JP2018036460A - Variable power optical system, camera, and inspection device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a novel variable power optical system comprising first to third lens groups having positive, negative, and positive or negative refractive power, respectively, and configured to vary power by changing inter-lens group distances, and to provide a camera and inspection device.SOLUTION: A variable power optical system is formed by arranging a first lens group G1 having positive refractive power, an aperture stop S, a second lens group G2 having negative refractive power, and a third lens group G3 having positive or negative refractive power in order from an object side to an image side. When varying power from a low magnification end to a high magnification end, at least the first lens group G1, the aperture stop S, and the second lens group G2 move in an optical axis direction. When varying power from the low magnification end to the high magnification end, the first lens group G1 simply moves integrally with the aperture stop S and the second lens group G2 moves to increase a distance to the first lens group G1. A distance D from a rear principal point position of the first lens group G1 to the aperture stop S, and a focal length f1 of the first lens group satisfy following conditional expression: 0.8<D/f1<1.2 ...(1).SELECTED DRAWING: Figure 1

Description

  The present invention relates to a variable magnification optical system, a camera, and an inspection apparatus.

There is known a variable power optical system that has first to third lens groups having positive, negative, and positive refractive powers, and performs zooming by changing the lens group interval (Patent Document 1, 2).
In the variable magnification optical system disclosed in Patent Document 1, the combined rear focal point of the first lens unit and the second lens unit is substantially matched with the front focal point of the third lens unit. In the variable magnification optical system disclosed in Patent Document 2, an aperture stop is disposed on the enlargement side of the first lens group.

  An object of the present invention is to realize a novel variable power optical system that has first to third lens units having positive, negative, and positive refractive powers and performs zooming by changing the lens group interval.

The zoom optical system according to the present invention includes, in order from the object side to the image side, a first lens group having a positive refractive power, an aperture stop, a second lens group having a negative refractive power, and a positive or negative refractive power. A third lens group having at least the first lens group, the aperture stop, and the second lens group move in the optical axis direction upon zooming from the low magnification end to the high magnification end. When zooming from the low magnification end to the high magnification end, the first lens group moves monotonously to the object side integrally with the aperture stop, and the second lens group is spaced from the first lens group. The distance from the rear principal point position of the first lens group to the aperture stop: D, and the focal length of the first lens group: f1 are the following conditional expressions:
(1) 0.8 <D / f1 <1.2
Satisfied.

  According to the present invention, it is possible to realize a novel variable power optical system that has first to third lens groups having positive, negative, and positive refractive powers and performs zooming by changing the lens group interval.

2 is an optical arrangement diagram of a variable magnification optical system according to Numerical Example 1. FIG. 6 is an optical arrangement diagram of a variable magnification optical system according to Numerical Example 2. FIG. 10 is an optical arrangement diagram of a variable magnification optical system according to Numerical Example 3. FIG. 10 is an optical arrangement diagram of a variable magnification optical system according to Numerical Example 4. FIG. FIG. 6 is an aberration curve diagram at a magnification of −3.5 × of the zoom optical system of Numerical Example 1. FIG. 6 is an aberration curve diagram when the zooming optical system of Numerical Example 1 has an imaging magnification of −4.0. FIG. 5 is an aberration curve diagram when the zooming optical system of Numerical Example 1 has an imaging magnification of −4.5. FIG. 6 is an aberration curve diagram when the zooming optical system of Numerical Example 2 has an imaging magnification of −3.5. FIG. 6 is an aberration curve diagram when the zooming optical system of Numerical Example 2 has an imaging magnification of −4.0. FIG. 6 is an aberration curve diagram when the zooming optical system of Numerical Example 2 has an imaging magnification of −4.5. FIG. 6 is an aberration curve diagram when the zooming optical system of Numerical Example 3 has an imaging magnification of −1.75. FIG. 6 is an aberration curve diagram at an imaging magnification of −2.0 × of the variable magnification optical system of Numerical Example 3. FIG. 10 is an aberration curve diagram when the zooming optical system of the numerical value example 3 is formed at an imaging magnification of −2.25. FIG. 12 is an aberration curve diagram when the zooming optical system of the numerical value example 4 has an imaging magnification of −1.25. FIG. 10 is an aberration curve diagram at a magnification of −1.5 × of the zoom optical system of Numerical Example 4. It is an aberration curve figure in imaging magnification: -1.75 times of the variable magnification optical system of Numerical Example 4. It is a figure for demonstrating one Embodiment of a camera. It is a figure for demonstrating the system of a camera. It is a figure for demonstrating one Embodiment of an inspection apparatus.

As described above, in the variable magnification optical system of the present invention, the first to third lens groups are arranged in order from the object side to the image side, and an aperture stop is provided between the first lens group and the second lens group. It is arranged.
The first lens group has a positive refractive power, and the second lens group has a negative refractive power. The third lens group can have a positive refractive power or a negative refractive power.
The zooming is performed by moving at least the first lens group and the second lens group of the first to third lens groups in the optical axis direction. At the time of zooming, the first lens unit and the aperture stop move “integrally” in the optical axis direction. That is, at the time of zooming from the low magnification end to the high magnification end, the first lens unit and the aperture stop integrally “monotonically move” toward the object side.
The second lens group moves so that the “interval with the first lens group increases” upon zooming from the low magnification end to the high magnification end. That is, the second lens group can be “increased the distance from the first lens group” by displacing to the image side during zooming from the low magnification end to the high magnification end. While increasing the distance from the group, it can be displaced toward the object side.
The third lens group can be moved during zooming or can be fixed during zooming.

The distance from the rear principal point position of one lens unit to the aperture stop: D, the focal length of the first lens unit: f1 is a conditional expression:
(1) 0.8 <D / f1 <1.2
Satisfied.
As described above, since the first lens unit and the aperture stop move “integrally” during zooming, the parameter D / f1 of conditional expression (1) is unchanged during zooming.
When the conditional expression (1) is satisfied, the image-side focal point of the first lens unit having positive refractive power is in the vicinity of the aperture position of the aperture stop on the optical axis. That is, the variable magnification optical system that satisfies the conditional expression (1) has “high telecentricity (telecentricity) on the object side”.
Conditional expression (1) parameter: As D / f1 increases (decreases), the incident direction of off-axis rays changes in a direction away (approaching) from the optical axis, and outside the range of conditional expression (1) “A sufficiently high object-side telecentricity” cannot be realized.
The parameter of the conditional expression (1): D / f1 is more preferably the following conditional expression (1A)
(1A) 0.9 <D / f1 <1.1
Good to be satisfied.
As described above, the first lens unit and the aperture stop are displaced together during zooming, and the relative positional relationship between the two companies remains unchanged, so the parameter D / f1 does not change regardless of the zoom magnification. . Therefore, the variable magnification optical system that satisfies the conditional expression (1) or (1A) has high object-side telecentricity regardless of the “magnification magnification” from the low magnification end to the high magnification end.

The third lens group is preferably fixed when zooming from the low magnification end to the high magnification end.
If the “third lens group moves” during zooming, the “degree of freedom for aberration correction” of the zoom optical system increases. Accordingly, higher aberration correction can be realized by moving the third lens during zooming.
However, as shown in the examples described later, various aberrations can be sufficiently corrected even if the third lens unit is fixed during zooming. Thus, if the third lens group is fixed and zooming is performed, the zooming mechanism is simplified, and the zooming optical system can be miniaturized.

In the above configuration, the variable magnification optical system of the present invention preferably satisfies any one or more of the following conditional expressions (2) to (4) together with the conditional expression (1).
(2) −1.5 <f1 / f2 <−0.3
(3) -0.9 <f1 / f3 <0.9
(4) 0.5 <D1 / Dsum <0.9
The meanings of symbols in the parameters of these conditional expressions are as follows.
“F1” is the focal length of the first lens group.
“F2” is the focal length of the second lens group.
“F3” is the focal length of the third lens group.
“D1” is the thickness of the first lens unit on the optical axis.
“Dsum” is a sum of thicknesses on the optical axes of the first lens group, the second lens group, and the third lens group.
Conditional expression (2) defines a preferable range of the ratio of the focal lengths of the first lens group and the second lens group.
When the parameter of the conditional expression (2): f1 / f2 becomes large (small), the focal length: f1 of the first lens group becomes relatively long (short), or the focal length: f2 of the second lens group becomes relative Becomes shorter (longer).
When the focal length f1 of the first lens group becomes relatively longer than the focal length f2 of the second lens group, the amount of movement of the second lens group during zooming from the low magnification end to the high magnification end increases. To do.
When the upper limit value of conditional expression (2) is exceeded, the amount of displacement of the second lens group necessary for zooming from the low magnification end to the high magnification end becomes excessive, and the zooming optical system tends to be enlarged. Alternatively, the focal length of the second lens group becomes long, the absolute value of the negative refractive power of the second lens group becomes too small, and correction of aberrations in the first lens group tends to be difficult.
When the lower limit value of conditional expression (2) is exceeded, the focal length f2 of the second lens group is shortened and the absolute value of the negative refractive power becomes excessive, ensuring high performance from the low magnification end to the high magnification end. It tends to be difficult.
By satisfying conditional expression (2), it is possible to ensure higher performance from the low magnification end to the high magnification end.

Conditional expression (3) defines a preferable range of the ratio between the focal length of the first lens group: f1 and the focal length of the third lens group: f3.
The parameter f1 / f3 in conditional expression (3) straddles the positive and negative regions. That is, the refractive power of the third lens group may be positive or negative.
When the upper limit value of conditional expression (3) is exceeded, the “positive focal length” of the third lens group becomes short, the positive refractive power of the third lens group becomes excessive, and various aberrations are corrected while correcting “image”. It is likely to be difficult to reduce the “incident angle to”.
When the lower limit of conditional expression (3) is exceeded, the negative focal length of the third lens group becomes short, the negative refractive power becomes excessive, and the “incident angle to the image” is reduced while correcting various aberrations. It tends to be difficult.
By satisfying conditional expression (3), it is possible to ensure higher performance from the low magnification end to the high magnification end.

Conditional expression (4) indicates that the thickness on the optical axis of the first lens group: D1 is the sum of the thicknesses on the optical axes of the one lens group, the second lens group, and the third lens group: the public benefit for Dsum Range is specified.
The first lens group in the variable magnification optical system of the present invention is mainly responsible for the image forming action of the variable magnification optical system. Therefore, the first lens group is sufficient on the optical axis as compared with the second lens group and the third lens group. Thickness (hereinafter also referred to as “space”) ”.
When the parameter: D1 / Dsum increases, the space of the first lens group increases in the variable magnification optical system, and the space of the second lens group and the third lens group decreases relatively.
When the upper limit value of conditional expression (4) is exceeded, the space of the second lens group and the third lens group becomes too small, and it is difficult to correct aberrations in the second lens group and the third lens group.
When the lower limit of conditional expression (4) is exceeded, the space in the first lens group becomes too small, and aberration correction in the first lens group tends to be difficult.
When the conditional expression (4) is satisfied, the first to third lens units can have an appropriate space, and it is easy to realize high performance and downsizing of the variable magnification optical system.

In the first lens group, correction of axial chromatic aberration is important because the axial marginal ray passes through a high position.
When the variable magnification optical system satisfies one or more of the above-described conditional expression (1) or conditional expression (1) and conditional expressions (2) to (4), “correction of monochromatic chromatic aberration and correction of axial chromatic aberration In order to make it possible to easily make “a”, at least one positive lens included in the first lens group is composed of “a glass type having anomalous dispersion” that satisfies the following conditional expressions (5) to (7): It is preferable to do.

_{(5) 1.45 <n d <} 1.65
(6) 60.0 <ν _d <100.0
(7) 0.010 <P _{g, F} − (− 0.001802 × ν _d +0.6483) <0.050
In the conditional expression (5), “n _d ” is the refractive index of the d-line of the glass material, “ν _d ” is the Abbe number, and “P _{g, F} ” is the partial dispersion ratio.

In order to prevent the third lens group having a positive or negative refractive power from having a large space while providing an aberration correction function, the third lens group is constituted by two lenses, a negative lens and a positive lens. Is preferred.
In this way, in the variable magnification optical system having the “third lens group composed of two lenses of the positive lens and the negative lens”, conditional expression (1) or conditional expression (1) and conditional expressions (2) to (4) It is preferable that the following conditional expression (8) is satisfied together with any one or more of:
(8) −2.0 <f31 / f32 <−0.5
In the parameter: f31 / f32, “f31” is the focal length of the negative lens of the two lenses, and “f32” is the focal length of the positive lens.
When the upper limit value of conditional expression (8) is exceeded, the focal length of the negative lens in the two positive and negative lenses constituting the third lens group becomes short, the absolute value of the negative refractive power of the negative lens becomes excessive, It is likely to be difficult to correct aberrations satisfactorily with a positive lens constituting the three lens group.
When the lower limit of conditional expression (8) is exceeded, the focal length of the negative lens in the third lens group becomes long, and aberration correction by the positive lens in the third lens group tends to be excessive.
By satisfying conditional expression (8), it is possible to correct the aberration generated in the negative lens of the third lens group with the positive lens of the third lens group, and to realize good aberration correction in the third lens group.
By satisfying conditional expression (8), it becomes possible to correct each aberration satisfactorily while suppressing an increase in the incident angle to the image.

The second lens group is preferably composed of “a cemented lens of a negative lens and a positive lens in order from the object side”.
The variable magnification optical system according to the present invention can be configured with “spherical lens only” as in the embodiments described later, and can be realized at low cost, but of course, an aspherical lens may be used.
When photographing an “object of a finite distance” with the variable magnification optical system of the present invention, if the object needs to be illuminated, a “prism-type beam splitter” is disposed on the object side of the third lens group. The incident light can be incident on the beam splitter to perform coaxial epi-illumination.

1 to 4 show four embodiments of the variable magnification optical system. These variable magnification optical systems according to the four embodiments correspond to numerical examples 1 to 4 described later in this order.
1 to 4, the upper diagram shows the optical arrangement at the “low magnification end”, the lower diagram shows the optical arrangement at the “high magnification end”, and the interruption diagram shows the optical arrangement at the “intermediate magnification”. . In these figures, the left side of the figure is the object side, and the right side is the image side.
In order to avoid complications, common reference numerals are used in FIGS.
1 to 4, “G1” represents a first lens group, “G2” represents a second lens group, “G3” represents a third lens group, and “S” represents an aperture stop.
Reference numerals for lenses constituting each lens group are determined as follows. That is, in the lenses constituting the i-th lens group (i = 1 to 3), the lens located at the jth position from the object side is denoted by reference symbol Lij.
The first lens group is constituted by eleven lenses L11 to L111 in the embodiment shown in FIG. 1 and FIG. 2, and is constituted by six lenses L11 to L16 in the embodiment shown in FIG. 3 and FIG. Has been.
In the embodiment shown in FIGS. 1 to 4, the second lens group G2 includes two lenses L21 and L22, and the third lens group G3 includes two lenses L31 and L32.

  The lenses L21 and L22 constituting the second lens group G2 are joined to form a “joint lens” in the embodiments shown in FIGS.

In FIG. 1 to FIG. 4, the symbol Im indicates an “image plane”.
Each variable power optical system of these embodiments is assumed to “capture an image formed with an image sensor”, and in FIGS. 1 to 4, a symbol CG indicates “a cover glass of the image sensor”.
The cover glass CG has a “parallel plate shape”, and the light receiving surface of the image sensor matches the image plane Im.

The cover glass CG has a function of shielding and protecting the light receiving surface of the image sensor, but can also have various filter functions such as an infrared cut filter.
The imaging optical system whose embodiments are shown in FIGS. 1 to 4 is, in order from the object side to the image side, a first lens group G1 having a positive refractive power, an aperture stop S, and a second lens having a negative refractive power. A lens group G2 and a third lens group G3 having positive or negative refractive power are arranged, and at the time of zooming from the low magnification end to the high magnification end, at least the first lens group G1, the aperture stop S, the first The two lens group G2 moves in the optical axis direction.
When zooming from the low magnification end to the high magnification end, the first lens group G1 moves monotonously to the object side integrally with the aperture stop S, and the distance between the second lens group G2 and the first lens group G1 increases. To move.
The distance from the rear principal point position of the first lens group G1 to the aperture stop: D, the focal length of the first lens group G1: f1, are conditional expressions:
(1) 0.8 <D / f1 <1.2
Satisfied.
In each embodiment, zooming from “low magnification end to high magnification end” is performed mainly by “monotonic movement of the first lens group G1 toward the object side”, but the second lens group G2 is also supplementarily described above. Contributes to scaling.
Also, in the variable magnification optical system whose embodiments are shown in FIGS. 1 to 4, the third lens group G3 is fixed when changing the magnification from the low magnification end to the high magnification end.
The third lens group G3 includes a negative lens L31 and a positive lens L32. The second lens group G2 is a cemented lens in which the negative lens L21 and the positive lens L22 are arranged in this order from the object side and cemented. is there.

Prior to describing specific numerical examples of the variable magnification optical system, a “camera” and an “inspection apparatus” using the variable magnification optical system lens of the present invention will be described.
As shown in FIG. 10, the system configuration of the camera shown in FIG. 9 includes a photographic lens 1 as a “magnification variable optical system” and a light receiving element 13 as an “imaging device”. An image of the object is captured by the light receiving element 13.
The output from the light receiving element 13 is processed by the signal processing device 14 under the control of the central processing unit 11 and converted into digital information.
The image converted into digital information is displayed on the liquid crystal monitor 7 and stored in the semiconductor memory 15 or used for communication to the outside by the communication card 16. As a simpler configuration of the “camera”, one configured by “a portion excluding the communication function” can be cited.
As the photographic lens 1, the zoom optical system according to any one of claims 1 to 9 can be used as appropriate.
The “monitored image” can be displayed on the liquid crystal monitor 7 or an image recorded in the semiconductor memory 15 can be displayed.

  When the shutter button 4 is depressed, shooting is performed, and thereafter the above processing is performed.

When an image recorded in the semiconductor memory 15 is displayed on the liquid crystal monitor 7 or transmitted to the outside using the communication card 16 or the like, the operation button 8 is operated. The semiconductor memory 15 and the communication card 16 are inserted into dedicated or general-purpose slots 9 for use.
The photographing lens 1 is in the “collapsed state” as shown in FIG. 17A when the camera is carried, and the lens barrel is extended from the housing 5 when the power is turned on by operating the power switch 6 (FIG. 17B). It is. When the photographing lens 1 is in the “collapsed state”, the lens groups of the imaging lens do not necessarily have to be arranged on the optical axis. For example, if the second lens group is retracted from the optical axis and is “stored in parallel with the first lens group”, the camera can be made thinner.

  In the imaging lenses of Examples 1 to 4, since the first lens group G1 has a larger “group thickness” than the second lens group G2, it is more “retracted” that the first lens group G1 is retracted from the optical axis. Greater contribution to “thinning”.

The camera shown in FIGS. 9 and 10 has an image sensor (light receiving element 13) that captures an image by the photographing lens 1 that is a variable power optical system.
Since this camera has a “communication function” as described above, it also has a function as a so-called “portable information terminal device”.

Hereinafter, an embodiment of the “inspection apparatus” will be described with reference to FIG.
The inspection apparatus described below is an inspection apparatus for performing so-called “product inspection”.
There may be various inspections and inspection items in the product inspection, but for the sake of simplicity, an example will be described in which “inspection for presence / absence” of a product manufactured by a large number is manufactured.
In FIG. 11A, reference numeral 20 indicates an “imaging unit”, reference numeral 23 indicates an “inspection process execution unit”, and reference numeral 24 indicates a “display unit”. Reference sign W indicates “a product to be inspected (hereinafter referred to as“ work ””), and reference numeral 26 indicates a “product transport belt (hereinafter simply referred to as“ transport belt 26 ”)”.
The imaging unit 20 is a camera function unit in the inspection apparatus, and includes a photographing optical system 21 and an image processing unit 22.
The workpieces W to be inspected are placed on the transport belt 26 at equal intervals, and are transported at a constant speed by the transport belt 26 in the direction of the arrow (to the right in the figure).
The imaging optical system 21 forms an image of the workpiece W. The variable magnification optical system according to any one of claims 1 to 9, specifically, numerical examples 1 to 4 described later. Any variable magnification optical system can be used. Therefore, hereinafter, the photographing optical system 21 is referred to as a variable magnification optical system 21.

The product inspection is performed over each of the “preparation process”, “inspection process”, and “result display process” shown in FIG. Among these processes, “inspection process and result display process” is “inspection process”.
In the “preparation process”, inspection conditions are set.
That is, depending on the size and shape of the work W conveyed by the conveying belt 26, the site to be inspected for the presence or absence of scratches, and the like, the photographing position and photographing position of the variable magnification optical system 21 (the direction of the imaging lens and the photographing object) Distance, that is, object distance).
Then, the position of the zoom optical system 21 is set according to the position and size of the “scratch” whose presence or absence is to be detected, and the photographing magnification is set by the zoom function of the zoom optical system.

On the other hand, a “model product that has been confirmed to be free from scratches” is placed at the inspection position on the conveyor belt 26 and is photographed by the variable magnification optical system 21.
Shooting is performed by imaging with an imaging device arranged in the image processing unit 22, and an image captured by the imaging device is converted into “image information” and image processing is performed to convert it into digital data.

The image-processed digital data is sent to the inspection process execution unit 23, and the inspection process execution unit 23 stores the digital data as “model data”.
In the “inspection process”, the workpiece W is placed in the “same state as the model product” on the conveyor belt 26 and is sequentially conveyed by the conveyor belt 26. When each conveyed workpiece W passes through the “inspection position”, photographing by the variable magnification optical system 21 is performed, converted into digital data by the image processing unit 22, and sent to the inspection process execution unit 23.
The inspection process execution unit 23 is configured as a “computer or CPU”, controls the image processing unit 22, and controls “photographing and focusing” of the imaging lens 21 via the image processing unit 22.

Upon receiving the “image data of the workpiece W” converted into digital data by the image processing unit 22, the inspection process execution unit 23 performs matching between the image data and the stored model data.
If the photographed workpiece W has “scratches”, the image data and the model data do not match. In this case, the product is determined to be “defective”.
If the workpiece W is not scratched, the image data of the product and the model data match, and in this case, it is determined that the product is “good”.
The “result display step” is a step of displaying the determination result of “good product, defective product” of each product by the inspection process execution unit 23 on the display unit 24.
In the configuration of the apparatus, the inspection process execution unit 23 and the display unit 24 constitute “inspection process execution means”.

Note that the variable magnification optical system 21 used as the photographing optical system is suitable as an imaging optical system for inspection because it has high telecentricity on the object side. The variable magnification optical system has a variable magnification function, and the object side telecentricity does not vary due to the variable magnification. Therefore, for example, when there is a “part that is suspected of being a defect” in the work W, an enlarged image of the work W can be obtained using the scaling function, and the part can be inspected in detail. Is possible.
In the variable power optical systems of the following specific numerical examples 1 to 4, the conjugate length, which is the distance between the object and the image, does not change regardless of the magnification at the time of zooming. The zooming can be performed during the inspection while maintaining the imaging distance between the zooming optical system and the workpiece.

"Numerical examples of variable magnification optical system"
Hereinafter, four specific numerical examples of the variable magnification optical system will be given.
Numerical Examples 1 to 4 correspond to the variable power optical system depicted in FIGS. 1 to 4 in this order, and an image of an object by the variable power optical system is picked up by an image pickup device.
As described above, the symbol CG on the object side of the image plane Im matched with the light receiving surface of the image pickup device is used to cover the cover glass of the image pickup device and various filters (such as an optical low-pass filter and an infrared cut filter), and is equivalent to these. It is shown as a parallel plate. In each of the following numerical examples, this transparent parallel plate is displayed as “filter or the like”.

The meanings of the symbols in the numerical examples are as follows.
f: Focal length of the entire system
F: F number
ω: Half angle of view (degrees)
R: radius of curvature
D: Surface spacing
N: Refractive index with respect to d-line (“n _d ” in the above description)
ν: Abbe number for d-line (“ν _d ” in the above explanation)
φ: Effective beam diameter
NA: Numerical aperture
A: Distance between the aperture stop and the most object side surface of the second lens unit
B: Distance between the most image side surface of the second lens unit and the most object side surface of the third lens unit
The unit of “amount having a dimension of length” is “mm” unless otherwise specified.
In each of the variable magnification optical systems of Numerical Examples 1 to 4, the first lens is set so that the conjugate length (distance on the optical axis between the object and the image plane) is constant from the low magnification end to the high magnification end. The displacement of the group G1 and the displacement of the second lens group are adjusted to each other.

"Numerical example 1"
Numerical Example 1 is a specific numerical example of the variable magnification optical system shown in FIG.
The data of Numerical Example 1 is shown in Table 1. The leftmost column in Table 1 is the surface number (surface number) counted from the object side, and includes “aperture stop surface”. The same applies to the other numerical examples described below.

`` Interval change ''
Table 2 shows the values of intervals A and B at the low magnification end (3.5 times), the intermediate magnification (4.0 times), and the high magnification end (4.5 times).

“Focal distance: f and object-side numerical aperture: NA”
Table 3 shows values at a low magnification end (3.5 times), an intermediate magnification (4.0 times), and a high magnification end (4.5 times) of focal length: f and object side numerical aperture: NA.

"Parameter values for conditional expressions"
Table 4 shows values of parameters according to the conditional expression.

In Table 4, L4, L6, L9, and L10 represent positive lenses L14, L16, L19, and L10 in the first lens group G1 shown in FIG.
The conjugate length in Numerical Example 1 is 215 mm regardless of the magnification.

“Numerical Example 2”
Numerical Example 2 is a specific numerical example of the variable magnification optical system shown in FIG.
Data of Numerical Example 2 are shown in Table 5.

`` Interval change ''
Table 6 shows the values of intervals A and B at the low magnification end (3.5 times), the intermediate magnification (4.0 times), and the high magnification end (4.5 times).

“Focal distance: f and object-side numerical aperture: NA”
Table 7 shows values of the focal length: f and the object-side numerical aperture: NA at the low magnification end (3.5 times), the intermediate magnification (4.0 times), and the high magnification end (4.5 times).

"Parameter values for conditional expressions"
Table 8 shows values of parameters according to the conditional expression.

  In Table 8, L4, L6, L9, and L10 represent positive lenses L14, L16, L19, and L10 in the first lens group G1 shown in FIG.

  The conjugate length in Numerical Example 2 is 207.5 mm regardless of the magnification.

“Numerical Example 3”
Numerical Example 3 is a specific numerical example of the variable magnification optical system shown in FIG.
Data of Numerical Example 3 are shown in Table 9.

`` Interval change ''
Table 10 shows the values of intervals A and B at the low magnification end (1.75 times), the intermediate magnification (2.0 times), and the high magnification end (2.25 times).

“Focal distance: f and object-side numerical aperture: NA”
Table 11 shows values of the focal length: f and the object-side numerical aperture: NA at the low magnification end (1.75 times), the intermediate magnification (2.0 times), and the high magnification end (2.25 times).

"Parameter values for conditional expressions"
Table 12 shows values of parameters according to the conditional expression.

In Table 12, L2 and L5 represent positive lenses L12 and L15 in the first lens group G1 shown in FIG.
The conjugate length in Numerical Example 3 is 265 mm regardless of the magnification.

“Numerical Example 4”
Numerical Example 4 is a specific numerical example of the variable magnification optical system shown in FIG.
Data of Numerical Example 4 are shown in Table 13.

`` Interval change ''
Table 14 shows the values of intervals A and B at the low magnification end (1.25 times), the intermediate magnification (1.5 times), and the high magnification end (1.75 times).

“Focal distance: f and object-side numerical aperture: NA”
Table 15 shows values of the focal length: f and the object-side numerical aperture: NA at the low magnification end (1.25 times), the intermediate magnification (1.5 times), and the high magnification end (1.75 times).

"Parameter values for conditional expressions"
Table 16 shows values of parameters according to the conditional expression.

In Table 16, L2 and L5 represent positive lenses L12 and L15 in the first lens group G1 shown in FIG.
The conjugate length of Numerical Example 4 is 265 mm regardless of the magnification.

  FIGS. 5A, 5B, and 5C are aberration curve diagrams of the variable magnification optical system of Numerical Example 1. FIG.

(A) is an aberration curve diagram at a magnification of -3.5 times, (b) is an aberration curve diagram at a magnification of -4.0 times, and (c) is an aberration curve diagram at a magnification of -4.5 times. The conjugate length is 215 mm at each magnification.
6A, 6B, and 6C are aberration curve diagrams of the variable magnification optical system of Numerical Example 2. FIG.

(A) is an aberration curve diagram at a magnification of -3.5 times, (b) is an aberration curve diagram at a magnification of -4.0 times, and (c) is an aberration curve diagram at a magnification of -4.5 times. The conjugate length is 207.5 mm at each magnification described above.
FIGS. 7A, 7B, and 7C are aberration curve diagrams of the variable magnification optical system according to Numerical Example 3. FIG.

(A) is an aberration curve diagram at magnification: -1.75 times, (b) is an aberration curve diagram at magnification: -2.0 times, and (c) is an aberration curve diagram at magnification: -2.25 times. The conjugate length is 265 mm at each magnification.
8A, 8B, and 8C are aberration curve diagrams of the variable magnification optical system of Numerical Example 4. FIG.

(A) is an aberration curve diagram at a magnification of -1.25 times, (b) is an aberration curve diagram at a magnification of -1.5 times, and (c) is an aberration curve diagram at a magnification of -1.75 times. The conjugate length is 215 mm at each magnification.
In these aberration diagrams, the broken line in the spherical aberration diagram represents the sine condition, the solid line in the astigmatism diagram represents the sagittal, and the broken line represents the meridional. The aberration curve by the thin line is for the “d line”, and the aberration curve by the thick line is for the “g line”.

  Further, “Y ′” in the diagrams of astigmatism and distortion is the maximum image height determined by the imaging region on the light receiving surface of the imaging device, and is 5.5 mm in each of Numerical Examples 1 to 4.

In each numerical example, the aberration is corrected at a high level, and the spherical aberration and the longitudinal chromatic aberration are so small as not to cause a problem. Astigmatism, curvature of field, and lateral chromatic aberration are sufficiently small, coma and disturbance of the color difference are well suppressed to the outermost periphery, and distortion is about 0.5% in absolute value.
That is, according to the present invention, as shown in Numerical Examples 1 to 4, it has a resolving power corresponding to an image pickup device having 5 million pixels or more, and can display a point image from the aperture stop to the periphery of the angle of view with high contrast. It is possible to describe a straight line as a straight line without distortion, and to realize a small and high-performance variable magnification optical system while ensuring a certain conjugate length and a photographing magnification of 1x or more.

  Each numerical example has high object-side telecentricity, and the object-side numerical aperture NA is constant regardless of the magnification.

  As described above, according to the present invention, the following variable magnification optical system, camera, and inspection apparatus can be realized.

[1]
In order from the object side to the image side, a first lens group (G1) having a positive refractive power, an aperture stop (S), a second lens group (G2) having a negative refractive power, and a positive or negative refractive power A third lens group (G3) having at least the first lens group (G1), the aperture stop (S), and the second lens upon zooming from the low magnification end to the high magnification end. When the lens group (G2) moves in the optical axis direction and changes the magnification from the low magnification end to the high magnification end, the first lens group (G1) moves integrally with the aperture stop (S) toward the object side. Monotonically moving, the second lens group (G2) moves so that the distance from the first lens group (G1) increases, and the distance from the rear principal point position of the first lens group to the aperture stop: D, the focal length f1 of the first lens group is the following conditional expression:
(1) 0.8 <D / f1 <1.2
Zoom optical system satisfying the above (Numerical Examples 1 to 4).

[2]
[1] The variable magnification optical system according to [1], wherein the third lens group (G3) is fixed when changing magnification from the low magnification end to the high magnification end (Numerical Examples 1 to 4). .

[3]
In the variable magnification optical system according to [1] or [2], a focal length: f1 of the first lens group (G1) and a focal length: f2 of the second lens group are the following conditional expressions:
(2) −1.5 <f1 / f2 <−0.3
Zoom optical system satisfying the above (Numerical Examples 1 to 4).

[4]
[1]-[3] The variable power optical system according to any one of [1] to [3], wherein a focal length: f1 of the first lens group (G1) and a focal length: f3 of the third lens group are as follows: Conditional expression:
(3) -0.9 <f1 / f3 <0.9
Zoom optical system satisfying the above (Numerical Examples 1 to 4).

[5]
The variable power optical system according to any one of [1] to [4], wherein the first lens group (G1) has a thickness D1 on the optical axis, the first lens group (G1), The sum of the thickness on the optical axis of each of the second lens group (G2) and the third lens group (G3): Dsum is the following conditional expression:
(4) 0.5 <D1 / Dsum <0.9
Zoom optical system satisfying the above (Numerical Examples 1 to 4).

[6]
[1]-[5] A variable power optical system according to any one of [5], wherein a refractive index: n _d , an Abbe number: ν _d , and a partial dispersion ratio: P _{g, F} have the following conditional expressions:
_{(5) 1.45 <n d <} 1.65
(6) 60.0 <ν _d <100.0
(7) 0.010 <P _{g, F} − (− 0.001802 × ν _d +0.6483) <0.050
A zoom optical system (Numerical Examples 1 to 4) in which at least one positive lens included in the first lens group (G1) is formed of a lens material satisfying the above.

[7]
[1]-[6] The variable power optical system according to any one of [6], wherein the third lens group (G3) includes a negative lens and a positive lens, and the focal length of the negative lens is f31, The focal length of the positive lens: f32 is the following conditional expression:
(8) −2.0 <f31 / f32 <−0.5
Zoom optical system satisfying the above (Numerical Examples 1 to 4).

[8]
In the variable power optical system according to any one of [1] to [7], the second lens group (G2) includes a negative lens (L21) and a positive lens (L22) from the object side. A variable magnification optical system (Numerical Examples 1 to 4) which is a cemented lens arranged in order.

[9]
The variable power optical system according to any one of [1] to [8], wherein a conjugate length is kept constant when zooming from the low magnification end to the high magnification end ( Numerical Examples 1-4).

[10]
[1] to [9] A camera having the zoom optical system according to any one of [9] as a photographing optical system (FIGS. 9 and 10).
[10]
An inspection apparatus (FIG. 11) having the zoom optical system according to any one of [1] to [9] as a photographing optical system of the camera function unit (20).

The preferred embodiments of the present invention have been described above. However, the present invention is not limited to the specific embodiments described above, and the invention described in the claims unless otherwise specified in the above description. Various modifications and changes are possible within the scope of the above.
The effects described in the embodiments of the present invention are merely a list of suitable effects resulting from the invention, and the effects of the present invention are not limited to those described in the embodiments.

The camera of the present invention is not limited to a digital camera, and is mainly a camera device dedicated to imaging, such as a video camera mainly for moving image shooting, a silver salt camera using a silver salt film, and a surveillance camera device. In addition, a variable magnification optical system as in Numerical Examples 1 to 4 can be used. In the variable magnification optical systems of Numerical Examples 1 to 4, the conjugate length is fixed, so that the camera of the present invention can be used for in-vehicle use and used for state inspection of the traveling road surface. A “stereo camera device or compound eye camera device” can also be configured.
Furthermore, the camera can be used as a camera function unit of various information devices (portable information terminal devices) including mobile phone devices, mobile terminal devices such as so-called smartphones and tablet terminals.

G1 first lens group
G2 second lens group
S Aperture stop
G3 Third lens group

Japanese Patent No. 2731481 JP-A-62-237415

Claims (11)

In order from the object side to the image side, a first lens group having a positive refractive power, an aperture stop, a second lens group having a negative refractive power, and a third lens group having a positive or negative refractive power are arranged. And
At the time of zooming from the low magnification end to the high magnification end, at least the first lens group, the aperture stop, and the second lens group move in the optical axis direction,
When zooming from the low magnification end to the high magnification end, the first lens group moves monotonically to the object side integrally with the aperture stop, and the second lens group is spaced from the first lens group. Move to increase,
The distance from the rear principal point position of the first lens group to the aperture stop: D, and the focal length f1 of the first lens group are the following conditional expressions:
(1) 0.8 <D / f1 <1.2
Variable magnification optical system that satisfies The variable magnification optical system according to claim 1,
A zoom optical system in which the third lens unit is fixed when zooming from the low magnification end to the high magnification end. The variable magnification optical system according to claim 1 or 2,
The focal length f1 of the first lens group and the focal length f2 of the second lens group are the following conditional expressions:
(2) −1.5 <f1 / f2 <−0.3
Variable magnification optical system that satisfies A variable magnification optical system according to any one of claims 1 to 3,
The focal length: f1 of the first lens group and the focal length: f3 of the third lens group are the following conditional expressions:
(3) -0.9 <f1 / f3 <0.9
Variable magnification optical system that satisfies The variable magnification optical system according to any one of claims 1 to 4,
Thickness on the optical axis of the first lens group: D1, and the sum of thicknesses on the optical axis of the first lens group, the second lens group, and the third lens group: Dsum is the following conditional expression:
(4) 0.5 <D1 / Dsum <0.9
Variable magnification optical system that satisfies A variable magnification optical system according to any one of claims 1 to 5,
Refractive index: n _d , Abbe number: ν _d , partial dispersion ratio: P _{g, F} is the following conditional expression:
_{(5) 1.45 <n d <} 1.65
(6) 60.0 <ν _d <100.0
(7) 0.010 <P _{g, F} − (− 0.001802 × ν _d +0.6483) <0.050
A variable magnification optical system in which at least one positive lens included in the first lens group is formed of a lens material satisfying the above. The variable magnification optical system according to any one of claims 1 to 6,
The third lens group includes a negative lens and a positive lens, and the focal length of the negative lens: f31 and the focal length of the positive lens: f32 are the following conditional expressions:
(8) −2.0 <f31 / f32 <−0.5
Variable magnification optical system that satisfies A variable magnification optical system according to any one of claims 1 to 7,
A variable magnification optical system in which the second lens group is a cemented lens in which a negative lens and a positive lens are arranged in this order from the object side and cemented. A variable magnification optical system according to any one of claims 1 to 8,
A zooming optical system in which a conjugate length is kept constant when zooming from the low magnification end to the high magnification end.   A camera having the zoom optical system according to any one of claims 1 to 9 as a photographing optical system.   An inspection apparatus comprising the variable magnification optical system according to claim 1 as a photographing optical system of a camera function unit.

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