JP7211926B2 - Zoom lens and imaging device - Google Patents

Description

The technology of the present disclosure relates to zoom lenses and imaging devices.

2. Description of the Related Art Conventionally, zoom lenses are used in cameras for remote surveillance at borders, forests, harbors, and the like. In such applications, near-infrared light is used for nighttime photography and for photography in poor viewing conditions such as fog or smoke.

For example, lens systems disclosed in Patent Documents 1 and 2 below are known as zoom lenses that take into account near-infrared light. Patent Documents 1 and 2 disclose, in order from the object side, a first lens group having positive refractive power, a second lens group having negative refractive power, and a third lens group having positive refractive power. , and a fourth lens group having positive refractive power.

Patent No. 5438620 specification JP 2018-146855 A

Among near-infrared light, SWIR (Short Wave Infra-Red) light, which can be classified as a wavelength band of 1000 nm to 2000 nm, is highly useful. In recent years, there has been an increasing demand for lens systems in which chromatic aberration is corrected over the wavelength range from the visible range to the SWIR range. If an attempt is made to maintain other optical performances well while achieving such wideband chromatic aberration correction, the size of the lens system tends to increase. However, in recent years, there has been a strong demand for compactness of the apparatus.

The present disclosure has been made in view of the above circumstances, and a zoom lens capable of supporting a wavelength range from the visible range to the SWIR range while suppressing an increase in the size of the lens system, and capable of achieving high performance. It is an object of the present invention to provide an imaging device with a zoom lens.

A zoom lens according to an aspect of the present disclosure includes, in order from an object side to an image side, a first lens group having positive refractive power, a second lens group having negative refractive power, and a second lens group having positive refractive power. It consists of three lens groups and a fourth lens group. During zooming, the first lens group is fixed with respect to the image plane, and the second and third lens groups are adjacent lens groups. Moving along the optical axis with varying spacing, let nF be the refractive index at the F line, n1970 be the refractive index at the wavelength of 1970.09 nm, and nC be the refractive index at the C line for each lens in all the lens groups. The dispersion ratio θ is defined as θ=(nC−n1970)/(nF−nC), the average of θ of all the lenses in the second lens group is θ2ave, and the incidence at the telephoto end in a state focused on an infinite object If the pupil diameter is EPt and the maximum image height is Hh, the following conditional expressions (1) and (2) are satisfied.
1.1<θ2ave<1.7 (1)
3<EPt/(2×Hh)<10 (2)

The zoom lens of the above aspect preferably satisfies at least one of the following conditional expressions (1-1) and (2-1).
1.25<θ2ave<1.5 (1-1)
4<EPt/(2×Hh)<9 (2-1)

The zoom lens of the above aspect is
θ1ave is the average of θ of all the lenses in the first lens group,
θ1Pave is the average of θ of all the positive lenses in the first lens group,
θ1Nave is the average of θ of all the negative lenses in the first lens group,
θ2Pave is the average of θ of all the positive lenses in the second lens group,
θ2Nave is the average of θ of all the negative lenses in the second lens group,
θ3ave is the average of θ of all the lenses in the third lens group,
θ3Pave is the average of θ of all the positive lenses in the third lens group,
θ3Nave is the average of θ of all the negative lenses in the third lens group,
θ4Pave is the average of θ of all the positive lenses in the fourth lens group,
θ4Nave is the average of θ of all the negative lenses in the fourth lens group,
f1 is the focal length of the first lens group on the d-line,
f2 is the focal length of the second lens group on the d-line,
ft is the focal length of the zoom lens on the d-line at the telephoto end when focused on an object at infinity,
, it is preferable to satisfy at least one of the following conditional expressions (4) and (6) to (13).
−0.5<θ2Pave-θ2Nave<0.05 (4)
−0.7<θ4Pave−θ4Nave<0 (6)
0<θ3Pave−θ3Nave<0.8 (7)
-0.2<f2/f1<-0.1 (8)
-0.08<f2/ft<-0.03 (9)
0.3<f1/ft<0.6 (10)
1.9<θ1ave<2.15 (11)
0<θ1Pave−θ1Nave<0.2 (12)
1.4<θ3ave<2.1 (13)

Further, in the zoom lens of the above aspect, for each lens in all the lens groups, the refractive index for the d-line is nd, the refractive index for the F-line is nF, the refractive index for the C-line is nC, and the Abbe number ν is ν=( nd-1)/(nF-nC),
ν2ave is the average of ν of all the lenses in the second lens group,
ν4Pave is the average of ν of all the positive lenses in the fourth lens group,
ν4Nave is the average of ν of all the negative lenses in the fourth lens group,
, it is preferable to satisfy at least one of the following conditional expressions (3), (3-1) and (5).
20<ν2ave<45 (3)
25<ν2ave<35 (3-1)
−20<ν4Pave−ν4Nave<5 (5)

The first lens group comprises, in order from the object side to the image side, a 1a lens group having a positive refractive power including a cemented lens in which two lenses having refractive powers of opposite signs are cemented, and a positive refractive power. and a 1c lens group having positive refractive power, and only the 1b lens group may move along the optical axis during focusing. In that case, the 1b lens group preferably consists of a cemented lens in which a positive lens and a negative lens are cemented in order from the object side.

The second lens group comprises, in order from the object side to the image side, a negative lens whose surface on the image side is concave, a cemented lens in which a negative lens and a positive lens are cemented in order from the object side, and a positive lens and a negative lens. is preferably composed of a cemented lens cemented in order from the object side.

When zooming from the wide-angle end to the telephoto end, it is preferable that the second lens group and the third lens group simultaneously pass through the -1x lateral magnification point.

An imaging device according to another aspect of the present disclosure includes the zoom lens according to the above aspects of the present disclosure.

In addition, "consisting of" and "consisting of" in this specification refer to lenses that have substantially no refractive power, and lenses such as diaphragms, filters, and cover glasses, in addition to the listed components. It is intended that other optical elements, lens flanges, lens barrels, imaging elements, and mechanical parts such as image stabilization mechanisms may be included.

In the present specification, the phrase "a group having positive refractive power" means that the group as a whole has positive refractive power. Similarly, "a group having negative refractive power" means that the group as a whole has negative refractive power. A "lens having positive refractive power" and a "positive lens" are synonymous. The terms “lens having negative refractive power” and “negative lens” are synonymous. The "-lens group" is not limited to a structure consisting of a plurality of lenses, and may be a structure consisting of only one lens.

A compound aspherical lens (a lens that functions as a single aspherical lens as a whole by integrally forming a spherical lens and an aspherical film formed on the spherical lens) is not considered a cemented lens. treated as a single lens. The sign of refractive power and surface shape for lenses containing aspherical surfaces are considered in the paraxial region.

The "focal length" used in the conditional expression is the paraxial focal length. The values used in the conditional expressions, other than the partial dispersion ratio, are values when the d-line is used as a reference when an object at infinity is focused. The "d-lines," "C-lines," "F-lines," "g-lines," and "t-lines" referred to herein are emission lines. The d-line has a wavelength of 587.56 nm, the C-line has a wavelength of 656.27 nm, the F-line has a wavelength of 486.13 nm, the g-line has a wavelength of 435.83 nm, and the t-line has a wavelength of 1013.98 nm. As used herein, "near-infrared" means a wavelength band of 700 nm to 2000 nm, and "SWIR" means a wavelength band of 1000 nm to 2000 nm. "nm" used as a unit of wavelength is nanometer.

According to the technology of the present disclosure, a zoom lens capable of supporting a wavelength range from the visible range to the SWIR range while suppressing an increase in the size of the lens system, and capable of achieving high performance, and an imaging device equipped with this zoom lens Equipment can be provided.

1 is a diagram showing a cross-sectional view of a configuration of a zoom lens according to an embodiment of the present disclosure, corresponding to the zoom lens of Example 1 of the present disclosure, and a movement trajectory; FIG. 2 is a sectional view showing the configuration of the zoom lens shown in FIG. 1 and light beams; FIG. FIG. 2 is each aberration diagram of the zoom lens of Example 1 of the present disclosure; FIG. 10 is a diagram showing a cross-sectional view of a configuration of a zoom lens and a movement trajectory of Example 2 of the present disclosure; FIG. 10 is a diagram of each aberration of the zoom lens of Example 2 of the present disclosure; FIG. 10 is a diagram showing a cross-sectional view of a configuration of a zoom lens and a movement trajectory of Example 3 of the present disclosure; FIG. 10 is a diagram of each aberration of the zoom lens of Example 3 of the present disclosure; 1 is a schematic configuration diagram of an imaging device according to an embodiment of the present disclosure; FIG.

An example of an embodiment according to the technology of the present disclosure will be described below with reference to the drawings. FIG. 1 is a cross-sectional view showing a configuration at the wide-angle end of a zoom lens according to an embodiment of the present disclosure and a diagram showing a movement trajectory. FIG. 2 is a cross-sectional view showing the configuration of this zoom lens and the luminous flux. The examples shown in FIGS. 1 and 2 correspond to the zoom lens of Example 1 described later. The sectional view of FIG. 1 and FIG. 2 show a state in which an object at infinity is focused, the left side being the object side and the right side being the image side. In FIG. 2, the upper row labeled "WIDE" shows the wide-angle end state, the middle row labeled "MIDDLE" shows the intermediate focal length state, and the lower row labeled "TELE" shows the telephoto end state. In FIG. 2, the luminous fluxes are the axial luminous flux wa in the wide-angle end state and the luminous flux wb at the maximum angle of view, the axial luminous flux ma in the intermediate focal length state and the luminous flux mb at the maximum angle of view, the axial luminous flux ta in the telephoto end state and the maximum angle of view mb. A luminous flux tb at an angle of view is shown. A zoom lens according to an embodiment of the present disclosure will be described below mainly with reference to FIG.

FIG. 1 shows an example in which a parallel plate-shaped optical member PP is arranged between the zoom lens and the image plane Sim, assuming that the zoom lens is applied to an imaging apparatus. The optical member PP is a member assuming various filters and/or cover glass. Various filters include, for example, a low-pass filter, an infrared cut filter, and a filter that cuts a specific wavelength band. The optical member PP is a member having no refractive power, and a configuration in which the optical member PP is omitted is also possible.

The zoom lens has, in order from the object side to the image side along the optical axis Z, a first lens group G1 having positive refractive power, a second lens group G2 having negative refractive power, and positive refractive power. It consists of a third lens group G3 and a fourth lens group G4 having refractive power. During zooming, the first lens group G1 is fixed with respect to the image plane Sim. move along.

In a four-group zoom lens for monitoring, a type in which the third lens group G3 has negative refractive power is also conceivable. Since the incident luminous flux becomes a divergent luminous flux, the lens diameter of the fourth lens group G4 becomes large, resulting in an increase in weight. Further, when attempting to correct axial chromatic aberration from the visible region to the SWIR region, residual chromatic aberration that cannot be completely corrected by the first lens group G1 on the telephoto side poses a problem. On the telephoto side, the luminous flux entering the third lens group G3 from the second lens group G2 having negative refractive power spreads out, so the third lens group G3 plays the role of correcting this residual chromatic aberration. . At that time, the type in which the third lens group G3 has a positive refractive power compared to the type in which the third lens group G3 has a negative refractive power is easier to correct for this residual chromatic aberration, resulting in higher performance. advantageous for conversion. Further, when the third lens group G3 is of a type having a positive refractive power, the light flux incident on the fourth lens group G4 becomes a converging light beam. It becomes easy to secure a large image circle.

In the zoom lens shown in FIG. 1, the fourth lens group G4 is fixed with respect to the image plane Sim during zooming. In FIG. 1, below the second lens group G2 and the third lens group G3, the loci of movement of each lens group when zooming from the wide-angle end to the telephoto end are schematically indicated by solid-line arrows. In the diagram of the movement locus in FIG. 1, the zoom positions corresponding to the wide-angle end, intermediate focal length state, and telephoto end are indicated by "WIDE", "MIDDLE", and "TELE", respectively.

Each lens group in the example of FIG. 1 is constructed as described below. That is, the first lens group G1 is composed of nine lenses L11 to L19 in order from the object side to the image side. The second lens group G2 consists of five lenses L21 to L25 in order from the object side to the image side. The third lens group G3 consists of six lenses L31 to L36 in order from the object side to the image side. The fourth lens group G4 includes an aperture stop St. The fourth lens group G4 in the example of FIG. 1 is configured to include an aperture stop St closest to the object side. consists of The aperture stop St in FIG. 1 does not indicate the shape, but indicates the position in the optical axis direction.

Each lens group is configured to include at least one positive lens and at least one negative lens. The material of the lens is selected in consideration of the wavelength regions of the visible region and the SWIR region. In the technology of the present disclosure, the Abbe number and partial dispersion ratio are defined as follows. That is, for each lens in all the lens groups, the refractive index for the d-line is nd, the refractive index for the F-line is nF, the refractive index for the C-line is nC, the refractive index for the wavelength of 1970.09 nm is n1970, the Abbe number ν and The partial dispersion ratio θ is respectively ν = (nd-1) / (nF-nC)
θ = (nC-n1970)/(nF-nC)
defined as ν is the d-line reference Abbe number. θ is the partial dispersion ratio between the C-line and the wavelength of 1970.09 nm. The amount of secondary spectrum can be adjusted by setting the range of the parameters related to θ.

The zoom lens according to the technology of the present disclosure is configured to satisfy the following conditional expression (1), where θ2ave is the average of θ of all the lenses in the second lens group G2. Conditional expression (1) relates to the secondary spectral quantity of the second lens group G2. Satisfying conditional expression (1) facilitates well-balanced correction of chromatic aberration over the entire zoom range from the wide-angle end to the telephoto end, which is advantageous for high performance. Furthermore, if the structure satisfies the following conditional expression (1-1), better characteristics can be obtained.
1.1<θ2ave<1.7 (1)
1.25<θ2ave<1.5 (1-1)

If EPt is the diameter of the entrance pupil at the telephoto end and Hh is the maximum image height when the object is focused on at infinity, the zoom lens is configured to satisfy the following conditional expression (2). By ensuring that the lower limit of conditional expression (2) is not reached, the F-number at the telephoto end does not become too large, so that the F-number required for surveillance camera applications can be ensured. By not exceeding the upper limit of conditional expression (2), it is possible to suppress the enlargement of the lens diameter of the first lens group G1, or to easily respond to the recent demand for a large image circle. becomes. Further, if the structure satisfies the following conditional expression (2-1), better characteristics can be obtained.
3<EPt/(2×Hh)<10 (2)
4<EPt/(2×Hh)<9 (2-1)

Furthermore, the zoom lens preferably has at least one of the configurations described below. When the average of ν of all the lenses in the second lens group G2 is ν2ave, it is preferable to satisfy the following conditional expression (3). Conditional expression (3) relates to the material forming the second lens group G2. Satisfying conditional expression (3) facilitates well-balanced correction of first-order chromatic aberration over the entire zoom range from the wide-angle end to the telephoto end, which is advantageous for high performance. Further, if the structure satisfies the following conditional expression (3-1), better characteristics can be obtained.
20<ν2ave<45 (3)
25<ν2ave<35 (3-1)

If the average θ of all positive lenses in the second lens group G2 is θ2Pave, and the average θ of all negative lenses in the second lens group G2 is θ2Nave, it is preferable to satisfy the following conditional expression (4). Conditional expression (4) relates to the distribution of secondary spectral amounts between the positive lens and the negative lens in the second lens group G2. Satisfying conditional expression (4) makes it easy to correct chromatic aberration while maintaining a good balance, especially axial chromatic aberration, over the entire zoom range from the wide-angle end to the telephoto end, which is advantageous for high performance. becomes. Furthermore, if the structure satisfies the following conditional expression (4-1), better characteristics can be obtained.
−0.5<θ2Pave−θ2Nave<0.05 (4)
−0.3<θ2Pave−θ2Nave<−0.1 (4-1)

Assuming that the average ν of all the positive lenses in the fourth lens group G4 is ν4Pave, and the average ν of all the negative lenses in the fourth lens group G4 is ν4Nave, it is preferable to satisfy the following conditional expression (5). Conditional expression (5) relates to the material of the fourth lens group G4. Satisfying conditional expression (5) is advantageous for well-balanced correction of first-order chromatic aberration over the entire zoom range. By ensuring that the lower limit of conditional expression (5) is not exceeded, it is possible to prevent the imaging position of light on the long wavelength side from being excessively close to the object side, particularly on the wide-angle side. By not exceeding the upper limit of conditional expression (5), in particular, it is possible to prevent the imaging position of light on the long wavelength side from becoming excessively close to the image side on the wide-angle side. Further, if the structure satisfies the following conditional expression (5-1), better characteristics can be obtained.
−20<ν4Pave−ν4Nave<5 (5)
−15<ν4Pave-ν4Nave<0 (5-1)

If the average θ of all the positive lenses in the fourth lens group G4 is θ4Pave, and the average θ of all the negative lenses in the fourth lens group G4 is θ4Nave, it is preferable to satisfy the following conditional expression (6). Conditional expression (6) relates to the distribution of secondary spectral amounts between the positive lens and the negative lens in the fourth lens group G4. By satisfying conditional expression (6), it becomes easy to correct chromatic aberration while maintaining a good balance over the entire zoom range from the wide-angle end to the telephoto end, and it is particularly easy to optimize the balance of chromatic aberration on the wide-angle end. Therefore, it is advantageous for high performance. Further, if the structure satisfies the following conditional expression (6-1), better characteristics can be obtained.
−0.7<θ4Pave−θ4Nave<0 (6)
−0.55<θ4Pave−θ4Nave<−0.12 (6-1)

If the average θ of all the positive lenses in the third lens group G3 is θ3Pave, and the average θ of all the negative lenses in the third lens group G3 is θ3Nave, it is preferable to satisfy the following conditional expression (7). Conditional expression (7) relates to the distribution of secondary spectral amounts between the positive lens and the negative lens in the third lens group G3. Satisfying conditional expression (7) facilitates well-balanced correction of chromatic aberration over the entire zoom range, which is advantageous for high performance. Furthermore, if the structure satisfies the following conditional expression (7-1), better characteristics can be obtained.
0<θ3Pave−θ3Nave<0.8 (7)
0.05<θ3Pave−θ3Nave<0.7 (7-1)

Assuming that the focal length of the first lens group G1 on the d-line is f1, and the focal length of the second lens group G2 on the d-line is f2, it is preferable to satisfy the following conditional expression (8). Since the refractive power of the first lens group G1 does not become too strong by ensuring that the conditional expression (8) does not fall below the lower limit, the off-axis principal ray incident on the second lens group G2 from the object side and the optical axis Z It is possible to suppress an excessive increase in the angle formed with the . This facilitates correction of distortion and chromatic aberration of magnification at the wide-angle end. By not exceeding the upper limit of conditional expression (8), the refracting power of the second lens group G2 does not become too strong, making it easy to suppress fluctuations in various aberrations during zooming. Further, if the structure satisfies the following conditional expression (8-1), better characteristics can be obtained.
-0.2<f2/f1<-0.1 (8)
-0.15<f2/f1<-0.11 (8-1)

If f2 is the focal length of the second lens group G2 for the d-line, and ft is the focal length of the zoom lens for the d-line at the telephoto end focused on an infinite object, then the following conditional expression (9) is satisfied: is preferred. If the lower limit of conditional expression (9) is not exceeded, the refractive power of the second lens group G2 will not become too weak. Since the amount can be suppressed, it is possible to suppress the lengthening of the total optical length, which is advantageous for achieving miniaturization. By not exceeding the upper limit of conditional expression (9), the refracting power of the second lens group G2 does not become too strong, thus facilitating correction of various aberrations, especially chromatic aberration of magnification on the wide-angle side. Furthermore, if the structure satisfies the following conditional expression (9-1), better characteristics can be obtained.
-0.08<f2/ft<-0.03 (9)
-0.07<f2/ft<-0.04 (9-1)

If f1 is the focal length of the first lens group G1 for the d-line, and ft is the focal length of the zoom lens for the d-line at the telephoto end focused on an infinite object, the following conditional expression (10) is satisfied. is preferred. By ensuring that the lower limit of conditional expression (10) is not reached, the positive refractive power of the first lens group G1 does not become too strong, making it easy to widen the angle of view at the wide-angle end. By not exceeding the upper limit of conditional expression (10), it becomes easy to give the first lens group G1 a strong positive refractive power, which is advantageous for shortening the total optical length. Further, if the structure satisfies the following conditional expression (10-1), better characteristics can be obtained.
0.3<f1/ft<0.6 (10)
0.35<f1/ft<0.55 (10-1)

When the average θ of all the lenses in the first lens group G1 is θ1ave, it is preferable to satisfy the following conditional expression (11). Abiding by the lower limit of conditional expression (11) facilitates the correction of first-order axial chromatic aberration from the visible range to the SWIR range. By not exceeding the upper limit of conditional expression (11), it becomes easy to correct secondary axial chromatic aberration from the visible range to the SWIR range. Further, if the structure satisfies the following conditional expression (11-1), better characteristics can be obtained.
1.9<θ1ave<2.15 (11)
1.95<θ1ave<2.1 (11-1)

If the average θ of all the positive lenses in the first lens group G1 is θ1Pave, and the average θ of all the negative lenses in the first lens group G1 is θ1Nave, it is preferable to satisfy the following conditional expression (12). Conditional expression (12) relates to the distribution of secondary spectral amounts between the positive lens and the negative lens in the first lens group G1. Satisfying conditional expression (12) makes it easy to correct chromatic aberration while maintaining a good balance, especially secondary longitudinal chromatic aberration, over the entire zoom range from the wide-angle end to the telephoto end, resulting in high performance. advantageous for conversion. Furthermore, if the structure satisfies the following conditional expression (12-1), better characteristics can be obtained.
0<θ1Pave−θ1Nave<0.2 (12)
0.005<θ1Pave−θ1Nave<0.17 (12-1)

When the average of θ of all the lenses in the third lens group G3 is θ3ave, it is preferable to satisfy the following conditional expression (13). Abiding by the lower limit of conditional expression (13) facilitates the correction of first-order axial chromatic aberration from the visible range to the SWIR range. By not exceeding the upper limit of conditional expression (13), it becomes easy to correct secondary axial chromatic aberration from the visible range to the SWIR range. Further, if the structure satisfies the following conditional expression (13-1), better characteristics can be obtained.
1.4<θ3ave<2.1 (13)
1.5<θ3ave<2 (13-1)

The first lens group G1 may be composed of three lens groups having positive refractive power. The first lens group G1 in FIG. 1 has, in order from the object side to the image side, a 1a lens group G1a having positive refractive power, a 1b lens group G1b having positive refractive power, and a positive refractive power. The 1c lens group G1c and the 1a lens group G1a include a cemented lens in which two lenses having refractive powers of opposite signs are cemented together. A cemented lens in which two lenses having refractive powers of opposite signs are cemented together may be a cemented lens in which a negative lens and a positive lens are cemented in order from the object side, and a positive lens and a negative lens are cemented in order from the object side. A cemented cemented lens may be used. By configuring the first lens group G1 as described above, the degree of freedom in aberration correction is increased, and it becomes easy to correct aberrations on the telephoto side, which are difficult to correct in a long focal length lens system, in a well-balanced manner. It is advantageous to realize a high-performance optical system that can handle a wide wavelength band up to a wavelength range.

In the example of FIG. 1, only the 1b lens group G1b is configured to move during focusing. In general, the first lens group G1, which is the lens group closest to the object side, has a large lens diameter and is heavy. Therefore, by constructing the lens group that moves during focusing (hereinafter referred to as the focus lens group) to consist only of the 1b lens group G1b, compared to the structure in which the focus lens group consists of the entire first lens group, , which is advantageous for rapid focusing, which is important in surveillance applications. The leftward arrow under the 1b lens group G1b in FIG. 1 indicates that the 1b lens group G1b is a focus lens group that moves toward the object side when focusing from an infinity object to a close object.

When the first lens group G1 is composed of the above three lens groups having positive refractive power, and the focus lens group is the 1b lens group G1b, the 1b lens group G1b has a positive lens and a negative lens on the object side. It preferably consists of a cemented lens cemented in order from . In this case, it is advantageous to suppress variations in chromatic aberration during focusing. In the example of FIG. 1, the 1ath lens group G1a consists of lenses L11 to L14, the 1bth lens group G1b consists of lenses L15 to L16, and the 1cth lens group G1c consists of lenses L17 to L19.

However, the example of FIG. 1 is only an example, and the focus lens group may be the 1ath lens group G1a, the 1cth lens group G1c, or the entire first lens group. Alternatively, the first lens group G1 may be provided with a plurality of focus lens groups, and a floating focus system configuration may be employed in which the plurality of focus lens groups are moved while changing the distance between them during focusing.

The second lens group G2 includes, in order from the object side to the image side, a negative lens having a concave surface on the image side, a cemented lens in which a negative lens and a positive lens are cemented in order from the object side, and a positive lens and a negative lens. and a cemented lens that are cemented in order from the object side. In this case, it becomes easy to satisfactorily correct each aberration over the entire zoom range, and in particular it becomes easy to correct astigmatism at intermediate focal lengths, axial chromatic aberration and lateral chromatic aberration at the telephoto end. .

It is preferable that the second lens group G2 and the third lens group G3 simultaneously pass through a point where their lateral magnifications are -1 when zooming from the wide-angle end to the telephoto end. In this case, the third lens group G3 can act not only on the correction of the image plane position but also on the zooming itself. It becomes a magnification, and since it becomes an enlargement magnification on the telephoto side, it is possible to increase the magnification. In the movement locus diagram of FIG. 1, the point at which the lateral magnification of the second lens group G2 and the third lens group G3 becomes -1 is indicated by "β=-1".

The fourth lens group G4 may be configured to include an anti-vibration group that corrects image blur by moving in a direction intersecting the optical axis Z. Further, the fourth lens group G4 may be configured such that an extender lens group for changing the focal length of the entire system to the long focal length side is detachably arranged. The fourth lens group G4 may be configured such that various filters such as an ND (Neutral Density) filter or a bandpass filter can be inserted.

Either surface of the zoom lens may be an aspherical surface in order to improve the degree of design freedom and correct aberrations. The aspheric surface may be formed by grinding or molding. A compound aspherical lens may also be used as the lens having an aspherical surface.

In order to correct chromatic aberration, one of the lens groups of the zoom lens may be configured to have a gradient index lens such as a diffractive optical element (Diffractive Optical Element) or a GRIN lens (Gradient Index Lens). .

In order to maintain transmittance over a wide wavelength range, the zoom lens may be provided with an antireflection coating. The antireflection film may suppress reflection in all wavelength ranges used, or may suppress reflection only in selected wavelength ranges. The anti-reflection film may be a special coat that is configured to suppress reflection by forming a nano-level structure on the lens surface in a moth-eye shape.

The preferred and possible configurations described above, including the configuration relating to the conditional expression, can be combined arbitrarily, and are preferably selectively employed as appropriate according to required specifications. According to the zoom lens of the present disclosure, it is possible to cope with the wavelength range from the visible range to the SWIR range while suppressing an increase in the size of the lens system, and it is possible to achieve high performance.

SWIR light can penetrate fog, haze, smoke, etc., which are detrimental to long-range surveillance. Further, imaging with SWIR light, unlike thermal sensing using far-infrared rays, captures photon reflection in the same way as with visible light, so a high-contrast image can be obtained. For these reasons, the zoom lens of the present disclosure, which is compatible with the SWIR wavelength range, is highly useful.

Next, examples of the zoom lens of the present disclosure will be described.
[Example 1]
A cross-sectional view of the configuration of the zoom lens of Example 1 is shown in FIG. 1, and the method of illustration is as described above, so redundant description is partially omitted here. The zoom lens of Example 1 comprises, in order from the object side to the image side, a first lens group G1 having positive refractive power, a second lens group G2 having negative refractive power, and a third lens group G2 having positive refractive power. It consists of a lens group G3 and a fourth lens group G4 having a negative refractive power. During zooming, the first lens group G1 and the fourth lens group G4 are fixed with respect to the image plane Sim, and the second lens group G2 and the third lens group G3 change the distance between them so that they are aligned with the optical axis Z. move along. The first lens group G1 includes, in order from the object side to the image side, a 1a lens group G1a having positive refractive power, a 1b lens group G1b having positive refractive power, and a 1c lens having positive refractive power. and the group G1c. During focusing from an infinity object to a close object, only the 1b lens group G1b moves toward the object side, and the other lens groups are fixed with respect to the image plane Sim. The 1ath lens group G1a consists of lenses L11 to L14, the 1bth lens group G1b consists of lenses L15 to L16, and the 1cth lens group G1c consists of lenses L17 to L19. The second lens group G2 consists of lenses L21 to L25. The third lens group G3 consists of lenses L31 to L36. The fourth lens group G4 consists of an aperture stop St and lenses L41 to L52 in order from the object side to the image side. The above is the outline of the zoom lens of the first embodiment.

Basic lens data of the zoom lens of Example 1 are shown in Tables 1A and 1B, specifications and variable surface spacing are shown in Table 2, and aspheric coefficients are shown in Table 3. Here, the basic lens data are divided into two tables, Table 1A and Table 1B, and displayed in order to avoid making one table too long. Table 1A shows the first lens group G1 to the third lens group G3, and Table 1B shows the fourth lens group G4 and the optical member PP.

In Tables 1A and 1B, the column of Sn shows the surface number when the surface closest to the object side is the first surface and the number is increased by one toward the image side, and the column of R shows the surface number of each surface. The radius of curvature is shown, and the column D shows the distance between each surface and the surface adjacent to the image side on the optical axis. The nd column shows the refractive index for the d-line of each component, the ν column shows the d-line reference Abbe number of each component, and the material column shows the material name of each component. All materials shown in Tables 1A and 1B are manufactured by Ohara Corporation.

In Tables 1A and 1B, the sign of the radius of curvature of the surface with the convex surface facing the object side is positive, and the sign of the radius of curvature of the surface with the convex surface facing the image side is negative. In Table 1A, the symbol DD [ ] is used for the variable surface distance during zooming. In Table 1B, the surface number and the phrase (St) are described in the surface number column of the surface corresponding to the aperture stop St. The value in the bottom column of D in Table 1B is the distance between the surface closest to the image side in the table and the image plane Sim.

In the upper row of Table 2, zoom magnification Zr, focal length f, F number FNo. , the maximum total angle of view 2ω, and the variable surface distance during zooming. (°) in the column of 2ω means that the unit is degree. In the upper part of Table 2, the values of the wide-angle end state, the intermediate focal length state, and the telephoto end state are shown in columns labeled WIDE, MIDDLE, and TELE, respectively. The lower part of Table 2 shows the total optical length (the distance on the optical axis from the lens surface closest to the object side to the image plane Sim) TL, the back focus Bf in air conversion distance, the focal length f1 of the first lens group G1, and the second lens. The focal length f2 of the group G2, the focal length f3 of the third lens group G3, and the focal length f4 of the fourth lens group G4 are indicated. Tables 1A, 1B, and 2 show data with the d-line as the reference, with an infinite object in focus.

In the basic lens data, the surface numbers of the aspherical surfaces are marked with an asterisk (*), and the paraxial radius of curvature is described in the column for the radius of curvature of the aspherical surfaces. In Table 3, the Sn column indicates the surface number of the aspherical surface, and the KA and Am (m=3, 4, 5, . . "E±n" (n: integer) in the numerical values of the aspheric coefficients in Table 3 means "×10 ^±n ". KA and Am are aspherical coefficients in the aspherical formula given below.
Zd=C×h ² /{1+(1−KA×C ² ×h ² ) ^1/2 }+ΣAm×h ^m
however,
Zd: Depth of aspherical surface (length of the perpendicular drawn from a point on the aspherical surface with height h to a plane perpendicular to the optical axis where the aspherical vertex is in contact)
h: height (distance from optical axis to lens surface)
C: Reciprocal of paraxial radius of curvature KA, Am: Aspherical surface coefficient, Σ in the aspherical expression means the summation with respect to m.

In the data in each table, degrees are used as units of angles and mm (millimeters) are used as units of length. Units can also be used. Also, in each table shown below, numerical values rounded to predetermined digits are described.

FIG. 3 shows aberration diagrams of the zoom lens of Example 1 when the object at infinity is focused. FIG. 3 shows spherical aberration, astigmatism, distortion, and chromatic aberration of magnification in order from the left. In FIG. 3, the upper row labeled “WIDE” shows the aberrations at the wide-angle end, the middle row labeled “MIDDLE” shows the aberrations at the intermediate focal length state, and the lower row labeled “TELE” shows the aberrations at the telephoto end. show. In spherical aberration diagrams, aberrations at d-line, C-line, F-line, g-line, t-line, wavelengths of 1530 nm and 1970 nm are represented by a solid line, a long dashed line, a short dashed line, a thin long dashed line, a dotted line, a thick short dashed line, and a two-dot chain line. In the astigmatism diagrams, the solid line indicates the aberration along the d-line in the sagittal direction, and the long dashed line indicates the aberration along the d-line in the tangential direction. In the distortion diagrams, the solid line indicates the aberration at the d-line. In the diagram of chromatic aberration of magnification, aberrations at the C-line, F-line, g-line, t-line, wavelength 1530 nm, and wavelength 1970 nm are indicated by a long dashed line, a short dashed line, a thin long-dotted line, a dotted line, a thick dashed-dotted line, and a two-dotted dashed line, respectively. show. FNo. in the spherical aberration diagram. means the F-number, and ω in other aberration diagrams means the half angle of view.

Unless otherwise specified, the symbol, meaning, description method, and illustration method of each data relating to Example 1 above are the same in the following Examples, and therefore duplicate descriptions will be omitted below.

[Example 2]
FIG. 4 shows the configuration and movement locus of the zoom lens of Example 2. As shown in FIG. The zoom lens of Example 2 has the same configuration as the zoom lens of Example 1, except that the third lens group G3 consists of eight lenses L31 to L38. For the zoom lens of Example 2, basic lens data are shown in Tables 4A and 4B, specifications and variable surface spacing are shown in Table 5, aspheric coefficients are shown in Table 6, and aberration diagrams are shown in FIG. All materials shown in Tables 4A and 4B are manufactured by OHARA Co., Ltd., except for CAF2.

[Example 3]
FIG. 6 shows the configuration and movement locus of the zoom lens of Example 3. In FIG. The zoom lens of Example 3 is the same as the zoom lens of Example 1 except that the fourth lens group G4 has a positive refractive power and the third lens group G3 consists of eight lenses L31 to L38. It has the same configuration as the outline. For the zoom lens of Example 3, basic lens data are shown in Tables 7A and 7B, specifications and variable surface spacing are shown in Table 8, aspheric coefficients are shown in Table 9, and aberration diagrams are shown in FIG. All materials shown in Tables 7A and 7B are manufactured by Ohara Corporation.

Table 10 shows the corresponding values of the conditional expressions (1) to (13) of the zoom lenses of Examples 1 to 3.

As can be seen from the above data, in the zoom lenses of Examples 1 to 3, an increase in the size of the lens system is suppressed, and various aberrations are well corrected over a wide wavelength range from the visible region to the SWIR region. and achieves high optical performance. In addition, the zoom lenses of Examples 1 to 3 have an F number of 7.4 or less at the telephoto end, ensuring a useful F number value as a long focal length lens system for monitoring purposes.

Next, an imaging device according to an embodiment of the present disclosure will be described. FIG. 8 shows a schematic configuration diagram of an imaging device 100 using the zoom lens 1 according to the embodiment of the present disclosure as an example of the imaging device of the embodiment of the present disclosure. Examples of the imaging device 100 include surveillance cameras, broadcast cameras, motion picture cameras, video cameras, and digital cameras.

The imaging device 100 includes a zoom lens 1 , a filter 2 arranged on the image side of the zoom lens 1 , and an imaging element 3 arranged on the image side of the filter 2 . Note that FIG. 8 schematically illustrates a plurality of lenses included in the zoom lens 1 .

The imaging element 3 converts an optical image formed by the zoom lens 1 into an electric signal, and may be, for example, a CCD (Charge Coupled Device) or a CMOS (Complementary Metal Oxide Semiconductor). The imaging element 3 is arranged so that its imaging plane coincides with the image plane of the zoom lens 1 .

The image capturing apparatus 100 also includes a signal processing unit 5 that performs arithmetic processing on the output signal from the image sensor 3, a display unit 6 that displays an image formed by the signal processing unit 5, and a zoom lens 1 that controls zooming. A magnification control unit 7 and a focus control unit 8 for controlling focus of the zoom lens 1 are provided.

Although only one imaging element 3 is shown in FIG. 8, the imaging apparatus 100 may be configured to include a plurality of imaging elements. The imaging device 100 may be configured such that a spectral prism and/or a dichroic mirror are inserted anywhere on the optical axis of the optical system, and light is split according to wavelength and captured by separate imaging devices. good.

Although the technology of the present disclosure has been described above with reference to the embodiments and examples, the technology of the present disclosure is not limited to the above-described embodiments and examples, and various modifications are possible. For example, the curvature radius, surface spacing, refractive index, Abbe number, partial dispersion ratio, etc. of each lens are not limited to the values shown in the above embodiments, and may take other values.

The zoom magnification is also not limited to the values in the above example. The technique of the present disclosure can also be applied to a zoom lens with a higher or lower magnification than the above embodiments. The aberration diagrams of the above examples show the range from the g-line (wavelength 435.83 nm) to the wavelength 1970 nm, but the technology of the present disclosure is not limited to this wavelength range, and the zoom lens with the wavelength range expanded or reduced It is also applicable to

The imaging apparatus according to the embodiments of the present disclosure is not limited to cameras compatible with the visible range and the SWIR range, and the technology of the present disclosure includes cameras for the visible range, cameras for the SWIR range, multispectral cameras, hyperspectral cameras, It can also be applied to a thermography camera or the like.

1 zoom lens 2 filter 3 image sensor 5 signal processing unit 6 display unit 7 zoom control unit 8 focus control unit 100 imaging device G1 1st lens group G1a 1a lens group G1b 1b lens group G1c 1c lens group G2 2nd lens group G3 3rd lens group G4 4th lens group L11-L19, L21-L25, L31-L38, L41-L52 Lenses ma, ta, wa On-axis light beams mb, tb, wb Maximum angle of view light beams PP Optical members Sim Image plane St Aperture stop Z Optical axis

Claims (18)

From the object side to the image side, from the first lens group having positive refractive power, the second lens group having negative refractive power, the third lens group having positive refractive power, and the fourth lens group become,
During zooming, the first lens group is fixed with respect to the image plane, and the second lens group and the third lens group are moved along the optical axis by changing the distance between adjacent lens groups. move and
The first lens group comprises, in order from the object side to the image side, a 1a lens group having positive refractive power including a cemented lens in which two lenses having refractive powers of opposite signs are cemented, and a positive lens. Consists of a 1b lens group having a positive refractive power composed of a cemented lens in which a negative lens is cemented in order from the object side, and a 1c lens group having a positive refractive power,
Only the 1b lens group moves along the optical axis during focusing,
For each lens in all the lens groups, nF is the refractive index at the F line, n1970 is the refractive index at the wavelength of 1970.09 nm, nC is the refractive index at the C line, and the partial dispersion ratio θ is θ = (nC - n1970) / ( nF-nC),
θ2ave is the average of θ of all the lenses in the second lens group,
EPt is the diameter of the entrance pupil at the telephoto end when the object is focused at infinity,
When the maximum image height is Hh,
1.1<θ2ave<1.7 (1)
3<EPt/(2×Hh)<10 (2)
A zoom lens that satisfies conditional expressions (1) and (2) expressed by: For each lens in all lens groups, let nd be the refractive index at the d-line, and define the Abbe number ν as ν=(nd−1)/(nF−nC),
When the average of ν of all the lenses in the second lens group is ν2ave,
20<ν2ave<45 (3)
2. The zoom lens according to claim 1, which satisfies conditional expression (3) represented by: θ2Pave is the average of θ of all the positive lenses in the second lens group,
When the average of θ of all the negative lenses in the second lens group is θ2Nave,
−0.5<θ2Pave-θ2Nave<0.05 (4)
3. The zoom lens according to claim 1, which satisfies conditional expression (4) represented by: For each lens in all lens groups, let nd be the refractive index at the d-line, and define the Abbe number ν as ν=(nd−1)/(nF−nC),
ν4Pave is the average of ν of all the positive lenses in the fourth lens group,
When the average of ν of all the negative lenses in the fourth lens group is ν4Nave,
−20<ν4Pave−ν4Nave<5 (5)
4. The zoom lens according to any one of claims 1 to 3, which satisfies conditional expression (5) represented by: θ4Pave is the average of θ of all the positive lenses in the fourth lens group,
When the average of θ of all the negative lenses in the fourth lens group is θ4Nave,
−0.7<θ4Pave−θ4Nave<0 (6)
5. The zoom lens according to any one of claims 1 to 4, which satisfies conditional expression (6) represented by: θ3Pave is the average of θ of all the positive lenses in the third lens group;
When the average of θ of all the negative lenses in the third lens group is θ3Nave,
0<θ3Pave−θ3Nave<0.8 (7)
6. The zoom lens according to any one of claims 1 to 5, which satisfies conditional expression (7) represented by: f1 is the focal length of the first lens group on the d-line,
When the focal length of the second lens group in the d-line is f2,
-0.2<f2/f1<-0.1 (8)
7. The zoom lens according to any one of claims 1 to 6, which satisfies conditional expression (8) represented by: The second lens group includes, in order from the object side to the image side, a negative lens having a concave surface on the image side, a cemented lens in which a negative lens and a positive lens are cemented in order from the object side, and a positive lens and a negative lens. 8. The zoom lens according to any one of claims 1 to 7 , comprising a cemented lens in which and are cemented in order from the object side. f2 is the focal length of the second lens group on the d-line,
When the focal length of the zoom lens for the d-line at the telephoto end when focused on an infinite object is ft,
-0.08<f2/ft<-0.03 (9)
9. The zoom lens according to any one of claims 1 to 8 , which satisfies conditional expression (9) represented by: f1 is the focal length of the first lens group on the d-line,
When the focal length of the zoom lens for the d-line at the telephoto end when focused on an infinite object is ft,
0.3<f1/ft<0.6 (10)
10. The zoom lens according to any one of claims 1 to 9 , which satisfies conditional expression (10) represented by: When the average of θ of all the lenses in the first lens group is θ1ave,
1.9<θ1ave<2.15 (11)
11. The zoom lens according to any one of claims 1 to 10 , which satisfies conditional expression (11) represented by: θ1Pave is the average of θ of all the positive lenses in the first lens group,
When the average of θ of all the negative lenses in the first lens group is θ1Nave,
0<θ1Pave−θ1Nave<0.2 (12)
12. The zoom lens according to any one of claims 1 to 11 , which satisfies conditional expression (12) represented by: When the average of θ of all the lenses in the third lens group is θ3ave,
1.4<θ3ave<2.1 (13)
13. The zoom lens according to any one of claims 1 to 12 , which satisfies conditional expression (13) represented by: 14. The lens according to any one of claims 1 to 13 , wherein when zooming from the wide-angle end to the telephoto end, the second lens group and the third lens group simultaneously pass through a point of -1x lateral magnification. Specified zoom lens. 1.25<θ2ave<1.5 (1-1)
2. A zoom lens according to claim 1, which satisfies conditional expression (1-1) expressed by: 4<EPt/(2×Hh)<9 (2-1)
2. The zoom lens according to claim 1, which satisfies conditional expression (2-1) expressed by: 25<ν2ave<35 (3-1)
3. The zoom lens according to claim 2, which satisfies conditional expression (3-1) expressed by: An imaging device comprising the zoom lens according to any one of claims 1 to 17 .

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