JP2014035482A - Infrared zoom lens, infrared multi-focal lens and infrared imaging device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To shorten an entire length of an optical system.SOLUTION: An infrared zoom lens is configured by arranging, in order from an object side, a first lens group G1 having a focus function and a positive refractive power as a whole, a second lens group G2 moving on an optical axis upon zooming and having a function of varying a magnification and having a positive refractive power as a whole, a third lens group G3 moving on the optical axis upon the zooming and having a function of compensating for a focus position varied by the zooming and having a positive refractive power as a whole, and a fourth lens group G4 having a function of forming an image on a detector surface I and having a positive refractive power as a whole. The infrared zoom lens forms an intermediate image, and re-images the intermediate image on the detector surface I.

Description

  The present invention relates to an infrared zoom lens, an infrared multifocal lens, and an infrared imaging device.

  An infrared zoom lens having a five-group configuration including a first lens group to a fifth lens group is known (see Patent Document 1). This infrared zoom lens is designed so that an intermediate image is formed between the fourth lens group and the fifth lens group, and the image forming position of the intermediate image does not move during zooming.

JP 2002-14283 A

  The infrared zoom lens described in Patent Document 1 described above has a problem that the entire length of the optical system is long and the overall size is large.

(1) An infrared zoom lens according to the first aspect of the present invention, in order from the object side, has a focusing function, and has a positive refractive power as a whole, and moves on the optical axis at the time of zooming. And a second lens group having a zooming function and having a positive refractive power as a whole, and a function of moving on the optical axis at the time of zooming to compensate for a focal position that has fluctuated due to zooming. A third lens group having a positive refractive power and a fourth lens group having a function of forming an image on the detector surface and having a positive refractive power as a whole are arranged to form an intermediate image, The image is re-imaged on the detector surface.
(2) An infrared multifocal lens according to the invention described in claim 9 has, in order from the object side, a first lens group having a focusing function and having a positive refractive power as a whole, and an optical axis at the time of zooming. A second lens unit that moves, has a zooming function, and has a positive refractive power as a whole, and has a function of moving on the optical axis at the time of zooming to compensate for a focal position that has fluctuated due to zooming, A third lens group having a positive refractive power and a fourth lens group having a function of forming an image on the detector surface and having a positive refractive power as a whole are disposed to form an intermediate image, The intermediate image is re-imaged on the detector surface.
(3) The infrared imaging device according to the invention described in claim 10 includes the infrared zoom lens according to any one of claims 1 to 8, or the infrared multifocal lens according to claim 9, and an infrared zoom lens. And an infrared detector that captures the formed image.

  According to the present invention, the total length of the optical system can be shortened.

It is a figure explaining the structure of the infrared imaging device by which the infrared zoom lens by one embodiment of this invention is mounted. It is a figure explaining the structure of the infrared zoom lens by 1st Example. It is a lateral aberration diagram in the telephoto end state of the infrared zoom lens according to the first example. It is a lateral aberration figure in the intermediate focal length state of the infrared zoom lens by 1st Example. FIG. 6 is a lateral aberration diagram in the wide-angle end state of the infrared zoom lens according to the first example. It is a figure explaining the structure of the infrared zoom lens by 2nd Example. It is a lateral aberration figure in the telephoto end state of the infrared zoom lens by 2nd Example. It is a lateral aberration figure in the intermediate focal length state of the infrared zoom lens by 2nd Example. It is a lateral aberration figure in the wide-angle end state of the infrared zoom lens by 2nd Example. It is a figure explaining the structure of the infrared zoom lens by 3rd Example. It is a lateral aberration figure in the telephoto end state of the infrared zoom lens by 3rd Example. It is a lateral aberration figure in the intermediate focal length state of the infrared zoom lens by 3rd Example. It is a lateral aberration figure in the wide-angle end state of the infrared zoom lens by 3rd Example. (A) is a figure which shows the structure of the infrared zoom lens of a prior art, (B) is a figure which shows the structure of the infrared zoom lens by 1st Example.

  Hereinafter, embodiments of the infrared zoom lens of the present invention will be described with reference to the drawings. FIG. 1 is a diagram illustrating a simplified configuration of an infrared imaging device 1 in which the infrared zoom lens 10 of the present embodiment is mounted. The infrared imaging device 1 mainly includes an infrared zoom lens 10 and an infrared detector (detector) 11. In FIG. 1, for the sake of simplicity, the infrared zoom lens 10 is illustrated as a single lens, but actually, it is composed of a plurality of lens groups as described later.

  The infrared zoom lens 10 collects heat radiated from an object to be examined, that is, infrared rays, and forms an image on the detector surface of the infrared detector 11. The infrared detector 11 is disposed at a position where infrared rays from an object to be examined are collected by the infrared zoom lens 10 and has a plurality of light receiving elements (CCD (charge coupled device)) on the detector surface. Then, an image formed by the infrared zoom lens 10 is captured.

  Between the infrared zoom lens 10 and the infrared detector 11, an opening mask called a cold door aperture 12 is arranged in order to prevent unwanted infrared rays emitted from other than the subject from entering the infrared detector 11. Yes. The cold door aperture 12 serves as an aperture stop of the infrared zoom lens 10 and is designed so that its position and size (diameter) coincide with the exit pupil of the infrared zoom lens 10. Such a state is generally called an “aperture-matched state”.

  Next, the infrared zoom lens 10 of this embodiment will be described. As shown in FIG. 2, the infrared zoom lens 10 includes a first lens group G1, a second lens group G2, a third lens group G3, and a fourth lens group G4 in order from the object side. The first lens group G1 has a focusing function and has a positive refractive power as a whole. The second lens group G2 has a zooming function and has a positive refractive power as a whole. The third lens group G3 has a function of compensating the focal position that has fluctuated due to zooming, and has a positive refractive power as a whole. The fourth lens group G4 has a function of forming an image on the detector surface (image surface) I of the infrared detector 11, and has a positive refractive power as a whole. The aperture stop AS is disposed between the fourth lens group G4 and the detector surface I.

  Heat, that is, infrared rays radiated from the object to be measured passes through the first lens group G1, the second lens group G2, the third lens group G3, and the fourth lens group G4 in this order, and passes through the aperture stop AS to the detector surface. The light is condensed on I and received by a light receiving element provided on the detector surface I. The infrared zoom lens 10 is designed to form an intermediate image of incident infrared light and re-image this intermediate image on the detector plane I. In the infrared zoom lens 10, the cold door aperture 12 needs to be provided as described above, and the aperture stop AS needs to be disposed immediately in front of the detector surface I. Therefore, a configuration that forms an intermediate image is used. .

  FIG. 2 shows, in order from the top, the telephoto end state, the intermediate focal length state, and the wide-angle end state, and shows how each lens group moves during zooming. In the infrared zoom lens 10, at the time of zooming, the first lens group G1, the fourth lens group G4, and the aperture stop AS are fixed, and the second lens group G2 and the third lens group G3 move on the optical axis. To do. Accordingly, the image formation position of the intermediate image (intermediate image formation position) also moves on the optical axis.

The infrared zoom lens 10 of the present embodiment desirably satisfies the following conditional expression (1). In conditional expression (1), f ₁ is the focal length of the first lens group G 1, and f _T is the total focal length at the telephoto end of the infrared zoom lens 10.
0.5 <f ₁ / f _T <1.5 (1)

Conditional expression (1) is a conditional expression for achieving both good imaging performance and miniaturization of the infrared zoom lens 10. In the telephoto end state, when f ₁ / f _T falls below the lower limit value of the conditional expression (1), the size of the intermediate image is reduced, and the burden of correcting off-axis aberrations is reduced, but the NA (aperture) of the intermediate image is reduced. Number) increases, and the burden of correcting aberrations for high NA light rays, that is, axial aberrations (especially spherical aberration), is increased.

On the contrary, if f ₁ / f _T exceeds the upper limit value of the conditional expression (1), the NA of the intermediate image becomes small, and the burden of correcting the aberration with respect to the light beam having a high NA becomes small. Increases, and the burden of correcting off-axis aberrations (particularly astigmatism, coma aberration, and lateral chromatic aberration) increases. If f ₁ / f _T exceeds the upper limit value of the conditional expression (1), the focal length of the first lens group G1 becomes long, and the total length of the infrared zoom lens 10 becomes long.

As described above, even if f ₁ / f _T exceeds either the lower limit value or the upper limit value of the conditional expression (1), the balance between the on-axis aberration and the off-axis aberration is greatly lost, and good imaging performance is obtained. This is not preferable. Therefore, it is preferable that conditional expression (1) is satisfied. Further ideally, it is desirable to satisfy 0.7 <f ₁ / f _T <1.2.

Furthermore, it is desirable that the infrared zoom lens 10 of the present embodiment satisfies the following conditional expression (2). In conditional expression (2), f ₁₂ is the combined focal length from the first lens group G 1 to the second lens group G 2 at the wide-angle end, and f _W is the total focal length at the wide-angle end of the infrared zoom lens 10. Distance.
0.9 <f ₁₂ / f _W <2.5 (2)

Conditional expression (2) is also a conditional expression for achieving both good imaging performance and miniaturization of the infrared zoom lens 10. In the wide-angle end state, if f ₁₂ / f _W falls below the lower limit value of the conditional expression (2), the size of the intermediate image becomes small and the burden of correcting off-axis aberrations becomes small, but the NA of the intermediate image becomes large. Therefore, the burden of correcting the aberration with respect to the high NA light beam, that is, the axial aberration (especially spherical aberration) is increased.

On the contrary, if f ₁₂ / f _W exceeds the upper limit value of the conditional expression (2), the NA of the intermediate image becomes small, and the burden of correcting the aberration for this high NA ray becomes small, but the size of the intermediate image Increases, the lens diameter of the third lens group G3 increases, and the burden of correcting off-axis aberrations (particularly astigmatism, coma aberration, lateral chromatic aberration) increases. When f ₁₂ / f _W exceeds the upper limit value of the conditional expression (2), the combined focal length from the first lens group G1 to the second lens group G2 becomes long, and the total length of the infrared zoom lens 10 becomes long. End up.

In this way, even if f ₁₂ / f _W exceeds either the lower limit value or the upper limit value of conditional expression (2), the balance between the on-axis aberration and the off-axis aberration is greatly lost, and good imaging performance is obtained. This is not preferable. Therefore, it is preferable that conditional expression (2) is satisfied. Further ideally, it is desirable to satisfy 1.2 <f ₁₂ / f _W <2.0.

-Example-
Next, examples according to the present embodiment will be described. Here, Table 1 shows refractive indexes of silicon, germanium, and zinc sulfide used as glass materials constituting the infrared zoom lens in each example. Table 1 shows the refractive indexes for infrared light having wavelengths of 3 to 5 μm corresponding to the first and second examples and wavelengths of 8 to 12 μm corresponding to the third example.

The infrared zoom lens of each embodiment includes an aspheric lens. The shape of this aspheric lens is assumed to be expressed by the following equation (3). In equation (3), y is the height from the optical axis, and Z (y) is the distance (sag) along the optical axis from the tangent plane of each vertex of the aspheric surface to each aspheric surface at height y. R) is the apex radius of curvature, κ is the conic coefficient, and C ₄ and C ₆ are the fourth and sixth order aspheric coefficients.

  In the table showing the values of the specifications of each example described later, FNo represents the F number of the entire optical system, λ represents the wavelength band of the optical system, and f represents the total focal length of the optical system. The surface number indicates the number of each optical surface from the object side, the surface interval indicates the distance on the optical axis from the optical surface to the next optical surface (or image surface I), and the optical surface belongs to the lens group The lens group to show is shown. In addition, d1-d3 shows the space | interval which changes with zooming. The optical surface with * (asterisk) before the surface number is an aspherical shape. In the table, each parameter of the above formula (3) defining the aspherical shape is also shown.

  “Mm” is generally used as the unit of other lengths such as the focal length f, the radius of curvature, and the surface interval. However, since the optical system can obtain the same optical performance even when proportionally enlarged or proportionally reduced, the unit is not limited to “mm”, and other appropriate units can be used. In the table, the curvature radius “0.0000” indicates a plane or an opening.

  In the following embodiments, the image circle diameter is 2y = 12 mm.

(First embodiment)
FIG. 2 shows the configuration of the infrared zoom lens according to the first embodiment. FIG. 2 shows a telephoto end state, an intermediate focal length state, and a wide-angle end state in order from the top, and shows how each lens unit moves during zooming. The infrared zoom lens according to the first example corresponds to a wavelength region of 3 to 5 μm (reference wavelength 4 μm), and has an F number of 2.0.

  In the infrared zoom lens according to the first example, as shown in FIG. 2, when zooming from the telephoto end to the wide-angle end, the second lens group G2 and the third lens group G3 move toward the object side along the optical axis. Moving. Along with this, the intermediate imaging position also moves to the object side along the optical axis.

  Specifically, in the telephoto end state, an intermediate image is formed by the front lens (object side) lens of the first lens group G1 and the second lens group G2, and the rear side (detector surface I side) of the second lens group G2. ), The third lens group G3, and the fourth lens group G4 form an intermediate image again. Therefore, there is an intermediate imaging position between the front lens and the rear lens of the second lens group G2.

  In the intermediate focal length state, an intermediate image is formed by the first lens group G1 and the second lens group G2, and the intermediate image is re-imaged by the third lens group G3 and the fourth lens group G4. Therefore, there is an intermediate imaging position between the second lens group G2 and the third lens group G3. That is, with the zooming from the telephoto end to the intermediate focal length, the rear lens in the second lens group G2 moves so as to straddle the intermediate imaging position. In addition, the intermediate image formation position slightly moves toward the object side as the magnification is changed from the telephoto end to the intermediate focal length.

  In the wide-angle end state, an intermediate image is formed by the first lens group G1 and the second lens group G2, and the intermediate image is re-imaged by the third lens group G3 and the fourth lens group G4. Therefore, there is an intermediate imaging position between the second lens group G2 and the third lens group G3. In addition, the intermediate image formation position is moved to the object side with zooming from the intermediate focal length to the wide angle end.

Tables 2 to 4 show values of specifications of the infrared zoom lens in the first example. Table 2 shows detailed numerical data of each optical surface, Table 3 shows each parameter of the above formula (3) that defines the aspherical shape, and Table 4 shows a surface interval that changes due to zooming. .

In the infrared zoom lens according to Example 1, f ₁ / f _T in conditional expression (1) is 0.810. Therefore, 0.5 <f ₁ / f _T = 0.810 <1.5, and this example satisfies the conditional expression (1). Further, f ₁₂ / f _W in conditional expression (2) is 1.328. Therefore, 0.9 <f ₁₂ / f _W = 1.328 <2.5, and this example also satisfies the conditional expression (2).

  3 to 5 are lateral aberration diagrams of the infrared zoom lens according to Example 1. FIG. 3 is a lateral aberration diagram in the telephoto end state, FIG. 4 is a lateral aberration diagram in the intermediate focal length state, and FIG. 5 is a lateral aberration diagram in the wide angle end state. In each aberration diagram, aberration curves on the tangential image surface and the sagittal image surface are shown for each image height. In each aberration diagram, a solid line indicates an aberration curve of a wavelength of 5 μm, a dotted line indicates an aberration curve of 4 μm, and an alternate long and short dash line indicates an aberration curve of 3 μm.

  Referring to the respective aberration diagrams shown in FIGS. 3 to 5, in the infrared zoom lens of the first embodiment, aberrations are almost reduced to the diffraction limit in each of the telephoto end state, the intermediate focal length state, and the wide-angle end state. It can be seen that the image is corrected and good imaging performance is ensured.

(Second embodiment)
FIG. 6 is a diagram illustrating a configuration of an infrared zoom lens according to the second embodiment. FIG. 6 shows a telephoto end state, an intermediate focal length state, and a wide-angle end state in order from the top, and shows how each lens group moves during zooming. The infrared zoom lens according to the second example corresponds to a wavelength region of 3 to 5 μm (reference wavelength 4 μm) as in the first example, but the F number is 4.0 unlike the first example. It has become.

  In the infrared zoom lens according to the second example, as shown in FIG. 6, when zooming from the telephoto end to the wide-angle end, the second lens group G2 and the third lens group G3 move toward the object side along the optical axis. Moving. Along with this, the intermediate imaging position also moves to the object side along the optical axis.

  Specifically, in the telephoto end state, an intermediate image is formed by the front lens of the first lens group G1 and the second lens group G2, and the rear lens of the second lens group G2, the third lens group G3, and the first lens group G3. The intermediate image is re-imaged by the four lens group G4. Therefore, there is an intermediate imaging position between the front lens and the rear lens of the second lens group G2.

  In the intermediate focal length state, an intermediate image is formed by the first lens group G1 and the second lens group G2, and the intermediate image is re-imaged by the third lens group G3 and the fourth lens group G4. Therefore, there is an intermediate imaging position between the second lens group G2 and the third lens group G3. That is, with the zooming from the telephoto end to the intermediate focal length, the rear lens in the second lens group G2 moves so as to straddle the intermediate imaging position. In addition, the intermediate imaging position is moved to the object side as the magnification is changed from the telephoto end to the intermediate focal length.

  In the wide-angle end state, an intermediate image is formed by the first lens group G1 and the second lens group G2, and the intermediate image is re-imaged by the third lens group G3 and the fourth lens group G4. Therefore, there is an intermediate imaging position between the second lens group G2 and the third lens group G3. In addition, the intermediate image formation position is moved to the object side with zooming from the intermediate focal length to the wide angle end.

Tables 5 to 7 show values of specifications of the infrared zoom lens in the second example. Table 5 shows detailed numerical data of each optical surface, Table 6 shows each parameter of the above formula (3) that defines the aspherical shape, and Table 7 shows a surface interval that changes due to zooming. .

In the infrared zoom lens according to Example 2, f ₁ / f _T in conditional expression (1) is 0.898. Therefore, 0.5 <f ₁ / f _T = 0.898 <1.5, and this example satisfies the conditional expression (1). Further, f ₁₂ / f _W in conditional expression (2) is 1.616. Therefore, 0.9 <f ₁₂ / f _W = 1.616 <2.5, and this example also satisfies the conditional expression (2).

  7 to 9 are lateral aberration diagrams of the infrared zoom lens according to Second Example. 7 is a lateral aberration diagram in the telephoto end state, FIG. 8 is a lateral aberration diagram in the intermediate focal length state, and FIG. 9 is a lateral aberration diagram in the wide angle end state. In each aberration diagram, aberration curves on the tangential image surface and the sagittal image surface are shown for each image height. In each aberration diagram, a solid line indicates an aberration curve of a wavelength of 5 μm, a dotted line indicates an aberration curve of 4 μm, and an alternate long and short dash line indicates an aberration curve of 3 μm.

  Referring to the respective aberration diagrams shown in FIGS. 7 to 9, in the infrared zoom lens of the second embodiment, the aberration is almost up to the diffraction limit in each of the telephoto end state, the intermediate focal length state, and the wide angle end state. It can be seen that the image is corrected and good imaging performance is ensured.

(Third embodiment)
FIG. 10 is a diagram illustrating a configuration of an infrared zoom lens according to the third embodiment. FIG. 10 shows a telephoto end state, an intermediate focal length state, and a wide-angle end state in order from the top, and shows how each lens group moves during zooming. Unlike the first embodiment, the infrared zoom lens according to the third embodiment corresponds to a wavelength region of 8 to 12 μm (reference wavelength 10 μm), but the F number is 2.0 as in the first embodiment. It has become.

  In the infrared zoom lens according to the third example, as shown in FIG. 10, the second lens group G2 and the third lens group G3 move toward the object side along the optical axis when zooming from the telephoto end to the wide-angle end. Moving. Along with this, the intermediate imaging position also moves to the object side along the optical axis.

  Specifically, in the telephoto end state, an intermediate image is formed by the front lens of the first lens group G1 and the second lens group G2, and the rear lens of the second lens group G2, the third lens group G3, and the first lens group G3. The intermediate image is re-imaged by the four lens group G4. Therefore, there is an intermediate imaging position between the front lens and the rear lens of the second lens group G2.

  In the intermediate focal length state, an intermediate image is formed by the first lens group G1 and the second lens group G2, and the intermediate image is re-imaged by the third lens group G3 and the fourth lens group G4. Therefore, there is an intermediate imaging position between the second lens group G2 and the third lens group G3. That is, with the zooming from the telephoto end to the intermediate focal length, the rear lens in the second lens group G2 moves so as to straddle the intermediate imaging position. In addition, the intermediate imaging position is moved to the object side as the magnification is changed from the telephoto end to the intermediate focal length.

  In the wide-angle end state, an intermediate image is formed by the first lens group G1 and the second lens group G2, and the intermediate image is re-imaged by the third lens group G3 and the fourth lens group G4. Therefore, there is an intermediate imaging position between the second lens group G2 and the third lens group G3. In addition, the intermediate image formation position is moved to the object side with zooming from the intermediate focal length to the wide angle end.

Tables 8 to 10 show values of specifications of the infrared zoom lens in the third example. Table 8 shows detailed numerical data of each optical surface, Table 9 shows each parameter of the above formula (3) that defines the aspherical shape, and Table 10 shows a surface interval that changes due to zooming. .

In the infrared zoom lens according to Example 3, f ₁ / f _T in conditional expression (1) is 0.977. Accordingly, 0.5 <f ₁ / f _T = 0.977 <1.5, and this example satisfies the conditional expression (1). Further, f ₁₂ / f _W in conditional expression (2) is 1.824. Therefore, 0.9 <f ₁₂ / f _W = 1.824 <2.5, and this example also satisfies the conditional expression (2).

  11 to 13 are lateral aberration diagrams of the infrared zoom lens according to Third Example. 11 is a lateral aberration diagram in the telephoto end state, FIG. 12 is a lateral aberration diagram in the intermediate focal length state, and FIG. 13 is a lateral aberration diagram in the wide-angle end state. In each aberration diagram, aberration curves on the tangential image surface and the sagittal image surface are shown for each image height. In each aberration diagram, a solid line indicates an aberration curve having a wavelength of 12 μm, a dotted line indicates 10 μm, and an alternate long and short dash line indicates an aberration curve of 8 μm.

  Referring to the respective aberration diagrams shown in FIGS. 11 to 13, in the infrared zoom lens of the third embodiment, aberrations are almost up to the diffraction limit in each of the telephoto end state, the intermediate focal length state, and the wide angle end state. It can be seen that the image is corrected and good imaging performance is ensured.

(Comparison between the first to third embodiments and the prior art)
Here, the infrared zoom lens according to the first to third embodiments described above and the prior art infrared zoom lens disclosed in the first embodiment of Patent Document 1 will be compared. The prior art infrared zoom lens and the infrared zoom lens according to the first to third embodiments have the same focal length and zoom ratio. As shown in FIG. 14 (A), the prior art infrared zoom lens has a first lens group G11 having a focusing function and a positive refractive power in order from the object side, and a negative magnification having a zooming function. A second lens group G12 having a refractive power, a third lens group G13 having a function of compensating the focal position and having a positive refractive power, a fourth lens group G14 for forming an intermediate image, and an intermediate image A fifth lens group G15 for forming a relay image on the detector surface I is provided, and an aperture stop AS is disposed between the fifth lens group G15 and the detector surface I.

  As can be seen from FIG. 14 (A), in the infrared zoom lens described in the prior art, there is an intermediate imaging position between the fourth lens group G14 and the fifth lens group G15, and this intermediate imaging position is changed. Designed to not move when doubled. As described above, in the configuration in which the intermediate image forming position is fixed between the fourth lens group G14 and the fifth lens group G15, the first to fourth lens groups G11 to G14 are conventionally used in a visible light zoom lens. Since the same configuration as that of the afocal 4-group zoom lens can be used, there is an advantage that the lens can be designed easily.

  However, in the infrared zoom lens described in the prior art, the total length in the optical axis direction of the optical system (distance from the first surface to the imaging surface) is about 340 mm. The typical size is getting bigger.

  Therefore, the infrared zoom lenses of the first to third examples of the present embodiment are all composed of first to fourth lens groups G1 to G4 having positive refractive power, and the intermediate image forming position is set at the time of zooming. By adopting a moving configuration, the overall length of the optical system was shortened. FIG. 14B is a diagram illustrating the configuration of the infrared zoom lens according to the first embodiment at the same scale as FIG. As can be seen from a comparison between FIGS. 14A and 14B, the infrared zoom lens according to the first embodiment has a significantly larger overall length in the optical axis direction than the infrared zoom lens described in the prior art. It has become shorter. Specifically, in the infrared zoom lens according to the first embodiment, the total length of the optical system in the optical axis direction is about 150 mm, which is less than half that of the infrared zoom lens described in the prior art. .

  In the infrared zoom lens according to the second embodiment, the total length of the optical system in the optical axis direction is about 100 mm. In the infrared zoom lens according to the third embodiment, the total length of the optical system in the optical axis direction is about 100 mm. 150 mm. Therefore, also in the infrared zoom lenses according to the second and third examples, the total length of the optical system is significantly shorter than the infrared zoom lenses described in the prior art.

According to the embodiment described above, the following operational effects can be obtained.
(1) The infrared zoom lens has, in order from the object side, a first lens group G1 that has a focusing function and has a positive refractive power as a whole, and moves on the optical axis at the time of zooming, and has a zooming function. The second lens group G2 having a positive refractive power as a whole, and a function of moving on the optical axis at the time of zooming to compensate for the focal position fluctuated by the zooming, and having a positive refractive power as a whole. A third lens group G3 and a fourth lens group G4 having a function of forming an image on the detector surface I and having a positive refractive power as a whole, forming an intermediate image, and detecting the intermediate image as a detector; The image was re-imaged on the surface I. And it was comprised so that the image formation position of an intermediate image might be moved with zooming. As a result, the overall length of the optical system can be significantly shortened compared to the conventional case, and a compact infrared zoom lens can be realized.

(2) The infrared zoom lens of (1) is configured to satisfy the following conditional expression (1).
0.5 <f ₁ / f _T <1.5 (1)
However,
f ₁ : Focal length of the first lens group G 1 f _T : Overall focal length at the telephoto end of the infrared zoom lens Thereby, it is possible to achieve both good imaging performance and downsizing of the infrared zoom lens.

(3) The infrared zoom lens of the above (1) or (2) is configured to satisfy the following conditional expression (2).
0.9 <f ₁₂ / f _W <2.5 (2)
However,
f ₁₂ : Composite focal length from the first lens group G1 to the second lens group G2 at the wide-angle end f _W : Overall focal length at the wide-angle end of the infrared zoom lens Thereby, good imaging performance and small size of the infrared zoom lens It is possible to achieve both.

(4) In the infrared zoom lens of (1) to (3) above, an intermediate image is formed by the first lens group G1 and the second lens group G2, and an intermediate image is formed by the third lens group G3 and the fourth lens group G4. It was configured to re-image. Thereby, at the time of zooming, the intermediate imaging position is moved by the movement of the second lens group G2, but the re-imaging position is adjusted to be the detector plane I by the movement of the third lens group G3. be able to.

  The above description is merely an example, and the present invention is not limited to the configuration described above, and various aspects may be changed. For example, the number of lenses constituting each lens group, the radius of curvature of each lens, the surface interval, the glass material, and the like may be appropriately changed.

  In the above-described embodiments, the intermediate imaging position is located in the second lens group G2 at the telephoto end, and a part of the lenses (rear side lens) of the second lens group is moved from the telephoto end to the wide-angle end. The example of moving so as to cross the intermediate imaging position with the zooming of the zoom ratio has been described. However, the intermediate imaging positions at the telephoto end and the wide-angle end may be changed as appropriate, and there may or may not be a lens that straddles the intermediate imaging position with zooming.

  In the above-described embodiment, an example of an infrared zoom lens in which the focal length continuously changes has been described. For example, a bifocal lens that can be switched between a telephoto end and a wide-angle end, a telephoto end, an intermediate focal length, The present invention may be applied to an infrared multifocal lens that can be switched to many focal lengths, such as a trifocal lens that can be switched to the wide-angle end.

DESCRIPTION OF SYMBOLS 1 ... Infrared imaging device, 10 ... Infrared zoom lens, 11 ... Infrared detector, G1 ... 1st lens group, G2 ... 2nd lens group, G3 ... 3rd lens group, G4 ... 4th lens group, AS ... Aperture stop , I ... Detector surface

Claims (10)

From the object side,
A first lens group having a focusing function and having a positive refractive power as a whole;
A second lens group that moves on the optical axis at the time of zooming, has a zooming function, and has a positive refractive power as a whole;
A third lens group having a function of moving on the optical axis at the time of zooming and compensating for the focal position fluctuated by zooming, and having a positive refractive power as a whole;
A fourth lens group having a function of forming an image on the detector surface and having a positive refractive power as a whole;
An infrared zoom lens, wherein an intermediate image is formed, and the intermediate image is re-imaged on the detector surface. The infrared zoom lens according to claim 1,
An infrared zoom lens, wherein the image forming position of the intermediate image is moved with zooming. The infrared zoom lens according to claim 2,
An infrared zoom lens, wherein the imaging position of the intermediate image is moved to the object side with zooming from the telephoto end to the wide-angle end. In the infrared zoom lens according to any one of claims 1 to 3,
An infrared zoom lens satisfying the following conditional expression (1):
0.5 <f ₁ / f _T <1.5 (1)
However,
f ₁ : focal length of the first lens group f _T : total system focal length at the telephoto end of the infrared zoom lens In the infrared zoom lens according to any one of claims 1 to 4,
An infrared zoom lens characterized by satisfying the following conditional expression (2):
0.9 <f ₁₂ / f _W <2.5 (2)
However,
f ₁₂ : Composite focal length from the first lens group to the second lens group at the wide-angle end f _W : Overall focal length at the wide-angle end of the infrared zoom lens In the infrared zoom lens according to any one of claims 1 to 5,
Forming the intermediate image by the first lens group and the second lens group;
An infrared zoom lens, wherein the intermediate image is re-imaged by the third lens group and the fourth lens group. In the infrared zoom lens according to any one of claims 1 to 6,
An infrared zoom lens characterized in that a part of the lenses of the second lens group moves so as to straddle the imaging position of the intermediate image as the magnification is changed from the telephoto end to the wide-angle end. In the infrared zoom lens according to any one of claims 1 to 7,
2. The infrared zoom lens according to claim 1, wherein an image formation position of the intermediate image is located in the second lens group at a telephoto end. From the object side,
A first lens group having a focusing function and having a positive refractive power as a whole;
A second lens group that moves on the optical axis at the time of zooming, has a zooming function, and has a positive refractive power as a whole;
A third lens group having a function of moving on the optical axis at the time of zooming and compensating for the focal position fluctuated by zooming, and having a positive refractive power as a whole;
A fourth lens group having a function of forming an image on the detector surface and having a positive refractive power as a whole;
An infrared multifocal lens, wherein an intermediate image is formed, and the intermediate image is re-imaged on the detector surface. The infrared zoom lens according to any one of claims 1 to 8, or the infrared multifocal lens according to claim 9,
An infrared detector that captures an image formed by the infrared zoom lens;
An infrared imaging device comprising:

Images