cycle was used to accommodate the time required for the lens to move from the maximum retracted position to the maximum extended position (or vice versa). Similar lens driving can be performed by using this instead of the lens signal. Further, the present invention is not limited to the above-described embodiment, and can be applied to various types of automatic focus detection control devices to prevent erroneous distance measurement due to insufficient image contrast.

As described above, according to the present invention, when the contrast of the image on the sensor is insufficient for distance measurement, the optical system is forcibly driven. can be prevented from occurring.

[Brief explanation of drawings]

The figure is a block diagram showing an embodiment of the present invention. CL D+, CL D*...Lack of contrast detection circuit, N0R1, N0R1...NOR circuit, FF, ~F
Fo...Flip-flop, AS, ~AS4...
Atero 1. Guswitch, A, ~A, ... and circuit,
N, ~N4... Inverter, EO... Exclusive OR circuit, OR,, OR1... OR circuit, OP... Operational amplifier.

Claims (1)

[Claims] In an automatic focus detection control device that drives and focuses the optical system by determining the position of the optical system based on the output signal of a sensor on which an image is projected via the optical system, the contrast of the image on the sensor is determined by the contrast of the optical system position. An automatic focus detection control device comprising means for detecting insufficient judgment, and means for forcibly driving a focus system using an output signal of the means.