JPH0544644B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention provides an automatic focus system having a so-called active type automatic focus detection device that projects light in a specific wavelength range onto a subject from the camera side and detects focus by receiving the reflected light. It's about cameras.

Active-type automatic focus detection devices are often employed in lens-shutter cameras, and include a light projecting/receiving lens separate from a photographic lens to perform distance measurement using a so-called triangular distance method. However, this method has drawbacks such as parallax and difficulty in replacing the photographic lens. In order to improve these drawbacks, a TTL active method is being considered in which both or one of the light emission and reception is performed via a photographing lens.

Figures 1a to 1c show the principle of this TTL active system.As shown in Figure 1a, a light projection lens system 2 that emits light from a light source 1 is aligned with the optical axis O of a photographic lens 3. It has a tilted optical axis 01, and the optical axis 02 of the light receiving lens system 4 is also arranged in a tilted state. A light beam L1 emitted from a light source 1 is primarily imaged by a projection lens system 2 onto a plane F that is conjugate with the film surface, and then projected onto a subject S via a photographic lens 3. The light beam L2 reflected by the subject S is primarily imaged in the vicinity of a plane F that is conjugate with the film surface via the photographic lens 3, and is focused on the light receiving lens system 4.
A secondary image is formed near the sensor 5.

In such a configuration, when the photographic lens 3 is in focus on the subject S, the image shown in FIG.
A projected light beam L1 as shown in FIG. On the other hand, in the case of an out-of-focus state, the projected light flux L1 deviates from the center of the subject S and moves upward or downward, as shown in Figure 1 a and c, depending on the rear focus and front focus states. Therefore, when the reflected light beam L2 is received by the sensor 5 through the photographing lens 3 and the light receiving lens system 4, the light receiving position similarly moves up and down. Therefore, by using a line sensor consisting of two light-receiving elements as the sensor 5 and detecting the position of the received light beam on the sensor, it is possible to determine each state of focus, rear focus, and front focus.

The above-mentioned TTL active method emits and receives light through the photographic lens 3, so it has advantages such as no parallax, lens exchangeability, and effective operation even when the brightness of the subject S is low. This is an excellent method.

However, this is a case where the wavelength of the projected light beam L1 is not far from the wavelength region that mainly contributes to photography. For example, if the wavelength of the projected light beam L1 is infrared, the photographing lens 3 generally has chromatic aberration. Therefore, a shift in focal position occurs between the two. Even in such a case, if the focus shift amount α is a single amount, the primary imaging plane F' of the projected and received light beams L1 and L2 at the time of focusing is set in advance to a plane conjugate with the film surface, as shown in FIG. It is sufficient to set it by shifting α from F, but if the shooting lens can be replaced, such as in a single-lens reflex camera, and the amount of shift α differs depending on each lens, this method is recommended. cannot provide sufficient correction.

The purpose of the present invention is to improve the above-mentioned problems and provide an autofocus camera that can perform sufficient focus correction even for interchangeable lenses with a large amount of chromatic aberration. It is equipped with an automatic focus detection device that detects the focus by projecting light with a wavelength different from that of the subject to be photographed and receiving the reflected light. The invention is characterized in that it has means for calculating the amount of correction necessary to offset the deviation of the focal position that occurs when the lens is moved, according to the focal length and extension amount of the photographing lens, and the focus of the photographing lens is corrected using the amount of correction. It is something to do.

The basic idea of the present invention is to provide means for calculating the amount of correction according to the focal length of the photographic lens and the focusing position, thereby correcting the deviation of the focal position due to chromatic aberration. The principles and embodiments of the present invention will be explained in detail below based on the drawings.

FIG. 3 shows the relationship between the amount of chromatic aberration Δ of light in the infrared region with respect to the wavelength that mainly contributes to photographing by the photographing lens (for example, Fraunhofer's d-line) and the focal length f of the photographing lens. In FIG. 3, the solid line indicates the focusing position of the lens at infinity, and the dotted line indicates the focusing position at close range. Strictly speaking, the tendency of chromatic aberration, active method,
Depending on the zoom method or chromatic aberration evaluation method,
Since each lens has a different amount of chromatic aberration, not all lenses necessarily match the curve shown in Figure 3, but in general, the longer the focal length f, the closer the focusing position becomes from infinity. The tendency for the amount of chromatic aberration to increase as the lens increases is common to many photographic lenses. As is clear from Figure 3, all of these photographic lenses are
In order to use it as a TTL active type photographic lens, some kind of correction is required even if a certain amount of depth of focus is taken into consideration.

FIG. 4 is a block diagram showing the focus correction means, including the photographing lens system 10 and the photographing lens system 10.
Photographic lens drive system 1 for focusing
1, and a correction amount calculation system 1 that calculates the correction amount based on the focal position of the photographic lens system 10 and zoom position information.
2, a focus detection system 13 consisting of a sensor etc. that receives the light flux from the photographic lens system 10, a drive control system 14 that generates signals for controlling the photographic lens drive system 11, and a correction system that generates signals necessary for correction. System 1
It consists of 5.

In FIG. 4, the operation up to focus detection is performed in the following steps.

(1) A light beam a obtained from the photographing lens system 10 is received by the focus detection system 13.

(2) The focus detection system 13 determines whether or not it is in focus according to the focus detection principle described above, and if it is out of focus, which side is out of focus?
Alternatively, an out-of-focus signal b representing the amount of defocus is transmitted to the drive control system 14.

(3) The drive control system 14 transmits a control signal c to the photographing lens drive system 11 based on the obtained out-of-focus signal b.

(4) The photographic lens drive system 11 drives the photographic lens system 10 according to the control signal c.

(5) When the focus state is reached by repeating steps (1) to (4), the focus detection system 13 stops transmitting the out-of-focus signal b and transmits the focus signal e to the correction system 15.

(6) The correction amount calculation system 12 calculates the correction amount g based on information f such as the focal position and focal length of the photographic lens system 10 at that time, or the zoom position in the case of a zoom lens, and sends it to the correction system 15. introduce.

(7) The correction system 15 receives the correction amount g from the correction amount calculation system 12 based on the focus signal e obtained in step (5), and generates a correction drive control signal h corresponding to the correction amount g. is transmitted to the photographing lens drive system 11.

(8) The photographing lens drive system 11 receives the correction drive control signal h
Accordingly, the correction drive i of the photographing lens system 10 is performed only by the necessary amount.

Through the above process, it is possible to guide the photographing lens system 10 to the original focused position. Although drives d and i are shown separately in FIG. 4 for ease of understanding, they are essentially the same in terms of driving the photographing lens system 10.

Furthermore, in FIG. 4, the correction drive control signal h output from the correction system 15 is directly transmitted to the photographic lens drive system 11; It's okay.
FIG. 5 shows the transmission and reception of signals in that case. The correction system 15, which has received the focus signal e and the correction amount g, sends a correction signal j to the drive control system 14, and the drive control system 14 receives this and performs the correction. The drive control signal k is transmitted to the photographing lens drive system 11, and a correction drive i is finally performed to reach a focused state.

FIG. 6 shows the process of reaching the above-mentioned in-focus state for a zoom lens, with the vertical axis representing the defocus amount and the horizontal axis representing the lens extension amount. On the vertical axis, the upper side corresponds to the rear focus state, and the lower side corresponds to the front focus state. Curve groups A and B are for the case where the subject distance is La and Lb (La>Lb), respectively. In each curve group, the solid lines A1 and B1 represent changes relative to the Fraunhofer d line, and the dotted lines A2 and B2 represent the focal length f. ₁ , and the dashed-dotted lines A3 and B3 represent the changes with respect to infrared light when the focal length is f ₂ (where f ₂ >f ₁ ), respectively.

First, considering a state where the subject distance is La, the focal length is _f1 , and the amount of extension of the photographic lens system 10 is _d1 , the process to reach the in-focus state is as follows. It is detected that the point P1 in the initial state is in rear focus, and as a result, in the process described above, the photographing lens system 10 is extended, and the point P1 representing the defocus state moves downward along the dotted line A2. The in-focus state for infrared light is detected at the intersection point P2 with _the horizontal axis, and the photographing lens system ₁₀ temporarily stops, but the amount to be corrected δ(d ₂ , f ₁ ) is the correction amount calculation system 12
In this case, the correction amount δ is renormalized, and the focus position _P3 for the d-line of the extension amount d
The photographing lens system 10 stops at this point. Also, the focal length
If f ₂ is set longer than f ₁ , the dashed line A
3, the amount of feed from point P4 reaches point P5 of d ₄ , and here the correction amount δ(d ₄ ,
f ₂ ), and the photographing lens system 10 stops at the normal in-focus position d ₃ .

Furthermore, when the subject distance is Lb (>La), it is represented by curve group B, and the same correction amount δ(d ₆ ,
f ₁ ) and δ(d ₇ , f ₂ ), the photographing lens system 10 is set to a normal focused state with a movement amount d ₅ . However, d ₆ and d ₇ represent the amount of delivery at points P6 and P7 where the curves B2 and B3 intersect with the horizontal axis, respectively.

In the above focus correction means, after once detecting the focus position of infrared light, the correction amount δ is calculated and correction is performed, so the photographic lens system 10 moves discontinuously, but this can be avoided. In order to do this, the following correction means are also possible. FIG. 7 is a block diagram of the correction means, and parts corresponding to FIGS. 4 and 5 are given the same numbers. This method is different from the above-mentioned method because, in the process of the correction system 15 reaching focus, the correction amount calculation system 12 always receives the correction amount g.
The focus detection system 13 receives the signal .delta., and performs focus detection in a state in which correction is performed within the focus detection system 13 using a correction signal l corresponding to the correction amount .delta..

In this case, as a specific method of correction performed within the focus detection system 13, for example, when a line sensor is used as the focus detection system 13, the received light beam L2 that is determined to be in focus on the line sensor It is conceivable to electrically shift the position from the center by an amount corresponding to the correction signal 1. As a result, it is determined that the received light beam L2 is in focus when it is at a position shifted to the rear of the center of the sensor, which is normally determined to be in focus. In addition, if a differential type sensor is used, correction can be made by mechanically moving the sensor by an amount corresponding to correction signal 1 in a direction perpendicular to the optical axis of the light receiving lens system. .

FIG. 8 is a graph similar to FIG. 6 that shows the process of reaching a focused state using this method. In Fig. 8, the definitions of the coordinate axes and curve groups A and B are the same as in Fig. 6, but curves C and D are the correction amounts when the focal lengths are f ₁ and f ₂ (f ₁ < f ₂ ), respectively. The correction amount δ output from the calculation system 12 is expressed with respect to the feeding amount d. Similar to the above case, the process of reaching the in-focus state when the focal length is f ₁ , the subject distance is La, and the initial extension amount of the photographic lens system 10 is d ₁ will be described next.

At point P1, which is the initial position of the photographic lens system 10, the defocus amount γ(d ₁ , f 1 ) is smaller than the correction amount δ′(d ₁ , f ₁ ) output from the correction amount calculation system 12 _.
Since this is large, the focus detection system 13 detects that the rear focus is in focus, and the photographing lens system 10 is extended. Along with this, the point P1 moves downward along the curve A2, and the correction amount δ moves upward along the curve C, and the focus is reached at the position of the extension amount _d3 corresponding to the point P8 where the two curves intersect. Detected. Focus detection system 13
Specifically, the above operation is realized by electrically comparing the correction amount δ' and the defocus amount γ. Note that the defocus amount γ is an amount determined from the position of the received light beam L2 on the sensor.

When the focal length of the photographic lens system 10 becomes f ₂ (>f ₁ ), the curve representing the correction amount δ becomes D,
If the subject distance La is the same, the two curves A
Feeding position corresponding to point P9 where 3 and D intersect
Focus is reached at d ₃ . Also, the subject distance is Lb (>
La), focus is detected in exactly the same way.

Next, the correction amount δ in the correction amount calculation system 12,
A specific method for calculating δ′ will be explained. Correction amount δ,
Since δ' changes depending on the extension amount d and the focal length f, it is first necessary to detect these quantities. To do this, for example, electrically connect movable parts such as the distance ring and zoom ring of the photographic lens system 10. It is relatively easy to provide a contact, find its position electrically, and determine d and f from these quantities. Furthermore, using the obtained d and f, the correction amounts δ(d, f) and δ'(d,
f) etc., if the functional system of the correction amounts δ and δ′ is simple, it is possible to actually perform the calculations using an electrical element with arithmetic functions. The values of correction amounts δ and δ' corresponding to each combination of d and f are stored in a memory element such as , and the correction amounts δ and δ' corresponding to the obtained d and f are read out as necessary. You can also do it like this.
In reality, it is not necessary to calculate continuous correction amounts δ and δ′ corresponding to continuous changes in d and f, but discrete correction amounts δ and δ′ for combinations of several divided d and f. It is sufficient for practical purposes to find. Note that when calculating the correction amounts δ and δ', the correction amounts δ and δ' may be directly calculated using the position information of the distance ring and the zoom ring as variables, without calculating d and f.

As described above, according to the autofocus camera according to the present invention, it is possible to calculate the correction amount corresponding to the extension amount and focal length of the photographing lens, and thereby correct the focal position, so that infrared light In focus detection using the TTL active method, which uses light in the infrared wavelength range, which is different from the wavelengths that mainly contribute to photography, the focus detection accuracy can be greatly improved, making it easier to replace lenses like single-lens reflex cameras. Even in this type of camera, effective correction can be made for various types of interchangeable lenses, and it is also possible to use photographic lenses with special chromatic aberrations.

[Brief explanation of the drawing]

Figures 1 a to c are optical diagrams showing the principle of the TTL active type automatic focus detection device, Figure 2 is an optical diagram showing the corrected state, and Figure 3 is the amount of infrared aberration. Graphs, FIGS. 4, 5, and 7 are block diagrams showing embodiments of the present invention, and FIGS. 6 and 8 are graphs showing the process up to focus detection. 10 is a photographing lens system, 11 is a photographing lens drive system, 12 is a correction amount calculation system, 13 is a focus detection system,
14 is a drive control system, and 15 is a correction system.

Claims (1)

[Claims] 1. An automatic focus detection device that detects the focus by projecting light of a wavelength different from the wavelength that mainly contributes to the photographing onto the subject and receiving the reflected light; and a means for forming a correction amount necessary for canceling out a shift in the focal position caused by a difference in the wavelength of the projected light beam according to the focal length and extension amount of the photographing lens, An automatic focus camera that performs focus correction of a photographic lens. 2. The autofocus camera according to claim 1, which receives reflected light from the subject through a photographic lens. 3. According to claim 1, the focus correction is performed by performing focus detection in a state where no correction is performed, and correcting the focal position of the photographing lens according to the correction amount calculated in the state. Autofocus camera as described. 4. The focus correction according to claim 1, wherein the correction amount is calculated in each state of the focus movement process leading to the in-focus state, and is performed over time according to the correction amount. autofocus camera. 5. The autofocus camera according to claim 1, wherein the photographing lens is a zoom lens and provides a signal according to a set focal length. 6. The autofocus camera according to claim 1, wherein the means for forming the correction amount includes a storage section that stores a correction amount corresponding to a combination of focal length and extension amount.