JP6815166B2 - Variable magnification optical system and imaging device - Google Patents

Description

The present invention relates to a variable magnification optical system suitable as an imaging optical system for a film camera, a video camera, a digital still camera, and the like, and an imaging device provided with the variable magnification optical system.

Image pickup devices using solid-state image sensors such as digital cameras and video cameras have become widespread. In recent years, with the miniaturization of optical systems in interchangeable lens systems, the market for interchangeable lens imagers such as single-lens reflex cameras and mirrorless interchangeable-lens cameras has expanded remarkably, and a wide range of users use interchangeable lens imagers. I'm starting to do it. With the expansion of the user base, in the lens interchangeable system, not only high performance and miniaturization of the optical system but also cost reduction are required.

Under such circumstances, for example, in order to realize cost reduction, a plastic lens is adopted as a part of an optical system. For example, Patent Document 1 proposes an optical system for a so-called compact camera for a high-magnification zoom lens, which is configured by using a plastic lens having a positive refractive power.

Further, Patent Document 2 proposes an optical system for a standard zoom lens for a so-called mirrorless camera, which is configured by using a plurality of plastic lenses.

JP 2013-61418 JP 2011-99250

However, a plastic lens has a larger coefficient of linear expansion than a glass lens, and the shape and refractive index of the lens change significantly depending on the change in atmospheric temperature. Therefore, in an optical system including a plastic lens, the focal position and various aberrations may fluctuate due to a change in atmospheric temperature, and an optical system having good temperature characteristics is required.

In the optical system described in Patent Document 1, only a plastic lens having a positive refractive power is used, and when the refractive index of the plastic lens changes due to a change in atmospheric temperature, the focal position and various aberrations change. It could not be corrected sufficiently.
The optical system described in Patent Document 2 includes not only a plastic lens having a positive refractive power but also a plastic lens having a negative refractive power, but the arrangement of each plastic lens and the refraction to each plastic lens are included. The distribution of power is not appropriate, and it cannot be said that the optical system also gives sufficient consideration to temperature characteristics.

Therefore, an object of the present invention is to provide a variable magnification optical system having good temperature characteristics and an image pickup apparatus provided with the variable magnification optical system while maintaining sufficient optical performance and reducing the cost.

In order to solve the above problems, the variable magnification optical system according to the present invention includes a first lens group having a positive refractive power, a second lens group having a negative refractive power, and at least one lens in order from the object side. A variable magnification optical system that has a group and changes the magnification by changing the distance between each lens group, and includes at least one plastic lens having a positive refractive power and one plastic lens having a negative refractive power. It is characterized by satisfying the following conditions.

-5.00 <fw / f12w <-0.60 ... (1)
-2.80 <Σi (φppi × hppi) / Σj (φpnj × hpnj) <−0.35 ・ ・ ・ (2)

However,
fw: Composite focal distance of the entire variable magnification optical system at the wide-angle end f12w: Composite focal distance of the first lens group and the second lens group at the wide-angle end φppi: Positive included in the variable magnification optical system When the plastic lens having a refractive force is represented as Gpp1, Gpp2, ... In order from the object side, the i-th (i = 1, 2, ...) Plastic lens Gppi having a positive refractive power from the object side. Refractive force hppi: Maximum height of the axial light beam from the optical axis when the axial light beam passes through the object-side surface of the plastic lens Gppi having a positive refractive force at the telephoto end φpnj: The variation When the plastic lens having a negative refractive force included in the magnification optical system is represented as Gpn1, Gpn2, ... In order from the object side, the jth (j = 1, 2, ...) Negative from the object side. Refractive force of the plastic lens Gpnj having the refractive power of Hpnj: From the optical axis of the axial light beam at the telephoto end when the axial light beam passes through the surface of the plastic lens Gpnj having the negative refractive force on the object side. Maximum height

The image pickup apparatus according to the present invention is characterized by comprising the above-mentioned optical system according to the present invention and an image pickup element that converts an optical image formed by the optical system into an electrical signal on the image side of the optical system. And.

According to the present invention, it is possible to provide a variable magnification optical system having good temperature characteristics and an image pickup apparatus provided with the variable magnification optical system while maintaining sufficient optical performance and reducing the cost.

It is sectional drawing which shows the lens structure example at the time of infinity focusing at the wide-angle end of the variable magnification optical system of Example 1 of this invention. It is a spherical aberration diagram, astigmatism diagram, and distortion diagram at the time of infinity focusing at the wide-angle end of the variable magnification optical system of Example 1. It is a spherical aberration diagram, astigmatism diagram and distortion diagram at the time of infinity focusing at the intermediate focal length of the variable magnification optical system of Example 1. It is a spherical aberration diagram, astigmatism diagram, and distortion diagram at the time of infinity focusing at the telephoto end of the variable magnification optical system of Example 1. It is sectional drawing which shows the lens structure example at the time of infinity focusing at the wide-angle end of the variable magnification optical system of Example 2 of this invention. It is a spherical aberration diagram, astigmatism diagram, and distortion diagram at the time of infinity focusing at the wide-angle end of the variable magnification optical system of the second embodiment. It is a spherical aberration diagram, astigmatism diagram, and distortion diagram at the time of infinity focusing at the intermediate focal length of the variable magnification optical system of the second embodiment. It is a spherical aberration diagram, astigmatism diagram, and distortion diagram at the time of infinity focusing at the telephoto end of the variable magnification optical system of the second embodiment. It is sectional drawing which shows the lens structure example at the time of infinity focusing at the wide-angle end of the variable magnification optical system of Example 3 of this invention. It is a spherical aberration diagram, astigmatism diagram, and distortion diagram at the time of infinity focusing at the wide-angle end of the variable magnification optical system of Example 3. FIG. It is a spherical aberration diagram, astigmatism diagram and distortion diagram at the time of infinity focusing at the intermediate focal length of the variable magnification optical system of Example 3. FIG. It is a spherical aberration diagram, astigmatism diagram, and distortion diagram at the time of infinity focusing at the telephoto end of the variable magnification optical system of Example 3. FIG. It is sectional drawing which shows the lens structure example at the time of infinity focusing at the wide-angle end of the variable magnification optical system of Example 4 of this invention. It is a spherical aberration diagram, astigmatism diagram and distortion diagram at the time of infinity focusing at the wide-angle end of the variable magnification optical system of Example 4. It is a spherical aberration diagram, astigmatism diagram and distortion diagram at the time of infinity focusing at the intermediate focal length of the variable magnification optical system of Example 4. It is a spherical aberration diagram, astigmatism diagram and distortion diagram at the time of infinity focusing at the telephoto end of the variable magnification optical system of Example 4. It is sectional drawing which shows the lens structure example at the time of infinity focusing at the wide-angle end of the variable magnification optical system of Example 5 of this invention. It is a spherical aberration diagram, astigmatism diagram, and distortion diagram at the time of infinity focusing at the wide-angle end of the variable magnification optical system of Example 5. 5 is a spherical aberration diagram, an astigmatism diagram, and a distortion diagram at infinity focusing at an intermediate focal length of the variable magnification optical system of Example 5. It is a spherical aberration diagram, astigmatism diagram, and distortion diagram at the time of infinity focusing at the telephoto end of the variable magnification optical system of Example 5. It is sectional drawing which shows the lens structure example at the time of infinity focusing at the wide-angle end of the variable magnification optical system of Example 6 of this invention. It is a spherical aberration diagram, astigmatism diagram, and distortion diagram at the time of infinity focusing at the wide-angle end of the variable magnification optical system of Example 6. 6 is a spherical aberration diagram, an astigmatism diagram, and a distortion diagram at infinity focusing at an intermediate focal length of the variable magnification optical system of Example 6. It is a spherical aberration diagram, astigmatism diagram, and distortion diagram at the time of infinity focusing at the telephoto end of the variable magnification optical system of Example 6. It is sectional drawing which shows the lens structure example at the time of infinity focusing at the wide-angle end of the variable magnification optical system of Example 7 of this invention. It is a spherical aberration diagram, astigmatism diagram, and distortion diagram at the time of infinity focusing at the wide-angle end of the variable magnification optical system of Example 7. It is a spherical aberration diagram, astigmatism diagram, and distortion diagram at the time of infinity focusing at the intermediate focal length of the variable magnification optical system of Example 7. It is a spherical aberration diagram, astigmatism diagram, and distortion diagram at the time of infinity focusing at the telephoto end of the variable magnification optical system of Example 7.

Hereinafter, embodiments of the variable magnification optical system and the image pickup apparatus according to the present invention will be described. However, the variable magnification optical system and the imaging device described below are one aspect of the variable magnification optical system and the imaging device according to the present invention, and the variable magnification optical system and the imaging device according to the present invention are limited to the following aspects. It is not something that is done.

1. 1. Variable magnification optical system 1-1. Configuration of Variable Magnification Optical System First, an embodiment of the variable magnification optical system according to the present invention will be described. The variable magnification optical system according to the present invention includes a first lens group having a positive refractive power, a second lens group having a negative refractive power, and at least one lens group in order from the object side, and each lens group. It is a variable magnification optical system that changes the magnification by changing the interval between the two, and includes at least one plastic lens having a positive refractive power and at least one plastic lens having a negative refractive power, respectively, and the conditional expression (1) described later. ) And the condition represented by the conditional expression (2).

(1) Lens Group Configuration The variable magnification optical system includes a first lens group having a positive refractive power and a second lens group having a negative refractive power in order from the object side, and follows the second lens group. The specific lens group configuration is not particularly limited as long as it has at least one lens group and satisfies the conditions represented by the conditional expression (1) and the conditional expression (2).

For example, the number of lens groups following the second lens group may be one, or may be two or more. Increasing the number of lens groups constituting the variable magnification optical system is advantageous in achieving a high magnification ratio and high optical performance. However, when the number of lens groups constituting the variable magnification optical system is large, it becomes difficult to reduce the size, weight, and cost of the variable magnification optical system. In addition, a moving mechanism for moving the lens group along the optical axis at the time of scaling becomes complicated. Therefore, from the viewpoint of miniaturization and cost reduction by simplifying the configuration of the variable magnification optical system, the number of lens groups following the second lens group is preferably two or less, and one. Is more preferable.

That is, it is preferable that the variable magnification optical system is composed of three lens groups, that is, a first lens group, a second lens group, and a third lens group in order from the object side. In this case, the third lens group preferably has a positive refractive power. By adopting such a configuration, while maintaining sufficient optical performance, the variable magnification optical system can be made smaller and lighter, and the moving mechanism for moving the lens group can be simplified to reduce the cost. It will be easier to realize the conversion.

(2) Plastic Lens The variable magnification optical system has at least one plastic lens having a positive refractive power and at least one negative plastic lens having a negative refractive power. As long as the conditional equation (1) and the conditional equation (2) are satisfied in the variable magnification optical system, the arrangement of the plastic lens having a positive refractive power and the plastic lens having a negative refractive power in the variable magnification optical system, respectively. The number of plastic lenses and the material of each plastic lens (acrylic, polycarbonate, etc.) are not particularly limited. In order to realize a variable magnification optical system having better temperature characteristics, the number, arrangement, surface shape, etc. of the plastic lenses are preferably in the following forms.

a) Number of plastic lenses In the variable magnification optical system, the number of plastic lenses having a positive refractive power and the number of plastic lenses having a negative refractive power are one or more, and as long as the above conditions are satisfied, the number of plastic lenses is one or more. , Not particularly limited. The number of plastic lenses having a positive refractive power and the number of plastic lenses having a negative refractive power may be the same or different. Since a plastic lens is cheaper than a glass lens, it is easier to reduce the cost of the optical system when the number of plastic lenses is large. However, when the ambient temperature changes, the lens surface shape and thickness of the plastic lens change, resulting in aberration fluctuations and focal position fluctuations. Therefore, from the viewpoint of realizing an optical system having good temperature characteristics, it is preferable that the number of plastic lenses arranged in the optical system is small. Therefore, from the viewpoint of realizing an optical system having good temperature characteristics while reducing the cost, the number of plastic lenses having a positive refractive power and one plastic lens having a negative refractive power should be one each. Is more preferable.

b) Arrangement In the variable magnification optical system, the arrangement of the plastic lens having a positive refractive power and the plastic lens having a negative refractive power is not particularly limited. It may be arranged in any lens group of the first lens group, the second lens group, and other lens groups following the second lens group. Further, the arrangement of the plastic lens having a positive refractive power and the plastic lens having a negative refractive power is not particularly limited. However, in the optical system, it is preferable that the plastic lens having a positive refractive power and the plastic lens having a negative refractive power are arranged adjacent to each other in this order from the object side. If such an arrangement is adopted, the height of the axial luminous flux passing through the plastic having a negative refractive power can be lowered by the converging action of the plastic lens having a positive refractive power. Then, by strengthening the curvature of the plastic lens having a negative refractive power, that is, by arranging a large refractive power on the plastic lens having a negative refractive power, spherical aberration, coma, and curvature of field can be corrected. It becomes possible to perform better, and it becomes possible to more easily realize an optical system having good optical performance.

Here, the above-mentioned "a plastic lens having a positive refractive power and a plastic lens having a negative refractive power are arranged adjacent to each other in this order" means that the plastic lens having a positive refractive power and the negative refractive power are arranged adjacent to each other. It means that the lens is arranged between the lens and the lens of the lens without containing other lens components, and an air gap may be provided between the two plastic lenses. That is, the plastic lens having a positive refractive power and the plastic lens having a negative refractive power may be arranged in the same order via the air gap, and the plastic lens having a positive refractive power and the negative refractive power may be arranged. The plastic lenses to be held may be joined and arranged in this order without an air gap.

c) Surface shape The surface shape of the plastic lens having a positive refractive power and the plastic lens having a negative refractive power is not particularly limited, and may be spherical or aspherical. Moreover, one side thereof may be a flat surface. However, among the plastic lenses arranged in the variable magnification optical system, it is preferable that at least one of the plastic lenses has at least one aspherical surface. By arranging at least one aspherical surface in the variable magnification optical system, spherical aberration, coma aberration, and curvature of field can be satisfactorily corrected with a smaller number of lenses as compared with the case where all the surfaces are spherical. Can be done. Therefore, it becomes easier to simplify the lens configuration and reduce the cost of the variable magnification optical system while ensuring good optical performance.

Further, the aspherical surface preferably has a shape that weakens the paraxial curvature. That is, it is preferable to arrange at least one aspherical surface having a shape that weakens the paraxial curvature in the variable magnification optical system. By arranging such a surface-shaped aspherical surface in the variable magnification optical system, spherical aberration, coma aberration, and curvature of field can be better corrected. Therefore, it becomes easier to simplify the lens configuration and reduce the cost of the optical system. However, the aspherical surface that weakens the paraxial curvature means an aspherical shape in which the curvature that approximates the surface shape of the peripheral portion of the lens is smaller than the paraxial curvature.

Further, in the variable magnification optical system, it is preferable that the plastic lens having a negative refractive power is arranged after the second lens group, and the side surface of the object is concave. Here, in the variable magnification optical system, by arranging the plastic lens having a negative refractive power in the lens group after the second lens group, the focused light is emitted to the object side surface of the plastic lens having the negative refractive power. The concave surface on the object side corrects the spherical aberration over. Therefore, the over spherical aberration generated in the plastic lens having a negative refractive power in the variable magnification optical system cancels out the under spherical aberration generated in the plastic lens having a positive refractive power, and good optical performance is obtained. It will be easier to achieve. Further, the correction effect of the spherical aberration is maintained even if the ambient temperature changes, and it becomes possible to provide an optical system having better temperature characteristics.

d) Single lens In the variable magnification optical system, at least one of the above-mentioned plastic lens having a positive refractive power and the plastic lens having a negative refractive power is preferably a single lens. Here, the single lens is a lens (optical) in which one optical surface is provided on the object side and one optical surface is provided on the image side, and no other optical surface is included between the optical surface on the object side and the optical surface on the image side. Element). By making at least one of the plastic lenses arranged in the optical system a single lens, the single lens is affected by the stress applied during bonding like a bonded lens in which a plurality of lenses are bonded on an optical surface. It is possible to prevent the shape of the optical surface of the plastic lens from changing and deteriorate the optical performance, and to realize a variable magnification optical system having better optical performance. It is sufficient that at least one of the plastic lens having a positive refractive power and the plastic lens having a negative refractive power is a single lens, but the plastic lens having a positive refractive power and the negative refractive power are used. It is more preferable that both of the plastic lenses having the above are single lenses. In this case, when there are a plurality of plastic lenses having a positive refractive power, it is preferable that all of them are single lenses, and at least one of them may be a single lens. The same applies to a plastic lens having a negative refractive power.

Here, the method for manufacturing a plastic lens as the single lens is not particularly limited, and includes various lenses manufactured by polishing, molding, injection molding, or the like. In addition, a single lens means that it is composed of one lens in principle, and the single lens also includes those having various coatings such as an antireflection film and a protective film on the optical surface thereof. To do. A bonded lens in which a plurality of lenses such as a positive lens and a negative lens are adhered or adhered to each other on the optical surface without interposing an air layer, and integrated with an air layer interposed between the optical surfaces of the plurality of lenses. It is assumed that the so-called composite aspherical lens in which an aspherical surface is formed by a thin resin layer on the surface of the spherical lens is excluded.

1-2. Conditional expression Next, the conditions that the variable magnification optical system should satisfy or the conditions that are preferable to satisfy will be described.

The variable magnification optical system is characterized by satisfying the conditions represented by the following conditional expression (1) and conditional expression (2).

-5.00 <fw / f12w <-0.60 ... (1)
-2.80 <Σi (φppi × hppi) / Σj (φpnj × hpnj) <−0.35 ・ ・ ・ (2)

However,
fw: Composite focal length of the entire variable magnification optical system at the wide-angle end f12w: Composite focal length of the first lens group and the second lens group at the wide-angle end

φppi: When the plastic lens having a positive refractive power included in the variable magnification optical system is represented as Gpp1, Gpp2, ... In order from the object side, the i-th (i = 1, 2, ... The refractive power of the plastic lens Gppi having a positive refractive power of () hppi: The axial light beam at the telephoto end when the axial light beam passes through the surface of the plastic lens Gppi having a positive refractive power on the object side. Maximum height from the optical axis

φpnj: When the plastic lens having a negative refractive power included in the variable magnification optical system is represented as Gpn1, Gpn2, ... In order from the object side, the jth lens from the object side (j = 1, 2, ... The refractive power of the plastic lens Gpnj having a negative refractive power of () hpnj: The axial light beam at the telephoto end when the axial light beam passes through the surface of the plastic lens Gpnj having a negative refractive power on the object side. Maximum height from the optical axis

1-2-1. Conditional expression (1)
The conditional equation (1) is an equation that defines the ratio of the combined focal length of the entire variable magnification optical system at the wide-angle end to the combined focal length of the first lens group and the second lens group at the wide-angle end. At the same time, the conditional expression (1) shows the combined lateral magnification of the third and subsequent lens groups at the wide-angle end. The variable magnification optical system is a zoom lens, a varifocal lens, or the like that changes the magnification by changing the distance between each lens group. In order to achieve good optical performance over the entire variable magnification range, it is necessary to properly design the refractive power of each lens group, the distance between each lens group, and the lateral magnification of each lens group. By satisfying the conditional equation (1), the refractive power of each lens group, the distance between each lens group, and the lateral magnification of each lens group are within an appropriate range, and even when the magnification ratio is increased, the magnification range Good optical performance can be achieved over the entire range.

On the other hand, when the value of the conditional expression (1) exceeds the upper limit value, the combined focal length of the entire variable magnification optical system at the wide-angle end with respect to the combined focal length of the first lens group and the second lens group at the wide-angle end. The ratio of is small as an absolute value. At the same time, the combined focal lengths of the first lens group and the second lens group at the wide-angle end become longer than the appropriate range, and the combined lateral magnification of the third lens group and subsequent lens groups at the wide-angle end is appropriate. It becomes smaller than the range. As a result, when trying to realize a predetermined magnification ratio, the amount of movement of each lens group at the time of magnification change becomes large, which leads to an increase in the size of the variable magnification optical system in the overall length direction. Further, as the amount of movement of each lens group increases, the movement mechanism for moving each lens group at the time of magnification change also becomes large. Therefore, it is not desirable because the lens barrel or the like accommodating the variable magnification optical system becomes large and the cost of the entire product such as a zoom lens increases, which makes it difficult to set an appropriate price. Further, when the combined lateral magnification of the lens group after the third lens group becomes smaller than the appropriate range, the back focus is longer than that of the imaging optical system for a single-lens reflex camera or the like, or the imaging optical system for a mirrorless single-lens camera. In an imaging optical system that requires the above, it is difficult to secure an appropriate back focus, which is not desirable.

On the other hand, when the numerical value of the conditional expression (1) becomes equal to or less than the lower limit value, the ratio of the combined focal length of the entire variable magnification optical system at the wide-angle end to the combined focal length of the first lens group and the second lens group at the wide-angle end becomes It becomes large as an absolute value. At the same time, the combined focal lengths of the first lens group and the second lens group at the wide-angle end are shortened beyond the appropriate range, and the combined lateral magnification of the third lens group and subsequent lens groups at the wide-angle end is appropriate. It grows beyond the range. As a result, spherical aberration and coma aberration generated in the first lens group and the second lens group become large. Since these aberrations are magnified in the third and subsequent lens groups, it becomes difficult to correct these aberrations in the entire optical system. For example, by increasing the number of lenses constituting each lens group, it is possible to correct these aberrations and realize a variable magnification optical system having high optical performance. However, in this case, the cost becomes high, it becomes difficult to set the product price at a low price, and the variable magnification optical system becomes large, which is not desirable. Further, when the combined lateral magnification of the lens group after the third lens group becomes larger than the appropriate range, eccentric coma and eccentric curvature of field occur when the first lens group and / or the second lens group are eccentric. Is expanded. That is, since the eccentric sensitivity becomes high, it becomes difficult to secure stable optical performance when manufacturing the variable magnification optical system, which is not desirable.

In order to obtain these effects, the lower limit of the conditional expression (1) is preferably -5.00, more preferably -3.00, and even more preferably -2.00. .. Further, in the conditional expression (1), the upper limit value is preferably −0.70, more preferably −0.85, and even more preferably −1.00.

1-2-2. Conditional expression (2)
In the conditional expression (2), the denominator is the j-th (jth) from the object side when the plastic lens having a negative refractive power included in the variable magnification optical system is expressed as Gpn1, Gpn2, ... In order from the object side. The refractive power of the plastic lens Gpnj having a negative refractive power of j = 1, 2, ...) And the axial light beam at the telephoto end pass through the surface of the plastic lens Gpnj having the negative refractive power on the object side. It is multiplied by the maximum height of the on-axis light beam from the optical axis to obtain the total sum of the plastic lenses having a negative refractive power included in the variable magnification optical system.

Further, in the conditional equation (2), when the plastic lens having a positive refractive power included in the variable magnification optical system is expressed as Gpp1, Gpp2, ... In order from the object side, the molecule i from the object side. The refractive power of the second (i = 1, 2, ...) Plastic lens Gppi having a positive refractive power and the surface of the plastic lens Gppi having an axial light beam at the telephoto end on the object side have the positive refractive power. It is multiplied by the maximum height of the on-axis light beam from the optical axis when passing through, and is the sum of the plastic lenses having a positive refractive power included in the variable magnification optical system.

Therefore, the conditional equation (2) is a variation on the sum of the products of the refractive power of the plastic lens Gpnj having a negative refractive power included in the variable magnification optical system and the maximum height of the axial light beam from the optical axis. It is an equation that defines the ratio of the sum of the products of the refractive power of the plastic lens Gppi having a positive refractive power included in the magnification optical system and the height of the axial light beam from the optical axis.

Here, as compared with the glass lens, the material cost of the plastic lens is low, and the surface shape of the plastic lens is formed by injection molding, so that it is easy to obtain an aspherical lens. For these reasons, plastic lenses are known as an elemental technology for improving optical performance at a lower cost than glass lenses. On the other hand, plastic as a material has a larger coefficient of linear expansion than glass and a large change in refractive index with respect to temperature change. Therefore, it is difficult to suppress fluctuations in spherical aberration and backfocus due to changes in atmospheric temperature.

The variable magnification optical system includes at least one plastic lens having a positive refractive power and at least one plastic lens having a negative refractive power, and is an optical system that satisfies the condition represented by the conditional equation (2). As a result, fluctuations in spherical aberration and back focus when the atmospheric temperature changes are canceled out by positive and negative plastic lenses, and cost reduction is achieved while maintaining sufficient optical performance, and scaling with good temperature characteristics is achieved. It becomes possible to provide an optical system.

On the other hand, when the numerical value of the conditional expression (2) becomes equal to or larger than the upper limit value, the total sum of the plastic lens Gppi having a positive refractive power becomes smaller than the sum of the plastic lens Gpnj having a negative refractive power. .. Therefore, with respect to spherical aberration and back focus when the ambient temperature changes, these fluctuations caused by the plastic lens having a negative refractive power become too large as opposed to those fluctuations caused by the plastic lens having a positive refractive power. .. That is, the correction becomes excessive. As a result, spherical aberration and back focus exceed the appropriate values, which is not preferable.

On the other hand, when the numerical value of the conditional expression (2) is equal to or less than the lower limit value, the total sum of the plastic lens Gppi having a positive refractive power becomes larger than the sum of the plastic lens Gpnj having a negative refractive power. Therefore, with respect to spherical aberration and back focus when the ambient temperature changes, these fluctuations caused by the plastic lens having a negative refractive power become too small with respect to these fluctuations caused by the plastic lens having a positive refractive power. That is, the correction is insufficient. As a result, spherical aberration and back focus are under the appropriate values, which is not preferable.

In order to obtain these effects, the lower limit of the conditional expression (2) is preferably −2.00, more preferably -1.40, and even more preferably -1.20. .. Further, in the conditional expression (2), the upper limit value is preferably −0.40, more preferably −0.50, and even more preferably −0.60.

1-2-3. Conditional expression (3)
It is preferable that the variable magnification optical system satisfies the condition represented by the following conditional expression (3).

0.10 <f1 / ft <1.70 ... (3)
However,
f1: Combined focal length of the first lens group ft: Combined focal length of the entire variable magnification optical system at the telephoto end

Conditional expression (3) defines the ratio of the combined focal length of the first lens group to the combined focal length of the entire variable magnification optical system at the telephoto end. When the conditional expression (3) is satisfied, the ratio of the combined focal length of the first lens group to the combined focal length of the entire variable magnification optical system at the telephoto end is within an appropriate range. Since the amount of movement of each lens group at the time of magnification change becomes appropriate, it becomes easy to realize miniaturization and weight reduction of the variable magnification optical system. Further, even when the refractive power of the first lens group with respect to the entire variable magnification optical system is within an appropriate range and the magnification ratio is increased, good optical performance can be realized in the entire variable magnification range.

On the other hand, when the numerical value of the conditional expression (3) exceeds the upper limit value, the combined focal length of the first lens group becomes an appropriate range with respect to the combined focal length of the entire variable magnification optical system at the telephoto end. Beyond and get longer. As a result, when trying to realize a predetermined magnification ratio, the amount of movement of each lens group at the time of magnification increase becomes large, which leads to an increase in the size of the magnification optical system in the overall length direction. As the amount of movement of each lens group increases, the movement mechanism for moving each lens group at the time of scaling also increases. Therefore, it is not desirable because the lens barrel or the like accommodating the variable magnification optical system becomes large and the cost of the entire product such as a zoom lens increases, which makes it difficult to set an appropriate price.

On the other hand, when the numerical value of the conditional expression (3) becomes equal to or less than the lower limit value, the combined focal length of the first lens group is shorter than the appropriate range with respect to the combined focal length of the entire variable magnification optical system at the telephoto end. Become. As a result, in order to cancel the spherical aberration and coma aberration generated in the first lens group by another lens group, it is necessary to shorten the focal length of the lens groups after the second lens group. That is, since the refractive power of each lens group is increased, the aberration fluctuation becomes large when each lens group is moved at the time of magnification change. Therefore, it is necessary to increase the number of lenses constituting each lens group in order to secure sufficient optical performance in the entire variable magnification range. In that case, the cost becomes high, it becomes difficult to set the product price at a low price, and the variable magnification optical system becomes large, which is not desirable.

In order to obtain these effects, the lower limit of the conditional expression (3) is preferably 0.15, more preferably 0.20, and even more preferably 0.30. Further, in the conditional expression (3), the upper limit value is preferably 1.50, more preferably 1.10, further preferably 0.90, and further preferably 0.80. preferable.

1-2-4. Conditional expression (4)
In the variable magnification optical system, when each lens group arranged after the second lens group is represented by the nth lens group (n = 2, 3 ...), each lens group has the following conditional equation (4). It is also preferable to satisfy the condition represented by.

bnt / bnw> 0.80 ・ ・ ・ (4)
However,
bnt: Lateral magnification of the nth lens group at the telephoto end bnw: Lateral magnification of the nth lens group at the wide-angle end

The conditional equation (4) is an equation that defines the rate of change in the lateral magnification of each lens group when the magnification is changed from the wide-angle end to the telephoto end for each group after the second lens group. When each of the second and subsequent lens groups included in the variable magnification optical system, such as the second lens group and the third lens group, satisfies the above condition formula (4), the lateral magnification of each lens group is in an appropriate range. The amount of movement of each lens group at the time of magnification change can be within an appropriate range, and it becomes easier to realize good optical performance in the entire range of magnification change.

On the other hand, when the value of the conditional expression (4) becomes equal to or less than the lower limit value, the rate of change in the lateral magnification when the magnification is changed from the wide-angle end to the telephoto end of the lens group becomes smaller than the appropriate range. .. Therefore, when the magnification is changed from the wide-angle end to the telephoto end, the lens group works to shorten the focal length of the variable magnification optical system. Therefore, in order to achieve a predetermined magnification ratio, the magnification of the entire system must be increased by increasing the amount of movement of the other lens groups or increasing the refractive power of the other lens groups. In that case, it is not preferable because the size of the product is increased or the correction of spherical aberration and coma is insufficient.

In order to obtain the above effect, the variable magnification optical system more preferably satisfies the following conditional expression (4)'instead of the above conditional expression (4), and satisfies the following conditional expression (4)''. Is even more preferable.

bnt / bnw ≧ 1.00 ・ ・ ・ (4)'
bnt / bnw> 1.00 ... (4)''

2. 2. Imaging Device Next, the imaging device according to the present invention will be described. The image sensor according to the present invention converts the variable magnification optical system according to the present invention and the optical image formed by the variable magnification optical system provided on the image side of the variable magnification optical system into an electric signal. It is characterized by being provided with an image pickup element. Here, the image pickup device is not particularly limited, and a solid-state image pickup device such as a CCD sensor or a CMOS sensor can also be used. The image pickup device according to the present invention is suitable for an image pickup device using these solid-state image pickup elements such as a digital camera and a video camera. Further, the image pickup device may be a lens-fixed image pickup device in which the lens is fixed to a housing, or may be an interchangeable lens type image pickup device such as a single-lens reflex camera or a mirrorless single-lens camera. Of course.

Next, the present invention will be specifically described with reference to Examples and Comparative Examples. However, the present invention is not limited to the following examples. The optical system of each example listed below is a photographing optical system used in an imaging device (optical device) such as a digital camera, a video camera, and a silver salt film camera. Further, in the cross-sectional view of the lens (FIG. 1, FIG. 5, FIG. 9, FIG. 13, FIG. 17, FIG. 21, FIG. 25), the left side is the object side and the right side is the image side when viewed from the drawing.

(1) Configuration of Optical System FIG. 1 is a cross-sectional view of a lens showing a configuration of a variable magnification optical system according to the first embodiment of the present invention. The variable magnification optical system includes a first lens group G1 having a positive refractive power, a second lens group G2 having a negative refractive power, and a third lens group G3 having a positive refractive power in order from the object side. It is a zoom lens that changes the magnification by changing the distance between each lens group.

In FIG. 1, the lens with the reference numeral L10 is the plastic lens Gpp1 having a positive refractive power according to the present invention, and the lens with the reference numeral L11 is the plastic lens having a negative refractive power according to the present invention. It is Gpn1. "S" shown in the optical system is an aperture diaphragm, and "I" shown on the image side of the optical system is an image plane. Specifically, the image pickup surface of a solid-state image sensor such as a CCD sensor or a CMOS sensor, or , The film surface of the silver salt film, etc. are shown. The specific lens configuration of each lens group is as shown in FIG. Since these reference numerals are the same in FIGS. 5, 9, 13, 17, 17, 21, and 25 shown in Examples 2 to 7, the description thereof will be omitted below.

It should be noted that the variable magnification optical system is a vibration-proof group that corrects image blurring by moving it in a direction perpendicular to the optical axis, and moves along the optical axis when focusing from an infinity object to a short-distance object. A focus group may be provided. In this case, any of the first lens group to the third lens group shown in FIG. 1 (or a partial lens group composed of at least one lens constituting the lens group) is referred to as an anti-vibration group and a focus group. However, for example, it is preferable that the second lens group is the vibration isolation group and the first lens group is the focus group.

(2) Numerical Example Next, Numerical Example 1 to which a specific numerical value of the variable magnification optical system is applied will be described. Table 1 shows the lens data of the variable magnification optical system. In Table 1, "No." is the order of the lens surfaces counted from the object side, "R" is the radius of curvature of the lens surface, "D" is the distance on the optical axis of the lens surface, and "Nd" is the d line (wavelength). The refractive index for λ = 587.5600 nm) and “νd” indicate the Abbe number for the d line (wavelength λ = 587.600 nm). Further, the aperture diaphragm (aperture S) is indicated by adding "STOP" next to the surface number. Further, when the lens surface is aspherical, "ASPH" is added next to the surface number, the column of radius of curvature R indicates the paraxial radius of curvature, and "inf." Indicates ∞.

Table 2 shows the aspherical coefficient and the conical constant when the shape of the aspherical surface is expressed by the following equation. The aspherical surface shall be defined by the following equation.

z = ch ² / [1 + {1- (1 + k) c ² h ² } ^1/2 ] + A4h ⁴ + A6h ⁶ + A8h ⁸ + A10h ¹⁰ ...
However, c is the curvature (1 / r), h is the height from the optical axis, k is the conical coefficient, and A4, A6, A8, A10 ... Are the aspherical coefficients of each order.

Table 3 shows the F number (Fno), the half angle of view (W), and the lens spacing on the image side of each lens group (movable group) that moves at the time of magnification at each focal length (f) of the variable magnification optical system. ..

Since the matters related to these tables are the same in Tables 4 to 21 shown in Examples 2 to 7, the description thereof will be omitted below.

FIGS. 2 to 4 show longitudinal aberration diagrams at infinity focusing at the wide-angle end, intermediate focal length, and telephoto end of the variable magnification optical system, respectively. Each longitudinal aberration diagram shows spherical aberration, astigmatism, and distortion in order from the left. In the figure showing spherical aberration, the vertical axis represents the ratio to the open F value, the horizontal axis represents the defocus, the solid line represents the d line (587.5600 nm), and the broken line represents the g line (435.8400 nm). In the figure showing astigmatism, the vertical axis represents the angle of view and the horizontal axis represents the defocus, the solid line represents the sagittal direction (X) of the d line, and the broken line represents the meridional direction (Y) of the d line. In the diagram showing distortion, the vertical axis represents the angle of view and the horizontal axis represents%. The order in which these aberrations are displayed, the arrangement, and the solid lines, wavy lines, and the like in each figure are shown in Examples 2 to 7, FIGS. 6 to 8, 10 to 12, and 14 to 16. Since the same applies to FIGS. 18 to 20, FIGS. 22 to 24, and FIGS. 26 to 28, the description thereof will be omitted below.

Table 22 shows the numerical values of the conditional expressions (1) to (4) and the combined focal lengths (f1, f2, f3) of each lens group.

(1) Configuration of Optical System FIG. 5 is a cross-sectional view of a lens showing a configuration of a variable magnification optical system according to a second embodiment of the present invention. The variable magnification optical system includes a first lens group G1 having a positive refractive power, a second lens group G2 having a negative refractive power, and a third lens group G3 having a positive refractive power in order from the object side. It is a zoom lens that changes the magnification by changing the distance between each lens group. In FIG. 5, the lens with the reference numeral L10 is a plastic lens (Gpp1) having a positive refractive power according to the present invention, and the lens with the reference numeral L11 has a negative refractive power according to the present invention. It is a plastic lens Gpn1. The specific lens configuration is as shown in FIG.

The variable magnification optical system may be provided with a vibration isolation group and a focus group. In this case, any of the first lens group to the third lens group shown in FIG. 5 (or a partial lens group) can be set as the vibration isolation group or the focus group. For example, the second lens group. Is preferably the anti-vibration group and the first lens group is the focus group.

(2) Numerical Example Next, Numerical Example 2 to which a specific numerical value of the variable magnification optical system is applied will be described. Table 4 shows the lens data of the variable magnification optical system. Table 5 shows the aspherical coefficient and the conical constant for the aspherical surface. Table 6 shows the F number (Fno), the half angle of view (W), and the lens spacing on the image side of each lens group (movable group) that moves at the time of magnification change at each focal length (f) of the optical system. Further, FIGS. 5 to 8 show a longitudinal aberration diagram of the variable magnification optical system at infinity focusing. Further, Table 22 shows the numerical values of the conditional expressions (1) to (4) and the combined focal lengths (f1, f2, f3) of each lens group.

(1) Configuration of Optical System FIG. 9 is a cross-sectional view of a lens showing a configuration of a variable magnification optical system according to a third embodiment of the present invention. The variable magnification optical system includes a first lens group G1 having a positive refractive power, a second lens group G2 having a negative refractive power, and a third lens group G3 having a positive refractive power in order from the object side. It is a zoom lens that changes the magnification by changing the distance between each lens group. In FIG. 9, the lens with the reference numeral L10 is a plastic lens (Gpp1) having a positive refractive power as referred to in the present invention, and the lens with the reference numeral L11 has a negative refractive power as referred to in the present invention. It is a plastic lens Gpn1. The specific lens configuration is as shown in FIG.

The variable magnification optical system may be provided with a vibration isolation group and a focus group. In this case, any of the first lens group to the third lens group shown in FIG. 9 (or a partial lens group) can be set as the vibration isolation group or the focus group. For example, the second lens group. Is preferably the anti-vibration group and the first lens group is the focus group.

(2) Numerical Example Next, Numerical Example 3 to which a specific numerical value of the variable magnification optical system is applied will be described. Table 7 shows the lens data of the variable magnification optical system. Table 8 shows the aspherical coefficient and the conical constant for the aspherical surface. Table 9 shows the F number (Fno), the half angle of view (W), and the lens spacing on the image side of each lens group (movable group) that moves at the time of magnification change at each focal length (f) of the optical system. Further, FIGS. 10 to 12 show a longitudinal aberration diagram of the variable magnification optical system at infinity focusing. Further, Table 22 shows the numerical values of the conditional expressions (1) to (4) and the combined focal lengths (f1, f2, f3) of each lens group.

(1) Configuration of Optical System FIG. 13 is a cross-sectional view of a lens showing a configuration of a variable magnification optical system according to a fourth embodiment of the present invention. The variable magnification optical system includes a first lens group G1 having a positive refractive power, a second lens group G2 having a negative refractive power, and a third lens group G3 having a positive refractive power in order from the object side. It is a zoom lens that changes the magnification by changing the distance between each lens group. In FIG. 13, the lens with the reference numeral L11 is a plastic lens (Gpp1) having a positive refractive power as referred to in the present invention, and the lens with the reference numeral L12 has a negative refractive power as referred to in the present invention. It is a plastic lens Gpn1. The specific lens configuration is as shown in FIG.

The variable magnification optical system may be provided with a vibration isolation group and a focus group. In this case, any of the first lens group to the third lens group shown in FIG. 13 (or a partial lens group) can be set as the vibration isolation group or the focus group. For example, the second lens group. Is preferably the anti-vibration group and the first lens group is the focus group.

(2) Numerical Example Next, Numerical Example 4 to which a specific numerical value of the variable magnification optical system is applied will be described. Table 10 shows the lens data of the variable magnification optical system. Table 11 shows the aspherical coefficient and the conical constant for the aspherical surface. Table 12 shows the F number (Fno), the half angle of view (W), and the lens spacing on the image side of each lens group (movable group) that moves at the time of magnification change at each focal length (f) of the optical system. Further, FIGS. 14 to 16 show longitudinal aberration diagrams of the variable magnification optical system at infinity focusing. Further, Table 22 shows the numerical values of the conditional expressions (1) to (4) and the combined focal lengths (f1, f2, f3) of each lens group.

(1) Configuration of Optical System FIG. 17 is a cross-sectional view of a lens showing a configuration of a variable magnification optical system according to a fifth embodiment of the present invention. The variable magnification optical system includes a first lens group G1 having a positive refractive power, a second lens group G2 having a negative refractive power, and a third lens group G3 having a positive refractive power in order from the object side. This is a zoom lens composed of a fourth lens group G4 having a negative refractive power, and changing the magnification by changing the distance between the lens groups. In FIG. 17, the lens with the reference numeral L11 is a plastic lens (Gpp1) having a positive refractive power according to the present invention, and the lens with the reference numeral L12 has a negative refractive power according to the present invention. It is a plastic lens Gpn1. The specific lens configuration is as shown in FIG.

The variable magnification optical system may be provided with a vibration isolation group and a focus group. In this case, any of the first lens group to the fourth lens group shown in FIG. 17 (or a partial lens group) can be set as the vibration isolation group or the focus group. For example, the second lens group. Is preferably the anti-vibration group and the first lens group is the focus group.

(2) Numerical Example Next, Numerical Example 5 to which a specific numerical value of the variable magnification optical system is applied will be described. Table 13 shows the lens data of the variable magnification optical system. Table 14 shows the aspherical coefficient and the conical constant for the aspherical surface. Table 15 shows the F number (Fno), the half angle of view (W), and the lens spacing on the image side of each lens group (movable group) that moves at the time of magnification change at each focal length (f) of the optical system. Further, FIGS. 18 to 20 show longitudinal aberration diagrams of the variable magnification optical system at infinity focusing. Further, Table 22 shows the numerical values of the conditional expressions (1) to (4) and the combined focal lengths (f1, f2, f3, f4) of each lens group.

(1) Configuration of Optical System FIG. 21 is a cross-sectional view of a lens showing a configuration of a variable magnification optical system according to a sixth embodiment of the present invention. The variable magnification optical system includes a first lens group G1 having a positive refractive power, a second lens group G2 having a negative refractive power, and a third lens group G3 having a positive refractive power in order from the object side. It is a zoom lens that changes the magnification by changing the distance between each lens group. In FIG. 21, the lens with the reference numeral L11 is a plastic lens (Gpp1) having a positive refractive power according to the present invention, and the lens with the reference numeral L12 has the negative refractive power according to the present invention. It is a plastic lens Gpn1. The specific lens configuration is as shown in FIG.

The variable magnification optical system may be provided with a vibration isolation group and a focus group. In this case, any of the first lens group to the third lens group shown in FIG. 21 (or a partial lens group) can be set as the vibration isolation group or the focus group. For example, the second lens group. Is preferably the anti-vibration group and the first lens group is the focus group.

(2) Numerical Example Next, Numerical Example 6 to which a specific numerical value of the variable magnification optical system is applied will be described. Table 16 shows the lens data of the variable magnification optical system. Table 17 shows the aspherical coefficient and the conical constant for the aspherical surface. Table 18 shows the F number (Fno), the half angle of view (W), and the lens spacing on the image side of each lens group (movable group) that moves at the time of magnification change at each focal length (f) of the optical system. Further, FIGS. 22 to 24 show longitudinal aberration diagrams of the variable magnification optical system at infinity focusing. Further, Table 22 shows the numerical values of the conditional expressions (1) to (4) and the combined focal lengths (f1, f2, f3) of each lens group.

(1) Configuration of Optical System FIG. 25 is a cross-sectional view of a lens showing a configuration of a variable magnification optical system according to a seventh embodiment of the present invention. The variable magnification optical system includes a first lens group G1 having a positive refractive power, a second lens group G2 having a negative refractive power, and a third lens group G3 having a positive refractive power in order from the object side. This is a zoom lens composed of a fourth lens group G4 having a negative refractive power, and varying the magnification by changing the distance between the lens groups. In FIG. 25, the lens with the reference numeral L10 is a plastic lens (Gpp1) having a positive refractive power as referred to in the present invention, and the lens with the reference numeral L11 has a negative refractive power as referred to in the present invention. It is a plastic lens Gpn1. The specific lens configuration is as shown in FIG.

The variable magnification optical system may be provided with a vibration isolation group and a focus group. In this case, in this case shown in FIG. 25, any lens group (or partial lens group) among the first lens group to the fourth lens group shown in FIG. 25 can be used as the vibration isolation group and the focus group. For example, it is preferable that the partial lens group (L11) included in the fourth lens group is the vibration isolation group and the partial lens group (L10) included in the third lens group is the focus group.

(2) Numerical Example Next, Numerical Example 7 to which a specific numerical value of the variable magnification optical system is applied will be described. Table 19 shows the lens data of the variable magnification optical system. Table 20 shows the aspherical coefficient and the conical constant for the aspherical surface. Table 21 shows the F number (Fno), the half angle of view (W), and the lens spacing on the image side of each lens group (movable group) that moves at the time of magnification change at each focal length (f) of the optical system. Further, FIGS. 26 to 28 show longitudinal aberration diagrams of the variable magnification optical system at infinity focusing. Further, Table 22 shows the numerical values of the conditional expressions (1) to (4) and the combined focal lengths (f1, f2, f3, f4) of each lens group.

According to the present invention, it is possible to provide a variable magnification optical system having good temperature characteristics and an image pickup apparatus provided with the variable magnification optical system while maintaining sufficient optical performance and reducing the cost.

G1 ... 1st lens group G2 ... 2nd lens group G3 ... 3rd lens group G4 ... 4th lens group S ... Aperture diaphragm I ... Image plane

Claims (9)

A first lens group having a positive refractive power, a second lens group having a negative refractive power, and at least one lens group are provided in order from the object side, and the magnification can be changed by changing the distance between the lens groups. It is a variable magnification optical system to be performed
At least one plastic lens having a positive refractive power and one plastic lens having a negative refractive power are provided.
When each lens group arranged after the second lens group is represented by the nth lens group (n = 2, 3 ...), each lens group satisfies the conditional expression (4).
A variable magnification optical system characterized by satisfying the following conditions.
-5.00 <fw / f12w <-1.00 ... (1)
-2.80 <Σi (φppi x hppi) / Σj (φpnj x hpnj) < -0.40 ... (2)
0.10 <f1 / ft <1.70 ... (3)
bnt / bnw> 0.80 ・ ・ ・ (4)
However,
fw: Synthetic focal distance of the entire variable magnification optical system at the wide-angle end f12w: Composite focal distance of the first lens group and the second lens group at the wide-angle end φppi: Positive included in the variable magnification optical system When the plastic lens having a refractive force is represented as Gpp1, Gpp2, ... In order from the object side, the i-th (i = 1, 2, ...) Plastic lens Gppi having a positive refractive power from the object side. Refractive force hppi: Maximum height of the axial light beam from the optical axis when the axial light beam passes through the object-side surface of the plastic lens Gppi having a positive refractive force at the telephoto end φpnj: The variation When the plastic lens having a negative refractive force included in the magnification optical system is represented as Gpn1, Gpn2, ... In order from the object side, the jth (j = 1, 2, ...) Negative from the object side. Refractive force of the plastic lens Gpnj having the refractive power of Hpnj: From the optical axis of the axial light beam at the telephoto end when the axial light beam passes through the surface of the plastic lens Gpnj having the negative refractive force on the object side. Maximum height f1: Synthetic focal distance of the first lens group ft: Synthetic focal distance of the entire variable magnification optical system at the telephoto end bnt: Lateral magnification of the nth lens group at the telephoto end bnw: nth at the wide-angle end Horizontal magnification of the lens group The variable magnification optical system according to claim 1, wherein at least one of the plastic lenses having a negative refractive power has a concave surface on the object side. The variable magnification optics according to claim 1 or 2, wherein at least one of the plastic lens having a positive refractive power and the plastic lens having a negative refractive power has at least one aspherical surface. system. Claims 1 to 3 include the plastic lens having a positive refractive power and the plastic lens having a negative refractive power, wherein at least one of the plastic lenses has at least one aspherical surface that weakens the paraxial curvature. The variable magnification optical system according to any one item. The variable magnification optical system according to any one of claims 1 to 4, wherein at least one of the plastic lens having a positive refractive power and the plastic lens having a negative refractive power is a single lens. .. From claim 1, in order from the object side, one of the plastic lenses having a positive refractive power and one of the plastic lenses having a negative refractive power are arranged adjacent to each other in the order. The variable magnification optical system according to any one of claim 5. The variable magnification optical system according to any one of claims 1 to 6, further comprising one plastic lens having a positive refractive power and one plastic lens having a negative refractive power. The variable magnification optical system includes 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 in order from the object side. The variable magnification optical system according to any one of items 1 to 7. The variable magnification optical system according to any one of claims 1 to 8 and an optical image formed by the variable magnification optical system provided on the image side of the variable magnification optical system are used as electrical signals. An image pickup device including an image pickup element for conversion.

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