JPS63191112A - Auto-focusing lens system - Google Patents

Abstract

PURPOSE:To attain continuous focusing from an infinite range up to a close range having equal photographing magnification and to prevent the titled lens system from generating malfunction by moving a focusing group so that the differential value of a composite focal distance changing value from the moving distance of a focusing lens group is changed from a positive value to zero or from a positive value to a negative value. CONSTITUTION:When a focusing lens is moved along the track of the focusing lens group, photographing magnification can be allowed to correspond to a photographing distance at the rate of 1 to 1 up to required photographing magnification. Consequently, a distance with a photographing magnification at which the differential value gammai of an image face moving factor is '0', i.e. a limit photographing distance Rc, can be moved to the outside of the required photographing magnification (beta=-1). Even if a focal distance is extended at the time of close range photographing, extremely close photographing based on auto-focusing can be easily executed and the software of a focusing servo can be simplified. Consequently, the generation of malfunction can be prevented and simple and accurate focus control can be attained.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to an autofocus lens system used in an autofocus device.

[Conventional technology]

As an automatic focusing device for a camera, there is a device that performs automatic focusing by detecting the amount of deviation of the subject image on a predetermined image forming plane and calculating the amount of movement necessary for focusing the photographing lens from this amount, for example, in Japanese Patent Publication No. It is known from Publication No. 59-14'0408. Various types of lens systems are known for use in such automatic focusing devices. For example, focusing is performed by moving the lens system as a whole, focusing is performed by moving only some lens components in the lens system, and even focusing is performed by moving only some lens components in the lens system. It is something to take.

Among these autofocus lens systems, those that can focus continuously from infinity to close distances where the imaging magnification is 1x are limited due to fluctuations in aberrations when focusing at close distances. Only these types are practical, for example:
JP-A-55-28038, JP-A-56-1072
There are those disclosed in Japanese Patent Application Laid-open No. 10, Japanese Patent Application Laid-open No. 59-228220, and Japanese Patent Application Laid-Open No. 60-188917.

[Problem that the invention seeks to solve]

As mentioned above, the lens systems that are capable of close-up photography that reach the same magnification are either equipped with a fixed lens component within the lens system in order to correct aberration fluctuations during close-up photography, or lenses with partially different movable modes. Because of this, the combined focal length of the entire system inevitably changes between focusing at infinity and shooting at close range. When the combined focal length of the entire system becomes shorter at short distances, it becomes possible to focus on objects at a shorter distance than when focusing by moving the entire lens system as a whole, but aberrations There is a tendency for complicated lens configurations to be required for correction. In addition, when the combined focal length of the entire system becomes long during close-range shooting, the lens configuration can be made relatively simple, and the close-up distance # (from the object to the image This has the advantage that the distance #) to the surface can be made longer.

However, if the combined focal length of the entire system becomes long during close-range shooting, the shooting distance will be the shortest when the shooting magnification is smaller than 1x, and the shooting distance will gradually increase when a higher magnification is obtained. I'm going to go. In other words, in this case, as shown in Figure 2, which shows the relationship between photographing distance and photographing magnification, there will be two conjugate points with different magnifications at the same photographing distance until the same magnification is reached, and so on. There are two different lens arrangements, that is, two different imaging magnifications at the same maximum shadow distance, which is inconvenient for autofocus control.

Specifically, when photographing in an area with the same magnification returned by automatic focusing, there is a risk of malfunction due to the presence of two focal points near the same magnification.

Therefore, an object of the present invention is to provide a lens system in which the combined focal length of the entire system in a close-up shooting state is larger than that in an infinity shooting state, and to continuously focus from infinity to a close-up distance where the shooting magnification reaches 1x. It is an object of the present invention to provide an automatic focusing lens system that can perform automatic focusing without causing any malfunction during automatic focusing.

[Means for solving problems]

The automatic focusing lens system according to the present invention is a lens system in which the focal length of the composite system when focusing at close range increases relative to the focal length when focusing at infinity, and as shown in Fig. 1, the photographing magnification β is The change rate of the focal length of the synthesis system is locally reduced in the vicinity of the same magnification in a state fi (-1<β<O) smaller than the same magnification (β=-1), and the entire system is The focusing group is moved so that the differential value of the synthetic focal length change amount changes from positive to zero or from positive to negative.

[For production]

By moving the focusing lens along the trajectory of the focusing lens group, it is possible to increase the minimum focusing distance Rc (even if the focusing lens is moved further toward the higher magnification side, the imaging distance will not become shorter, but will instead become longer). At (shooting distance that starts), obtain as large a photographic magnification βe (<-1) as possible, and correspond one-to-one between the photographing distance and the amount of movement of the focusing lens group up to the desired photographing magnification near the same magnification. This eliminates the risk of malfunction of the automatic focusing device, and allows the automatic focusing device to perform accurate It enables control.

In this way, the configuration is such that there is only one shooting magnification for the shooting distance until the shooting state of 1x is reached, and the automatic focusing device Automatic focusing can be performed accurately and easily.

The structure and operation of the present invention as described above will be explained below. A lens system that moves the lens system as a whole toward the object side while enlarging the aperture space will be described with reference to the drawings. Such a lens system consisting of two positive refractive power lens groups is used as a close-up lens called a micro lens or a macro lens, as disclosed in Japanese Patent Application Laid-Open No. 55-28 by the same applicant as the present application.
This lens is known from Japanese Patent Application No. 038, etc., and is capable of maintaining excellent imaging performance even at short distances where the photographing magnification reaches 1:1.

In Figures 1 to 4, the vertical axis represents the relationship between the in-focus state ↑most shadow magnification β and the photographing distance R (distance from the object to the image plane) for any lens arrangement. It is shown in association with the trajectory. FIG. 1 shows the movement trajectory and photographing distance of the lens group G and the second lens group G2 according to the present invention, and FIGS. 2 to 4 are explanatory diagrams to help understand the present invention. be.

The relative coupling constant 021 written in each figure is the amount of change ΔB in the distance between the film surface ■ and the second lens group G due to focusing.
C! It is expressed as l=ΔD/ΔBf.

FIG. 2 shows the case of a microlens known from the above-mentioned Japanese Patent Application Laid-Open No. 55-28038, etc., and the 1121st group G1
This is a case where the aperture space between the lens group G2 and the second lens group G2 continuously expands as the distance becomes shorter, and the composite focal length of the entire system increases monotonically. In this case, when the focal lengths of the 1121st lens group G1 and the second lens group G2 are f, , ft, respectively, f, > 0, f, > Q, and C, , > O, so it The focal length of the system becomes longer, and the photographing magnification β at the limit photographing distance Rc becomes Iβc 1<1, which is lower than the same magnification. For this reason, the photographing distance R gradually increases as it becomes larger than the photographing magnification βC, and as shown in FIG. 2, the locus of the photographing distance R makes a U-turn at Rc. Therefore, in the vicinity of the limit photographing path MRc, it can be seen that two photographic magnifications correspond to one photographing path HR.It is easy to correct aberrations for a lens type with such a focusing method, but Since the I-most shadow magnification β is a bivalent function with respect to the distance R, it may cause malfunction of the automatic focusing device, and the servo control becomes difficult and the software becomes complicated.

FIG. 3 shows a case of an entire-extrusion focusing method in which the 1121st lens group G1 and the second lens group G2 are integrated, and the relative coupling constant Cz+=0. In this case, the limit photographing distance R6 corresponds to a lens arrangement having the same magnification, β-β.

=-1.

FIG. 4 is an explanatory diagram of the case where, contrary to the case of FIG. 2, the distance between the first lens group G and the second lens group G2 decreases at close range, and since CZ+>O, at close range As the focus increases, the focal length of the entire system becomes shorter.

Therefore, as shown in the figure, the photographing magnification β at the limit photographing distance R6 shifts from the same magnification to the higher magnification side, and ↑ U at the maximum shadow distance R.
Since the turn point can be excluded to the outside of the same magnification position, it can be seen that the photographing magnification is reliably a monovalent function with respect to the photographing distance up to the desired photographing magnification (β=-1).

However, in the movement mode of the lens group as shown in FIG. 4, it is generally difficult to correct aberrations at close range, and a simple structure cannot be achieved.

Therefore, as described above, the present invention is directed to a state B (-1<β<
0), the rate of change in the focal length of the composite system is locally reduced in the vicinity of the same magnification return, so that the differential value of the change in the composite focal length of the entire system with respect to the amount of movement of the focusing lens group changes from positive to zero or from positive to positive. The focusing group is configured to move so that the focusing group changes negatively.

The lower part of Figure 1 shows a geometrical optical optical path diagram, the upper side of the optical axis Ax shows the position and optical path of each lens group in the infinity focusing state, and the lower part of the optical axis Ax shows the short distance focusing state. The position and optical path of each lens group in each state are shown.

As shown in FIG. 1, in the present invention, when focusing from infinity to a short distance, the second lens group G2 linearly moves toward the object side, and along with this, the 1121st lens group G1 also moves closer to the object side. Move towards the object at a fast speed.

The second lens group G moves linearly in the first focusing area F1 until it reaches a predetermined object distance Rx+ (imaging magnification βx+), and then moves linearly in the second focusing area F1 at a shorter distance than this. In this case, the amount of movement of the second lens group G2 relative to the second lens group G2 becomes small. In the example of FIG. 4, the object distance RX in the second focusing area F8! For distances closer than (imaging magnification βX2), the amount of movement of the 1121st group G1 relative to the second lens group G2 becomes smaller, and the object distance Rx, (imaging magnification βx+) and object distance Rx1 (the closest shadow magnification βXs) object distance R between
At x6 (imaging magnification βX), the differential value of the amount of change in the combined focal length of the entire system with respect to the amount of change in image magnification, that is, the amount of movement of the movable lens group, becomes zero. That is, object distance RX6
At (imaging magnification βXs), the lens group Gl is instantaneously
The moving speeds of the lens group G and the second lens group G become equal, and at a shorter distance, the moving speed of the second lens group G becomes smaller than that of the second lens group Gt.

Now, in the autofocus lens system according to the present invention as described above, close-range focusing is performed by a plurality of moving lens groups having different movement forms, so information processing in the device for autofocus control becomes complicated. However, as a result of the following analysis, even in the case of focusing by moving a multi-group lens, the previous patent application filed in 1983 by the same applicant as the present application
Automatic focusing can be performed using the same calculation method as the device disclosed in No. 12391. In other words, the focus detection device determines the amount of defocus Δ on a predetermined image plane.
The calculation formula for detecting Bf and calculating the amount of movement ΔX of the focusing lens group necessary to focus on the object point from this value is: It turns out that there is something.

Below, the relationship between the amount of defocus and the amount of movement of the focusing lens group necessary for focusing in order to perform automatic focusing by moving a plurality of lens groups as in the present invention will be described in detail.

First, for the sake of simplicity, we will discuss the case where focusing is performed by moving the entire lens system as a unit, and then extend this to a multi-group system, and then discuss the case of a two-group system as in the present invention. explain.

a) Second part of the lens Figure 5 is a diagram for explaining the relationship between the magnification β and the photographing distance R in close focusing of a single positive lens, in order to express the focusing situation.

R-FF'-1 (β+1/β )...There is the relationship (1), and in order to show this relationship in an easy-to-understand manner, (
R-FF')/f is shown with β plotted on the vertical axis. Furthermore, Fig. 5 corresponds to the case of Fig. 3 mentioned above, and as shown in Fig. 5, when considering a positive lens, the first quadrant represents the virtual image space and the third quadrant represents the real image space. There is.

FIG. 6 corresponds to the explanatory diagram of FIG. 5, and the upper part of FIG. 01 and its statue 0
In addition to the conjugate relationship with 0.1', the object point 0.1' is out of focus. Figure 6 CB) at the bottom shows the conjugate relationship between the image Ot' and the image Ot'. Indicates the completed state. At this time, object point O1 and its image ○.

The distance (photographing distance) from the object to the object becomes R2, and the object point 01 which was in focus in FIG. 6(A) becomes out of focus as shown as object point 04.

In Fig. 6 (A), let S3 be the finite distance from the principal point H on the object side of the lens system to the object point oI, and St' be the distance from the principal point H' on the image side to the image point 01'. The magnification β is as follows.

β−3+ ′/S+ (2) Next, the object point 0. object point o for the conjugate point of and its image point 01'
I moves to 02 by ΔS, and at this time, the image point ○, ゛ becomes 01
If it moves by ΔS' toward ', the following relationship holds true.

ΔS−ΔS′/β! (1-ΔS'/βf)...(3)
Furthermore, since the object point has moved, a defocus of O+'Ot' occurs with respect to the predetermined image plane I (film surface). When focused on, the amount of movement of the object point Δ
The relationship between S and the focusing movement amount ΔX of the lens is as follows.

......(4) From equations (3) and (4), Ami ΔS'/ (1-ΔS' /fβ), which is normally used for reduction, is -1〈β〈O. It is a negative root.

As an approximate solution at low magnification of (5) and (6),
Equation (6) can be simplified as follows.

1 ΔS′ γ (1+ΔS' β/γr) However, γ=1−β2 (8).

Therefore, when the defocus amount ΔS' is detected, T, β
, f are given, the amount of movement ΔX required for the lens system to focus from 0□゛ to 0°' can be determined, and automatic focusing control is possible. Even if ΔS' in equation (7) has a certain degree of magnitude, focusing can be achieved with sufficient efficiency.

Next, as shown in Fig. 7, the entire optical system is composed of n lens groups from lens group 61 to n-th lens group G7. Let me explain the case. In FIG. 7, in the same way as shown in FIG. 6, the upper part of FIG. In addition to the conjugate relationship with the image 01, the conjugate relationship between the out-of-focus object point O2 and the image 02' is shown.

Also, Figure 7 (B) at the bottom shows the lens system as shown in Figure 7 (A).
This shows a state in which the object point O1 corresponding to the object point 0□ has been completely moved by ΔX from the state shown in FIG. At this time, object point O3 and its image 0. The distance (photographing distance) from ' is R2, and the object point ○, which was in focus in Fig.
It is shown that the object point 04 is out of focus.

In this case, as shown in the figure, the image point of each lens group corresponds to the object point of the subsequent lens group, and is transmitted one after another by each lens group to form an image on the film surface as the final image surface I. Ru. Here, by setting the photographing distance between a pair of conjugate points in the i-th lens group to R8, and adding a subscript i to all the specifications of each group, if each lens group does not include an afocal part, , i.e. (β,≠O,R
8≠oo) Equations (1) to (8) 2 above can be rewritten as they are to form relational expressions in a multigroup configuration. The photographing distance R and the photographing magnification β are as follows.

R=ΣR8 =Σ (FF positive '-f, (β, +1/β,))・
...... (9) β=■βI (β,≠0)... (10
)β+=St'/St...
(11) In FIG. 7, when the object point 01 moves to 0□ by ΔS5, the image point 01' is defocused to Ox' by Δβr. At this time, the relationship in the first group is as follows.

However, ΔS1' - ΔBf ΔSt '=ΔS...1 In order to reduce this defocus amount to O by focusing, each lens group is simultaneously moved by ΔXi to form an image on a predetermined image plane I (film plane). The image point is from Ox' to O
Move to 1'. At this time, in equation (12), ○ and 0. If we consider the amount of deviation of the object point and the amount of deviation of the image point by associating the conjugate relationship with 04 and 04' with the conjugate relationship with
i.

Δs,' = ΔX, +Δsi,, + ΔS, = Δ'l+
By simply replacing ΔS7゜1 = 0, the relationship of Os Os' to o, o, ' can be reduced.

Δs, = Here, the defocus amount ΔBf (=ΔSll') is calculated from the n-th lens group using the above equation (12), and ΔS,
At the same time, ΔS1 can be obtained by solving ΔS1 from the nth lens group by solving equation (13) sequentially until i=1. . By eliminating ΔS1 from these equations, the relationship between ΔBf and ΔX can be derived, and the amount of movement of each group required for focusing can be calculated from the defocus amount ΔBf detected by the focus detection device. ΔX can be obtained.

Since the defocus amount ΔBf is given as a function of the movement amount ΔXi for focusing of each of the n lens groups, Q(ΔXl+ΔXz,"', Δx7)=ΔBr−(
14) can be written.

The above equations (12), (13), and (14) are equations that always hold if ΔS1 is sufficiently large but not much aberration occurs, and show the relationship between two different conjugate points. These conjugate points are accurately connected by the focusing movement amount ΔX.

On the other hand, assuming that ΔS4, ΔBf, and ΔX are extremely small amounts, they will be expressed as dS, dBf, and dxH, respectively. At this time, (12), (13), (14
) is expressed as the following equation, and is a relational expression that holds only near the in-focus point.

That is, equation (12) is dsl = dS1++ /β, 2... (15) (
13) The formula is β,! If Equations (15) and (16) are sequentially solved from the n-th lens group to the n-th lens group, and ΔSl is determined and eliminated, Equation (14) holds true near the in-focus point as follows.

However, β. −1, β, ≠0.

C- Now, next, we will define the physical quantity, which is the field movement coefficient, and the coupling constant between the movement amount of the multiple lens groups.

As shown in Fig. 8, when the object point moves from the initial focused state, that is, the conjugate points o, o,' to 0□, in the case of n lens groups, the image point O2' becomes It moves by ΔBf with respect to o,'.

At this time, each lens group Gl, G2. G3. ..., Gn are moved simultaneously, 030. Focusing on the main lens group (i-th group) that focuses and moves so as to obtain a conjugate relationship of .

"5.=ΔBf/ΔX, ......(18
) On the other hand, when the movement amount dBf of the image plane is minute compared to the minute movement amount Δs1 of the object point, similarly, the i-th group is
The differential image plane movement coefficient (image plane movement coefficient near the in-focus point) when the image plane is moved by l is defined as follows.

In addition, as can be seen from Figure 8, the movement mode of the focusing lens group is the amount of movement ΔX of the main lens group, while the lens groups other than the main lens group move approximately or exactly linearly in a specific imaging area. shall be carried out. The ratio of the movement amount ΔXj of the j-th group to the movement amount ΔXi of the i-th group is defined as an absolute coupling constant K
ij is defined as follows.

Kl, Mi Δxj/ΔXz --(20) On the other hand, the 8th
As shown in the figure, the ratio of the amount of change ΔD in the image-side space of the i-th group to the amount of change ΔD in the image-side space of the other j-th group before and after focusing is defined as a relative coupling constant Cij, and the following Define it like this.

C direct j=ΔDJ/ΔD, (21) Through these constants, the following relationship exists between ΔXi and ΔD.

(1≦i≦l≦j≦n) Cij= 1 /Cji, Cr== 1% CtJ=
Cth-Ckj...(23) Kij='CrL...-(24)ΔTL=
ΔXI, ΔD, = Δx, l-(25) where ΔTL is the amount of change in the total length of the lens group due to focusing.

When equation (19) is obtained for simultaneous movement of the n lens groups using these coupling constants, equation (17) is obtained as follows.

...... (26) As a special case of equation (26), when the movable group due to focusing is only the first group, K ii =1-, l≧1, and the following is obtained. .

However, Equation 27) is for the case where ill does not include an afocal system where β1=0. Further, equation (28) is a case where an afocal system is included between the (n-1)th group and the nth group.

In addition, when focusing on the first group of a zoom lens, etc., since i = 1, if β1 = 0 when focusing on infinity, (27), (2
8) The formula holds true. If n is 1, equation (27) becomes (
8) Consistent with Eq. That is, equation (26) is expressed including all focusing methods, and is also true for inner focus and rear focus, for example.

Equation (14) mentioned above is a formal expression, so in order to find it concretely, we will consider a lens system that adopts a short-distance correction method consisting of a two-group system. . By sequentially solving equation (12), we get the following.

Δs, = From formula (13), low magnification approximation 1ΔXz/fz l<<l (1-β!')/β2
1...(30) Furthermore, if we reply to the numerator of the above equation Δx+(1-βz)β2'+Δx2(1-β2') by assuming that the subsequent terms can be ignored, that is, ΔXl/ Assuming that f 1 and ΔX2 / f z are not very large, equation (30) becomes as follows.

...(31) rz "'ni!I(L L")'rz" + (1
-rz")r+ -(1-β+")rz""K+z(
1-β2')...(32) From the relationship (29) = (31) and equation (32), the following is obtained.

...(33) It is also easy to solve for ΔX from equations (29) and (30).

Furthermore, in equation (33), If ΔX,”O,Kz+-0, T2=1-β2' It becomes equal to equation (7).

Furthermore, in equation (32), Δx! ;0, K+z-0 indicates a lens system in which focusing is performed by only one group. At this time, r+ = (1-βI2)β2', and from equation (29) and (30), Δz and x are obtained. This corresponds to a zoom lens that focuses by extending the first group. β2 is the zoom magnification, and T2 is the focal length of the zoom section.

As can be seen from the example of equation (35), β1 becomes 1/
When the magnification is as low as 10 times, the effect of β1/γl T1 term is small, so 1/11 mi (
1/f zβ2−β1/γ, f,) may be regarded as almost constant. In each shooting area, γ, and!
If the value of , is given, Δx1 can be easily calculated from the defocus amount ΔBf, so that focus control can be performed with high accuracy.

e) The above is an analysis of a two-group system, but as an analogy, even when autofocus is controlled by focusing by simultaneous movement of a general multi-group lens system, (33
) As can be seen from the equation, it can be reduced to the following equation.

Equation (36) is expressed as ΔXi=ΔB f / r as before.
Compared to the case expressed by r, the accuracy of autofocus control can be improved even if the defocus amount Bf is large to some extent, and focusing can be completed with fewer distance measurements.

f) A However, in practice, care must be taken when formula (36) is used because the accuracy of the approximation deteriorates when the magnification returns to the same magnification or when the defocus amount ΔBf is extremely large. be. That is, 2
(2) Calculate multiple values of γ(, l) over the shadow area, each corresponding to a sample point, and fix the representative value only in a limited imaging area that includes one of each sample point. At a shooting distance that deviates from this area, accurate focusing is possible by calculating the extension amount Δx8 using T1,!!, and N corresponding to that area.However, at this time, (36 ) As can be seen from the equation, it is necessary that γ1≠0 at all times in the range where the desired imaging magnification is achieved.

Equation (36) shows the relationship when controlling the lens from a defocused state to a focused state. As can be seen from FIG. 8, the conjugate points of o, o' and 0, 0. The conjugate point ' is a state where focusing is completed in each lens arrangement. By the way, when we look at the object point o, (Ol) which should be in the focusing lens arrangement of Ox's' in the focusing lens arrangement state of 0+O+', the image point shifts from 02' and OI', resulting in a defocused state. ing. Similarly, if you look at the object point OI from the focusing lens arrangement 0ses', it will be in a defocused state.In this case, although the focusing movement amount ΔX is the same value,
The defocus amount ΔBf, the correction parameter 1, and the differential image plane movement coefficient TI have different values.

Here, focusing is performed by dividing the focusable shooting distance region into m finite sections, and the specific lens arrangement state that is in focus is the p-th lens arrangement state, where p is a number from 1 to m. The lens arrangement is an integer and corresponds to the representative sample point of each section. On the other hand, each specific position of the object is defined as the q-th position, where q is an integer from 1 to m. When the subscripts of p and q are equal, it indicates that focusing is complete. At this time, γ becomes γreq“ripp, and the 11th time becomes Ai□, and when p≠q, 1/1.□≠0.

On the high magnification side of the same magnification, the number m of all sample points is increased by narrowing the interval of sample points. This allows 1/1=pq to become a specific constant that approximately does not change much in each interval. As a result, equation (36) can accurately calculate ΔX( by giving ΔBf. However, 1/1.□ and 1
/11q- have different values, but the smaller absolute value of 1/18 may be used to prevent the image plane from overrunning due to focusing.

Also, when determining the constant of 1 / l + pq, ΔX ipq, ΔX ipq, Δ
Since Bf, *, and T ipp can be determined, they can be calculated as follows.

To make it easier to understand these relationships, please refer to Figures 5 and 6.
To explain using a diagram, the p configuration state indicates a focused state of 0301', and the q state position of the object is OiO□
' indicates a defocus state - Os Os
'corresponds to the focused state in the q arrangement state.

States pp and qq are sample points of each in-focus state.

〔Example〕

As shown in the explanatory diagram of FIG.
This is a so-called microlens that is capable of short-range focusing and is composed of lens group G2. 1171st lens group G1 and second lens group G2
This is to correct aberration fluctuations at short distances by moving both of them toward the object side and expanding the space of the aperture S between both lens groups at short distances.

During close-range focusing when the imaging magnification reaches the same magnification, the trajectory of the second lens group Gl has a nonlinear trajectory with respect to the movement of the second lens group aX, so that the first focusing area F+ with a low magnification is Then, as shown in Figure 2, the combined focal length changes to become longer, and the second focusing head-mounted F8 with a high magnification returns the same magnification.
As shown in FIG. 4, the focal length has a short change rate, and it is possible to focus at a magnification of more than 100%. The focal length at I & close range is longer than the focal length at infinity lens arrangement. It should be noted that if −S has the above-mentioned characteristics, the trajectory of the focusing movement of the second lens group G2 may also be non-linear. By selecting such a focusing trajectory, Aberrations can also be easily corrected.

The lens configuration diagram of the example is shown in Fig. 9 (A) and (B). Fig. 9 (A) shows the infinity focus state, and Fig. 9 (B) shows the photographing magnification of 1x (β = -1). As shown in the diagram, the in-focus state of
The autofocus lens system of this embodiment is of a so-called Gaussian type, and the lens group G includes a biconvex positive lens component L1 and a positive meniscus lens component L with a convex surface facing the object side.
The second lens group G2 is composed of a negative meniscus lens component L4 and a negative meniscus lens component with a convex surface facing the object side, and the second lens group G2 is composed of a negative lens component L4, a positive lens component cemented thereto, and a biconvex lens component L4. It consists of a positive lens component and a positive lens component.

In this embodiment, as shown in FIG. 10, a lens group G and a second lens group G8 are used to focus from an infinite shooting distance (R=06) to a shooting magnification β=-1,0. The movement locus is such that the second lens group G linearly moves toward the object side, while the 1171st lens group G1 has an imaging magnification of approximately β−0,
Up to the state of 85, it moves toward the object side at a faster speed than the second lens group G2, and from the state of β=-0°85, it changes to the same magnification (β--
1,0), the movement speed for focusing becomes small. At this time, the second lens group G up to the imaging magnification β=-0.85,
The relative coupling constant Cz+ (−
0,85) and the photographing magnification β=-0,85 to the same magnification (β=
The difference between the relative coupling constant C1+(-1,0) of the second lens group G and the second lens group G up to
, then ΔCH−Czl (−0,85) Cz
l(1,0), and Oku ΔC! ! <
It is desirable to satisfy the condition of 0.2.

If the lower limit of this condition is not met, as shown in FIG. 2, the change in photographing distance with respect to photographing magnification becomes a bivalent function, making it impossible to achieve the object of the present invention. In addition, if the upper limit of the above conditions is exceeded, the first lens group G at close range,
Since the distance between the lens group G2 and the second lens group G2 becomes too small, the correction function for aberration fluctuations at short distances deteriorates, making it difficult to maintain good sharpness performance.

Note that within the above range, the first lens group Gl and the second lens group G3 are not limited to moving linearly, but may also move nonlinearly.

Table 1 below shows lens configuration specifications of Examples.

In the table, the leftmost number represents the order from the object side, and the refractive index and Atsube number are values for the d-line (λ=587.6n+w).

L Focal length f = 55.0 F number 2.8 In this lens system, in order to focus from infinity to close range where the image magnification β = -1 is reached, the lens group G1
The values of the aperture space d6 and the back focus Bf between the lens group G2 and the second lens group G2 are as shown in Table 2 below. The value of the composite focal path jilf of the system is also shown.

When focusing in the close-range correction method consisting of two groups as shown in FIG. 1, the photographing distance R is calculated as follows from equation (9).

R=F+ F+ ' f+ (β1+1/β1)
+Fz Ft ′fz (β2+1/βri...(
38) β1- β2=-(Δx,-βzo f z) / f z
-(40) However, β2° is the magnification of the second lens group G2 when the lens arrangement is focused at infinity. The overall composite magnification is as follows.

β-β, β2 = If f is the lens composite focal length in an arbitrary lens arrangement, the following relationship holds.

1/f=1/f, β! OcttΔX z/ f 1 f
t''·(42) The change in focal length with respect to the movement of the second lens group G2 can be expressed as follows.

Δf/ΔXz = Cz+f” /f+ fz −(
43) Therefore, the change in focal length and the relative coupling constant are proportional. From equation (34), if fl>0 and β2×0, then Δx2
〉0, when CWt>0, Δf/Δx2〈0, and ΔX
=>0, when CWt〈O, Δf/Δx2〉0,
It can be seen that the change Δf of the composite focal length with respect to CWt is opposite to that shown in the examples of FIGS. 2 and 3. When there is a region where the short-range correction changes on the high magnification side so that Δf<Q at any time, γ2≠0
The following conditions are satisfied up to the desired magnification.

Attached Table 3 shows the specifications necessary for automatic focusing in the above embodiment for the same four positions as described above.

The values necessary for automatic focusing shown in Table 3 are the values obtained from the analysis results described above, and these values enable accurate and reliable focusing between each position. be. These specifications have the same meaning as "Table 1" disclosed in the earlier Japanese Patent Application No. 12391/1983 by the applicant. The correspondence relationship with the above in the earlier application is as follows.

Image plane movement amount conversion coefficient: 0-γ.

Correction factor 200=-1/7! pq ΔBfpq= r sxΔX9m γ1. , 9-γ2. (1-ΔBfpq/' pJHere, in the case of a low magnification focusing area, or the assumed subject classification (
In the case of a defocus amount of several positions of sample position), the average value of 'IIQI'QD can be taken at the time of focusing, and it can be approximated to a one-dimensional parameter as 1, = (βpq + l1Q11) / 2. .

At this time, the above formula for ΔX□ is given by a value represented by a one-dimensional parameter.

According to the embodiments of the present invention as described above, it is possible to continuously focus from infinity to close range where the photographing magnification reaches 1:1, and the photographing distance and photographing magnification are 1:1 over the entire focusing area. 11 (A), (B), (C). As shown in the figure, it is clear that extremely good imaging performance is maintained not only at infinity but also at close distances reaching the same magnification. B) is the in-focus state with the imaging magnification β = -0.85x, the 11th
Figure (C) is a diagram of various aberrations in a focused state with an imaging magnification of β-1,0.

FIG. 12 is a diagram showing a schematic configuration of the entire device when the autofocus lens system according to this embodiment is combined with an autofocus device.

Reference numeral 1 denotes an automatic focusing lens system as in the above embodiment that is attached to the camera body, and includes a lens group G and a second lens group Gt that are movable along the optical axis ζ for focusing. are doing. The light flux that has passed through the lens system 1 is guided to a light receiving element 5 for focus detection via a quick return mirror 2 and a sub-mirror 3, the center of which is formed into a semi-transmissive mirror, arranged inside the camera body. The output of the light-receiving element 5 is input to the image plane deviation amount detection section 6, and the image deviation amount ΔBf from a predetermined image plane 4 (film plane) is calculated including the signs of the front bin and the rear bin. 7 is a ROM provided in the lens barrel (not shown) of the lens system l.
This is a lens information storage unit consisting of, etc., and information regarding conversion coefficients as shown in Table 3 specific to the lens system 1, that is, image plane movement amount conversion coefficients, correction coefficients, etc. are stored in advance. 8
1 is a movement amount calculation unit for focusing the lens system, and 1 is a drive control unit for the focusing lens, which controls the drive motor 10 based on the output ΔX of the lens movement amount calculation unit to control the focusing lens. to drive. Reference numeral 11 denotes a pulse generating section using a detector for detecting the amount of movement of the lens group for focusing the lens system 1, and transmits the position of the focusing lens group to the lens drive control section 9 based on the number of pulses.

The details of the function and operation of such an automatic focusing device are as follows.
The details are omitted since it is as disclosed in the previous Japanese Patent Application No. 12391/1982.

〔effect〕

As described above, by adopting the focusing mode according to the present invention, it is possible to make a one-to-one correspondence with the close-up distance ME up to the desired imaging magnification as shown in FIG. As a result, the photographing magnification at which the differential value γi of the image plane movement coefficient becomes O, that is, the limit photographing distance Rc, is set to the desired photographing magnification (β=-1).
can be moved outside. Therefore, even when the focal length is long for close-up photography, it is now possible to easily perform close-up photography using autofocus. That is, since the software for focusing servo by autofocus is simple, there is no fear of malfunction, and easy and accurate focusing control is possible.

Furthermore, when the focal length becomes long in close-up photography, when performing high-magnification photography with the lens of the focusing mode according to the present invention, the photography distance can be relatively long, which makes the illumination conditions of the subject advantageous.

In addition, even in a focusing method that involves the movement of a complex lens group, as mentioned above, in autofocus focusing control, focus control is performed simply and accurately in the same manner as focusing control using a group of lenses. becomes possible.

[Brief explanation of the drawing]

FIG. 1 is a diagram showing an example of an automatic focusing lens system according to the present invention, and is a diagram showing the relationship between the photographing distance R and the photographing magnification β, which change in relation to the movement of the lens group during focusing. 2, 3, and 4 are explanatory diagrams for comparison with the focusing mode according to the present invention, and FIG. 5 shows a case where short-distance focusing is performed by integrally extending the entire lens system. Shooting distance R
FIGS. 6(A) and 6(B) are optical path diagrams showing the conjugate relationship of object points in the case of finite photographing distances R7 and R2 in relation to FIG. Figure (A) CB)
is an optical path diagram showing the conjugate relationship of winter object points when focusing is performed by moving a multi-group lens system, and FIG. 8 is an optical path diagram for explaining the coupling constant when focusing is performed by moving a multi-group lens system.
FIGS. 9(A) and 9(B) are lens configuration diagrams of an embodiment of the present invention, in which (A) is the infinity focus state, and CB) is the close focus state RB (β=-1,0). 10 is an explanatory diagram of the movement form of the n-th lens group G1 and the second lens group G in the embodiment, and FIGS. 11(A), (B), and (C) are various diagrams regarding the embodiment according to the present invention These are aberration diagrams, in which (A) shows the state in focus at infinity, (B) shows the state in focus at the imaging magnification β=-0, 85, and (C) shows the various conditions in the focus state at the imaging magnification β--1, 0. The amount of aberration is shown, and FIG. 12 is a schematic configuration showing the entire apparatus when the automatic focusing lens system according to the embodiment is combined with an automatic focusing device. [Explanation of symbols of main parts] G1...nth lens group G2...second lens group GIl...nth lens group R...imaging distance β...imaging magnification Applicant Nippon Kogaku Kogyo Co., Ltd. Company agent Patent attorney Takashi Watanabe Engraving of the drawings (no changes to 8) Town side Figure 1 CTlCr2' Figure 6 Figure 9 Figure 10 Figure 7 Contents of amendment Procedure amendment (method) % formula % 3. Relationship with the case of the person making the amendment Patent applicant address 3-2-3 Marunouchi, Chiyoda-ku, Tokyo Name
(411) Nippon Kogaku Kogyo Co., Ltd. Representative: Shigetada Fukuoka, President and CEO 4, Agent address: 1-6-3-5 Nishi-Oi, Honbunagawa-ku, Tokyo 8140
Date of amendment order January 7, 1985 Procedural amendment (formality) Engravings of Figures 1 to 8 of the drawings originally attached to the application, as attached (no change in content) March 1986
8th, 1986 Patent side Relationship with vehicle No. 232168
Patent applicant address: 3-2-3 Marunouchi, Chiyoda-ku, Tokyo Name
(411) Nippon Kogaku Kogyo Co., Ltd. Representative: Shigetada Fukuoka, President and CEO 4, Agent address: 1-6-3-5 Nishi-Oi, Honbunagawa-ku, Tokyo 0140
As per the date attached to the amendment order, l) "Fig. 6 (A) and (B)" in the first line of page 45 of the specification is corrected to "Fig. 6 is". 2) On page 45, lines 3 and 4, "Fig. 7 (A) and (B)" are corrected to "Fig. 7 is".

Claims (1)

[Claims] It has a focusing lens group that moves on the optical axis by different amounts of movement with respect to a predetermined image plane during focusing, and can continuously focus on objects from infinity to close objects with imaging magnification of 1x. In an autofocus lens system that is capable of focusing, and in which the combined focal length of the entire system in the close-range focusing state is longer than the combined focal length of the entire system in the infinity focusing state, the shooting magnification is 1x. The focusing group is moved so that the differential value of the synthetic focal length change amount of the entire system with respect to the moving amount of the focusing lens group changes from positive to zero or from positive to negative in a smaller state. Features an autofocus lens system.