JP2006106537A - 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 positive refractive power, a 2nd lens group L2 having negative refractive power and a 3rd lens group L3 having positive refractive power in order from the front. In the case of varying power from the lowest afocal power to the highest afocal power, the 1st lens group L1 monotonously moves forward and the 2nd lens group L2 monotonously moves backward. The moving amounts of the 1st lens group L1 and the 2nd lens group L2 in the case of varying the power are 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 in the state of 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 is difficult to reduce the overall length, 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. One lens group, a second lens group having a negative refractive power, and a third lens group having a positive refractive power. When changing the magnification from the lowest afocal magnification to the highest afocal magnification, the first lens group It is characterized in that it moves forward monotonously and the second lens group monotonously moves backward (on the master lens side, or on the image side when the taking lens is a master lens). When the movement amounts of the first lens unit and the second lens unit at the time of zooming from the lowest afocal magnification to the highest afocal magnification are M ₁ and M ₂ , respectively,

Is set appropriately to satisfy 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 a positive refractive power (optical power = reciprocal of focal length), a second lens unit L2 having a negative refractive power, and a third lens unit L3 having a positive 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, when zooming from the lowest afocal magnification to the highest afocal magnification, the first lens unit L1 is monotonously forward and the second lens unit L2 is monotonously backward (master lens side, photographic lens In this case, it is moved to the image side).

  In the converter lens of this example, at the lowest afocal magnification, the first lens unit L1 and the second lens unit L2 constitute a front group LFw having a negative refractive power as a whole, and the third lens unit L3 is positive. 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 constitutes a front group LFt having a positive refractive power, and the second lens unit L2 and the third lens unit L3 as a whole have a rear group having a negative refractive power. Considering that LRt is configured, it can be regarded as a power arrangement similar to that of a 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.

  When changing the magnification from the minimum magnification to the maximum magnification, when the first lens unit L1 is fixed and the second lens unit L2 is moved backward, the front lens diameter passes off-axis rays at the minimum magnification with a wide angle of view. It is determined by the height (distance from the optical axis). In order to achieve both a reduction in the front lens diameter and a high zoom ratio, the amount of movement of the second lens unit L2 needs to be sufficiently large. As a result, the distance between the second lens unit L2 and the third lens unit L3 in the minimum magnification state cannot be shortened, so that the total length of the converter lens cannot be shortened in the minimum magnification state. As a result, the height of the off-axis light beam cannot be reduced in the minimum magnification state, and it is difficult to reduce the front lens diameter.

  Therefore, in this embodiment, as described above, the first lens unit L1 is moved forward when zooming from the minimum magnification to the maximum magnification. By moving the first lens unit L1 forward, the distance between the first lens unit L1 and the second lens unit L2 is increased, so that the amount of movement of the second lens unit L2 can be shortened. The distance between the second lens group L2 and the third lens group L3 in the minimum magnification state can be shortened by the amount of movement of the second lens group L2. As a result, the total length of the converter lens C in the state of the minimum magnification is shortened, and the height of the off-axis light beam of the first lens unit L1 can be reduced, so that the front lens diameter can be reduced.

  However, if the movement amount of the first lens unit L1 is increased too much, the total length of the converter lens C in the maximum magnification state becomes long, so that the off-axis ray height in the maximum magnification state is in the minimum magnification state. Thus, the front lens diameter is determined by the maximum magnification, and a problem arises in terms of downsizing the front lens diameter.

  Therefore, in this embodiment, the second lens group L2 is a lens group having a zooming function, the first lens group L1 is a lens group having a function of maintaining an afocal system, and the first lens group L1 and the second lens group L2 The moving amount of the lens unit L2 is set so as to satisfy the following conditions.

Here, M ₁ and M ₂ are the movement amounts of the first lens unit L1 and the second lens unit L2 at the time of zooming from the minimum magnification to the maximum magnification, respectively. However, the backward movement (image side) on the optical axis is the positive direction.

  Conditional expression (1) is an expression that defines the amount of movement of the first lens unit L1 relative to the amount of movement of the second lens unit L2 at the time of zooming from the minimum magnification to the maximum magnification.

  If the lower limit of conditional expression (1) is exceeded, the movement amount of the first lens unit L1 becomes excessive, and not only the total length at the maximum magnification is increased, but also the first lens unit L1 at the minimum magnification is passed. Since the height of the off-axis light beam passing through the first lens unit L1 at the maximum magnification is higher than the height of the off-axis light beam, the front lens diameter is determined at the maximum magnification, and the front lens diameter is reduced. This is not preferable.

  On the other hand, if the upper 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 amount of movement of the second lens unit L2 is assured. The interval between the second lens unit L2 and the third lens unit L3 in the magnification state must be increased. As a result, not only the total length in the state of the minimum magnification is increased, but also the height of the off-axis light beam passing through the first lens unit L1 is increased, so that the front lens diameter is determined in the state of the minimum magnification, and the front lens This is not preferable in terms of reducing the diameter.

  The converter lens of the present embodiment continuously changes the afocal magnification while maintaining the afocal system by appropriately setting the movement amounts of the first lens unit L1 and the second lens unit L2. The aim is to achieve both a reduction in the front lens diameter and a 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 of compensating for the degree of afocal displacement caused by the movement of the second lens unit L2 by moving the first lens unit L1 to 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 7 to be described later will be described.

  First, common points in each numerical example will be described. In the converter lens of the present embodiment, the first lens unit L1 becomes an independent group in the state of the maximum magnification. Therefore, 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 negative 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 negative refractive power is configured to have at least two negative lenses. By sharing the negative refractive power of the second lens unit L2 between the two negative lenses, the refractive power of each lens is weakened, the Petzval sum is prevented from increasing to the negative side, and the field curvature is corrected well. ing.

  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 a negative meniscus lens 11 having a convex surface facing forward and a positive meniscus lens 12 having a convex surface facing the object side in order from the front to the rear. The negative meniscus lens 11 is effective in suppressing the occurrence of various aberrations such as coma aberration, astigmatism, and field curvature when the zoom ratio is increased in an optical system with a large change in field angle.

  The second lens unit L2 includes, in order from the front to the rear, a negative meniscus lens 21 having a convex surface forward, a biconcave negative lens 22, and a positive meniscus lens 23 having a convex surface forward. Thus, by arranging the positive lens (positive meniscus lens 23) in the second lens unit L2, axial chromatic aberration at the maximum magnification and magnification chromatic aberration correction of the entire variable magnification region are performed.

  The third lens unit L3 includes, in order from the front to the rear, a biconvex positive lens 31 and a negative meniscus lens 32 having a concave surface forward. Since the third lens unit L3 is an independent unit in the state of the minimum magnification similarly to the first lens unit L1, the third lens unit L3 includes a negative lens, and corrects longitudinal chromatic aberration and lateral chromatic aberration in the lens unit. .

  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 with a convex surface facing forward and a positive meniscus lens 12 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, two negative meniscus lenses 21 and 22 having a convex surface forward and a positive meniscus lens 23 having a convex surface forward. In Numerical Example 2, the refractive power of the negative lens 22 is changed to a meniscus shape, whereby the distance between the negative lenses 21 and 22 is shortened and the thickness of the second lens unit L2 is reduced.

  The third lens unit L3 includes a biconvex positive lens. By configuring the third lens unit L3 with only one lens, cost reduction is achieved.

  FIG. 15 is a cross-sectional view of the converter lens C of Numerical Example 3 attached to the master lens M.

  In the numerical example 3, the basic configuration is the same as that of the numerical example 1, but the total length is shortened at the maximum magnification, and the cost is reduced by changing the glass material of the first lens unit L1 to an inexpensive one. It is.

  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. Numerical Example 4 is an example in which the total length is shortened in the maximum magnification state by changing the power arrangement.

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

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

  The third lens unit L3 includes, in order from the front to the rear, a biconvex positive lens 31 and a negative meniscus lens 32 having a convex surface forward. By making the negative lens 32 have a meniscus shape with a convex surface facing forward, it is possible to correct an over-curve of the field curvature with a minimum magnification as compared with a meniscus shape with a concave surface facing forward.

  FIG. 27 is a cross-sectional view of the converter lens C of Numerical Example 5 attached to the master lens M. Numerical Example 5 is an example in which the total length is shortened and the front lens diameter is reduced in the state of the minimum magnification by changing the power arrangement.

  In FIG. 27, the first lens unit L1 includes a negative meniscus lens 11 with a convex surface facing forward and a positive meniscus lens 12 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, two negative meniscus lenses 21 and 22 having a convex surface forward and a positive meniscus lens 23 having a convex surface forward.

  The third lens unit L3 includes, in order from the front to the rear, a biconvex positive lens 31 and a negative meniscus lens 32 having a convex surface forward. By making the negative lens 32 have a negative meniscus shape with the convex surface facing forward, the under tendency of the curvature of field in the state of the minimum magnification is corrected.

  FIG. 33 is a cross-sectional view in a state where the converter lens C of Numerical Example 6 is attached to the master lens M.

  In FIG. 33, the first lens unit L1 includes, in order from the front to the rear, a negative meniscus lens 11 having a convex surface directed forward, a negative lens 12 having a biconcave shape, and a positive meniscus lens 22 having a convex surface directed to the object side. ing.

  The second lens unit L2 includes two negative meniscus lenses 21 and 22 having convex surfaces facing forward in order from the front to the rear. Cost reduction is achieved by using two second lens units L2.

  The third lens unit L3 includes, in order from the front to the rear, a biconvex positive lens 31 and a negative meniscus lens 32 having a convex surface directed toward the object side. By making the negative lens 32 have a negative meniscus shape with a convex surface facing forward, an under tendency of the image surface in the state of the minimum magnification is corrected.

  FIG. 39 is a cross-sectional view in a state where the converter lens C of Numerical Example 7 is attached to the master lens M.

  In FIG. 39, the first lens unit L1 includes, in order from the front to the rear, a negative meniscus lens 11 having a convex surface directed forward, a negative lens 12 having a biconcave shape, and a positive meniscus lens 22 having a convex surface directed forward. Yes.

  The second lens unit L2 includes, in order from the front to the rear, a negative meniscus lens 21 having a convex surface forward, a biconcave negative lens 22, and a positive lens 23 having a convex surface forward. In Numerical Example 7, an aspherical surface is used for the second lens unit L2 in order to reduce the front lens diameter and correct distortion. Specifically, the front surface of the negative lens 21 is an aspherical surface.

  The third lens unit L3 includes, in order from the front to the rear, a biconvex positive lens 31 and a negative meniscus lens 32 having a convex surface forward.

  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 1N} is the focal length of the negative lens in the first lens group, _{m w} is the minimum afocal magnification, _{m t} is the maximum afocal magnification, _{f 2} is the The focal length of the second lens unit L2, e _2w is the distance between the rear principal point of the second lens unit L2 and the front principal point of the third lens unit L3 in the state of the minimum afocal magnification, and TD _t is the maximum afocal magnification. the total length of the converter lens C in the state, TD _w synthesis minimum afocal magnification total length of the converter lens C in the state, f _Fw minimum afocal first lens group at a magnification of state L1 and the second lens group L2 The focal length, _fRT, is the combined focal length of the second lens unit L2 and the third lens unit L3 at the maximum afocal magnification.

  Conditional expression (2) is a condition that defines the focal length of the negative lens in the first lens unit L1, that is, a condition that defines the refractive power of the negative lens in the first lens unit L1.

  If the lower limit of conditional expression (2) is exceeded, the refractive power of the negative lens in the first lens unit L1 becomes excessive, and the Petzval sum increases to the negative side, increasing the tendency of the image surface to overshoot. On the other hand, if the upper limit of conditional expression (2) is exceeded, the refractive power of the negative lens will be too small, so that chromatic aberration correction will be insufficient, and this will cause color blurring.

  Conditional expression (3) is a condition that defines the distance between the first lens unit L1 and the second lens unit L2 with respect to the focal length of the second lens unit L2.

If the lower limit of conditional expression (3) is exceeded, the distance between the second lens unit L2 and the third lens unit L3 is small, and in order to obtain a desired minimum magnification, both f _Fw and f _Rw become small, and the minimum magnification It becomes difficult to correct distortion aberration in the state. On the other hand, if the upper limit of conditional expression (3) is exceeded, the distance between the second lens unit L2 and the third lens unit L3 in the state of the desired minimum afocal magnification becomes long, and the converter lens C in the state of the minimum magnification becomes longer. Not only is the total length excessive, but the position of off-axis rays passing through the first lens unit L1 is increased, which is not preferable for reducing the front lens diameter.

  Conditional expression (4) defines the total length in the maximum magnification state relative to the total length in the minimum magnification state. Since the relationship between the total length in the state of the minimum magnification and the total length in the state of the maximum magnification 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 conditional expression (4) is exceeded, the total length of the converter lens C in the maximum magnification state is short. Therefore, in order to obtain a desired zoom ratio, the second lens unit L2 and the second lens group L2 in the minimum magnification state The interval between the three lens units L3 must be increased. As a result, not only the total length of the converter lens C in the state of the minimum magnification becomes excessive, but also the height of the off-axis light beam passing through the first lens unit L1 increases, so that the front lens diameter becomes small in the state of the minimum magnification. This is not preferable from the viewpoint of reducing the front lens diameter.

  On the other hand, if the upper limit of conditional expression (4) is exceeded, the total length of the converter lens C in the maximum magnification state becomes excessive, and the maximum magnification is greater 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 in this state becomes high, it is not preferable in terms of downsizing the front lens diameter.

  In particular, it is preferable to satisfy both conditional expression (1) and conditional expression (4) in order to reduce the front lens diameter.

  Conditional expression (5) is an expression that defines the focal length of the first lens unit L1 with respect to the focal length of the second lens unit L2. Since the relationship between the focal length of the first lens unit L1 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 conditional expression (5) is exceeded, the refractive power of the first lens unit L1 becomes too strong, so the Petzval sum increases to the plus side, and the field curvature tends to be under, which is not preferable. On the other hand, if the upper limit of conditional expression (5) is exceeded, the refractive power of the first lens unit L1 will be weakened. Therefore, in order to obtain a desired maximum magnification, the second lens unit L2 and the third lens in the maximum magnification state. The interval between the groups L3 is increased, and the total length in the maximum magnification state is increased. Thereby, the height of the off-axis light beam that passes through the first lens unit L1 in the maximum magnification state is increased, which is not preferable in terms of downsizing the front lens diameter.

  Conditional expression (6) is an expression that defines the focal length of the first lens unit L1 relative to the combined focal length of the first lens unit L1 and the second lens unit L2 in the state of the minimum magnification.

  Exceeding the lower limit of conditional expression (6) is not preferable because the refractive power of the first lens unit L1 becomes too large and the Petzval sum increases to the plus side, which increases the tendency of the under curvature of field curvature.

  On the other hand, when the upper limit of conditional expression (6) is exceeded, the refractive power of the first lens unit L1 becomes too small. Since the first lens unit L1 corresponds to the front unit of the teleconverter lens in the maximum magnification state (LFt in FIG. 1), if the refractive power of the first lens unit L1 becomes too small, the first lens unit L1 in the maximum magnification state A sufficient interval between the second lens unit L2 and the third lens unit L3 must be ensured, and the total length in the maximum magnification state becomes excessive. Furthermore, since the total length in the maximum magnification state increases, the height of the off-axis light beam passing through the first lens unit L1 becomes higher in the maximum magnification state than in the minimum magnification state. This is also not preferable.

  Conditional expression (7) defines the ratio of the focal length of the third lens unit L3 to the combined focal length of the second lens unit L2 and the third lens unit L3 at the maximum magnification.

  If the lower limit of conditional expression (7) is exceeded, the refractive power of the third lens unit L3 increases, and astigmatism correction becomes difficult.

  On the other hand, when the upper limit of conditional expression (7) is exceeded, the refractive power of the third lens unit L3 becomes too small. Since the third lens unit L3 corresponds to the rear group of the wide converter lens in the minimum magnification state (LRw in FIG. 1), if the refractive power of the third lens unit L3 becomes too small, the third lens unit L3 in the state of the minimum magnification. A sufficient interval between the second lens unit L2 and the third lens unit L3 must be ensured, and the total length in the state of the minimum magnification becomes excessive. Further, the increase in the total length in the state of the minimum magnification increases the height of the off-axis light beam passing through the first lens unit L1, which is not preferable in terms of reducing the front lens diameter.

  Next, numerical data of numerical examples 1 to 7 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 spacing, NMi and νMi are the refractive index and Abbe number, respectively, with reference to the d-line of the i-th member. 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 7.

  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, 28 to 32, 34 to 38, and 40 to 44 are numerical examples 1 to 7 in the state of each combination of zoom 1 to zoom 5 in Table 1. FIG. 6 is various aberration diagrams in a state where the converter lens is attached to the master lens.

  Table 10 shows the relationship between the above-described conditional expressions and numerical examples.

(Numerical example 1)
f = 5.62 to 31.99 Fno = 2.87 to 5.06 2ω = 15.8 ° to 76.6 °
R 1 = 86.964 D 1 = 4.06 N 1 = 1.922860 ν 1 = 18.9
R 2 = 70.033 D 2 = 1.50
R 3 = 77.411 D 3 = 7.81 N 2 = 1.772499 ν 2 = 49.6
R 4 = 226.283 D 4 = variable
R 5 = 131.804 D 5 = 2.75 N 3 = 1.487490 ν 3 = 70.2
R 6 = 25.694 D 6 = 11.00
R 7 = -103.979 D 7 = 2.02 N 4 = 1.487490 ν 4 = 70.2
R 8 = 29.095 D 8 = 2.50
R 9 = 53.170 D 9 = 3.00 N 5 = 1.846660 ν 5 = 23.9
R10 = 175.970 D10 = variable
R11 = 50.519 D11 = 3.50 N 6 = 1.603112 ν 6 = 60.6
R12 = -46.869 D12 = 0.20
R13 = -58.331 D13 = 1.06 N 7 = 1.846660 ν 7 = 23.9
R14 = -237.086 D14 = variable

(Master lens)
fm = 8.03 to 22.85 FNom = 2.87 to 5.06 2ω = 22.0 ° to 57.9 °
RM 1 = 63.353 DM 1 = 1.60 NM 1 = 1.683430 νM1 = 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 νM 3 = 40.7
RM 7 = 58.781 DM 7 = 0.70 NM 4 = 1.805181 νM 4 = 25.4
RM 8 = 5.189 DM 8 = 0.87
RM 9 = 18.702 DM 9 = 1.80 NM 5 = 1.603112 νM 5 = 60.6
RM10 = -18.469 DM10 = variable
RM11 = 17.220 DM11 = 1.90 NM 6 = 1.487490 νM 6 = 70.2
RM12 = -136.717 DM12 = variable
RM13 = ∞ DM13 = 0.38 NM 7 = 1.544270 νM 7 = 70.6
RM14 = ∞ DM14 = 0.80 NM 8 = 1.494000 νM 8 = 75.0
RM15 = ∞ DM15 = 0.40 NM 9 = 1.544270 νM 9 = 70.6
RM16 = ∞ DM16 = 0.38 NM10 = 1.544270 νM10 = 70.6
RM17 = ∞ DM17 = 0.50
RM18 = ∞ DM18 = 0.50 NM11 = 1.516330 νM11 = 64.1
RM19 = ∞

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

(Numerical example 2)
f = 5.62 to 31.99 Fno = 2.87 to 5.06 2ω = 15.8 ° to 76.6 °
R 1 = 98.549 D 1 = 4.06 N 1 = 1.922860 ν 1 = 18.9
R 2 = 78.128 D 2 = 1.50
R 3 = 88.135 D 3 = 7.81 N 2 = 1.772499 ν 2 = 49.6
R 4 = 347.567 D 4 = variable
R 5 = 240.734 D 5 = 2.75 N 3 = 1.487490 ν 3 = 70.2
R 6 = 38.772 D 6 = 7.00
R 7 = 664.277 D 7 = 2.02 N 4 = 1.487490 ν 4 = 70.2
R 8 = 25.419 D 8 = 3.00
R 9 = 39.588 D 9 = 3.00 N 5 = 1.846660 ν 5 = 23.9
R10 = 47.821 D10 = variable
R11 = 62.353 D11 = 3.50 N 6 = 1.603112 ν 6 = 60.6
R12 = -141.500 D12 = variable

Master lens data is the same as in Numerical Example 1

(Numerical Example 3)
f = 5.62 to 31.99 Fno = 2.87 to 5.06 2ω = 15.8 ° to 76.6 °
R 1 = 65.862 D 1 = 4.06 N 1 = 1.846660 ν 1 = 23.9
R 2 = 52.913 D 2 = 1.50
R 3 = 58.672 D 3 = 8.50 N 2 = 1.603112 ν 2 = 60.6
R 4 = 236.334 D 4 = Variable
R 5 = 120.390 D 5 = 2.70 N 3 = 1.487490 ν 3 = 70.2
R 6 = 32.943 D 6 = 9.00
R 7 = -263.295 D 7 = 2.02 N 4 = 1.487490 ν 4 = 70.2
R 8 = 20.382 D 8 = 6.00
R 9 = 51.432 D 9 = 3.00 N 5 = 1.846660 ν 5 = 23.9
R10 = 145.442 D10 = variable
R11 = 104.666 D11 = 3.00 N 6 = 1.603112 ν 6 = 60.6
R12 = -35.609 D12 = 0.20
R13 = -71.485 D13 = 1.06 N 7 = 1.846660 ν 7 = 23.9
R14 = -569.809 D14 = variable

Master lens data is the same as in Numerical Example 1

(Numerical example 4)
f = 5.62 to 31.99 Fno = 2.87 to 5.06 2ω = 15.8 ° to 76.6 °
R 1 = 56.735 D 1 = 3.00 N 1 = 1.922860 ν 1 = 18.9
R 2 = 46.744 D 2 = 3.00
R 3 = 53.400 D 3 = 10.00 N 2 = 1.772499 ν 2 = 49.6
R 4 = 139.492 D 4 = Variable
R 5 = 152.465 D 5 = 2.75 N 3 = 1.487490 ν 3 = 70.2
R 6 = 25.283 D 6 = 15.00
R 7 = -171.469 D 7 = 2.02 N 4 = 1.487490 ν 4 = 70.2
R 8 = 30.154 D 8 = 5.00
R 9 = 100.966 D 9 = 3.00 N 5 = 1.846660 ν 5 = 23.9
R10 = -487.740 D10 = variable
R11 = 43.484 D11 = 3.00 N 6 = 1.603112 ν 6 = 60.6
R12 = -73.865 D12 = 0.20
R13 = 91.588 D13 = 1.80 N 7 = 1.846660 ν 7 = 23.9
R14 = 40.278 D14 = variable

Master lens data is the same as in Numerical Example 1

(Numerical example 5)
f = 5.62 to 31.98 Fno = 2.87 to 5.06 2ω = 15.8 ° to 76.6 °
R 1 = 63.520 D 1 = 3.00 N 1 = 1.922860 ν 1 = 18.9
R 2 = 53.807 D 2 = 2.00
R 3 = 60.451 D 3 = 8.00 N 2 = 1.772499 ν 2 = 49.6
R 4 = 123.540 D 4 = Variable
R 5 = 305.221 D 5 = 1.50 N 3 = 1.487490 ν 3 = 70.2
R 6 = 21.462 D 6 = 9.00
R 7 = 539.235 D 7 = 1.50 N 4 = 1.487490 ν 4 = 70.2
R 8 = 27.085 D 8 = 2.50
R 9 = 49.976 D 9 = 2.00 N 5 = 1.846660 ν 5 = 23.9
R10 = 81.728 D10 = variable
R11 = 31.045 D11 = 4.00 N 6 = 1.603112 ν 6 = 60.6
R12 = -87.032 D12 = 0.20
R13 = 42.959 D13 = 1.50 N 7 = 1.846660 ν 7 = 23.9
R14 = 29.024 D14 = variable

Master lens data is the same as in Numerical Example 1

(Numerical example 6)
f = 5.62 to 31.99 Fno = 2.87 to 5.06 2ω = 15.8 ° to 76.6 °
R 1 = 70.914 D 1 = 3.00 N 1 = 1.922860 ν 1 = 18.9
R 2 = 59.442 D 2 = 2.00
R 3 = 65.804 D 3 = 8.00 N 2 = 1.772499 ν 2 = 49.6
R 4 = 148.733 D 4 = Variable
R 5 = 300.542 D 5 = 2.50 N 3 = 1.487490 ν 3 = 70.2
R 6 = 26.577 D 6 = 7.00
R 7 = 170.285 D 7 = 2.02 N 4 = 1.487490 ν 4 = 70.2
R 8 = 27.805 D 8 = variable
R 9 = 36.848 D 9 = 3.00 N 5 = 1.603112 ν 5 = 60.6
R10 = -137.883 D10 = 0.20
R11 = 11.191 D11 = 2.00 N 6 = 1.846660 ν 6 = 23.9
R12 = 9.686 D12 = variable

Master lens data is the same as in Numerical Example 1

(Numerical example 7)
f = 5.62 to 31.99 Fno = 2.87 to 5.06 2ω = 15.8 ° to 76.6 °
R 1 = 57.745 D 1 = 3.00 N 1 = 1.922860 ν 1 = 18.9
R 2 = 47.663 D 2 = 1.80
R 3 = 51.680 D 3 = 7.50 N 2 = 1.772499 ν 2 = 49.6
R 4 = 110.729 D 4 = Variable
R 5 = 252.703 D 5 = 2.00 N 3 = 1.487490 ν 3 = 70.2
R 6 = 25.378 D 6 = 10.00
R 7 = -85.678 D 7 = 2.00 N 4 = 1.487490 ν 4 = 70.2
R 8 = 19.395 D 8 = 5.00
R 9 = 55.566 D 9 = 3.00 N 5 = 1.846660 ν 5 = 23.9
R10 = 318.194 D10 = variable
R11 = 29.721 D11 = 5.00 N 6 = 1.603112 ν 6 = 60.6
R12 = -51.002 D12 = 0.20
R13 = 312.072 D13 = 2.00 N 7 = 1.846660 ν 7 = 23.9
R14 = 49.750 D14 = variable

Aspheric coefficient
R5
k = -2.00000e + 00
B = 1.50000e-06 C = 1.00000e-09 D = 1.00000e-13 E = 0.00000e + 00
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. It is lens sectional drawing in the state which mounted | wore the master lens with the converter lens of Numerical Example 6. FIG. FIG. 11 is an aberration diagram for a combination of zoom1 in Numerical Example 6; FIG. 12 is an aberration diagram for the combination of zoom2 in Numerical Example 6. FIG. 11 is an aberration diagram for the combination of zoom3 in Numerical Example 6. FIG. 11 is an aberration diagram for a combination of zoom4 in Numerical Example 6. FIG. 11 is an aberration diagram for the combination of zoom5 in Numerical Example 6. It is lens sectional drawing in the state which mounted | wore the master lens with the converter lens of Numerical Example 7. FIG. 10 is an aberration diagram for the combination of zoom1 in Numerical Example 7. FIG. 11 is an aberration diagram for a combination of zoom2 in Numerical Example 7. FIG. 10 is an aberration diagram for the combination of zoom3 in Numerical Example 7. FIG. 11 is an aberration diagram for a combination of zoom4 in Numerical Example 7. FIG. 12 is an aberration diagram for the combination of zoom5 in Numerical Example 7.

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 positive refractive power, the second lens group having a negative refractive power, and a positive refractive power. A third lens group, and when zooming from the lowest afocal magnification to the highest afocal magnification, the first lens group moves forward monotonously and the second lens group moves backward monotonously. When the movement amounts of the first lens group and the second lens group at the time of zooming from the lowest afocal magnification to the highest afocal magnification are M ₁ and M ₂ , respectively,

A converter lens characterized by satisfying the following conditions. The first lens group includes at least one negative 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 _1N , 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 converter lens according to claim 1, wherein the third lens group includes two or less lenses.   The converter lens according to claim 1, wherein the first lens group includes two or less lenses. When the focal length of the second lens group is f ₂ and the distance between the rear principal point of the second lens group and the front principal point of the third lens group in the state of the lowest afocal magnification is e _2w ,

The converter lens according to claim 1, wherein the following condition is satisfied. The total length of the converter lens at the highest afocal magnification is TD _t , the total length of the converter lens at the lowest afocal magnification is TD _w , the lowest afocal magnification is m _w , and the highest afocal magnification is m _t

The converter lens according to claim 1, wherein the following condition is satisfied. The focal length f ₁ of the first lens _group, the focal length of the second lens group f _2, the lowest afocal magnification m _w, the highest afocal magnification and m _t,

The converter lens according to claim 1, wherein the following condition is satisfied. When the focal length of the first lens group is f ₁ , and the combined focal length of the first lens group and the second lens group in the state of the lowest afocal magnification is f _Fw ,

The converter lens according to claim 1, wherein the following condition is satisfied. When the focal length of the third lens group is f ₃ , and the combined focal length of the second lens group and the third lens group in the state of the highest afocal magnification is f _RT ,

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

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