JP2006106538A - Converter lens - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To realize a compact zoom converter lens while obtaining a desired variable power ratio. <P>SOLUTION: The converter lens C attached to the front of a master lens M and capable of converting the focal distance of the master lens M has a 1st lens group L1 having negative refractive power, a 2nd lens group L2 having positive refractive power and a 3rd lens group L3 having negative refractive power in order from the front. In the case of varying power from the lowest afocal power to the highest afocal power, both the 1st lens group L1 and the 2nd lens group L2 monotonously move forward while changing a distance to each other. The moving amount of the 1st lens group L1 in the case of varying the power is appropriately set. <P>COPYRIGHT: (C)2006,JPO&NCIPI

Description

  The present invention relates to a converter lens, for example, a converter lens that is mounted on the object side of a photographing lens such as a digital camera or a video camera as a master lens.

  A converter lens that can be mounted on the object side of a photographic lens such as a digital camera or video camera to change the photographic range is a teleconverter lens that increases the focal length and enhances the telephoto effect. There is a wide converter lens that widens the corners.

  A converter lens that realizes these two functions in one system is disclosed in Patent Document 1, for example. The converter lens disclosed in Patent Document 1 switches between a teleconverter lens and a wide converter lens by reversing the mounting direction to the master lens.

  In Patent Document 2, a converter lens having a three-group configuration including a first lens group having a positive refractive power, a second lens group having a negative refractive power, and a third lens group having a negative refractive power, An example in which the afocal magnification is changed from 1.6 to 2 times by moving the second lens group is disclosed.

  In Patent Document 3, only the second lens group is moved by a converter lens having a three-group configuration including a first lens group having a positive refractive power, a second lens group having a negative refractive power, and a third lens group having a positive refractive power. An example in which zooming is performed by doing is disclosed.

In Patent Document 4, at least two groups are moved by a converter lens having a three-group configuration including a first lens group having a positive refractive power, a second lens group having a negative refractive power, and a third lens group having a positive refractive power. An example of performing zooming by this is disclosed.
JP-A-7-64164 JP 2000-292695 A JP-A-53-27044 Japanese Patent Laid-Open No. 9-5625

  In Patent Document 1, there is a trouble of reattaching to the master lens when properly using the wide converter lens and the teleconverter lens, and there is a problem in terms of usability.

  Patent Document 2 has problems such as not having a configuration capable of zooming including the same magnification, and a zooming ratio as small as 1.25 times.

  Since Patent Document 3 performs zooming by moving only the second lens group, the afocal magnification cannot be continuously changed while maintaining the afocal system. In addition, since the first lens group has a single lens configuration, there is a problem in terms of correcting chromatic aberration of magnification.

  In Patent Document 4, in the three-group configuration of positive, negative, and positive, the second lens group does not move during zooming from the lowest afocal magnification to the highest afocal magnification, and the first lens group and the third lens group An example of changing the magnification by moving the lens to the object side is disclosed. In this example, since the second lens group is fixed, an attempt to increase the highest afocal magnification increases the amount of movement of the first lens group. As a result, the total length at the highest afocal magnification becomes long. Further, since the front lens diameter is determined by the height through which the off-axis light beam passes at the highest afocal magnification, an increase in the total length leads to an increase in the front lens diameter. For this reason, in realizing a high zoom ratio, there is a problem in terms of downsizing the overall length and the front lens diameter.

  In Patent Document 4, in the three-group configuration of positive, negative, and positive, when zooming from the lowest afocal magnification to the highest afocal magnification, the first lens group is stationary, and the second lens group is moved to the image side. An example of changing the magnification by moving the third lens group so as to draw a convex locus on the image side is also disclosed. In this example, since the first lens group is fixed, the second lens group is a group having a zooming function. In such a configuration, if the highest afocal magnification is to be increased, the second lens group has to move greatly to the image side, so the second lens group and the third lens group in the state of the lowest afocal magnification are the same. It becomes impossible to reduce the distance between the lens groups. As a result, it becomes difficult to reduce the total length at the lowest afocal magnification, and the height at which the off-axis light beam passes at this time is increased, so there is also a problem in terms of downsizing the front lens diameter.

  The present invention has been made in consideration of these conventional examples, and an object thereof is to realize a small zoom converter lens while obtaining a desired zoom ratio.

The present invention is a converter lens that is attached to the front of the master lens (on the object (subject) side when the photographing lens is a master lens) and can convert the focal length of the master lens. A first lens group, a second lens group having a positive refractive power, and a third lens group having a negative refractive power, and when changing the magnification from the lowest afocal magnification to the highest afocal magnification, Both the second lens groups are monotonously moved forward while changing the interval between them. When the movement amount of the first lens unit at the time of zooming from the lowest afocal magnification to the highest afocal magnification is M ₁ and the total length in the state of the lowest afocal magnification is TD _w ,

It is characterized by satisfying the following conditions.

  According to the present invention, it is possible to provide a small zoom converter lens while obtaining a desired zoom ratio.

  The basic configuration of the converter lens of the present invention will be described with reference to FIG.

  In FIG. 1, C represents a converter lens, and M represents a master lens which is a photographing lens. As shown in FIG. 1, the converter lens C is attached in front of the master lens M (on the object side of the photographing lens), thereby playing a role of converting the focal length of the master lens M. G in the master lens M is an optical block provided for optical design corresponding to various optical filters such as an optical low-pass filter and an infrared cut filter, a face plate, and the like. IP is an image plane on which a solid-state imaging device such as a CCD sensor or a CMOS sensor is arranged.

  The converter lens C includes a first lens unit L1 having negative refractive power (optical power = reciprocal of focal length), a second lens unit L2 having positive refractive power, and a third lens unit L3 having negative refractive power. The In the present embodiment, zooming is performed by moving the first lens unit L1 and the second lens unit L2 in order to continuously change the afocal magnification while maintaining the afocal system. Specifically, at the time of zooming from the lowest afocal magnification to the highest afocal magnification, both the first lens unit L1 and the second lens unit L2 are moved forward monotonously while changing the mutual distance. Yes.

  In the converter lens of this example, when the afocal magnification is the lowest, the first lens unit L1 forms a front group LFw having a negative refractive power, and the second lens unit L2 and the third lens unit L3 are positive as a whole. If it is considered that the rear group LRw of this refractive power is constituted, it can be regarded as a power arrangement similar to that of the wide converter lens. At the highest afocal magnification, the first lens unit L1 and the second lens L2 form a front group LFt having a positive refractive power as a whole, and the third lens unit L3 has a rear group LRt having a negative refractive power. It can be considered that the power arrangement is the same as that of the teleconverter lens. Thus, the converter lens of the present embodiment can realize a converter lens that achieves both the effects of the wide converter lens and the teleconverter lens by appropriately moving the first lens group L1 and the second lens group L2. Hereinafter, the lowest afocal magnification is referred to as the minimum magnification, and the highest afocal magnification is referred to as the maximum magnification.

  Next, the effect of the moving group and the moving direction will be described.

  The converter lens of the present embodiment changes from the minimum magnification to the maximum magnification by changing the size relationship between the distance between the first lens group L1 and the second lens group L2 and the distance between the second lens group L2 and the third lens group L3. The zooming is done.

  Specifically, as described above, when changing the magnification from the minimum magnification to the maximum magnification, the second lens unit having a positive refractive power is moved forward, and the distance between the first lens unit L1 and the second lens unit L2 is reached. Is reduced and the distance between the second lens unit L2 and the third lens unit L3 is increased to perform zooming. Then, the afocal degree changed by the movement of the second lens unit L2 is compensated by moving the first lens unit L1.

  In order to obtain a high zoom ratio while maintaining the afocal system, it is not preferable that the distance between the first lens unit L1 and the second lens unit L2 in the maximum magnification state is too small, and a certain amount of space is provided. It is necessary to make it.

  Therefore, in this embodiment, when changing the magnification from the minimum magnification to the maximum magnification, the first lens unit L1 is used to suppress the increase in the total length in the state of the minimum magnification and perform the magnification while maintaining the afocal system. It is moving forward.

  Points to note when moving the first lens unit L1 will be described. When the amount of movement of the second lens unit L2 is extremely large, it is necessary to ensure a large interval between the first lens unit L1 and the second lens unit L2 in the state of the minimum magnification more than the amount of movement of the second lens unit L2. Therefore, the total length at the minimum magnification is excessive. In addition, since the front lens diameter is determined with the minimum magnification having a wide angle of view, it is not preferable in terms of downsizing the front lens diameter. Furthermore, since the change (displacement) in the afocal degree accompanying the movement of the second lens unit L1 also increases, the amount of movement of the first lens unit L1 that compensates for it must also be increased.

  Therefore, in this embodiment, the second lens unit L2 is a lens unit having a zooming function, the first lens unit L1 is a lens unit having a function of maintaining an afocal system, and the amount of movement of the first lens unit L1 The following conditions were satisfied.

Here, M ₁ is, the amount of movement of the first lens unit L1 at the time of zooming from a minimum afocal magnification to a maximum afocal magnification, TD _w is the total length of the converter lens C in the state of minimum afocal magnification . However, regarding the amount of movement, the forward movement on the optical axis (the master lens side or the image side in the case of a taking lens) is the positive direction.

  Conditional expression (1) is an expression that defines the total amount of the first lens unit L1 in the state of movement and minimum magnification.

  When the upper limit of conditional expression (1) is exceeded, the amount of movement of the first lens unit L1 increases, and in order to maintain an appropriate relationship of the amount of movement to obtain a desired zoom ratio, the second lens unit L1 Must be moved to the object side. As a result, an excessive amount of movement of the second lens unit L2 is anticipated, and the distance between the first lens unit L1 and the second lens unit L2 in the minimum magnification state must be sufficiently long. The total length of becomes excessive. Further, due to this, the height of the off-axis light beam passing through the first lens unit L1 in the state of the minimum magnification becomes high, which is not preferable in terms of reducing the front lens diameter.

  On the other hand, when the lower limit of conditional expression (1) is exceeded, the amount of movement of the first lens unit L1 becomes small, and in order to obtain a desired zoom ratio, the degree of afocal caused by the movement of the second lens unit L2 This is not preferable because the fluctuation of the above cannot be corrected sufficiently.

  In the converter lens of this embodiment, by appropriately setting the moving amount of the first lens unit L1 in this way, the afocal magnification is continuously changed while maintaining the afocal system, and the front lens diameter is small. To achieve both high speed and high zoom ratio.

  When the master lens M is a single focus lens, the converter lens C of this embodiment is attached to the master lens M, so that it can be used as a zoom lens as a whole. In addition, since the converter lens of the present embodiment is a converter having a variable afocal magnification including equal magnification, when the zoom lens is mounted as the master lens M, the wide angle end of the zoom lens can be further widened. The telephoto effect can be further enhanced at the telephoto end of the zoom lens. In a numerical example to be described later, as the master lens M, a zoom lens as shown in FIG. 2 composed of three lens groups of negative, positive, and positive refractive power in order from the object side is used.

  In the above description, the form in which the degree of afocal change caused by the movement of the second lens unit L2 is compensated by moving the first lens unit L1 toward the object side is shown. However, the converter lens of the present invention is not limited to such a form, and the distance between the first lens group L1 and the second lens group L2, the second lens group L2, and the third lens group can be moved by moving the third lens group L3. It is also possible to change the size relationship of the distance of L3 to change the magnification from the minimum magnification to the maximum magnification.

  The configuration of each lens group of the converter lens shown in Numerical Examples 1 to 5 described later will be described.

  First, common points in each numerical example will be described.

  In the converter lens of this embodiment, since the first lens unit L1 has a strong (large) refractive power, it is necessary to correct axial chromatic aberration and lateral chromatic aberration in the lens unit. Therefore, in each numerical example, the first lens unit L1 is configured to have at least one positive lens. Accordingly, there is an advantage that the longitudinal chromatic aberration and the lateral chromatic aberration are corrected, and an increase in color blur due to the mounting of the converter lens C can be minimized.

  The second lens unit L2 having a positive refractive power is configured to have at least two positive lenses. Since the positive refractive power of the second lens unit L2 is shared by the two positive lenses, the refractive power of each lens is weakened and the radius of curvature of the lens can be set to be loose (large), thereby correcting spherical aberration. It is effective. In addition, by including at least one negative lens in the second lens unit L2 having a positive refractive power, the axial chromatic aberration and the lateral chromatic aberration are corrected, and the color blur increases due to the mounting of the converter lens C. Is suppressed.

  Since the third lens unit L3 has a weak refractive power compared to the first lens unit L1 and the second lens unit L3, it can be configured with a single lens, thereby simplifying the lens configuration.

  Next, a specific configuration of the converter lens of each numerical example will be described.

  FIG. 3 is a cross-sectional view in a state where the converter lens C of Numerical Example 1 is attached to the master lens M.

  In FIG. 3, the first lens unit L1 includes, in order from the front to the rear, a negative meniscus lens 11 having a convex surface facing forward, a biconcave negative lens 12, and a positive meniscus lens 13 having a convex surface facing forward. Yes. The negative meniscus lens 11 is effective for suppressing the occurrence of various aberrations such as coma, astigmatism, and field curvature when the zoom ratio is increased in an optical system having a large change in the angle of view.

  The second lens unit L2 includes, in order from the front to the rear, two biconvex positive lenses 21 and 22, and a negative meniscus lens 23 having a convex surface forward.

  The third lens unit L3 includes a biconcave negative lens 31.

  FIG. 9 is a cross-sectional view in a state where the converter lens C of Numerical Example 2 is attached to the master lens M.

  In FIG. 9, the first lens unit L1 includes a negative meniscus lens 11, a biconcave negative lens 12, and a biconvex positive lens 13 having a convex surface directed forward from the front to the rear. In Numerical Example 2, an aspheric surface is used in the first lens unit L1, thereby reducing both the front lens diameter and correcting distortion. In addition, the positive lens 13 has a biconvex shape, so that it is easy to correct the under tendency of the curvature of field at the maximum magnification, which was difficult to correct with the positive meniscus shape.

  The second lens unit L2 includes, in order from the front to the rear, two biconvex positive lenses 21 and 22, and a negative meniscus lens 23 having a convex surface forward.

  The third lens unit L3 includes a negative meniscus lens 31 having a concave surface facing forward.

  FIG. 15 is a cross-sectional view of the converter lens C of Numerical Example 3 attached to the master lens M. Numerical Example 3 is an example in which the total length in the maximum magnification state is shortened by increasing the refractive power of the second lens unit L2.

  In FIG. 15, the first lens unit L1 includes, in order from the front to the rear, a negative meniscus lens 11 having a convex surface forward, a biconcave negative lens 12, and a positive meniscus lens 13 having a convex surface forward. Yes. Similarly to Numerical Example 2, the use of an aspherical surface for the first lens unit L1 makes it possible to reduce the size of the front lens and correct distortion.

  The second lens unit L2 includes, in order from the front to the rear, two biconvex positive lenses 21 and 22, and a negative meniscus lens 23 having a convex surface forward.

  The third lens unit L3 includes a negative meniscus lens 31 having a concave surface facing forward.

  FIG. 21 is a cross-sectional view in a state where the converter lens C of Numerical Example 4 is attached to the master lens M.

  In FIG. 21, the first lens unit L1 includes a negative meniscus lens 11, a biconcave negative lens 12, and a biconvex positive lens 13 with a convex surface facing forward, in order from the front to the rear.

  The second lens unit L2 includes, in order from the front to the rear, a biconvex positive lens 21, a positive meniscus lens 22 having a convex surface forward, and a negative meniscus lens 23 having a convex surface forward. The positive lens 22 has a meniscus shape with a convex surface facing forward, thereby providing an effect of correcting the under-trend of field curvature.

  The third lens unit L3 includes a negative meniscus lens 31 having a concave surface facing forward. Then, distortion is corrected by using an aspherical surface for the negative lens 31. Since the third lens unit L3 has the smallest diameter, it is effective in reducing the aspherical processing cost.

  FIG. 27 is a cross-sectional view of the converter lens C of Numerical Example 5 attached to the master lens M.

  In FIG. 27, the first lens unit L1 includes, in order from the front to the rear, a negative meniscus lens 11 having a convex surface forward, a biconcave negative lens 12, and a positive meniscus lens 22 having a convex surface forward. Yes. Also in the present numerical example, by using an aspherical surface for the first lens unit L1, both miniaturization and correction of distortion are achieved.

  The second lens unit L2 includes, in order from the front to the rear, two biconvex positive lenses 21 and 22 and a biconcave negative lens 23. Further, by using an aspherical surface for the second lens unit L2, correction of higher-order field curvature is facilitated.

  The third lens unit L3 includes a negative meniscus lens 31 having a concave surface facing forward. By making the negative lens 33 into a biconcave shape, it becomes possible to correct an under tendency of field curvature in the state of the minimum magnification.

  Next, preferable conditions that the converter lens of the present invention should satisfy will be described. The converter lens of the present example satisfies the following conditional expression.

Here, _{f 1} is the focal length of the first lens unit L1, _{f 2} is the focal length of the second lens unit _{L2, f 1P} is the focal length of the positive lens 13 of the first lens unit _{L1, f 2N} second lens focal length of the negative lens 23 in the group L2, m _w is the minimum afocal magnification, m _t is the maximum afocal magnification, M ₂ is the second lens group upon zooming from a minimum afocal magnification to a maximum afocal magnification A moving amount of L2 (moving backward on the optical axis in the positive direction), e _1t is a distance between the rear principal point of the first lens unit L1 and the front principal point of the second lens unit L2 in the state of the maximum afocal magnification. , TD _t is the full length of the converter lens C in the state of the maximum afocal magnification, TD _w is the full length of the converter lens C in the state of the minimum afocal magnification, and f _Ft is the first lens unit L1 in the state of the maximum afocal magnification. And the second lens unit L2 Focal length, r _1, r ₂ are each radius of curvature of the anterior and posterior surfaces of the lens positioned most forward in the first lens unit L1.

  Conditional expression (2) is a condition that defines the focal length of the positive lens in the first lens unit L1, that is, a condition that defines the refractive power of the positive lens in the first lens unit L1. Since the relationship between the focal length of the positive lens in the first lens unit L1 and the focal length of the first lens unit L1 is a relationship that does not depend on the maximum magnification and the minimum magnification, it is normalized by the maximum magnification and the minimum magnification.

  If the lower limit of conditional expression (2) is exceeded, the refractive power of the positive lens in the first lens unit L1 becomes excessive, and in order to keep the refractive power of the first lens unit L1 at a predetermined value, The refractive power must also be increased. As a result, the radius of curvature of each lens becomes tight (small), and the angle fluctuation of the incident angle and the exit angle of off-axis rays becomes large, and it is difficult to correct coma and astigmatism especially at the minimum magnification. This is not preferable. On the other hand, when the upper limit of conditional expression (2) is exceeded, the refractive power of the positive lens is too small, so that chromatic aberration correction becomes insufficient, causing color blurring.

  Conditional expression (3) is a condition that defines the refractive power of the negative lens in the second lens unit L2. Since the relationship between the focal length of the negative lens in the second lens unit L2 and the focal length of the second lens unit L2 is a relationship that does not depend on the maximum magnification and the minimum magnification, it is standardized by the maximum magnification and the minimum magnification.

  If the lower limit of the conditional expression (3) is exceeded, the refractive power of the negative lens in the second lens unit L2 becomes excessive, and in order to keep the refractive power of the second lens unit L2 at a predetermined value, The refractive power must also be increased. As a result, the radius of curvature of each lens becomes tight, so that the fluctuations in the incident angle and exit angle of off-axis rays become large, and it is difficult to correct coma and astigmatism particularly at the maximum magnification. . On the other hand, if the upper limit of conditional expression (3) is exceeded, the refractive power of the negative lens is too small, so that chromatic aberration correction becomes insufficient, causing color blurring.

  Conditional expression (4) is a condition that defines the amount of movement of the second lens unit L2 with respect to the amount of movement of the first lens unit L1 upon zooming from the minimum magnification to the maximum magnification.

  If the lower limit of conditional expression (4) is exceeded, the amount of movement of the second lens unit L2 is too small, and a desired zoom ratio cannot be obtained. On the other hand, if the upper limit of conditional expression (4) is exceeded, the amount of movement of the second lens unit L2 becomes excessive, so the distance between the first lens unit L1 and the second lens unit L2 at the minimum magnification is set to the second lens unit. In view of the amount of movement of the group L2, it must be sufficiently wide. As a result, not only the total length of the converter lens C becomes excessive in the minimum magnification state, but also the height of the off-axis light beam passing through the first lens unit L1 cannot be reduced in the minimum magnification state. The front ball diameter is determined, which is not preferable in terms of downsizing the front ball diameter.

  Conditional expression (5) is a condition that defines the shape factor of the lens (negative lens 11) disposed in the forefront in the first lens unit L1.

  If the lower limit of conditional expression (5) is exceeded, the shape of the negative lens 11 becomes a negative lens with a concave surface facing forward, and the angle formed between the off-axis light beam and the object-side surface of the negative lens 11 becomes large. It is not preferable in terms of correction. On the other hand, if the upper limit of conditional expression (5) is exceeded, in order to obtain a desired zoom ratio, the radius of curvature of the rear surface of the lens 11 must be reduced, and over-side spherical aberration occurs, which is not preferable. .

  Conditional expression (6) indicates that the rear principal point of the first lens unit L1 and the front principal point of the second lens unit L2 with respect to the combined focal length of the first lens unit L1 and the second lens unit L2 at the maximum magnification state. This is a condition that defines the interval.

  If the lower limit of the conditional expression (6) is exceeded, the distance between the principal points of the first lens unit L1 and the second lens unit L2 in the maximum magnification state becomes small. Therefore, in order to obtain a desired maximum magnification, the first lens The power of the group must be strengthened. As a result, the Petzval sum increases to the plus side, and the under-curve tendency of field curvature is increased, which is not preferable.

  On the other hand, if the upper limit of conditional expression (6) is exceeded, the distance between the first lens unit L1 and the second lens unit L2 in the maximum magnification state becomes long, and the total length becomes excessive in the maximum magnification state. The height of the off-axis light beam that passes through the first lens unit L1 at the maximum magnification is higher than the height of the off-axis light beam that passes through the first lens unit L1 at the minimum magnification. It is not preferable.

  Conditional expression (7) is a condition that defines the total length of the converter lens C in the maximum magnification state relative to the total length of the converter lens C in the minimum magnification state.

  If the lower limit of conditional expression (7) is exceeded, the total length in the maximum magnification state is short, and in order to obtain a desired zoom ratio, the second lens unit L2 must move greatly forward and zoom. . For this reason, the interval between the first lens unit L1 and the second lens unit L2 must be widened in the state of the minimum magnification so as to ensure the amount of movement of the second lens unit L2, and as a result, in the state of the minimum magnification. Not only is the total length excessive, but the height of the off-axis light beam that passes through the first lens unit L1 increases, so that the front lens diameter is determined at the minimum magnification, which is also preferable in terms of reducing the front lens diameter. Absent.

  On the other hand, if the upper limit of conditional expression (7) is exceeded, the total length in the maximum magnification state becomes excessive, and the first magnification in the maximum magnification state is higher than the height of the off-axis light beam passing through the first lens unit L1 in the minimum magnification state. Since the height of the off-axis light beam passing through the lens unit L1 is increased, it is not preferable in terms of reducing the front lens diameter.

  In particular, it is preferable to satisfy both conditional expression (1) and conditional expression (7) in order to reduce the front lens diameter.

  Conditional expression (8) defines the focal length of the first lens unit L1 with respect to the movement amount of the first lens unit L1.

  Exceeding the lower limit of conditional expression (8) is not preferable because the refractive power of the first lens unit L1 increases, and the Petzval sum increases to the plus side, which tends to increase the under tendency of field curvature. On the other hand, if the upper limit of conditional expression (8) is exceeded, the refractive power of the first lens unit L1 is weakened. Therefore, in order to obtain a desired zoom ratio, the first lens unit L1 and the second lens unit are in a state of minimum magnification. The interval of L2 must be increased. For this reason, not only the total length becomes excessive in the state of the minimum magnification, but also the height of the off-axis light beam passing through the first lens unit L1 increases, so that the front lens diameter is determined in the state of the minimum magnification, and the front lens It is not preferable also from the point of size reduction.

  Conditional expression (9) is a condition that defines the focal length of the second lens unit L2 with respect to the movement amount of the second lens unit L2.

  Exceeding the lower limit of conditional expression (9) is not preferable because the refractive power of the second lens unit L2 increases, and the Petzval sum increases to the plus side, which tends to increase the under tendency of field curvature. On the other hand, if the upper limit of conditional expression (9) is exceeded, the refractive power of the second lens unit L2 will be weakened. Therefore, in order to obtain a desired zoom ratio, the distance between the first lens unit L1 and the second lens unit L2 is increased. I have to let it. For this reason, not only the total length becomes excessive in the state of the minimum magnification, but also the height of the off-axis light beam that passes through the first lens unit L1 in the state of the minimum magnification becomes high. This is also not preferable in terms of reducing the front lens diameter.

  Next, numerical data of numerical examples 1 to 5 will be shown. In each numerical example, i represents the order of surfaces from the front (object side), Ri is the radius of curvature of the i-th surface (i-th surface), and Di is the distance between the i-th surface and the (i + 1) -th surface. , Ni and νi are the refractive index and Abbe number based on the d-line of the i-th member, respectively. f, Fno, and ω represent the focal length, the F number, and the half angle of view, respectively, but are attached to the master lens M.

  In the numerical example of the master lens M, the i-th surface is the i-th surface without the converter lens C, RMi is the radius of curvature of the i-th surface, DMi is the i-th surface and the (i + 1) -th surface. ) Surface spacings, NMi and νMi are the refractive index and Abbe number based on the d-line of the i-th member, respectively. f, Fno, and ω are the focal length, F number, and half angle of view of the master lens alone. In the numerical data of the master lens, a plurality of planes on the image side are surfaces constituting the optical block G. The numerical data of the master lens is common to the numerical examples 1 to 5.

  The aspherical shape is the X axis in the optical axis direction, the H axis in the direction perpendicular to the optical axis, the light traveling direction is positive, R is the paraxial radius of curvature, K is the conic constant, and B, C, D, and E are respectively When the aspheric coefficient is used,

It is expressed by the following formula.

  When the master lens M is a zoom lens, the focal length of the master lens M changes from the minimum afocal magnification to the maximum afocal magnification 1 while the focal length of the master lens M changes from the wide-angle end to the telephoto end. Since it changes to the focal magnification, the focal length of the entire optical system is determined by a combination of these. This combination is shown in Table 1 below.

  In Table 1, the case where the converter lens C has the lowest afocal magnification and the master lens M is at the wide-angle end is defined as zoom1. In the zoom1 combination, the wide angle end of the master lens M can be further widened. Also, zoom 3 is set when the converter lens C is at the highest afocal magnification and the master lens is at the telephoto end. The combination of zoom 3 can further increase the focal length of the telephoto end of the master lens M.

  4 to 8, 10 to 14, 16 to 20, 22 to 26, and 28 to 32 are attached to the master lens with the converter lenses of Numerical Examples 1 to 5 in the combinations of zoom 1 to zoom 5 in Table 1, respectively. It is an aberration diagram in the state.

  Table 2 shows the relationship between the above-described conditional expressions and numerical examples.

(Numerical example 1)
f = 5.63-32.12 Fno = 2.86-5.06 2ω = 15.72 °-76.46 °
R 1 = 86.466 D 1 = 2.00 N 1 = 1.603112 ν 1 = 60.6
R 2 = 43.785 D 2 = 14.00
R 3 = -589.317 D 3 = 3.00 N 2 = 1.603112 ν 2 = 60.6
R 4 = 75.047 D 4 = 2.00
R 5 = 115.595 D 5 = 3.50 N 3 = 1.922860 ν 3 = 18.9
R 6 = 215.141 D 6 = variable
R 7 = 65.806 D 7 = 5.50 N 4 = 1.603112 ν 4 = 60.6
R 8 = -124.415 D 8 = 0.10
R 9 = 55.260 D 9 = 4.50 N 5 = 1.603112 ν 5 = 60.6
R10 = -828.380 D10 = 0.10
R11 = 573.631 D11 = 2.00 N 6 = 1.846660 ν 6 = 23.9
R12 = 75.519 D12 = variable
R13 = -124.973 D13 = 1.50 N 7 = 1.603112 ν 7 = 60.6
R14 = 131.474 D14 = variable

(Master lens)
fm = 8.03 to 22.85 FNom = 2.86 to 5.06 2ω = 21.97 ° to 57.83 °
RM1 = 63.353 DM 1 = 1.60 NM 1 = 1.683430 νM 1 = 52.4
RM 2 = 5.800 DM 2 = 2.37
RM 3 = 9.820 DM 3 = 2.00 NM 2 = 1.761821 νM 2 = 26.5
RM 4 = 20.460 DM 4 = variable
RM 5 = Aperture DM 5 = 0.80
RM 6 = 5.974 DM 6 = 2.80 NM 3 = 1.802380 νM3 = 40.7
RM 7 = 58.781 DM 7 = 0.70 NM 4 = 1.805181 νM4 = 25.4
RM 8 = 5.189 DM 8 = 0.87
RM 9 = 18.702 DM 9 = 1.80 NM 5 = 1.603112 νM5 = 60.6
RM 10 = -18.469 DM10 = variable
RM 11 = 17.220 DM11 = 1.90 NM 6 = 1.487490 νM6 = 70.2
RM 12 = -136.717 DM12 = variable
RM 13 = ∞ DM13 = 0.38 NM 7 = 1.544270 νM 7 = 70.6
RM 14 = ∞ DM14 = 0.80 NM 8 = 1.494000 νM 8 = 75.0
RM 15 = ∞ DM15 = 0.40 NM 9 = 1.544270 νM 9 = 70.6
RM 16 = ∞ DM16 = 0.38 NM10 = 1.544270 νM10 = 70.6
RM 17 = ∞ DM17 = 0.50
RM 18 = ∞ DM18 = 0.50 NM11 = 1.516330 νM11 = 64.1
RM 19 = ∞

Aspheric coefficient
RM2
k = -2.06688e + 00
B = 9.18231e-04 C = -6.44332e-06 D = 6.14727e-08
RM6
k = -4.03021e-01
B = 1.55298e-05 C = 2.08342e-06 D = 0.00000e + 00

(Numerical example 2)
f = 5.60-31.73 Fno = 2.86-5.06 2ω = 15.92 °-76.7 °
R 1 = 101.088 D 1 = 2.00 N 1 = 1.563839 ν 1 = 60.7
R 2 = 50.765 D 2 = 10.50
R 3 = -350.721 D 3 = 3.00 N 2 = 1.651597 ν 2 = 58.5
R 4 = 53.919 D 4 = 5.00
R 5 = 286.366 D 5 = 3.50 N 3 = 1.922860 ν 3 = 18.9
R 6 = -1760.018 D 6 = variable
R 7 = 119.356 D 7 = 5.00 N 4 = 1.658441 ν 4 = 50.9
R 8 = -118.734 D 8 = 0.10
R 9 = 55.313 D 9 = 7.00 N 5 = 1.603112 ν 5 = 60.6
R10 = -202.074 D10 = 0.20
R11 = 220.220 D11 = 2.00 N 6 = 1.922860 ν 6 = 18.9
R12 = 80.000 D12 = variable
R13 = -49.994 D13 = 1.50 N 7 = 1.487490 ν 7 = 70.2
R14 = -466.484 D14 = variable

Aspheric coefficient
R4
k = -4.59384e-01
B = -4.92969e-07 C = -6.91713e-11 D = -3.08187e-13
Master lens data is the same as in Numerical Example 1

(Numerical Example 3)
f = 5.60-31.58 Fno = 2.86-5.06 2ω = 15.98 °-76.8 °
R 1 = 80.227 D 1 = 2.00 N 1 = 1.568832 ν 1 = 56.4
R 2 = 51.877 D 2 = 11.50
R 3 = -177.766 D 3 = 3.00 N 2 = 1.603112 ν 2 = 60.6
R 4 = 51.038 D 4 = 5.50
R 5 = 303.870 D 5 = 3.50 N 3 = 1.922860 ν 3 = 18.9
R 6 = 2150.796 D 6 = variable
R 7 = 226.082 D 7 = 4.00 N 4 = 1.670029 ν 4 = 47.2
R 8 = -96.174 D 8 = 0.10
R 9 = 46.169 D 9 = 7.00 N 5 = 1.603112 ν 5 = 60.6
R10 = -187.282 D10 = 0.10
R11 = 161.158 D11 = 2.00 N 6 = 1.922860 ν 6 = 18.9
R12 = 73.239 D12 = variable
R13 = -67.359 D13 = 1.50 N 7 = 1.487490 ν 7 = 70.2
R14 = 149.296 D14 = variable

Aspheric coefficient
R4
k = 2.35813e-02
B = -3.20823e-07 C = -1.09681e-09 D = 5.80903e-13
Master lens data is the same as in Numerical Example 1

(Numerical example 4)
f = 5.62-31.98 Fno = 2.86-5.06 2ω = 15.78 °-76.56 °
R 1 = 109.688 D 1 = 2.00 N 1 = 1.571351 ν 1 = 53.0
R 2 = 51.029 D 2 = 12.50
R 3 = -140.197 D 3 = 3.00 N 2 = 1.603112 ν 2 = 60.6
R 4 = 91.030 D 4 = 3.00
R 5 = 309.291 D 5 = 3.50 N 3 = 1.922860 ν 3 = 18.9
R 6 = -57421.716 D 6 = variable
R 7 = 101.143 D 7 = 5.00 N 4 = 1.651597 ν 4 = 58.5
R 8 = -71.798 D 8 = 0.10
R 9 = 46.181 D 9 = 4.00 N 5 = 1.603112 ν 5 = 60.6
R10 = 210.398 D10 = 0.70
R11 = 872.995 D11 = 2.00 N 6 = 1.846660 ν 6 = 23.9
R12 = 89.005 D12 = variable
R13 = -1273.641 D13 = 1.50 N 7 = 1.516330 ν 7 = 64.1
R14 = 53.836 D14 = variable

Aspheric coefficient
R13
k = 1.06117e + 04
B = -1.76055e-06 C = -2.02794e-08 D = -4.31509e-11
Master lens data is the same as in Numerical Example 1

(Numerical example 5)
f = 5.62-31.98 Fno = 2.86-5.06 2ω = 15.78 °-76.56 °
R 1 = 149.989 D 1 = 2.00 N 1 = 1.603112 ν 1 = 60.6
R 2 = 57.354 D 2 = 12.50
R 3 = -117.029 D 3 = 3.00 N 2 = 1.603112 ν 2 = 60.6
R 4 = 75.293 D 4 = 1.50
R 5 = 95.418 D 5 = 3.50 N 3 = 1.846660 ν 3 = 23.9
R 6 = 327.038 D 6 = variable
R 7 = 151.414 D 7 = 6.00 N 4 = 1.603112 ν 4 = 60.6
R 8 = -74.935 D 8 = 0.50
R 9 = 61.909 D 9 = 7.00 N 5 = 1.603112 ν 5 = 60.6
R10 = -142.249 D10 = 0.20
R11 = -201.553 D11 = 2.00 N 6 = 1.846660 ν 6 = 23.9
R12 = 149.954 D12 = variable
R13 = -50.568 D13 = 1.50 N 7 = 1.603112 ν 7 = 60.6
R14 = -175.995 D14 = variable

Aspheric coefficient
R3
k = 4.11111e-01
B = 6.90442e-07 C = 6.82468e-10 D = -1.15147e-12 E = 4.36825e-16
R11
k = 6.20342e + 00
B = -4.72320e-07 C = -1.30507e-10 D = 6.15168e-13
Master lens data is the same as in Numerical Example 1

  According to the converter lens of the present embodiment described above, the functions of the teleconverter lens and the wide converter can be made compatible without attaching to and detaching from the master lens. In addition, various aberrations such as chromatic aberration, spherical aberration, and curvature of field are well corrected. Therefore, it is possible to provide a high-performance and small variable magnification converter lens that can be used for high-pixel digital still cameras and video cameras. Is possible.

It is a basic block diagram of the converter lens of this invention. It is a block diagram of a master lens. It is lens sectional drawing in the state which mounted | wore the master lens with the converter lens of Numerical Example 1. FIG. FIG. 5 is an aberration diagram for the combination of zoom1 in Numerical Example 1. FIG. 6 is an aberration diagram for the combination of zoom2 in Numerical Example 1. FIG. 5 is an aberration diagram for the combination of zoom3 in Numerical Example 1. FIG. 5 is an aberration diagram for the combination of zoom4 in Numerical Example 1. FIG. 6 is an aberration diagram for the combination of zoom5 in Numerical Example 1. It is lens sectional drawing in the state which mounted | wore the master lens with the converter lens of Numerical Example 2. FIG. FIG. 9 is an aberration diagram for a combination of zoom1 in Numerical Example 2. FIG. 9 is an aberration diagram for a combination of zoom2 in Numerical Example 2. FIG. 11 is an aberration diagram for a combination of zoom3 in Numerical Example 2. FIG. 11 is an aberration diagram for a combination of zoom4 in Numerical Example 2. FIG. 10 is an aberration diagram for the combination of zoom5 in Numerical Example 2. It is lens sectional drawing in the state which mounted | wore the master lens with the converter lens of Numerical Example 3. FIG. FIG. 11 is an aberration diagram for the combination of zoom1 in Numerical Example 3. It is an aberration diagram in the combination of zoom2 of Numerical Example 3. FIG. 11 is an aberration diagram for a combination of zoom3 in Numerical Example 3. It is an aberration diagram in the combination of zoom4 of Numerical Example 3. It is an aberration diagram in the combination of zoom5 of Numerical Example 3. It is lens sectional drawing in the state which mounted | wore the master lens with the converter lens of Numerical Example 4. FIG. FIG. 11 is an aberration diagram for a combination of zoom1 in Numerical Example 4. FIG. 9 is an aberration diagram for a combination of zoom2 in Numerical Example 4. FIG. 11 is an aberration diagram for a combination of zoom3 in Numerical Example 4. FIG. 11 is an aberration diagram for a combination of zoom4 in Numerical example 4; FIG. 11 is an aberration diagram for a combination of zoom5 in Numerical Example 4. It is a lens sectional view in the state where the converter lens of Numerical Example 5 is attached to the master lens. FIG. 11 is an aberration diagram for the combination of zoom1 in Numerical Example 5. FIG. 11 is an aberration diagram for the combination of zoom2 in Numerical Example 5. FIG. 10 is an aberration diagram for the combination of zoom3 in Numerical Example 5. FIG. 11 is an aberration diagram for a combination of zoom4 in Numerical Example 5. FIG. 11 is an aberration diagram for a combination of zoom5 in Numerical Example 5.

Explanation of symbols

C converter lens M master lens L1 first lens group L2 second lens group L3 third lens group IP imaging surface G glass block △ M meridional image surface △ S sagittal image surface

Claims (9)

In a converter lens that is mounted in front of the master lens and can convert the focal length of the master lens, in order from the front, the first lens group having a negative refractive power, the second lens group having a positive refractive power, and a negative refractive power. It has a third lens group, and at the time of zooming from the lowest afocal magnification to the highest afocal magnification, both the first lens group and the second lens group move monotonously forward while changing the distance between them. In addition, when the movement amount of the first lens group at the time of zooming from the lowest afocal magnification to the highest afocal magnification is M ₁ and the total length in the state of the lowest afocal magnification is TD _w ,

A converter lens characterized by satisfying the following conditions. The first lens group includes at least one positive lens, the focal length of the first lens group is f ₁ , the focal length of the negative lens in the first lens group is f _1P , and the lowest afocal magnification is m _w. , when the highest afocal magnification m _t,

The converter lens according to claim 1, wherein the following condition is satisfied. The second lens group includes at least one negative lens, the focal length of the second lens group is f ₂ , the focal length of the negative lens in the second lens group is f _2N , and the lowest afocal magnification is m _w. , when the highest afocal magnification m _t,

The converter lens according to claim 1 or 2, wherein the following condition is satisfied. When the M ₂ the amount of movement of the second lens group at the time of the highest magnification of the afocal magnification from the lowest afocal magnification,

The converter lens according to claim 1, wherein the following condition is satisfied. When the radii of curvature of the front and rear surfaces of the foremost lens of the first lens group are r ₁ and r ₂ respectively,

The converter lens according to claim 1, wherein the following condition is satisfied. The distance between the rear principal point of the first lens group in the state of the lowest afocal magnification and the front principal point of the second lens group is e1 _t , and the first lens group in the state of the lowest afocal magnification When the combined focal length of the second lens group is _fFT ,

The converter lens according to claim 1, wherein the following condition is satisfied. When the total length in the state of the lowest afocal magnification is TD _W and the total length in the state of the highest afocal magnification is TD _T ,

The converter lens according to claim 1, wherein the following condition is satisfied. When the focal length of the first lens group and f _1,

The converter lens according to claim 1, wherein the following condition is satisfied. When the focal length of the second lens group is f ₂ and the amount of movement of the second lens group at the time of zooming from the lowest afocal magnification to the highest afocal magnification is M ₂ ,

The converter lens according to claim 1, wherein the following condition is satisfied.

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