JP2005352183A - Variable-focal-length lens system and imaging unit - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a variable-focal-length lens system in which the amount of movement is reduced at short-range focusing, and to provide an imaging unit using the variable-focal-length lens system. <P>SOLUTION: The variable-focal-length lens system is constituted by arranging, in order from an object side, a first lens group G1 that is positive, a second lens group G2 that is negative, a third lens group G3 that is positive, a fourth lens group G4 that is negative, and a fifth lens group G5 that is positive. In the variable-focal-length lens system, when a lens position changes from a wide angle end to a telephoto end, the first lens group is fixed, the second lens group is moved towards an image side, the third lens group is fixed, the fourth lens group is moved for focusing and for compensating for variation in image face position resulting from the movement of the second lens group, the fifth lens group is fixed, and an aperture diaphragm S is disposed near the third lens group. In the case, where f1 is the focal length of the first lens group, fw is the focal length of the entire system at the wide angle end, ft is the focal length of the entire system, and f2 is the focal length of the second lens group, the following conditions are satisfied: (1) 2<f1/(fw×ft)<SP>1/2</SP><2.5 and (2) -1.6<f2/fw<-1.2. <P>COPYRIGHT: (C)2006,JPO&NCIPI

Description

  The present invention relates to a novel variable focal length lens system and an imaging apparatus. More specifically, the present invention relates to a variable focal length lens system suitable for a camera that receives light by an imaging element such as a video camera or a digital still camera, and an imaging apparatus using the variable focal length lens system.

  2. Description of the Related Art Conventionally, as a recording means in a camera, an object image formed on an image sensor surface by an image sensor using a photoelectric conversion element such as a CCD (Charge Coupled Device) or a CMOS (Complementary Metal-Oxide Semiconductor), A method is known in which the light amount of a subject image is converted into an electrical output by a conversion element and recorded.

  With recent advances in microfabrication technology, the central processing unit (CPU) has been increased in speed and the storage medium has been highly integrated, so that large-capacity image data that could not be handled before can be processed at high speed. It has become. In addition, image sensors have also been highly integrated and miniaturized, and higher integration enables recording at higher spatial frequencies, and miniaturization has made it possible to reduce the size of the entire camera.

  However, due to the high integration and miniaturization described above, there has been a problem that the light receiving area of each photoelectric conversion element is narrowed, and the influence of noise increases with a decrease in electrical output. In order to prevent this, an attempt has been made to increase the amount of light reaching the image pickup device by increasing the aperture ratio of the optical system. In addition, attempts have been made to increase the amount of light reaching each photoelectric conversion element by arranging a minute lens element (so-called microlens array) immediately before each photoelectric conversion element. This microlens array can increase the amount of light reaching each photoelectric conversion element by guiding the light beam between adjacent photoelectric conversion elements onto each photoelectric conversion element. Was given a constraint. That is, when the exit pupil position of the lens system approaches the photoelectric conversion element, the angle formed with the optical axis of the chief ray that reaches the photoelectric conversion element increases, and the off-axis light beam toward the screen periphery becomes a large angle with respect to the optical axis. As a result, it does not reach the photoelectric conversion element, resulting in insufficient light quantity.

  Conventionally, various zoom types have been proposed as zoom lenses for video cameras. For example, those disclosed in Patent Document 1, Patent Document 2, Patent Document 3, Patent Document 4, Patent Document 5, Patent Document 6, and the like are known.

  The zoom lens disclosed in each of the above patent documents has a first lens group having a positive refractive power, a second lens group having a negative refractive power, a third lens group having a positive refractive power, and a negative refractive power. And a fifth lens group having a positive refractive power.

  In the zoom lens disclosed in Patent Document 1, the first lens group is fixed in the optical axis direction regardless of the lens position state, and the fifth lens group moves when focusing at a short distance.

  The zoom lenses disclosed in Patent Literature 2, Patent Literature 3, Patent Literature 4, Patent Literature 5, and Patent Literature 6 have the first lens group, the third lens group, and the fifth lens group when the lens position changes. It is fixed in the optical axis direction.

JP-A-5-215967

JP-A-8-146295 JP 2000-180722 A

Japanese Patent Laid-Open No. 2000-23310

JP 2001-33697 A

JP 2001-33703 A

  By the way, in the zoom lens disclosed in Patent Document 1, when the lens position changes, at least three lens groups are movable, and the driving mechanism cannot be complicated.

  In the zoom lens disclosed in Patent Document 2, the refractive power of the second lens group is too strong, and the off-axis light beam passing through the first lens group is separated from the optical axis, so that the lens diameter can be sufficiently reduced. It wasn't.

  In the zoom lens disclosed in Patent Document 3, since the refractive power of the second lens group is weak, the amount of movement of the second lens group necessary to ensure a predetermined zoom ratio cannot be reduced. It was a factor that hindered downsizing.

  In the zoom lenses disclosed in Patent Document 4 and Patent Document 6, the refractive power of the first lens group is weak, and it is difficult to shorten the entire lens length.

  In the zoom lens disclosed in Patent Document 5, the refractive power of the first lens group and the second lens group is very strong, and the off-axis light beam passing through the first lens group is separated from the optical axis, and the lens diameter is reduced. It was difficult to downsize.

  Accordingly, the present invention provides a variable focal length lens system that solves the above-described problems of conventional zoom lenses and that has a small amount of movement during focusing at a short distance, and an imaging device using the variable focal length lens system. It is an object to do.

In order to solve the above-described problem, the variable focal length lens system of the present invention has, in order from the object side, a first lens group having a positive refractive power, a second lens group having a negative refractive power, and a positive refractive power. A third lens group having a negative refractive power, a fourth lens group having a negative refractive power, and a fifth lens group having a positive refractive power, and when the lens position changes from the wide-angle end state to the telephoto end state, The first lens group is fixed in the optical axis direction, the second lens group is moved to the image side, the third lens group is fixed in the optical axis direction, and the fourth lens group is the second lens group. It moves in the optical axis direction to compensate for variations in the image plane position due to movement and focus at a short distance, the fifth lens group is fixed in the optical axis direction, and an aperture stop is disposed in the vicinity of the third lens group F1 is the focal length of the first lens group, and fw is the entire system in the wide-angle end state. Point distance, the focal length of the entire system to ft in the telephoto end state, the f2 as the focal length of the second lens group, the conditional expression (1) 2 <f1 / ( fw · ft) 1/2 <2.5 and (2 ) -1.6 <f2 / fw <-1.2.

Further, in order to solve the above-described problem, the imaging apparatus of the present invention has, in order from the object side, a first lens group having a positive refractive power, a second lens group having a negative refractive power, and a positive refractive power. A variable focal length lens system in which a third lens group, a fourth lens group having negative refractive power, and a fifth lens group having positive refractive power are arranged, and an optical image formed by the variable focal length lens system The variable focal length lens system has the first lens group fixed in the optical axis direction when the lens position changes from the wide-angle end state to the telephoto end state. The second lens group is moved to the image side, the third lens group is fixed in the optical axis direction, and the fourth lens group is compensated for variations in the image plane position accompanying the movement of the second lens group, and It moves in the optical axis direction for focusing at a short distance, and The first lens group is fixed in the optical axis direction, the aperture stop is disposed in the vicinity of the third lens group, f1 is the focal length of the first lens group, fw is the focal length of the entire system in the wide-angle end state, and ft is the telephoto end. Conditional expressions (1) 2 <f1 / (fw · ft) ^1/2 <2.5 and (2) −1.6 <f2 where f2 is the focal length of the entire system in the state, and f2 is the focal length of the second lens group. /Fw<-1.2 is satisfied.

  Therefore, according to the present invention, in the variable focal length lens system, the aperture stop is disposed in the vicinity of the third lens group, the fourth lens moves when focusing at a short distance, and the first lens group and the second lens group are further moved. The focal length of each lens group is set appropriately.

The variable focal length lens system of the present invention includes, in order from the object side, a first lens group having a positive refractive power, a second lens group having a negative refractive power, a third lens group having a positive refractive power, and a negative refraction. In a variable focal length lens system in which a fourth lens group having power and a fifth lens group having positive refractive power are arranged,
When the lens position changes from the wide-angle end state to the telephoto end state, the first lens group is fixed in the optical axis direction, the second lens group moves to the image side, and the third lens group moves to the optical axis. The fourth lens group is moved in the optical axis direction to compensate for the variation of the image plane position accompanying the movement of the second lens group and focus at a short distance, and the fifth lens group is moved to the optical axis. Fixed in the direction,
An aperture stop is disposed in the vicinity of the third lens group, and satisfies the following conditional expressions (1) and (2):

(1) 2 <f1 / (fw · ft) ^1/2 <2.5
(2) -1.6 <f2 / fw <-1.2
However,
f1: focal length of the first lens group fw: focal length of the entire system in the wide-angle end state ft: focal length of the entire system in the telephoto end state f2: focal length of the second lens group

The imaging apparatus according to the present invention includes, in order from the object side, a first lens group having a positive refractive power, a second lens group having a negative refractive power, a third lens group having a positive refractive power, and a negative refractive power. A variable focal length lens system in which a fourth lens group having a positive refractive power and a fifth lens group having a positive refractive power are arrayed, and imaging that converts an optical image formed by the variable focal length lens system into an electrical signal An imaging device comprising an element,
In the variable focal length lens system, when the lens position state changes from the wide-angle end state to the telephoto end state, the first lens group is fixed in the optical axis direction, and the second lens group moves to the image side, The third lens group is fixed in the optical axis direction, and the fourth lens group moves in the optical axis direction for compensation of variation in image plane position accompanying the movement of the second lens group and focusing at a short distance, An imaging apparatus characterized in that the fifth lens group is fixed in the optical axis direction, an aperture stop is disposed in the vicinity of the third lens group, and satisfies the following conditional expressions (1) and (2).

(1) 2 <f1 / (fw · ft) ^1/2 <2.5
(2) -1.6 <f2 / fw <-1.2
However,
f1: focal length of the first lens group fw: focal length of the entire system in the wide-angle end state ft: focal length of the entire system in the telephoto end state f2: focal length of the second lens group

  Therefore, in the present invention, it is possible to achieve both miniaturization and high performance of the variable focal length lens system. In addition, it is possible to reduce the size and increase the performance of an imaging apparatus using the variable focal length lens system.

  In the invention described in claim 2, β4t is the lateral magnification of the fourth lens group in the telephoto end state, β2w is the lateral magnification of the second lens group in the wide-angle end state, and β2t is the second lens group in the telephoto end state. Since the horizontal magnification of the above condition satisfies at least one of conditional expression (3) 0.25 <1 / β4t <0.4 and (4) 0.6 <β2w · β2t <1.2, It is possible to further reduce the size of the variable focal length lens system by reducing the amount of movement of the lens group.

  In the invention described in claims 3 and 4, conditional expression (5) 0.4 <Db / ft <, where Db is the distance along the optical axis from the lens surface closest to the object side to the aperture stop. Since 0.9 is satisfied, the variable focal length lens system can be further reduced in size by further reducing the diameter of the front lens.

  The best mode for carrying out the variable focal length lens system and imaging apparatus of the present invention will be described below with reference to the accompanying drawings.

  In the present invention, in order from the object side, a first lens group having a positive refractive power, a second lens group having a negative refractive power, a third lens group having a positive refractive power, and a first lens group having a negative refractive power. 4 lens groups and a fifth lens group having positive refractive power are arranged, and when the lens position changes from the wide-angle end state to the telephoto end state, the first lens group, the third lens group, and the fifth lens The group is fixed in the optical axis direction, the second lens group moves toward the image side, and the variable focal length lens compensates for the variation of the image plane position caused by the movement of the second lens group by the movement of the fourth lens group. In the system, by focusing on the following points (a) to (d), it was possible to achieve both miniaturization and high performance of the variable focal length lens system.

(A) An aperture stop is disposed in the vicinity of the third lens group. (B) The focal length of the first lens group is set appropriately. (C) The focal length of the second lens group is set appropriately. The fourth lens unit moves during focusing. In the variable focal length lens system, the arrangement of the aperture stop is important when increasing the zoom ratio.

  Since off-axis rays passing through the lens group arranged away from the aperture stop are separated from the optical axis, it is difficult to reduce the lens diameter in the lens group arranged away from the aperture stop, and at the same time, the angle of view changes. Correction of off-axis aberrations becomes difficult. In particular, since the first lens group is disposed away from the image plane, the lens diameter tends to increase. Therefore, it is important that the aperture stop is not too far from the first lens group.

  In addition, in order to satisfactorily correct the fluctuation of off-axis aberration due to the change of the lens position state, it is important to positively change the height of the off-axis light beam passing through each lens group. It is desirable to arrange one or more movable lens groups before and after the lens.

  For this reason, in the present invention, a lens diameter can be reduced by disposing an aperture stop in the vicinity of the third lens group located between the second lens group and the fourth lens group, which are movable lens groups. Achieving compatibility with high performance (above (A)).

  Since the first lens unit is disposed closest to the object side, the off-axis light beam is separated from the optical axis, the lens diameter tends to be large, and at the same time, the on-axis light beam is incident in a spread state, resulting in an on-axis aberration. Cheap.

  For this reason, by appropriately setting the refractive power of the first lens group, it is possible to reduce the diameter of the front lens and to suppress the occurrence of axial aberration. Therefore, it is necessary to satisfy the following conditional expression (1), where f1 is the focal length of the first lens group, fw is the focal length of the entire system in the wide-angle end state, and ft is the focal length of the entire system in the telephoto end state. It is.

(1) 2 <f1 / (fw · ft) ^1/2 <2.5
Conditional expression (1) is a conditional expression that defines the focal length of the first lens group, that is, the refractive power, and by satisfying this, the refractive power of the first lens group is appropriately set (the above ( A)).

  If the upper limit of conditional expression (1) is exceeded, it will be difficult to shorten the total lens length.

  On the other hand, if the lower limit value of conditional expression (1) is not reached, the off-axis light beam passing through the first lens group in the wide-angle end state moves away from the optical axis and causes an increase in the lens diameter. .

  In the present invention, when the lens position changes, the first lens group, the third lens group, and the fifth lens group are fixed, the second lens group functions as a variable power group, and the fourth lens group functions as a compensation group. To do.

  For this reason, as the refractive power of the second lens group is stronger, it is possible to ensure a predetermined zoom ratio with a smaller amount of movement.

  However, when the refractive power of the second lens group is increased, the off-axis light beam passing through the second lens group approaches the optical axis, so that it is difficult to correct on-axis aberration and off-axis aberration at the same time. In this state, it becomes difficult to satisfactorily correct the fluctuation of off-axis aberration due to the change of the angle of view.

  From the above, it is important to set the refractive power of the second lens group appropriately. Therefore, it is necessary to satisfy the following conditional expression (2), where f2 is the focal length of the second lens group.

(2) -1.6 <f2 / fw <-1.2
Conditional expression (2) is a conditional expression that defines the focal length, that is, the refractive power of the second lens group. By satisfying this, the refractive power of the second lens group is appropriately set (the above (c) )).

  If the upper limit of conditional expression (2) is exceeded, the off-axis light beam that passes through the second lens group in the wide-angle end state approaches the optical axis, so that fluctuations in off-axis aberrations due to changes in the field angle are corrected well. It becomes difficult.

  When the lower limit value of conditional expression (2) is not reached, the amount of movement of the second lens group necessary to ensure a predetermined zoom ratio increases, so the second lens group and the third lens group in the wide-angle end state. And the off-axis light beam passing through the first lens group in the wide-angle end state is too far from the optical axis, and the fluctuation of off-axis aberrations due to the change in the angle of view can be corrected well. It will be difficult.

  Furthermore, in the present invention, the fourth lens group is configured to perform a so-called focus function of correcting a change in the image plane position due to a change in the subject distance by the movement of the fourth lens group, and the fourth lens group includes the compensation group and the focus group. The number of movable lens groups is reduced by simultaneously fulfilling the above function ((D) above).

  In the present invention, as described above, the fourth lens group is moved in the optical axis direction when focusing on a short distance.

  Since the fourth lens group has negative refracting power, the axial light beam emitted from the fourth lens group is (a) diverged (the lateral magnification β4 of the fourth lens group is −1 <β4 <0). (B) A state close to parallel light (-1 <1 / β4 <1) is assumed.

  In the case of (a), since the axial light beam is strongly diverged by the fourth lens group, it is difficult to shorten the total lens length. For this reason, in the present invention, it is preferable to set the lateral magnification of the fourth lens group as in (b) above.

  In the present invention, since the third lens group and the fifth lens group are fixed in the optical axis direction and the fourth lens group moves between them, the movement range of the fourth lens group (according to the movement of the second lens group) Reduction of the sum of the movement range necessary to compensate for variations in the image plane position and the movement range necessary for focusing on a short distance leads to a reduction in the overall size of the lens system and simplification of the drive mechanism.

  Furthermore, at present, the autofocus function is common, but when the autofocus speed is slow, the focusing operation on a fast-moving subject is slowed, which makes the user feel uncomfortable. For this reason, it is necessary to increase the autofocus speed, and it is important to reduce the amount of movement when focusing on a short distance.

  In order to reduce the amount of movement of the fourth lens group, it is desirable to set the inverse 1 / β4 of the lateral magnification of the fourth lens group close to 0. In the present invention, β4t is the lateral magnification of the fourth lens group in the telephoto end state. Therefore, it is desirable to set the lateral magnification of the fourth lens group so as to satisfy the following conditional expression (3).

(3) 0.25 <1 / β4t <0.4
If the upper limit value of conditional expression (3) is exceeded, the amount of movement required when focusing on a short distance in the telephoto end state becomes too large.

  Conversely, if the lower limit of conditional expression (3) is not reached, it is possible to reduce the amount of movement required when focusing on a short distance, but the divergence action by the fourth lens group becomes stronger, and the total lens length becomes longer. As a result, the off-axis light beam passing through the fifth lens group is separated from the optical axis, and the coma aberration cannot be corrected sufficiently at the periphery of the screen.

In the present invention, β2w is set as the lateral magnification of the second lens group in the wide-angle end state in order to narrow the moving range of the fourth lens group necessary to compensate for the fluctuation of the image plane position accompanying the movement of the second lens group. , Β2t is preferably set as the lateral magnification of the second lens group in the telephoto end state, and the following conditional expression (4) is preferably satisfied.
(4) 0.6 <β2w · β2t <1.2
Conditional expression (4) is a conditional expression that defines the product of the lateral magnification in the wide-angle end state and the lateral magnification in the telephoto end state of the second lens group.

  In the present invention, for example, when the position of the fourth lens group in the wide-angle end state and the telephoto end state coincides in the optical axis direction, the second lens group is the product of the lateral magnification in the wide-angle end state and the lateral magnification in the telephoto end state. Becomes 1. When the lateral magnification of the second lens group changes from this state, the position of the fourth lens group changes between the wide-angle end state and the telephoto end state, and accordingly the lens position state of the fourth lens group changes. The range of movement required for is widened.

  When the upper limit value of conditional expression (4) is exceeded, the position of the fourth lens group is at the position in the optical axis direction of the fourth lens group (the telephoto end state is located on the image side compared to the wide-angle end state). When attention is paid, the fourth lens unit moves in a wide range because it is located on the object side in the wide-angle end state.

  If the lower limit value of conditional expression (4) is not reached, the fourth lens group is set to an aperture stop in the wide-angle end state (the position of the fourth lens group is closer to the object side than the wide-angle end state). Therefore, the negative distortion can be corrected well, but the positive distortion generated in the telephoto end state is good because the distance between the fourth lens unit and the aperture stop is too close in the telephoto end state. It will be difficult to correct.

  In the present invention, particularly when the conditional expressions (3) and (4) are satisfied at the same time, the moving range of the fourth lens group can be more appropriately narrowed, and the entire lens system can be further reduced in size and drive mechanism. Can be simplified.

  In order to reduce the size of the lens barrel, there are two elements: shortening the total lens length and reducing the lens diameter. When considering the volume of the lens barrel, the lens diameter is effective in two directions, ie, the height direction and the width direction, which is effective for miniaturization.

  In the present invention, in order to further reduce the diameter of the front lens and to reduce the size of the lens barrel, Db is set along the optical axis from the lens surface closest to the object side of the zoom lens to the aperture stop. It is desirable to configure the distance so as to satisfy the following conditional expression (5).

(5) 0.4 <Db / ft <0.9
If the upper limit value of conditional expression (5) is exceeded, the off-axis light beam incident on the first lens group will be separated from the optical axis, making it difficult to further reduce the lens diameter.

  On the other hand, if the lower limit of conditional expression (5) is not reached, the movement range of the second lens group necessary for zooming becomes narrow, and the second lens is used in order to secure a predetermined zoom ratio with a small movement amount. The refractive power of the group must be increased, and as a result, the off-axis light beam passing through the first lens group is too far from the optical axis, causing an increase in the lens diameter.

  In the present invention, by configuring each lens group as follows, it is possible to reduce the variation of various aberrations accompanying the change in the lens position state, and to further improve the performance.

  The first lens group is a cemented lens composed of a meniscus negative lens having a convex surface facing the object side and a positive lens having a convex surface facing the object side in order to satisfactorily correct negative spherical aberration occurring in the telephoto end state. In addition, it is desirable to use a meniscus positive lens having a convex surface facing the object side.

  The second lens group is preferably composed of a meniscus negative lens having a convex surface facing the object side, and a cemented lens of a biconcave lens and a positive lens having a convex surface facing the object side. In particular, the negative lens on the object side corrects off-axis aberrations that occur in the wide-angle end state, and the cemented lens on the image side corrects aberrations by configuring it to correct on-axis aberrations. The above functions are separated, making it easy to achieve high performance.

  In order to further improve the performance, it is desirable to adopt a doublet configuration in which the cemented lenses are separated or a triplet configuration with three negative and positive.

  The third lens group has a strong refractive power in order to converge the light beam diverged by the second lens group. For this reason, it is desirable to form a positive lens having a strong convex surface on the image side, and a cemented positive lens of a biconvex lens and a meniscus negative lens having a concave surface on the object side.

  The fourth lens group preferably has at least one positive lens and one negative lens in order to correct variations in various aberrations that occur during focusing at close distances.

  Since the off-axis light beam enters the fifth lens group in a state of being diverged by the fourth lens group, it is important to correct not only the on-axis aberration but also the off-axis aberration. For this reason, it is desirable to comprise a positive lens having a strong convex surface facing the image side, and a cemented lens of a negative lens and a positive lens. The positive lens on the object side refracts the off-axis light beam so that it approaches the optical axis, and the cemented lens functions to correct the occurrence of on-axis aberrations well so as to correct on-axis aberrations and off-axis aberrations simultaneously. I have to.

  In the present invention, higher optical performance can be realized by using an aspheric lens. In particular, by introducing an aspherical surface to the fifth lens group, it is possible to further improve the central performance. In addition, by using an aspheric lens in the second lens group, it is possible to satisfactorily correct coma variation due to the angle of view that occurs in the wide-angle end state.

  Furthermore, it goes without saying that higher optical performance can be obtained by using a plurality of aspheric surfaces in one optical system.

  By the way, according to another aspect of the present invention, an image can be obtained by shifting one lens group or a part of one lens group in a direction substantially perpendicular to the optical axis among the lens groups constituting the lens system. In combination with a detection system that detects camera shake, a drive system that shifts the lens group, and a control system that gives a shift amount to the drive system according to the output of the detection system, It is possible to function as a system.

  In particular, in the present invention, it is possible to shift the image with a small aberration variation by shifting the third lens group or a part or the whole of the fifth lens group in a direction substantially perpendicular to the optical axis. is there.

  It is of course possible to arrange a low-pass filter on the image side of the lens system in order to prevent the occurrence of moire fringes or an infrared cut filter according to the spectral sensitivity characteristics of the light receiving element.

  Embodiments of the variable focal length lens system of the present invention and numerical examples in which specific numerical values are applied to the embodiments will be described below. In each numerical example, the aspherical surface is expressed by the following equation (1).

In the above formula 1, y is the height from the optical axis, x is the sag amount, c is the curvature, κ is the conic constant, C ₄ , C ₆ ,... Are aspheric coefficients.

  FIG. 1 shows the refractive power distribution of each lens group in each embodiment of the variable focal length lens system of the present invention. In order from the object side, a first lens group G1 having a positive refractive power, a negative refractive power. A second lens group G2 having negative refractive power, a third lens group G3 having negative refractive power, a fourth lens group G4 having negative refractive power, and a fifth lens group G5 having positive refractive power. During zooming from the wide-angle end state to the telephoto end state, the air gap between the first lens group G1 and the second lens group G2 increases, and the air between the second lens group G2 and the third lens group G3. The second lens group G2 moves to the image side so that the interval decreases. At this time, the first lens group G1, the third lens group G3, and the fifth lens group G5 are fixed, and the fourth lens group G4 corrects the variation of the image plane position accompanying the movement of the second lens group G2. And move to the image side when focusing on a short distance.

  FIG. 2 to FIG. 5 show Numerical Example 1 in which specific numerical values are applied to the first embodiment and the first embodiment of the variable focal length lens system of the present invention.

  FIG. 2 is a diagram showing a lens configuration in the first embodiment of the variable focal length lens system of the present invention. The first lens group G1 includes a meniscus negative lens having a convex surface facing the object side and a convex surface facing the object side. The second lens group G2 includes a meniscus negative lens L21 having a concave surface facing the image side and a biconcave lens, and a cemented lens L11 with a positive lens facing the lens and a meniscus positive lens L12 having a convex surface facing the object side. The third lens group G3 is composed of a positive lens L31 having a strong convex surface facing the image side and a concave surface facing the object side, the positive lens L31 having a strong convex surface facing the image side. The fourth lens group G4 is composed of a cemented negative lens L4 composed of a positive lens and a negative lens, and the fifth lens group G5 is composed of a positive lens. Bonding between's L51 and a negative lens and a positive lens constructed by a positive lens L52.

  An aperture stop S is disposed on the object side of the third lens group G3 and is fixed when the lens position changes. A low pass filter LPF is disposed on the image side of the fifth lens group G5.

  Table 1 lists values of specifications of Numerical Example 1 in which specific numerical values are applied to the variable focal length lens system 1 according to the first embodiment. In the following tables, “si” is the i-th surface from the object side, “ri” is the radius of curvature of the i-th surface from the object side, and “di” is the i-th surface from the object side. “ni” is the refractive index for the d-line (λ = 587.6 nm) of the i-th glass material from the object side, and “νi” is the i-th glass material from the object side. The Abbe numbers for the d-line are respectively shown. “INFINITY” indicates that the surface is a flat surface, and “ASP” indicates that the surface is an aspheric surface.

  In the variable focal length lens system 1, during zooming, the surface distance d5 between the first lens group G1 and the second lens group G2, the surface distance d10 between the second lens group G2 and the aperture stop S, the third lens The surface distance d16 between the group G3 and the fourth lens group G4 and the surface distance d19 between the fourth lens group G4 and the fifth lens group G5 are variable. Therefore, the values in the wide-angle end state, the intermediate focal length state between the wide-angle end and the telephoto end, and the telephoto end state of the surface spacings d5, d10, d16, and d19 in Numerical Example 1 are set as the focal length, F number, Table 2 shows the angle of view 2ω (degrees).

In the variable focus lens system 1, the most object side surface s12 of the third lens group G3 and the most image side surface s24 of the fifth lens group G5 are aspherical. Accordingly, Table 4 shows the fourth-order, sixth-order, eighth-order, and tenth-order aspheric coefficients C ₄ , C ₆ , C ₈ , and C ₁₀ of the surfaces s12 and s24 in Numerical Example 1 together with the conic constant κ. .

  Table 4 shows values corresponding to the conditional expressions in Numerical Example 1.

  3 to 5 show the wide-angle end state, the intermediate focal length state between the wide-angle end and the telephoto end, and spherical aberration, astigmatism and distortion in the telephoto end state in Numerical Example 1. FIG. In the astigmatism diagrams, the solid line indicates the sagittal image plane, and the broken line indicates the meridional image plane. In the coma aberration diagram, A indicates the angle of view.

  As shown in these respective aberration diagrams, each aberration is corrected in a balanced manner in the wide-angle end state, the intermediate focal length state between the wide-angle end and the telephoto end, and the telephoto end state.

  6 to 9 show a second embodiment 2 of the variable focal length lens system according to the present invention and a numerical example 2 in which specific numerical values are applied to the second embodiment.

  FIG. 6 is a diagram showing a lens configuration in the second embodiment of the variable focal length lens system of the present invention. The first lens group G1 includes a meniscus negative lens having a convex surface facing the object side and a convex surface facing the object side. The second lens group G2 includes a meniscus negative lens L21 having a concave surface facing the image side and a biconcave lens, and a cemented lens L11 with a positive lens facing the lens and a meniscus positive lens L12 having a convex surface facing the object side. The third lens group G3 is composed of a positive lens L31 having a strong convex surface facing the image side and a concave surface facing the object side, the positive lens L31 having a strong convex surface facing the image side. The fourth lens group G4 is composed of a cemented negative lens L4 composed of a positive lens and a negative lens, and the fifth lens group G5 is composed of a positive lens. Bonding between's L51 and a negative lens and a positive lens constructed by a positive lens L52.

  An aperture stop S is disposed on the object side of the third lens group G3 and is fixed when the lens position changes. A low pass filter LPF is disposed on the image side of the fifth lens group G5.

  Table 5 lists the values of specifications of Numerical Example 2 in which specific numerical values are applied to the variable focal length lens system 2 according to the second embodiment.

  In the variable focal length lens system 2, during zooming, the surface distance d5 between the first lens group G1 and the second lens group G2, the surface distance d10 between the second lens group G2 and the aperture stop S, the third lens The surface distance d16 between the group G3 and the fourth lens group G4 and the surface distance d19 between the fourth lens group G4 and the fifth lens group G5 are variable. Therefore, the values in the wide-angle end state, the intermediate focal length state between the wide-angle end and the telephoto end, and the telephoto end state of the surface spacings d5, d10, d16, and d19 in Numerical Example 2 are expressed as the focal length, F number, Table 6 shows the angle of view 2ω (degrees).

In the variable focus lens system 2, the most object-side surface s12 of the third lens group G3 and the most image-side surface s24 of the fifth lens group G5 are aspheric. Accordingly, Table 4 shows the fourth-order, sixth-order, eighth-order, and tenth-order aspheric coefficients C ₄ , C ₆ , C ₈ , and C ₁₀ of the surfaces s12 and s24 in Numerical Example 2 together with the conic constant κ. .

  Table 8 shows values corresponding to the conditional expressions in Numerical Example 2.

  7 to 9 show the wide-angle end state, the intermediate focal length state between the wide-angle end and the telephoto end, and spherical aberration, astigmatism and distortion in the telephoto end state in Numerical Example 2. FIG. In the astigmatism diagrams, the solid line indicates the sagittal image plane, and the broken line indicates the meridional image plane. In the coma aberration diagram, A indicates the angle of view.

  As shown in these respective aberration diagrams, each aberration is corrected in a balanced manner in the wide-angle end state, the intermediate focal length state between the wide-angle end and the telephoto end, and the telephoto end state.

  10 to 13 show the third embodiment 3 of the variable focal length lens system according to the present invention and a numerical example 3 in which specific numerical values are applied to the third embodiment.

  FIG. 10 is a diagram showing a lens configuration in the third embodiment of the variable focal length lens system of the present invention. The first lens group G1 has a meniscus negative lens with a convex surface facing the object side and an object side. The second lens group G2 includes a cemented lens L11 with a positive lens facing the convex surface and a meniscus positive lens L12 with the convex surface facing the object side. The second lens group G2 includes a meniscus negative lens L21 with a concave surface facing the image side The third lens group G3 includes a negative lens having a concave shape and a positive lens having a convex surface facing the object side. The third lens group G3 includes a positive lens L31 having a strong convex surface facing the image side and a concave surface facing the positive lens and the object side. The fourth lens group G4 is composed of a cemented negative lens L4 composed of a positive lens and a negative lens, and the fifth lens group G5 is composed of a cemented positive lens L32 with a negative meniscus lens. It composed of a cemented positive lens L52 of the lens L51 and the negative lens and a positive lens.

  An aperture stop S is disposed on the object side of the third lens group G3 and is fixed when the lens position changes. A low pass filter LPF is disposed on the image side of the fifth lens group G5.

  Table 9 lists values of specifications of Numerical Example 3 in which specific numerical values are applied to the variable focal length lens system 3 according to the third embodiment.

  In the variable focal length lens system 3, during zooming, the surface distance d5 between the first lens group G1 and the second lens group G2, the surface distance d10 between the second lens group G2 and the aperture stop S, the third lens The surface distance d16 between the group G3 and the fourth lens group G4 and the surface distance d19 between the fourth lens group G4 and the fifth lens group G5 are variable. Therefore, the values in the wide-angle end state, the intermediate focal length state between the wide-angle end and the telephoto end, and the telephoto end state of the surface intervals d5, d10, d16, and d19 in Numerical Example 3 are set as the focal length, F number, Table 10 shows the angle of view 2ω (degrees).

In the variable focus lens system 3, the most object-side surface s12 of the third lens group G3 and the most image-side surface s24 of the fifth lens group G5 are aspheric. Therefore, Table 11 shows the fourth-order, sixth-order, eighth-order, and tenth-order aspheric coefficients C ₄ , C ₆ , C ₈ , and C ₁₀ of the surfaces s12 and s24 in Numerical Example 3 together with the conic constant κ. .

  Table 12 shows values corresponding to the conditional expressions in Numerical Example 3.

  11 to 13 show the wide-angle end state, the intermediate focal length state between the wide-angle end and the telephoto end, and spherical aberration, astigmatism and distortion in the telephoto end state in Numerical Example 3. FIG. In the astigmatism diagram, the solid line indicates the sagittal image plane, and the broken line indicates the meridional image plane. In the coma aberration diagram, A indicates the angle of view.

  As shown in these respective aberration diagrams, each aberration is corrected in a balanced manner in the wide-angle end state, the intermediate focal length state between the wide-angle end and the telephoto end, and the telephoto end state.

  In each numerical example described above, the variable focal length lens system according to the present invention is applied as a zoom lens in which the image plane position is fixed at the time of zooming. However, the variable focal length lens system fluctuates at the time of zooming. Of course, it can also be applied as a focal lens.

  FIG. 14 shows an embodiment of the imaging apparatus of the present invention.

  The imaging apparatus 10 includes a variable focal length lens system 20 and includes an imaging element 30 that converts an optical image formed by the variable focal length lens system 20 into an electrical signal. For example, a device using a photoelectric conversion device such as a charge coupled device (CCD) or a complementary metal-oxide semiconductor (CMOS) can be used as the image pickup device 30. The variable focal length lens system 20 can be applied with the variable focal length lens system according to the present invention. For example, the variable focal length lens systems 1 and 2 shown in the first to third embodiments described above. 3 can be used.

  The electrical signal formed by the image pickup device 30 is sent to the control circuit 50 by the video separation circuit 40, and the video signal is sent to the video processing circuit. The signal sent to the video processing circuit is processed into a form suitable for the subsequent processing, and is subjected to various processes such as display by a display device, recording on a recording medium, and transfer by a communication means.

  For example, an operation signal from the outside such as an operation of a zoom button is input to the control circuit 50, and various processes are performed according to the operation signal. For example, when a zooming command by the zoom button is input, the drive units (for example, motors) 61 and 71 are operated via the driver circuits 60 and 70 to set the focal length state based on the command, and the second lens group. G2 and the fourth lens group G4 are moved to predetermined positions. Position information of the second lens group G2 and the fourth lens group G4 obtained by the sensors 62 and 72 is input to the control circuit 50 and is referred to when command signals are output to the driver circuits 60 and 70. Further, the control circuit 50 checks the focus state based on the signal sent from the video separation circuit 40, and controls the fourth lens group G4 via the driver circuit 70, for example, so as to obtain the optimum focus state. To do.

  The above-described imaging apparatus 10 can take various forms as specific products. For example, the present invention can be widely applied as a digital still camera, a digital video camera, a mobile phone incorporating a camera, a camera unit of a digital input / output device such as a PDA (Personal Digital Assistant) incorporating a camera.

  It should be noted that the specific shapes, structures, and numerical values of the respective parts shown in the respective embodiments and numerical examples described above are merely examples of the implementation performed in carrying out the present invention. The technical scope of the present invention should not be construed in a limited manner.

  It is suitable for application to an imaging apparatus that requires downsizing and high performance, such as a video camera and a digital still camera.

2 to 13 show an embodiment of the variable focal length lens system according to the present invention, and this figure shows the refractive power distribution of each lens group. 3 to 5 show a first embodiment of the variable focal length lens system of the present invention, and this figure shows a lens configuration. FIG. FIG. 6 is a diagram showing spherical aberration, astigmatism, distortion and coma aberration in Numerical Example 1 in which specific numerical values are applied to the first embodiment together with FIG. 4 and FIG. It shows aberrations. It is a figure which shows the spherical aberration, astigmatism, distortion aberration, and coma aberration in the intermediate focal length state of a wide angle end and a telephoto end. It is a figure which shows the spherical aberration, astigmatism, distortion aberration, and coma aberration in a telephoto end state. 7 to 9 show a second embodiment of the variable focal length lens system of the present invention, and this figure shows a lens configuration. FIG. 10 is a diagram showing spherical aberration, astigmatism, distortion aberration, and coma aberration in Numerical Example 2 in which specific numerical values are applied to the second embodiment together with FIGS. 8 and 9, and this figure shows these in the wide-angle end state It shows aberrations. It is a figure which shows the spherical aberration, astigmatism, distortion aberration, and coma aberration in the intermediate focal distance state of a wide angle end and a telephoto end. It is a figure which shows the spherical aberration, astigmatism, distortion aberration, and coma aberration in a telephoto end state. 11 to 13 show a third embodiment of the variable focal length lens system of the present invention, and this figure shows a lens configuration. FIG. 14 is a diagram showing spherical aberration, astigmatism, distortion and coma aberration in Numerical Example 3 in which specific numerical values are applied to the third embodiment together with FIGS. 12 and 13, and FIG. It shows aberrations. It is a figure which shows the spherical aberration, astigmatism, distortion aberration, and coma aberration in the intermediate focal distance state of a wide angle end and a telephoto end. It is a figure which shows the spherical aberration in a telephoto end state, astigmatism, a distortion aberration, and a coma aberration state. It is a block diagram which shows embodiment of the imaging device of this invention.

Explanation of symbols

  DESCRIPTION OF SYMBOLS 1 ... Variable focal length lens system, 2 ... Variable focal length lens system, 3 ... Variable focal length lens system, G1 ... 1st lens group, G2 ... 2nd lens group, G3 ... 3rd lens group, G4 ... 4th lens Group, G5: fifth lens group, S: aperture stop, 10: imaging device, 20: variable focal length lens system, 30 ... imaging device

Claims (5)

In order from the object side, a first lens group having a positive refractive power, a second lens group having a negative refractive power, a third lens group having a positive refractive power, a fourth lens group having a negative refractive power, and a positive lens In a variable focal length lens system in which a fifth lens group having a refractive power of
When the lens position changes from the wide-angle end state to the telephoto end state, the first lens group is fixed in the optical axis direction, the second lens group moves to the image side, and the third lens group moves to the optical axis. The fourth lens group is moved in the optical axis direction to compensate for the variation of the image plane position accompanying the movement of the second lens group and focus at a short distance, and the fifth lens group is moved to the optical axis. Fixed in the direction,
An aperture stop is disposed in the vicinity of the third lens group, and satisfies the following conditional expressions (1) and (2):
(1) 2 <f1 / (fw · ft) ^1/2 <2.5
(2) -1.6 <f2 / fw <-1.2
However,
f1: focal length of the first lens group fw: focal length of the entire system in the wide-angle end state ft: focal length of the entire system in the telephoto end state f2: focal length of the second lens group The variable focal length lens system according to claim 1,
A variable focal length lens system satisfying at least one of the following conditional expressions (3) and (4):
(3) 0.25 <1 / β4t <0.4
(4) 0.6 <β2w · β2t <1.2
However,
β4t: lateral magnification of the fourth lens group in the telephoto end state β2w: lateral magnification of the second lens group in the wide-angle end state β2t: lateral magnification of the second lens group in the telephoto end state The variable focal length lens system according to claim 1,
A variable focal length lens system satisfying the following conditional expression (5):
(5) 0.4 <Db / ft <0.9
However,
Db: Distance along the optical axis from the lens surface closest to the object side to the aperture stop. The variable focal length lens system according to claim 2,
A variable focal length lens system satisfying the following conditional expression (5):
(5) 0.4 <Db / ft <0.9
However,
Db: Distance along the optical axis from the lens surface closest to the object side to the aperture stop. In order from the object side, a first lens group having a positive refractive power, a second lens group having a negative refractive power, a third lens group having a positive refractive power, a fourth lens group having a negative refractive power, and a positive lens An imaging apparatus comprising: a variable focal length lens system in which a fifth lens group having a refractive power of 1 is arranged; and an imaging element that converts an optical image formed by the variable focal length lens system into an electrical signal. There,
In the variable focal length lens system, when the lens position state changes from the wide-angle end state to the telephoto end state, the first lens group is fixed in the optical axis direction, and the second lens group moves to the image side, The third lens group is fixed in the optical axis direction, and the fourth lens group moves in the optical axis direction for compensation of variation in image plane position accompanying the movement of the second lens group and focusing at a short distance, An imaging apparatus characterized in that the fifth lens group is fixed in the optical axis direction, an aperture stop is disposed in the vicinity of the third lens group, and satisfies the following conditional expressions (1) and (2).
(1) 2 <f1 / (fw · ft) ^1/2 <2.5
(2) -1.6 <f2 / fw <-1.2
However,
f1: focal length of the first lens group fw: focal length of the entire system in the wide-angle end state ft: focal length of the entire system in the telephoto end state f2: focal length of the second lens group

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