JPH04296709A - Camera - Google Patents

Abstract

PURPOSE:To prevent the erroneous correction of a moving body executed because the detecting accuracy of moving speed is not high from being executed prolonging time lag in a camera provided with a range-finding means which corrects the moving body. CONSTITUTION:Range-finding executed twice by the range-finding means 1 by delaying a prescribed time. When the range-finding values thereof are nearer than a prescribed distance or when the moving speed of an object along the optical axis direction of a lens is a prescribed value or under, it is decided by a decision means 2 that the output of a speed arithmetic means 4 is reliable and the position of the object at the starting time of exposure is obtained by a driving quantity arithmetic means 3. Besides, the lens is driven to the position by a driving means 5.

Description

[Detailed description of the invention]

0001

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a camera, and more particularly to a camera that drives a photographic lens to a focusing position based on the output of a distance measuring means.

0002

2. Description of the Related Art As is well known, cameras with automatic focus adjustment devices have a large release time lag from when the shutter is released until the actual exposure starts, so when shooting a subject moving in the direction of the camera's optical axis. When doing so, there is a problem that the focus of the photographic lens may be out of focus.

In order to solve this problem, when the first release switch is turned on in response to a half-press of the release button, distance measurement is performed multiple times at different times to detect the moving speed of the subject. For example, Japanese Patent Laid-Open Nos. 118133-1982 and 1983-1989 disclose technical means for predicting the subject position at the start of exposure to prevent focal shifts of the photographing lens due to movement of the subject that occurs during the release time lag.
No. 159817 and the like.

0004

[Problem to be Solved by the Invention] However, the above-mentioned Japanese Patent Application Laid-Open No. 63-118133 and Japanese Patent Application Laid-Open No. 63-159817
The technical means disclosed in the respective issues are based on the assumption that the moving speed of the subject can be ideally and accurately determined, so the influence of errors in the moving speed is not taken into account, and it is difficult to put the above means into practical use. To do so, the following problems must be resolved.

That is, in the case of an active triangulation method, for example, the distance measurement output of the distance measurement device, which is the basis for determining the moving speed of the subject, varies depending on the distance measurement, as shown in FIG. It has a certain uncertainty range. For example, subject distance L
At distance 0, the distances are distributed from a to c, and at distance L1, they are distributed from d to f. This uncertainty width is small at short distances where the amount of reflected light is relatively large, but increases as the distance increases.

Therefore, when the subject moves from distance L0 to L1, the distance measurement value may change from a to d, from b to e, or from c to f. This change from a to d is a severe example, and even though the subject is moving toward the camera, the velocity output will appear as if the subject is moving away from the camera. Furthermore, if correction is performed based on the change in distance measurement output from c to f, the correction will be made more than the actual amount of movement, that is, from 1/L0 to 1/L1, resulting in a loss of focus.

Furthermore, if the time required for multiple distance measurements to determine the amount of movement of the subject is, for example, 50 mSec, and the release time lag is 400 mSec, then the above 50 mSec
The distance to the subject at the start of exposure after 400 mSec is predicted based on the amount of movement of the subject during c.
Movement amount error is 400/50=8
... (1) The image will be magnified twice as much, which increases the possibility that it will be out of focus.

On the other hand, if the time taken to measure the amount of movement of the subject is increased in order to minimize the distance measurement error, the release time lag will further increase, causing the shutter opportunity itself to be missed. Another problem arises. This problem of increased release time lag is a problem that occurs simply by adding the calculation time required to predict the subject distance. must also be considered.

SUMMARY OF THE INVENTION Therefore, an object of the present invention is to provide a camera that solves the above problems and prevents erroneous moving object corrections caused by insufficient accuracy in detecting moving speed without increasing the time lag.

0010

[Means for Solving the Problems] As the concept of the camera is shown in FIG. Based on the output of the speed calculating means 4 for calculating the moving speed of the subject along the optical axis direction of the system and the distance measuring means 1,
A determining means 2 for determining whether or not the output of the speed calculating means 4 is reliable;
When it is determined that the output of is reliable, the distance to the subject at the time of starting the exposure operation is predicted based on the output of the distance measuring means 1 and the speed calculating means 4, and the photographing is performed to focus the photographing optical system on this distance. It is characterized by comprising a driving amount calculating means 3 for calculating the driving amount of the optical system, and a driving means 5 for driving the photographing optical system by the output of the driving amount calculating means 3.

[0011]

[Operation] In this camera, [1] the distance value of the distance measuring means 1 is compared with a predetermined distance and the distance is on the short distance side, or [2] the distance of the subject along the optical axis direction of the photographing optical system is detected. When the moving speed is below a predetermined value, the determining means 2 determines that the output of the speed calculating means 4 is reliable. Further, the driving amount calculating means 3 determines the driving amount of the photographing optical system, taking into consideration the depth of field of the photographing lens.

0012

DESCRIPTION OF THE PREFERRED EMBODIMENTS The present invention will be specifically described below with reference to the drawings. Although the present invention is a technical idea that can be commonly applied to both active type and passive type distance measuring devices, the following embodiments will be explained using an active type triangular distance measuring device as an example. The first embodiment of the present invention is configured as shown in the flowchart of FIG. 3, and the second embodiment is configured as shown in the flowchart of FIG. 4, but since the hardware configuration is the same, FIG. 2 shows the block configuration. Let's first explain.

A detailed explanation of the circuit configuration and operation of the distance measuring device 11 that measures distance using the well-known active triangulation method is described in Japanese Patent Laid-Open No. 1-150809, which was previously filed by the applicant. Therefore, a detailed explanation will be omitted here and a brief explanation will be given.
Upon receiving the distance measurement start signal from 1, the device 11 pulse-drives an infrared light emitting element (hereinafter abbreviated as IRED) 13, and the pulsed light emitted by the element 13 is transmitted to the projection lens 14. The light is focused and projected toward the subject 15. The reflected light reflected by the subject 15 is transmitted to a semiconductor position detection element (hereinafter abbreviated as PSD) 1 via a light receiving lens 16.
The image is formed on 7.

Since the imaging point on this PSD 17 changes depending on the object distance, the object distance can be determined by calculating the signal photocurrents I1 and I2 taken out from both ends of the PSD 17 using the well-known principle of triangulation. Desired.

The object distance information obtained by the distance measuring device 11 is transmitted to the determining means 2 and the driving amount calculating means 3 in FIG.
, is input to a control means 21 consisting of a CPU which also serves as the speed calculation means 4 and controls the operation sequence of the entire camera. The control means 21 also receives an output of the amount of reflected light from the subject 15. In addition, the same means 21
A first-stage release switch 22 that is turned on in response to a half-press operation of the shutter release button, and a second-stage release switch 23 that is turned on in response to a full-press operation are connected to the shutter release button.

Information regarding the driving amount of the photographing optical system calculated by the control means 21 is applied to the photographing lens driving motor 24 as the driving means 5 in FIG. I. (Photo interrupter) While counting the pulse output of 26, the photographing lens 25 is moved to the in-focus point.

FIG. 3 is a flowchart of the focusing operation of the camera showing the first embodiment of the present invention. is designed to limit motion correction. When this flow starts, the control means 21 (see FIG. 2) waits until the first stage release switch 22 is pressed down (step S1), and when the same switch 22 is pressed down, step S
Proceed to step 2.

In this step S2, the distance measurement device 11 is enabled by a distance measurement start signal from the control means 21, and the distance measurement device 11 is enabled.
Perform the second distance measurement. As a result, the reciprocal of the first distance measurement value is 1.
/L0 is obtained, this value is stored in the memory M(0
).

In step S3, the time interval between the first and second distance measurements (hereinafter referred to as a predetermined time) for measuring the distance to a moving object is determined.
Activate a timer that counts and wait for 50 mSec.

[0020] Proceeding to step S4, a second distance measurement is performed after a predetermined period of time has elapsed by the timer. The reciprocal 1/L1 of this second distance measurement value is stored in a memory M(1) (not shown).

In step S5, it is checked whether the first-stage release switch 22 is still on, and if it is off, the process returns to step S1 and the first-stage release switch 22 is turned on again.
It will be in a standby state until it is pressed. On the other hand, if the first stage release switch 22 is still turned on, step S
Proceed to step 6.

In this step S6, it is checked whether the second stage release switch 23 (see FIG. 2) is turned on, and if the second stage release switch 23 is turned on, the process advances to step S7.
If it is not turned on, the process repeats the flow of steps S2 to S5 and waits until the second release switch 23 is turned on. During this time, memory M(0), M
(1) continues to store the first and second distance measurement values carried out at predetermined time intervals for moving object distance measurement.

[0023] In step S7, the second distance measurement value 1/L1
is larger than a determination level CP corresponding to a predetermined distance. This determination level CP is preset to a short distance value at which the distance measurement output is sufficiently stable, as shown in FIG. 6. This value is determined in advance as an appropriate value based on variations in distance measurement output.

Now, if 1/L1>CP, the speed output Δ
Since (1/L)=(1/L1)-(1/L0) is considered to be sufficiently accurate, the process proceeds to steps S8 and S9 to find the photographic lens extension amount β corrected by the moving speed of the moving object. On the other hand, if 1/L1≦CP, the process proceeds to step S10 to obtain the lens extension amount β based on the normal distance measurement value, in this case the second distance measurement value.

In step S9, the coefficient determined from the time from when the second release switch 23 is turned on until the start of exposure, in this case 8 (see the problem to be solved by the invention), is calculated by Δ( 1/L) to 1/L
The photographic lens extension amount β is determined from the sum of the sum of 1 and 1.

In step S11, the photographing lens is extended in accordance with the lens extension amount β. I. This is done while counting the pulse output.

As described above, according to the first embodiment, since moving object correction is prohibited at long distances where the detection accuracy of moving speed is not good, it is possible to prevent the frequent occurrence of the problem of out of focus due to incorrect moving object correction. Can be done. Normally, even if a long-distance subject moves fairly quickly, the focus does not move that much, and correction is performed with high precision at the short distance side where the focus movement is large, so there is no practical problem.

In step S7, it is determined whether the accuracy of the moving speed is stable based on the magnitude of the distance measurement output 1/L1, but the invention is not limited to this, for example, Of course, it may be determined from the reflected light amount output.

FIG. 4 is a flowchart of a focusing operation of a camera showing a second embodiment of the present invention, and corresponds to claim 3, in which the output difference of the distance measuring means within a predetermined time is larger than a predetermined value. , and limits motion correction. In the explanation of this second embodiment, the same steps S1 to S6 and S11 as in the first embodiment shown in FIG. The steps will be explained below with step numbers.

In step S107, in order to calculate the predicted position after the moving object correction, the output difference of the distance measuring means within a predetermined time,
In other words, the speed output Δ(1/L) is calculated.

In step S108, the speed output Δ(
1/L) with a predetermined value CQ, and if it is larger than the predetermined value CQ, it is determined that the amount of change to the predicted position is too large. Therefore, the process proceeds to step S109, where Δ(1/L)=CQ is established, and the process proceeds to step S112. On the other hand, if it is less than or equal to CQ, the process advances to step S110. In this step S110, it is determined whether or not the speed output Δ(1/L) is smaller than 0. If it is smaller, Δ(1/L) is set to 0 in step S111, and on the other hand, if it is greater than or equal to 0, immediately followed by step S112. Proceed to. If Δ(1/L) is smaller than 0 in this way, it means that the subject is moving away from the camera, so in this case, the moving object correction is not applied.

To explain the reason for this, in the case of normal photography,
The reason for this is that a subject that is far away from the camera faces backwards and can hardly be photographed, and the depth of field on the far side is large, so there is little need for moving object correction. This is because if the image is corrected, the pattern from a to d in FIG. 6 will more easily become out of focus. In step S112, the lens extension amount β is determined. Then, the photographing lens is extended based on this extension amount β (step S11).

In FIG. 5, the vertical axis represents the amount of extension of the photographic lens;
In other words, it is a diagram in which the amount of deviation from the lens setting position with respect to ∞ is plotted, and the reciprocal of the subject distance is plotted on the horizontal axis.The focusing curve δ1, which shows the amount of extension during focusing for each subject distance, and the point image of the subject The drawing-out limit curves δ2 and δ3 are plotted, respectively, which indicate the feeding amount at which the maximum permissible circle of confusion occurs on the film surface.

Now, assuming that the diameter of the maximum permissible circle of confusion is D and the F number of the photographing lens is F, and by making a rough approximation, the limit curve δ is obtained.
2, the focusing curve δ1 is shifted to the plus side by F·D, and the limit curve δ3 is shifted by the focusing curve δ1 to the minus side.

Now, if the predetermined value CQ is set to the above F.D, the depth of field of focus after moving object correction will be the maximum allowable circle of confusion even when the reciprocal of the object distance is 1/L1 without correction. It is possible to imprint using the rear focus.

Now, the fact that the above design is very effective in practice will be explained using specific design values. As an example, if the F number is 7, the maximum permissible circle of confusion diameter D is 60 μm, the focal length f is 70 mm, and the subject distance L1 is 3 m,
The short distance L3 that can be covered with a focus of 1/L2 is

003
7]

[0038] At this point, it takes 40 minutes from the end of distance measurement to the start of exposure.
Assuming there is a release time lag of 0mSec,

0
039]

[0040] In other words, from a stationary subject to 9
This means that objects moving at km/hour will be in focus.

Furthermore, when L1 = 2 m, objects moving at 4.5 km/hour will be in focus, and a so-called person walking toward the object will be in focus. In this case, if you want to increase the speed even more, you can shorten the release time lag, which can usually be easily shortened to 200 mSec.

In any case, it is almost impossible to take a photograph of a subject approaching at high speed at a short distance, and generally, even when photographing a child running towards you, the speed is 4km/h.
It is sufficient for practical use if a certain amount of moving object correction can be made.

By the way, the above predetermined value CQ is strictly F.D.
There is no need to set it to F. like 1/L4, 1/L5.
Even a value approximately equal to D is sufficiently effective.

In each of the above embodiments, the moving speed of a moving object is determined from two measured distance values separated by a time interval.
The calculation of the moving speed is not limited to this, and if possible, a dedicated speed detection circuit may be used, or it may be calculated from the least squares approximation formula of the distance measurement data more often. Needless to say.

By the way, in each of the above embodiments, when it is determined that the detected value of the moving speed of the subject is unreliable,
Although moving object correction is prohibited, it goes without saying that instead of prohibiting moving object correction, changes may be made as appropriate, such as displaying a warning on the LCD in the viewfinder, or issuing an audio warning. .

In addition, the calculations are performed by the CPU calculation unit, but if there is a problem with the operating speed, it is of course possible to perform the calculations in advance, write them to the ROM, and then read out the calculated values by specifying an address. It is.

Furthermore, the present invention is also effective in multi-point distance measurement. In this case, for example, one selected from a plurality of distance measurement outputs may be replaced as the distance measurement output in the embodiment.

Furthermore, although the active type triangulation distance measuring device has been described as an example, the technical concept of the present invention can also be applied to a passive type distance measuring device.

According to each of the above-mentioned embodiments, practical problems related to moving object correction, namely (1) loss of focus due to overcorrection, and (2) loss of shutter opportunities due to increased release time lag, are prevented, and accuracy is not very good. Even in distance measuring devices, it becomes possible to perform moving object correction which is very effective in practice.

[0050]

As described above, according to the present invention, the determining means determines whether (1) the output of the distance measuring means is on the shorter distance side than the predetermined distance, or (2) the above distance measurement within a predetermined time. Only when the difference in the output of the means is less than a predetermined value, the output of the speed calculation means is judged to be reliable and moving object correction is executed.In cases other than the above, moving object correction is limited. This provides a remarkable effect in that erroneous moving object corrections that occur due to insufficient speed detection accuracy can be prevented without increasing the time lag.

[Brief explanation of drawings]

FIG. 1 is a conceptual diagram of the present invention.

FIG. 2 is a block diagram of main parts of a camera according to the present invention.

FIG. 3 is a flowchart showing a focusing operation in the first embodiment of the present invention.

FIG. 4 is a flowchart showing a focusing operation in a second embodiment of the present invention.

FIG. 5 is a diagram showing the amount of extension of the photographic lens relative to the reciprocal of the subject distance.

FIG. 6 is a diagram showing the distance measurement output versus the reciprocal of the subject distance in the conventional active triangulation method.

[Explanation of symbols]

1... Distance measuring means 2... Judgment means 3... Drive amount calculation means 4...Speed calculation means 5...Driving means

Claims (3)

[Claims] Claim 1: A distance measuring means for detecting a distance to a subject;
Based on the output of the distance measuring means, a speed calculating means calculates the moving speed of the subject along the optical axis direction of the photographing optical system; and based on the output of the distance measuring means, the output of the speed calculating means is reliable. determining means for determining whether or not the speed calculation means is reliable; A driving amount calculating means for predicting and calculating a driving amount of the photographing optical system for focusing the photographing optical system on the distance, and a driving means for driving the photographing optical system by the output of the driving amount calculating means. A camera characterized by: 2. The determining means determines that the output of the speed calculating means is reliable when the output of the distance measuring means is closer than a predetermined distance. 1) The camera described. 3. The determining means determines that the output of the speed calculating means is reliable when the difference in output of the distance measuring means within a predetermined time is less than a predetermined value. The camera described in item (1).