JP2610235B2 - Focus detection device - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION (Field of Application of the Invention) The present invention is suitable for a camera or the like, and forms a plurality of light amount distributions by a light beam transmitted through a plurality of divided regions of a pupil of an objective lens. The present invention relates to an improvement in a focus detection device that detects a focus state of an objective lens from a relative positional relationship of a light amount distribution.

BACKGROUND OF THE INVENTION Various types of focus detection devices such as cameras have been proposed, one of which is shown in FIG.

In FIG. 4, 1 is an objective lens, 2 is an objective lens 1
3 is a field mask, 4 is a field lens arranged near the planned imaging plane 2, and 5 is two secondary imaging lenses arranged symmetrically with respect to the optical axis of the objective lens 1. Five
The secondary imaging optical system 6 includes a photoelectric conversion element array 6a and a photoelectric conversion element array 6a disposed behind the secondary imaging lenses 5a and 5b corresponding to the two secondary imaging lenses 5a and 5b. Conversion system,
Reference numeral 7 denotes an aperture stop having two openings 7a and 7b arranged corresponding to the two secondary imaging lenses 5a and 5b, and 8 denotes an exit pupil of the objective lens 1 which divides the two regions 8a and 8b. Including.

The field lens 4 has the function of forming images of the apertures 7a and 7b of the stop 7 near the regions 8a and 8b of the exit pupil 8 of the objective lens 1, respectively. Light intensity distributions are formed on the photoelectric exchange element arrays 6a and 6b, respectively.

In the focus detection device shown in FIG. 4, when the image forming point of the objective lens 1 is in front of the predetermined image forming plane 2, the light amount distributions formed on the two photoelectric conversion element arrays 6a and 6b are different. When they are close to each other and the image forming point of the objective lens 1 is behind the predetermined image forming plane 2, the light amount distributions formed on the two photoelectric conversion element arrays 6a and 6b are separated from each other. State. Moreover, two photoelectric conversion element arrays 6
Since the shift amount of the light amount distribution formed on a and 6b has a certain functional relationship with the shift amount of the focus of the objective lens 1, if the shift amount is calculated by appropriate arithmetic means, the direction of the shift of the focus of the objective lens 1 And the amount can be detected.

In such a focus detection device, in order to perform accurate focus detection, it is necessary that a light amount distribution of light amount distributions formed on the two photoelectric conversion element arrays 6a and 6b be balanced.

FIG. 5 (A) shows a cross section on the plane of the exit pupil 8 of the objective lens 1 in FIG. In the figure, 9
Denotes an exit pupil of the objective lens 1, and 10a and 10b denote openings of the aperture 7 projected by the field lens 4 on the surface of the exit pupil 9.
7A and 7B respectively show projected images. In other words, the projected images 10a and 10b can be said to be entrance pupils of a focus detection system (hereinafter abbreviated as an AF system) composed of the field mask 3 and the subsequent ones in FIG. Since the amount of light (illuminance) on each of the photoelectric conversion element arrays 6a and 6b is considered to be proportional to the area of the entrance pupil of the AF system, as shown in FIG. When the entrance pupils 10a and 10b of the system are completely included, the light amounts on both photoelectric conversion element arrays 6a and 6b become equal.
On the other hand, for example, when a part of the entrance pupil 10a of the AF system is vignetted by the exit pupil 9 of the objective lens 1 due to some error as shown in FIG. 5 (B), the photoelectric conversion element array 6a
The upper light amount decreases. On the other hand, when the exit pupil 9 of the objective lens 1 does not completely include the entrance pupils 10a and 10b of the AF system as shown in FIG. The reduction in the amount of light on the conversion element arrays 6a and 6b is equivalent, and it can be said that the balance is maintained. However, FIG. 5 (C) shows a special state, and if a slight error occurs and the vignetting of both becomes asymmetric, the light quantity balance will be lost. Therefore, when the focus detection device as shown in FIG. 4 is configured, even if some error occurs, the entrance pupils 10a and 10b of the AF system do not vignet at the exit pupil 9 of the objective lens 1. The sizes of the apertures 7a and 7b of the stop 7 are determined so as to have a relative relationship as shown in FIG. In particular, like a single-lens reflex camera, the objective lens 1
When the photographing lens corresponding to is interchangeable, it is necessary to determine the size of the apertures 7a and 7b of the diaphragm 7 in accordance with the smallest exit pupil among all the usable photographing lenses. .

By the way, among these conventional photographing lens systems of single-lens reflex cameras, there are special lenses called shift lenses and tilt lenses. The shift lens is a lens that can move the optical axis of the taking lens in parallel, and enables correction of perspective. The tilt lens is a lens that can tilt the optical axis of the photographing lens, and usually makes it possible to tilt a focusable visual field interface that is parallel to the film surface.

When such a shift lens or tilt lens is used as the objective lens 1 in FIG. 4, if the lens has a certain level of brightness in a state where no shift or tilt is performed, the above-described entrance pupil 10a is used. , 10b are not generated, but in a state of large shift or tilt, the vignetting of the entrance pupils 10a, 10b is generated due to the aperture touch, and there is a possibility that the light amount balance on both photoelectric exchange element arrays 6a, 6b is lost. If the focus detection is carelessly performed in such a state, the detection accuracy is reduced, and in the worst case, the focus is largely out of focus. As a countermeasure, there is a method of not including a shift lens or a tilt lens in the photographing lens series for the autofocus camera, or a method of devising such that conventional lenses cannot be attached to the autofocus camera. Conceivable. However, this is extremely inconvenient when using a shift lens or a tilt lens because an autofocus camera must be prepared in addition to the autofocus camera. Considering that the automatic focusing of cameras will increase more and more in the future, such a measure is not preferable. Also, most of auto-focusing cameras can be manually adjusted by switching, and it can be said that such a shift lens or tilt lens cannot be used at all. Further, even in the case of a shift lens or a tilt lens, if the shift amount and the tilt amount are within a certain range, there is no vignetting of the entrance pupil and the focus can be detected. .

(Object of the Invention) An object of the present invention is to solve the above-mentioned problems, and even when a shift lens or a tilt lens is used as an objective lens, the focus detection operation is performed carelessly, and the focus detection accuracy is reduced. Another object of the present invention is to provide a focus detection device capable of preventing occurrence of a large defocus.

(Features of the Invention) In order to achieve the above object, the present invention relates to a method of converting the substantial F number of the objective lens, which is determined according to the direction and amount of parallel movement or tilt of at least a part of the optical axis of the objective lens, into the objective lens A real F-number input terminal input from the lens side, and a limit F-number storage unit for storing a minimum F-number required for a focus detection operation to be performed normally;
Before the operation of the calculating means, the real F number and the limit F
Comparing with the number, when the former is greater than the latter, providing a determination means for inhibiting the operation of the arithmetic means,
By comparing the real F-number with the limit F-number, the presence or absence of vignetting of the entrance pupil of the AF system is detected to determine whether the focus detection operation is prohibited or permitted.

(Embodiment of the Invention) FIG. 1 is a block diagram showing an embodiment of the present invention when a shift lens is mounted, and FIG. 2 is a flowchart showing an automatic focusing operation (hereinafter abbreviated as AF operation). FIG. 3 is a diagram showing vignetting of the entrance pupil of the AF system in the embodiment shown in FIG.

 First, FIG. 3 will be described.

FIG. 3A shows the exit pupil 11-1 of the shift lens and the entrance pupils 12a and 12b of the AF system when the shift amount of the shift lens is 0, and there is no vignetting in the entrance pupils 12a and 12b. FIG. 3 (B) shows the relationship with the exit pupil 11-2 when it is shifted to some extent. Even in this state, there is no vignetting of the entrance pupils 12a and 12b, so that the focus detection operation is performed normally. . FIG. 3 (C) shows the exit pupil 11-3 when further shifted.
The focus detection operation is not performed normally because the lower entrance pupil 12a of the AF system is vignetting.

Now, in each shift state, the exit pupils 11-1, 11
Considering the smallest circles centered on the optical axis of the camera, inscribed at −2, 11-3, they are 13-1, 13-2, 13-3, respectively.
If the F-numbers corresponding to these inscribed circles are called real F-numbers Fs in each shift state, as the shift amount increases, the real F-number Fs also increases. On the other hand, assuming that the maximum F number of the objective lens which is the minimum required for the focus detection operation to be performed normally is the limit F number F1, as long as Fs ≦ Fl (1), the normal focus detection operation can be performed even in the shift lens. It can be said that it is possible.

If the real F-number Ft in each tilt state is similarly defined for the tilt lens, a normal focus detection operation can be performed when Ft ≦ Fl (2).

Therefore, in order to attach a shift lens or a tilt lens to the autofocus camera so that the focus detection operation is not performed inadvertently with the pupil vignetting, the shift amount or the tilt amount of the objective lens must be adjusted. Real F-number F
s, Ft may be compared with a limit F number Fl determined by the AF system, and the focus detection operation may be prohibited when the condition (1) or (2) is not satisfied.

FIG. 1 is a block diagram of an embodiment of the present invention for realizing this. There is no essential difference between the shift lens and the tilt lens in applying the present invention.
Although a shift lens is shown in the figure, the present invention can be similarly applied to a tilt lens.

In FIG. 1, the left side of the broken line indicates the objective lens side, and the right side indicates the camera body side. On the objective lens side, 21 is a shift lens, 22 is a focusing lens of the shift lens 21, 23 is a focusing encoder for detecting the moving amount of the focusing lens 22, and 24 is a shift lens 21.
, A shift encoder for detecting the shift amount of the shift mechanism, a drive motor, a drive control circuit, and a defocus amount of the shift lens 21 converted to a movement amount of the focusing lens 22 A lens data memory in which data unique to each lens such as defocus sensitivity is stored. 29 is a real F-number converter for converting the shift amount of the shift lens 21 into the real F-number Fs defined above. is there.

On the camera body side, reference numeral 30 denotes an AF system including the components from the field mask 3 to the photoelectric conversion element arrays 6a and 6b in FIG. 4, 31 denotes an arithmetic control circuit, and 32 denotes focusing, front focus, and rear focus. A focus state display circuit for displaying; a warning display circuit for warning that focus detection is impossible; a limit F number memory for storing a limit F number Fl determined by the AF system; Real F-number converter 29
F-number Fs and limit F-number Fl sent from
And the AF of the arithmetic and control circuit 31 is determined according to the comparison result.
A comparison circuit that inhibits or permits operation, 36 is a quick return mirror, 37 is a sub mirror, 38 is a pentaprism, 39
Is an eyepiece.

In between the driving control circuit 27 and the arithmetic control circuit 31, a drive end signal and the lens drive amount is transmitted through the connecting terminals t ₁ ~t _4, from the lens data memory 28 to the arithmetic control circuit 31,
Lens data is transmitted through the lens data output terminal t ₅ and the lens data input terminal t _6, substantially F-number converter 29
To the comparison circuit 35 from the substantially F-number Fs is transmitted through a substantially F-number output terminal t ₇ and substantially F-number input terminal t _8.

The arithmetic control circuit 31 calculates the defocus amount of the shift lens 21 from the light amount distribution information obtained from the AF system 30, and outputs a signal indicating front focus, rear focus, or focus to the focus state display circuit 32 accordingly. I do. The focus state display circuit 32 displays the focus state in the viewfinder or by sound according to the input signal. On the other hand, the arithmetic control circuit 31 reads the defocus sensitivity from the lens data memory 28, calculates the driving amount of the focusing lens 22 from this and the calculated defocus amount, and outputs it to the drive control circuit 27. The drive control circuit 27 drives the drive motor 26 by the specified lens drive amount while monitoring the movement amount of the focusing lens 22 with the focusing encoder 23, and when the drive is completed, sends a drive end signal to the arithmetic control circuit 31. I will send it back. At this point, the arithmetic control circuit 31 calculates the defocus amount again. If the defocus amount is within a certain focusing range, a series of AF operations is ended. To bring the camera into focus. Above is basic AF
In the operation shown in FIG. 1, prior to this,
The following judgment is made on the presence or absence of pupil vignetting.

That is, the real F-number converter 29 converts the shift amount from the shift encoder 25 provided in the shift mechanism 24 of the shift lens 21 into the above-described real F-number Fs, and outputs it to the comparison circuit 35 on the camera body side. . The comparison circuit 35 compares the obtained real F-number Fs with the limit F-number Fl read from the limit F-number memory 34, and permits the AF operation of the arithmetic control circuit 31 only when Fs ≦ Fl (1) holds. I do.
If the expression (1) does not hold, the comparison circuit 35 inhibits the AF operation of the arithmetic and control circuit 31 and simultaneously outputs a warning display circuit.
33 is displayed as a warning that focus detection is not possible. Note that the warning display circuit 33 may also be used as the focus state display circuit 32.

In practice, it is considered that one microcomputer is often used as the arithmetic control circuit 31 and the comparison circuit 35. The flowchart showing the processing flow in that case is shown in FIG.
Shown in the figure. Such a microcomputer often performs, for example, control of a photometric system in addition to the AF operation, and only the AF operation will be described on the premise thereof.

When the control is shifted from the control other than the AF operation to the AF operation, first, in step 1, the lens data is read from the lens data memory 28. Here, the lens data is a set of a series of lens-specific data including the aforementioned defocus sensitivity and the substantial F-number Fs. Next, in step 2, substantially F
The number Fs is compared with the limit F number Fl. When Fs ≦ Fl (1), the process proceeds to step 3 and the output of the AF system 30 is read. In step 4, the defocus amount d is calculated from the output of the AF system 30, and the focus state display circuit 32 displays the front focus, the rear focus, or the in-focus state accordingly. In step 6, when | d | <ε (3) holds for the defocus amount d with respect to the predetermined focusing range ε, the AF operation is terminated, and control is shifted to a control other than the AF operation. If the equation (3) does not hold, the lens drive amount is calculated from the defocus sensitivity obtained in step 1 and output to the drive control circuit 27. Step 9
After waiting for the drive end signal from the drive control circuit 27, the flow returns to step 1 again, and the above routine is repeated until the focusing state is reached. On the other hand, if the equation (1) does not hold in step 2, the process proceeds to step 10 and the warning display circuit 33
Warning display, aborts the AF operation, and shifts to control other than the AF operation.

According to the illustrated embodiment, it is possible to attach a shift lens or a tilt lens to the auto-focus camera, and furthermore, the entrance pupils 12a, 12b of the AF system 30 by the shift or the tilt.
Inadvertent focus detection can be prevented in a vignetting state, thereby preventing a decrease in focus detection accuracy and a large defocus.

(Correspondence between Invention and Embodiment) Field mask 3, field lens 4, and aperture 7 in FIG.
The secondary imaging optical system 5 corresponds to the optical means of the present invention, the arithmetic control circuit 31 in FIG. 1 corresponds to the arithmetic means, the limit F-number memory 34 corresponds to the limit F-number storage means, and the comparison circuit
35 corresponds to the determination means.

(Modification) In general, since the shift lens and the tilt lens can freely change the direction of the shift and the tilt, the real F-number converter 29 can output the real F-number for each direction. In that case, the luminous flux can be used more effectively, and the possible range of the AF operation can be expanded.

Further, it is more effective for a lens that can simultaneously shift and tilt to be configured so that the substantial F number is obtained in a matrix from the respective amounts and directions.

The real F-number converter 29 is an arithmetic circuit that calculates the real F-number from the shift and tilt amounts,
A memory such as a ROM in which a substantial F-number is stored in advance corresponding to the shift and tilt amounts may be used.

(Effects of the Invention) As described above, according to the present invention, the substantial F-number of the objective lens, which is determined according to the direction and amount of parallel movement or inclination of at least a part of the optical axis of the objective lens, A real F-number input terminal input from the lens side, and a limit F-number storage unit for storing a minimum F-number required for a focus detection operation to be performed normally;
Before the operation of the calculating means, the real F number and the limit F
Comparing with the number, when the former is greater than the latter, providing a determination means for inhibiting the operation of the arithmetic means,
By comparing the real F-number and the limit F-number, the presence or absence of vignetting of the entrance pupil of the AF system is determined to determine whether the focus detection operation is prohibited or permitted. Therefore, a shift lens or a tilt lens is used as an objective lens. Also when used, the focus detection operation is carelessly performed, and it is possible to prevent a decrease in focus detection accuracy and a large defocus.

[Brief description of the drawings]

1 is a block diagram showing one embodiment of the present invention, FIG. 2 is a flowchart showing the operation of one embodiment of the present invention, FIG. 3 is a diagram showing vignetting of a pupil in the case of a shift lens, and FIG. FIG. 5 is a schematic diagram showing a conventional focus detection device, and FIG. 5 is a diagram showing vignetting of a pupil in the case of a normal lens. 1. Objective lens 2. Planned focal plane 3. Field mask 4. Field lens 5. Secondary imaging optical system
6a, 6b: photoelectric conversion element array, 7: stop, 8: exit pupil, 8a, 8b: area, 11-1, 11-2, 11-3 ... exit pupil, 1
2a, 12b: entrance pupil, 21: shift lens, 22: focusing lens, 23: focusing encoder,
24 ... shift mechanism, 25 ... shift encoder, 26 ...
Drive motor, 29: Real F-number converter, 30: AF
System, 31 ... arithmetic control circuit, 33 ... warning display circuit, 34 ...
Limit F-number memory, 35... Comparison circuit, t ₈ ... Substantial F-number input terminal.

Claims (1)

(57) [Claims] An optical means for forming a plurality of light quantity distributions by at least two light beams transmitted through different regions of a pupil of an objective lens; a plurality of photoelectric conversion element arrays for converting the plurality of light quantity distributions into electric signals; A focus detecting device comprising: a calculating unit configured to calculate a relative positional relationship of the light quantity distribution from the electric signal, wherein the focus detecting apparatus is determined according to a direction and an amount of parallel movement or inclination of at least a part of the optical axis of the objective lens. A real F-number input terminal for inputting a real F-number of the objective lens from the objective lens side, and a limit F-number storage unit for storing a minimum F-number required for a focus detection operation to be performed normally; Before the operation of the calculating means, the actual F number is compared with the limit F number, and when the former is larger than the latter, it is determined that the operation of the calculating means is prohibited. Focus detection device which is characterized by providing a stage.