JPS61282827A - Focus detecting device - Google Patents

Abstract

PURPOSE:To detect a repetitive pattern which is hard to detect accurately by a simple device by correcting a photoelectrically converted signal at the time of use of auxiliary light by using the output of a photoelectric converted signal in the absence of the auxiliary light. CONSTITUTION:The photoelectric conversion output 201 of a sensor 101 in the absence of the auxiliary light is A/D-converted 102 and stored in a memory 104 with a control signal 208 through a multiplexer 103. Then, an auxiliary light source 108 ius energized with a control signal 210and the output of the sensor 101 is A/D-converted and inputted to a multiplexer 103. The signal of this time is subtracted 105 from the signal stored in the memory 104 last time with a control signal 208. Further, the result is divided 106 by a signal 105 from the memory 104 to obtain a signal 207, which drives a focus adjusting device 107 to drive a lens by a lens driving device 109, thereby making a display on a display device 110. Consequently, even a repetitive pattern which is hard to detect a focus can be detected accurately by the easy modification of software.

Description

DETAILED DESCRIPTION OF THE INVENTION Field of Application The present invention relates to a focus detection device such as a camera or an inspection device, and more particularly to a device that illuminates a target object with artificial light and performs focus detection using the reflected light.

<Prior art> Various methods have been known for focus detection systems used in cameras, and various methods have already been put into practical use. The pupil of the photographic lens is divided into two, and the image with parallax formed by the light flux passing through each divided pupil area is received by the sensor array and photoelectrically converted, and the phase difference between each photoelectrically converted signal is determined. Detects focus adjustment and status of photographic lens.

However, if the brightness or contrast of the subject is too low, the S/N of the photoelectric conversion signal will deteriorate, and if the subject has a periodic pattern, it will be easy to detect a false phase difference, and both will focus WtM operation becomes difficult.

As a solution to this, in the case of low brightness, the subject is supplementally illuminated with uniform light during focus adjustment to increase the subject brightness, and in the case of low contrast, the subject is illuminated with supplementary light with a pattern. A supplementary light illumination device is known that provides contrast.

The problem of the present application will be explained below using one drawing.

FIG. 1(L) shows the state when the auxiliary light having a pattern is illuminated. 1 is in the viewfinder field of view.

Assume that you are currently looking at a plain object with a reflectance of 90%.

2 represents the observation field of the focusing device.

3 represents the projection pattern of the auxiliary light. The light projection pattern illustrated here has a configuration in which a transparent zone and a shading zone are adjacent to each other in the center, with a gray zone sandwiching these.
) represents the photoelectric conversion signal, and the X coordinate corresponds to the distance in the horizontal direction.

Signal 4 is a signal obtained when the subject is illuminated with auxiliary light, and signal 5 is a photoelectric conversion signal obtained when only external light is used.

In this way, even if the object has almost no contrast, when a pattern is projected, a signal similar to that when there is contrast is obtained, so signal processing is possible and focus adjustment operation is performed.

On the other hand, some objects have a periodic pattern, and FIG. 2(a) depicts a case where such an object is observed within the viewfinder field of view 1. This pattern consists of repeating black and white bars to reduce the reflectance of each white and black background to 90%.
Figure (b) shows the photoelectric conversion signal 7 when only external light illuminates the subject.

It is difficult to process this signal to perform focus detection.

Furthermore, when a subject is illuminated with the fill light pattern in Figure 1, the photoelectric conversion signal can take the shape of 8 in Figure 3. The information of the target pattern is larger, and it is extremely difficult to perform focus adjustment using this photoelectric conversion signal. Further, although not shown in the drawings, it is clear that uniform fill-in illumination is ineffective against a subject with a periodic pattern.

Purpose The present invention aims to solve the above-mentioned problems and realize accurate detection without being limited by the appearance of a target object.

In order to achieve the above object, in a device that receives a light distribution corresponding to the image of the object, performs photoelectric conversion, and performs focus detection using the photoelectric conversion signal, the object is illuminated with auxiliary light. The photoelectric conversion signal when the auxiliary light is not illuminated is used to correct the photoelectric conversion signal when the auxiliary light is illuminated. Note that other features will become clear from the embodiments to be described subsequently.

<Embodiment> First, before explaining the detailed configuration of the embodiment, a signal correction method will be explained using mathematical formulas.

That is, let X be the distance coordinate in the horizontal direction.

If the reflectance of the subject is h (x), the intensity of external light on the subject is r (x), and the intensity of the auxiliary light is a (x), then the photoelectric conversion signal f of the subject image without auxiliary light illumination is
x(x) is f 1(x) = h (x) ・r (x)
(1), and the photoelectric conversion signal f2(x) under auxiliary light illumination is.

f2(x) = h (x) [r (x) +a (x
) ] (2) From equation (2), h (x) and from equation (1), Since, by substituting this into equation (3), r (x) is obtained. Here, assuming that normal external light has uniform intensity, r (x) = Cr -'i? D
(5), then the intensity distribution of the auxiliary light can be known from f 1 (x) and f 2 (x). However, formula (6).

contains an unknown constant Cr, but this is not a problem since the absolute value of the intensity distribution is not required to detect the phase difference in cases such as phase difference and detection methods.

In the following, a configuration applied to a single-lens reflex camera incorporating the focus detection device shown in FIG. 4 will be explained.The focus detection optical system shown in FIG.
In step 2), the pupil of the photographic lens is divided, and the light flux that has passed through each divided pupil is imaged on the sensor array of the sensor 101, causing a positional shift in each camera according to the degree of focus adjustment of the photographic lens IO. It is something. Specifically, 11 is a double wedge prism, 12 is an imaging lens, and 13 is a field lens placed on a planned imaging plane. 14 is a quick reference return mirror having a transparent area in the center; 15 is a sub-mirror that reflects a luminous flux toward the bottom; and 16 is a photographic film. Further, 17 is a condenser lens, 18 is a pentagonal prism, and 19 is an eye bead, and these constitute a finder for observing the copy image on the condenser lens 17.

20 is a plate having a pattern projected by auxiliary light, and 21 is a projection lens.

Reference numeral 108 denotes an auxiliary light source, for example, a flash tube can be used.

Reference numeral 110 denotes a display device, which is placed on a predetermined imaging plane near the condenser lens 17 and facing the pentagonal prism 18 in order to display the focus adjustment state. Figure 5 shows the electrical circuit.

Reference numeral 101 denotes a sensor, which photoelectrically converts a plurality of subject images formed by light fluxes that have passed through areas obtained by dividing the pupil of the photographic lens using a plurality of sensor arrays, as described above, and generates a photoelectrically converted signal 20.
1 to the AD converter 102. The AD converter 102 is an AD
After conversion, the digital signal 202 is sent to multiplexer 1
A multiplexer 103 is controlled by a control signal 208 from a focus adjustment device 107, which will be described later, and selectively outputs the input signal 202 to a memory 104 or a subtracter 105. The subtracter 105 inputs the signal 204 from the multiplexer 103 and the signal 205 from the memory 104, and its output 206 is sent to the divider 10B.The 0 divider 106 also receives the signal 205 from the memory 104. The output 207 is sent to the focus adjustment device 107.

The focus adjustment device 107 performs a well-known phase difference calculation process based on the input signal 207, calculates the current focus state of the photographic lens 10, and sends control signals 211 and 212 to the lens drive device 109 or the display device 110, respectively. Auxiliary light source 108 that performs appropriate lens movement and display
receives light projection control from the focus adjustment device 107 via a control signal 210.

The operation of the embodiment having the above configuration will be explained.

First, for example, during a release operation, the sensor 101 performs photoelectric conversion of a subject image using a sensor drive signal 209, and the photoelectric conversion signal 201 is converted into an AD converter 102.
The converted output signal 202 is input to multiplexer 163.

The multiplexer 103 is selected to the memory 104 side □ by the control signal 208 at the time of input.

The input signal 202 is output to 203.

It is stored in memory 104. The signal 203 at this time corresponds to the above-mentioned equation (1) f 1 (x).

Next, after a certain period of time has passed after the memory process has finished.

Or when proper signal processing is not performed.

The control signal 210 turns on the auxiliary light source 108 to project auxiliary light, and at the same time drives the sensor 101, and as before, the digital signal after AD conversion is input to the multiplexer 103. The multiplexer 103 is now selected to the subtracter 105 side, and the input signal 20
2 becomes the output signal 204. This signal 204 corresponds to f2(x) in equation (2) described above. An output signal 205 from the memory 104 is also input to the subtracter 105, and this signal is the signal previously stored in the memory 104 and is expressed as fl(x
), the output 206 is f2(x)-ft (x)
It means. This output 206 is then passed to the divider 106
The signal 206, that is, fl(
x) is also entered.

The output 207 of 106 is [f2(x)-ft(x)]/
It means f 1 (x).

This signal 207 is the intensity distribution of the auxiliary light when Cr=1 in the previous equation (6), and by inputting the signal 207, the focus adjustment device 107 can execute the calculations necessary for focus detection. Become.

<Effects> According to the present invention described above, there is an excellent effect that detection is possible even in the case of an object having a repetitive pattern, which has conventionally been difficult to detect automatically. In addition, the configuration for detection can be realized by simply changing the software of the signal processing Tametsu MicroΦ processor, and does not require major modifications such as adding one component or deforming the device, which is extremely convenient, especially for cameras. Use and be effective.

[Brief explanation of the drawing]

FIG. 3 is a diagram showing a subject having a sexual pattern, (b) is a diagram showing a photoelectric conversion signal, FIG. 3 is a diagram showing a photoelectric conversion signal, and FIG.
The figure is an optical sectional view showing the embodiment, and FIG. 5 is an electrical block diagram. In the figure, 11 is a photographing lens, 11 and 12 are secondary imaging systems, and l
Ol is a sensor, 104 is a memory, 105 is a subtracter, 10
5 is a divider, 107 is a focus adjustment device, 108 is an auxiliary light source, and 109 is a lens drive device.

Claims (1)

[Claims] (1) Receives a light distribution corresponding to the image of an object and performs photoelectric conversion,
When performing focus detection using a photoelectric conversion signal, in a device that illuminates an object with an auxiliary light, when the auxiliary light is illuminated using a photoelectric conversion signal in a state where the auxiliary light is not illuminated. A means for correcting the photoelectric conversion signal is provided,
A focus detection device characterized in that focus detection is performed using a corrected photoelectric conversion signal.