JPS5936204A - Detector for image-formation state of picture - Google Patents

Abstract

PURPOSE:To establish the range where the depth of focusing is approved and to enable the detection of the deviation between an image-formation point and a film plane, by determining the function corresponding to the contrast value in the detection of a photodetecting part and further determining the image- formation point. CONSTITUTION:The transmitted light of a main mirror 1 is totally reflected by an auxiliary mirror 3 and is made incident to a beam splitter 4, by which the light is trisected. The splitter 4 has semitransparent parts 4a, 4b, and a total reflection part 4c, and the energy of the luminous fluxes are equal to each other. A range finding element 5 has three line sensors 5a, 5b, 5c, to which the light of the splitters 4a-4c are respectively inputted. The contrast value Y indicating the sharpness of the photographing light near the image-formation point peaks at the image-formation point and decreases as it moves further from said point. If the entire part of the contrast curve is known, the peak position thereof is known and the peak position, i.e., the image-formation point is determined from the X-coordinates thereof.

Description

[Detailed description of the invention] Technical field The present invention relates to an image forming state detection device.

Prior art Conventionally, by detecting the contrast, that is, the sharpness of the image, it is possible to determine whether the imaging point is within the certified depth of focus, or whether the imaging point is in front of the certified depth of focus on the subject side of the intended focal plane, or When determining whether the image is in focus after the imaging point is outside the certified depth of focus on the opposite side of the subject from the intended focal plane, the defocus amount, which is the amount of deviation between the imaging point and the intended focal plane, that is, the film plane, is calculated. There was no way to detect it.

However, it is easy to quantitatively detect the amount of deviation between the lens imaging point and the film surface, where the contrast value is highest, and to judge whether the object is in focus, front focus, or rear focus based on that value. Become.

Purpose The present invention has been made in view of the above circumstances, and its purpose is to provide a detection device that determines the amount of deviation between an imaging point and a film surface by detecting contrast, which was conventionally considered impossible. .

Summary In the image forming state detection device according to the present invention, a plurality of light receiving sections are provided one point near the planned focal plane of the optical system, and coordinate values corresponding to the contrast value of the image detected by each light receiving section are provided. is calculated, a predetermined function having these coordinate values is obtained, and an imaging point is obtained from the coordinate values of the peak of this function.

An embodiment of the present invention will be described below based on the drawings.

In the optical system using the present invention, as shown in FIG. Transmits light. The light transmitted through this main mirror 1 is
It is totally reflected by the sub mirror 3 and enters the beam splitter 14,
This beam splitter 4 divides the beam into three parts. The beam splitter 4 has semi-transparent parts 4a, 4b and a total reflection part 4c,
The semi-transparent part 4a transmits 173 of the incident light beam and 2
When //3 is reflected, 1/2 of the incident light beam is transmitted through the semi-transparent portion 4b, and 1/2 is reflected, the energies of the three divided light beams become equal. Reference numeral 5 designates a distance measuring element, and as shown in FIG. The line sensors 5a and 5CJ are provided on the front side, that is, the front focus side, and the rear side, that is, the rear focus side, of the line sensor 5b on the optical axis, respectively, at equal intervals from the line sensor 5b. Each of the line sensors 5a+5b, 5c is an array of a plurality of charge coupled devices (CC0). In the distance measuring element 5, the light transmitted through the semi-transparent part 4a of the beam splitter 4 is transmitted to the line sensor 5.
a, the light reflected by the semi-transparent part 4'b of the beam splitter 4 enters the line sensor 5b, and the light reflected by the total reflection part 4c of the beam splitter 4 enters the line sensor 5c. Ru.

As shown in FIG. 3, the contrast value Y representing the sharpness of the photographing light that has passed through the lens near the image formation point reaches a peak value at the image formation point, and decreases as the distance from this image formation point increases.

By the way, the contrast curve shown in FIG. 3 has a certain regularity and can be approximated to a predetermined function. That is,
The contrast curve shown in Figure 3 changes the peak position and the width of the base on both sides depending on the position of the imaging point and the condition of the subject, but these changes can be understood as constant changes in a predetermined function. . Therefore, the entire contrast curve can be obtained by obtaining a sufficient number of coordinate points using a corresponding number of line sensors to determine the constant for determining the above-mentioned predetermined function (from the position of the line sensor, the X coordinate is The Y coordinate can be determined from the measured values. If the entire contrast curve is known, the position of its peak is also known, so the position of the peak, that is, the imaging point, can be found from its X coordinate.

The above is the principle of the present invention, but in the embodiment of the present invention, the following means are used to obtain constants for determining a predetermined function. That is, according to experiments, it has been found that the contrast curve shown in FIG. 3 can be well approximated to a parabola when graphed by taking the reciprocal of the Y coordinate. There are three constants in the general formula for a parabola, so in this case 3
If one line sensor is provided, a function can be obtained from the position and the reciprocal of the measured value, which simplifies the configuration.

In FIG. 4, three line sensors are provided according to the above, and if the image forming point of the photographing light incident on the distance measuring element is between the line sensor 5a and the line sensor 5b, the line sensor 5at5b+5C Cone trust values observed in YA respectively.

Assuming that YB and Yc, as shown in FIG. 5, the vertical axis represents the contrast fifY, and the horizontal axis represents the distance IsX of the optical axis passing through the line sensor, and if the position of the line sensor 5b is taken as the origin, then The peak of the contrast curve occurs between the line sensor 5a and the line sensor 5b, and the value of the contrast curve at the position of the line sensor 5a is YA, and the value of the contrast curve at the position of the line sensor 5b, that is, on the Y axis, is Y13, line sensor 5
The value of the contrast curve at position c is Yc.

Next, as shown in FIG. 6, the vertical axis is the reciprocal of the contrast value Y, y=l/Y, and the position of the line sensor f5a is -X with the position of the line sensor 5b on the film surface as the origin.
The line sensor 5a15b1 is plotted on a graph whose horizontal axis is the optical axis distance X, where the position of the line sensor 5C is Xo.
5C contrast value YA, YB, reciprocal of Yc A=l/YA IVB=1/YB, γc
= 1/Yc, this point γA・VB・V
A parabola containing C can be drawn. However, since the parabola is determined by the coordinate values of the three points as described above, the parabola corresponding to the contrast curve is determined from the reciprocals of the contrast values of the three line sensors.

Once the parabola corresponding to the contrast curve has been determined in this way, the coordinates of the apex of this parabola can be calculated, so that the position of the peak of the contrast curve, that is, the imaging point can be determined.

By calculating the distance between this imaging point and the film surface, it can be determined whether the imaging point is in front focus, within the range of the certified depth of focus, or in rear focus.

Now, the formula of the parabola determined from the reciprocal of the contrast value of the line sensor is Y=aX −4−bx−)−c −・・・−・・−(
1), the coordinates of line sensor 5a+5b+5c (
-Xo, O), (0,0), γA at (Xo, O)
.

The value of yBlyC is yA=aX2o-bXo0C concave...(2]yB=C
・・・・・・・・・(3)yc=ax+bxo+C
−−−−・・・・・・(4), and this (2), (
3) From equation (4), coefficients a, b, on the right side of equation (1),
Find c: 2 x.

C= yB ・・・・・・・・・(7
) When the coordinates (x, y) of the apex of the parabola are determined from equations (5), (6), and (7), it becomes 2a 2γB ''A-yC.

From the equation representing the coordinates of the apex of this parabola, the depth of focus is determined as follows. That is, line sensor 5
If b coincides with the film plane, I is different. Here, ε
is a predetermined constant. Further, when the film surface is separated from the line sensor 5b by a distance δ, the coordinates are moved by δ to be in focus, and the rear focus is to be γ4+VC.

Next, a circuit for performing the above-mentioned calculations and determining focus, front focus, or rear hint will be explained in detail.

As shown in FIG. 7, contrast calculation circuits 6a#6bt6C are connected to the line sensors 5ae5be5C, respectively. This contrast calculation circuit 5a.

6b*6c, licensor sa*sb+sc △ The reciprocal of each observed contrast value YA-'! B.

γ. Calculate. As shown in FIG. 8, this contrast calculation circuit is, for example, a circuit that subtracts the difference in electromotive force between adjacent charge-coupled devices in an array of charge-coupled devices forming the line sensor 5a via a 1-bit delay circuit a. The output is squared by a square circuit C, and the contrast value YA is calculated by integrating the squared product of the electromotive force difference between all charge-coupled devices by an integrating circuit d. e in yA
Calculate =1/YA.

7.8.9 is a subtraction circuit, and the subtraction circuit 7 performs subtraction between γ output from the contrast calculation circuit 6a and YB output from the contrast calculation circuit 6b.
γ + γB is output.

Further, in the subtraction circuit 8, subtraction is performed between VC output from the contrast calculation circuit 6C and y output from the contrast calculation circuit 6b. -YB is output.

Further, in the subtraction circuit 9, YA outputted from the contrast calculation circuit 6a and y outputted from the contrast calculation circuit 6C. Subtraction is performed and γ□−γ. is output.

10 is an adder circuit, and in this adder circuit 10, yA-yB outputted from the subtraction circuit 7 and y outputted from the subtraction circuit 8. -yB is added to 2yB-yA
−γ. is output. 11 is an absolute value circuit, and this absolute value circuit 11 outputs an adder circuit 10, and furthermore, the output of this absolute value circuit 11 is multiplied by 6 in an amplification/width circuit 12, and 12VB VA )'C1ε is outputted. . In this amplifier circuit 12, the depth of focus range can be changed by adjusting the variable resistor 12a, without being affected by the subject brightness distribution, subject spatial frequency, aperture F value and focal length of the lens used. A linear change in the resistance value of the variable resistor 12a corresponds one-to-one to a change in the focus recognition depth range.

In the amplifier circuit 13, the output of the adder circuit lO is multiplied by 6 (2
YB YA Yo) δ is output. The distance δ between the film surface and the line sensor 5b is positive when the film surface is closer to the object than the line sensor 5b, and negative when the line sensor 5b is closer to the object than the film surface.Switch 14 is terminal 1 when δ is positive.
4a side, and when δ is negative, it is closed to the terminal 14b side. This is the output of the amplifier circuit 13 (2γB
)'A-y()δ is output as it is to the adder circuit 15, which will be described later, via the switch 14 if δ is positive; if δ is negative, the sign is inverted by the inverting circuit 16 and the signal is output to the switch 14.
The signal is output to the adder circuit 15 via.

17 is an amplifier circuit, and this amplifier circuit 17 converts the output of the subtraction circuit 9 into X. (yA-γ.) and outputs Xo.

This (yA-yo) Addition and subtraction are performed by selecting 14, and (yA-yo)xo±(2γB-
VA-VC) δ is output. Addition or subtraction between the output of the amplifier circuit 17 and the output of the amplifier circuit 13 selected by the switch 14 corresponds to the coordinate movement described above. 18 is an absolute value circuit, and in this absolute value circuit 18, the adder circuit 1
5 is converted into an absolute value.

Reference numeral 19 denotes a comparator, and this comparator 19 becomes 'Low' when the upper image point is within or outside the certified focus depth, and at this time, the output of the inverter 20 becomes 'High'. This signal is input to the light emitting diode D2 via the current limiting resistor R2, causing the light emitting diode D2 to emit light. The light emitting diode D2 indicates that the object is in focus on the focus display section 21 on the finder F shown in FIG. Also, the output of the comparator 19 is +(γA-VC)Xo±(2yB-yA-VC)δl
>1zyB-γ6-γ. 1ε, that is, when the imaging point is outside the certified focus depth, it becomes 'High'.

In this case, if the front is in focus, the output of the subtraction circuit 9 becomes ``High'' level at γ〉yo, and the AND circuit 22
The output of becomes 'High', and this signal is passed through the current limiting resistor to the light emitting diode DiJ for a short time.
The light emitting diode D□ is made to emit light. Light emitting diode D□
Accordingly, the focus display section 2 on the finder F shown in FIG.
1 indicates that the front focus is on. Furthermore, if the imaging point is outside the certified focus depth, the output of the comparator 19 is 'H'.
In the case of rear focus, yA<y.

The output of the subtraction circuit 9 becomes ``Low'' level, and the output of the inverter 23 becomes ``High'', and the AND circuit 2
4 becomes ``High'', and this signal is input to the light emitting diode D3 via the current limiting resistor R3, causing the light emitting diode D3 to emit light. Rear focus is displayed on the display portion 21.

Effects As explained above, in the present invention, a function having the coordinate value is determined from the coordinate value corresponding to the contrast value detected by a plurality of light receiving sections, and an imaging point is determined from this function. Since we have decided whether to focus or not based on the amount of deviation between this imaging point and the film surface, the depth range for which the focus is certified depends on the brightness distribution of the subject, the spatial frequency of the subject, the aperture f-number of the lens used, and the focal point. It is not affected by distance and does not change carelessly. Further, it is not necessary to make the planned focal direction and the film plane coincide, and it is sufficient to move the coordinates by the amount of deviation between the planned focal direction and the film plane by arithmetic processing, which is advantageous in terms of arrangement of the light receiving element.

[Brief explanation of the drawing]

Fig. 1 is an optical line diagram showing an optical system using the present invention, Fig. 2 is a plan view of the ranging element shown in Fig. 1, Fig. 3 is a graph showing a contrast curve, and Fig. 4 is a line sensor and photographing light. 5 is a graph showing the relationship between the position of the line sensor and the contrast value, FIG. 6 is a graph showing the function corresponding to the contrast value of the line sensor, and FIG. 7 is a graph showing the relationship between the line sensor position and the contrast value. FIG. 8 is a circuit diagram showing one embodiment, FIG. 8 is a partial circuit diagram of FIG. 7, and FIG. 9 is an explanatory diagram showing a focus display section of the finder. l...Main mirror, 2...Photographing lens, 3.
...Secondary mirror, 4...Beam splitter, 5.
... Distance measuring element, 5a, 5b, 5c... Line sensor,
Y A, t Y B. Yc...contrast value. Patent Applicant: Minolta Camera Co., Ltd. Patent Attorney Aoyama, 2 persons Figure 1 Figure 3 Figure 25 Figure 4 Figure 5 Figure 6

Claims (1)

[Claims] (1) A plurality of light receiving sections are provided close to the planned focal plane of the optical system, and a coordinate value corresponding to the contrast value of the image detected by each light reception % jc is calculated, and a predetermined point having this coordinate value is calculated. An imaging state detection device for an image, characterized in that a function is determined and an imaging point is determined from the coordinate values of the peaks of this function.