Spectroscopic camera

Abstract

To provide a spectroscopic camera that allows the selection of lenses according to the application and obtains desired spectral characteristics. [Solution] The spectroscopic camera 10 includes an etalon 14 that transmits light of a wavelength corresponding to the gap dimension of a pair of reflective films, a detachable mount lens 13, an image sensor 15, and a relay optical system 20 that relays the intermediate image 31 formed by the mount lens 13 to re-image it to the image sensor 15 and is adjusted to incident light on the etalon 14 at a desired angle. The relay optical system 20 includes a first lens group 21 that relays the intermediate image 31 and emits collimated light to be incident on the etalon 14, and a second lens group 22 that images the light emitted from the etalon 14 to the image sensor 15. The image height L1 of the intermediate image 31 and the focal length f1 of the first lens group 21 satisfy the relationship E≦0.27, given by the evaluation formula E1=(L1 / f1).

Description

Technical Field

[0001] The present invention relates to a spectroscopic camera.

Background Art

[0002] An etalon (Fabry-Perot type wavelength variable filter) is used in a spectroscopic camera (see Patent Document 1). By continuously changing the distance between the opposing reflecting surfaces, the wavelength of the transmitted light can be continuously changed in an etalon.

Prior Art Documents

Patent Documents

[0003]

Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0004] In a spectroscopic camera using an etalon, if the light incident on the etalon is not incident perpendicularly to the reflecting surface of the etalon, the half-value width of the transmitted wavelength deteriorates, the position of the peak wavelength shifts, and there is a possibility that the desired spectroscopic characteristics cannot be obtained. Among spectroscopic cameras using an etalon, a lens selection type spectroscopic camera has the advantage that lenses with various focal lengths and specifications can be used according to the application. However, the principal ray angles of the lenses used are different, the angular characteristics of the light incident on the etalon change depending on the lens, and there are cases where the desired spectroscopic characteristics cannot be obtained. On the other hand, there is a spectroscopic camera in which the lens to be used is limited to a specific standard lens so that the desired spectroscopic characteristics can be surely obtained, and the incident angle to the etalon is within the allowable range. However, in such a standard lens type spectroscopic camera, the lens cannot be changed according to the application.

[0005] One of the objectives of this invention is to provide a spectroscopic camera that allows the selection of lenses to be used according to the application and that can obtain desired spectral characteristics. [Means for solving the problem]

[0006] A spectroscopic camera according to one aspect of the present disclosure includes an etalon that transmits light of a wavelength corresponding to the gap dimension of a pair of reflective films, a detachable mount lens, an image sensor, and a relay optical system adjusted to relay the intermediate image formed by the mount lens to re-image it to the image sensor and to incident light on the etalon at a desired angle, wherein the relay optical system includes a first lens group that relays the intermediate image and emits collimated light to be incident on the etalon, and a second lens group that images the light emitted from the etalon to the image sensor, and the image height L1 of the intermediate image and the focal length f1 of the first lens group satisfy the relationship E≦0.27, given by the evaluation formula E1=(L1 / f1). [Brief explanation of the drawing]

[0007] [Figure 1] A schematic diagram showing the configuration of a spectroscopic camera according to one embodiment of this disclosure. [Figure 2] Optical path diagram of the spectroscopic camera according to the above embodiment. [Figure 3] This figure shows the relationship between the image height L1 of the intermediate image, the focal length f1 of the first lens group, and the incident angle θ on the etalon in the above embodiment. [Figure 4] A graph showing the relationship between the incident angle θ and the evaluation formula E1=(L1 / f1) in the above embodiment. [Figure 5] A graph showing the relationship between the incident angle θ and the spectral spectrum in the above embodiment. [Figure 6] A graph showing the relationship between the focal length f2 of the second lens group and the evaluation formula E2=(L2 / L1) in the above embodiment. [Figure 7] A graph showing the relationship between the F-number of the second lens group and the evaluation formula E2=(L2 / L1) in the above embodiment. [Modes for carrying out the invention]

[0008] An embodiment of this disclosure will be described below. In Figure 1, the spectroscopic camera 10 has a housing 11, to which a lens barrel 12 is connected, and a mount lens 13 is attached to the lens barrel 12. The mount lens 13 is detachable from the lens barrel 12 and can be replaced with one of several lenses with different characteristics, selected according to the application.

[0009] Inside the housing 11 are an etalon 14 that transmits light of a wavelength corresponding to the gap dimension of a pair of reflective films, and an image sensor 15 that detects the incident light beam as an image. These etalon 14, image sensor 15, and mount lens 13 are each arranged along the reference optical axis 19.

[0010] The first lens group 21 is located on the side of the Etalon 14 where the lens barrel 12 is located. The second lens group 22 is located between the Etalon 14 and the image sensor 15. The mount lens group 23 is located inside the mount lens 13. The first lens group 21 and the second lens group 22 constitute a relay optical system 20 that relays the intermediate image formed by the mount lens group 23 to the image sensor 15 for re-imaging. The relay optical system 20 is adjusted to direct light onto the etalon 14 at a desired angle.

[0011] In Figure 2, the light beam from a light source (not shown) forms an intermediate image 31 by the mount lens group 23. The first lens group 21 relays the intermediate image 31 to emit collimated light, which is then incident on the etalon 14. In order to emit collimated light onto the etalon 14, the first lens group 21 has at least one concave lens 211, and a plurality of convex lenses 212 are arranged on the incident side of the concave lens 211. The distance from the principal point pp1 on the object side to the focal point fp1 on the object side of the first lens group 21 is the focal length f1.

[0012] The etalon 14 transmits light of a specified wavelength and emits it to the second lens group 22. The etalon 14 is positioned at the aperture position ap of the relay optical system 20. The second lens group 22 focuses the light emitted from the etalon 14 onto the image sensor 15 to generate an image 32. The distance from the principal point pp2 on the image side to the focal point fp2 on the image side of the second lens group 22 is the focal length f2.

[0013] In the relay optical system 20, the image height L1 of the intermediate image 31 and the focal length f1 of the first lens group 21 are set to satisfy the relationship E≦0.27, given by the evaluation formula E1=(L1 / f1). As shown in Figure 3, the image height L1 of the intermediate image 31 satisfies the relationship θ = arctan(L1 / f1) with respect to the focal length f1 of the first lens group 21, where θ is the maximum angle of incidence to the etalon 14. Here, if we define the evaluation formula E1 = (L1 / f1), then in order to suppress the maximum angle of incidence θ to the etalon 14, we can either reduce the evaluation formula E1, that is, reduce the image height L1, or increase the focal length f1.

[0014] Figure 4 shows the relationship between the incident angle θ on the etalon 14 and the evaluation formula E1 = (L1 / f1). In this figure, as the evaluation formula E1 = (L1 / f1) increases, the incident angle θ also increases. Figure 5 shows the relationship between the incident angle θ on etalon 14 and the spectral spectrum. In this figure, curves S0 to S20 represent the spectral spectra at a set wavelength of 600 nm when the incident angle θ is 0 degrees, 5 degrees, 10 degrees, 15 degrees, and 20 degrees, respectively.

[0015] In FIG. 5, as the incident angle θ increases, the spectral spectrum shifts toward the shorter wavelength side with respect to the set wavelength for curves S0 to S20. And, while curves S0 to S15 with an incident angle θ up to 20 degrees maintain a single peak, curve S20 with an incident angle θ of 20 degrees has a double peak. Since it is difficult to correct such double-peak characteristics, it is necessary to perform an optical design so that light with an incident angle θ of 20 degrees or more does not enter the etalon 14. Therefore, in the relay optical system 20, the range (curves S0 to S15) with an incident angle θ up to 20 degrees where no double peak occurs is used, and the maximum value of the incident angle θ to the etalon 14 is set to 15 degrees. In FIG. 4, when the incident angle θ to the etalon 14 is 15 degrees, the evaluation formula E1 = (L1 / f1) is 0.27. Based on the above findings, in the relay optical system 20, it is set so as to satisfy the relationship of the evaluation formula E1 = (L1 / f1) ≤ 0.27.

[0016] In the relay optical system 20, the image height L1 of the intermediate image 31 and the image height L2 of the image 32 formed on the image sensor 15 by the second lens group 22 are set so as to satisfy the relationship of 0.2 ≤ E2 = (L2 / L1) ≤ 1.35. Since the etalon 14 generally stabilizes the spectral wavelength by suppressing the inclination and deflection of the reflection film, the reflection film is designed to be relatively small, and the image circle tends to be smaller compared to the full sensor size (L1 > L2). In the second lens group 22, since there is a relationship of L1:f1 = L2:f2 between the image height L2 and the focal length f2, when the magnification L2 / L1 becomes small, the focal length f2 becomes short.

[0017] In FIG. 6, when the magnification L2 / L1 becomes small and the focal length f2 becomes 3 mm or less, it is necessary to increase the power of the second lens group 22, which leads to an increase in cost such as an increase in the number of lenses. Therefore, in the relay optical system 20, it is preferable that the magnification L2 / L1, that is, the evaluation formula E2 ≥ 0.2. In Figure 7, increasing the magnification L2 / L1 increases the F-number of the optical system of the second lens group 22, reducing the amount of light reaching the image sensor 15. In particular, if the F-number exceeds 8.0, the shooting time for the spectroscopic camera 10 increases, which is a practical problem. Therefore, it is preferable that the magnification L2 / L1, or the evaluation formula E2 ≤ 1.35, is used for the relay optical system 20. Based on the above findings, the relay optical system 20 is set such that the evaluation formula E2 = (L2 / L1) satisfies the relationship 0.2 ≤ E2 ≤ 1.35.

[0018] [Effects of this embodiment] The spectroscopic camera 10 of this embodiment includes an etalon 14 that transmits light of a wavelength corresponding to the gap dimension of a pair of reflective films, a detachable mount lens 13, an image sensor 15, and a relay optical system 20 that relays the intermediate image 31 formed by the mount lens 13 to re-image an image 32 to the image sensor 15, and is adjusted to incident light on the etalon 14 at a desired angle. Furthermore, the relay optical system 20 includes a first lens group 21 that relays the intermediate image 31 to emit collimated light and incident it on the etalon 14, and a second lens group 22 that images the light emitted from the etalon 14 onto the image sensor 15, wherein the image height L1 of the intermediate image 31 and the focal length f1 of the first lens group satisfy the relationship E≦0.27, given by the evaluation formula E1=(L1 / f1). That is, the maximum incident angle of light from the first lens group 21 to the etalon 14 is 15 degrees. With this configuration, an intermediate image 31 is formed by the mount lens 13, and then this intermediate image 31 is relayed by the relay optical system 20 to be re-imaged to the image sensor 15, so that any lens can be selected and used as the mount lens 13. In the relay optical system 20, the incident angle to the etalon 14 is set so that the image height L1 of the intermediate image 31 and the focal length f1 of the first lens group satisfy the relationship E≦0.27, given by the evaluation formula E1=(L1 / f1). This makes it possible to set the incident angle of the intermediate image 31 to the etalon 14 to an appropriate angle (15 degrees or less) that avoids double peaks that are difficult to correct in the spectral spectrum, and thus obtain the desired spectral characteristics.

[0019] In the spectroscopic camera 10 of this embodiment, the relay optical system 20 satisfies the relationship 0.2 ≤ E2 ≤ 1.35 between the image height L1 of the intermediate image 31 and the image height L2 of the image 32 formed on the image sensor 15 by the second lens group 22, as expressed by the evaluation formula E2 = (L2 / L1). With this configuration, by setting the evaluation formula E2 ≥ 0.2, the power of the second lens group 22 can be secured, and cost increases such as an increase in the number of lenses can be avoided. Furthermore, by setting the evaluation formula E2 ≤ 1.35, the amount of light reaching the image sensor 15 can be secured, and an increase in the shooting time of the spectroscopic camera 10 can be avoided.

[0020] In the spectroscopic camera 10 of this embodiment, the first lens group 21 has at least one concave lens 211 that emits collimated light to the etalon 14, and a plurality of convex lenses 212 are arranged on the incident side of the concave lens 211. With this configuration, by passing the light from the incident convex lens 212 through at least one concave lens 211, appropriate collimated light can be emitted to the etalon 14.

[0021] In the spectroscopic camera 10 of this embodiment, the etalon 14 is positioned at the aperture position ap of the relay optical system 20. With this configuration, the etalon 14 is positioned at the aperture position ap of the relay optical system 20, which minimizes the diameter of the light beam incident on the etalon 14, suppressing the deviation in spectral characteristics between the center and the outer edge and obtaining appropriate spectral performance.

[0022] [Differentiation] The present invention is not limited to the embodiments described above, and any modifications that can achieve the objectives of the present invention are included in the present invention. In the above embodiment, the lens configurations of the first lens group 21 and the second lens group 22 of the relay optical system 20 can be set as appropriate. In the first lens group 21, the configuration is not limited to having multiple convex lenses 212 arranged on the incident side of the concave lens 211 as in the embodiment described above; there may be one convex lens 212 or three or more. Similarly, there may be one concave lens 211 or more. However, it is preferable that the concave lens 211 be arranged on the side of the first lens group 21 facing the etalon 14.

[0023] [Summary of this disclosure] A spectroscopic camera according to one aspect of the present disclosure includes an etalon that transmits light of a wavelength corresponding to the gap dimension of a pair of reflective films, a detachable mount lens, an image sensor, and a relay optical system that relays the intermediate image formed by the mount lens to re-image it to the image sensor and is adjusted to incident light on the etalon at a desired angle. The relay optical system includes a first lens group that relays the intermediate image and emits collimated light that is incident on the etalon, and a second lens group that forms an image of the light emitted from the etalon onto the image sensor. The image height L1 of the intermediate image and the focal length f1 of the first lens group satisfy the relationship E ≤ 0.27, given by the evaluation formula E1 = (L1 / f1). With this configuration, an intermediate image is formed by the mount lens, and then this intermediate image is relayed by the relay optical system to be re-imaged to the image sensor, allowing any lens to be selected and used as the mount lens. In the relay optical system, the angle of incidence to the etalon is set such that the image height L1 of the intermediate image and the focal length f1 of the first lens group satisfy the relationship E≦0.27, given by the evaluation formula E1=(L1 / f1). This makes it possible to set the angle of incidence of the intermediate image to the etalon to an appropriate angle that avoids double peaks that are difficult to correct in the spectral spectrum, and thus obtain the desired spectral characteristics.

[0024] In the spectroscopic camera according to the above embodiment, the relay optical system satisfies the relationship 0.2 ≤ E2 ≤ 1.35 between the image height L1 of the intermediate image and the image height L2 of the image 32 formed on the image sensor by the second lens group, as expressed by the evaluation formula E2 = (L2 / L1). With this configuration, setting the evaluation formula E2 ≥ 0.2 ensures sufficient power for the second lens group 22, avoiding cost increases such as an increase in the number of lenses. Furthermore, setting the evaluation formula E2 ≤ 1.35 ensures sufficient light reaching the image sensor, avoiding an increase in the shooting time as a spectroscopic camera.

[0025] A spectroscopic camera according to one aspect of the present disclosure includes an etalon that transmits light of a wavelength corresponding to the gap dimension of a pair of reflective films, a detachable mount lens, an image sensor, and a relay optical system that relays the intermediate image formed by the mount lens to re-image it to the image sensor and is adjusted to incident light on the etalon at a desired angle. The relay optical system includes a first lens group that relays the intermediate image and emits collimated light that is incident on the etalon, and a second lens group that forms an image of the light emitted from the etalon onto the image sensor. The maximum angle of incidence of light from the first lens group onto the etalon is 15 degrees. With this configuration, an intermediate image is formed by the mount lens, and then this intermediate image is relayed by the relay optical system to be re-imaged to the image sensor, allowing any lens to be selected and used as the mount lens. In the relay optical system, by setting the incident angle to the etalon to a maximum of 15 degrees, an appropriate angle can be set that avoids double peaks in the spectral distribution that are difficult to correct, and the desired spectral characteristics can be obtained.

[0026] In the spectroscopic camera according to the above embodiment, the first lens group has at least one concave lens that emits collimated light to the etalon, and a convex lens is arranged on the incident side of the concave lens. With this configuration, by passing the light from the convex lens on the incident side through at least one concave lens, appropriate collimated light can be emitted from the etalon.

[0027] The spectroscopic camera according to the above embodiment, wherein the etalon is positioned at the aperture of the relay optical system, as described in claim 1 or claim 2. With this configuration, the etalon is positioned at the aperture of the relay optical system, thereby enabling the acquisition of appropriate spectral performance. [Explanation of symbols]

[0028] 10...Spectroscopic camera, 11...Housing, 12...Lens barrel, 13...Mount lens, 14...Etalon, 15...Image sensor, 19...Reference optical axis, 20...Relay optical system, 21...First lens group, 211...Concave lens, 212...Convex lens, 22...Second lens group, 23...Mount lens group, 31...Intermediate image, 32...Image, E1, E2...Evaluation formula, f1, f2...Focal length, fp1...Object-side focus, fp2...Image-side focus, L1, L2...Image height, pp1...Object-side principal point, pp2...Image-side principal point, θ...Angle of incidence.

Claims

1. The system comprises an etalon that transmits light of a wavelength corresponding to the gap dimension of a pair of reflective films, a detachable mount lens, an image sensor, and a relay optical system that relays the intermediate image formed by the mount lens to re-image it to the image sensor and adjusts to incident light on the etalon at a desired angle. The relay optical system includes a first lens group that relays the intermediate image and emits collimated light that is incident on the etalon, and a second lens group that forms an image of the light emitted from the etalon onto the image sensor. A spectroscopic camera in which the image height L1 of the intermediate image and the focal length f1 of the first lens group satisfy the relationship E ≤ 0.27, given by the evaluation formula E1 = (L1 / f1).

2. The spectroscopic camera according to claim 1, wherein the relay optical system satisfies the relationship 0.2 ≤ E2 ≤ 1.35 between the image height L1 of the intermediate image and the image height L2 of the image formed on the image sensor by the second lens group, given by the evaluation formula E2 = (L2 / L1).

3. The system comprises an etalon that transmits light of a wavelength corresponding to the gap dimension of a pair of reflective films, a detachable mount lens, an image sensor, and a relay optical system that relays the intermediate image formed by the mount lens to re-image it to the image sensor and adjusts to incident light on the etalon at a desired angle. The relay optical system includes a first lens group that relays the intermediate image and emits collimated light that is incident on the etalon, and a second lens group that forms an image of the light emitted from the etalon onto the image sensor. A spectroscopic camera in which the maximum angle of incidence of light from the first lens group onto the etalon is 15 degrees.

4. The spectroscopic camera according to any one of claims 1 to 3, wherein the first lens group has at least one concave lens that emits collimated light to the etalon, and a convex lens is disposed on the incident side of the concave lens.

5. The spectroscopic camera according to any one of claims 1 to 3, wherein the etalon is positioned at the aperture of the relay optical system.

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