Infrared wide-angle single lens for use in an infrared optical system

Abstract: In an infrared wide-angle single lens which is in a form of a positive meniscus lens, the following conditional expressions (1) through (6) are satisfied: (1) -50.0 th < r₁ < -3.5 th (2) -5 th < r₂ < -1.1 th (3) 2 < n < 4.5 (4) 0.1 f < d < 0.8 f (5) 0.5 f < bf < 1.5 f (6) 0.5 f < th < 2f where, an aperture stop (S) being disposed between an object plane (O) and a first surface (A1), d is the distance between the aperture stop and the first surface, th is the lens thickness, bf is the backfocus, r₁ is the radius of curvature of the first surface, r₂ is the radius of curvature of a second surface (A2), n is the refractive index of a vitric material at a wavelength of 10 µm, and f is the focal length.

Description: BACKGROUND OF THE INVENTION Field of the Invention The present invention relates to an infrared wide-angle single lens for use in an infrared optical system, which is employed in a non-contact type temperature measuring device serving primarily for detection of temperature conditions in a room and the like. Description of the Prior Art In a conventional non-contact type temperature measuring device, there has been used an inexpensive single-element infrared-ray detector. In such an infrared detector, a thermal image of infrared rays is formed on an infrared detector through an infrared optical system having a narrow angle of view. Therefore, when a temperature is measured over a wide range of a thermal object, a scanning operation is effected to measure temperatures of individual ranges. However, such infrared detectors have been so complicated in construction in all cases that it is difficult to reduce the size and price of the device, disadvantageously. US-A-4 507 551 defining the closest prior art from which the invention proceeds discloses an improved optical system for thermal imaging systems using wide field of view optics in conjunction with large detector arrays in which a detector cold shield, system aperture stop and scanning subassembly are placed in substantially the same location such that the size of the scanning optics is minimized and cold shielding efficiency is maximized. With the conventional arrangement of the infrared detector, the detector is involved with a problem that two-dimensional scanning is necessitated, which leads to difficulties in reducing the size and price of the device. In recent years, researches and studies have been advanced upon inexpensive arrayed or two-dimensional infrared detectors. As a result, there is a desire for making an infrared wide-angle lens for use in an infrared optical system capable of forming an image of an object in a wide range at a time on the detector and yet capable of making the system small in size and low in price. SUMMARY OF THE INVENTION Accordingly, an essential objective of the present invention is to provide an infrared wide-angle single lens which meets requirements of optical performance that an MTF (Modulation Transfer Function) is 50% or more (5 lp/mm) and that a peripheral light-quantity ratio is 85% or more over an entire range of a half angle of view of 35 degrees, despite being a single lens. In order to achieve the above objective, the present invention provides an infrared wide-angle optical system comprising a single lens which is in a form of a positive meniscus lens having a first surface made concave facing toward an object as an infrared source and a second surface made convex facing toward an imaging plane of the lens, and a aperture stop, wherein the infrared wide-angle single lens satisfies the following formula expressions (1) through (6) under the condition that an aperture stop is disposed between the object plane and the first surface of the lens: (1) -50.0 th < r 1 < -3.5 th (2) -5 th < r 2 < -1.1 th (3) 2 < n < 4.5 (4) 0.1 f < d < 0.8 f (5) 0.5 f < bf < 1.5 f (6) 0.5 f < th < 2f where d is the distance between the aperture stop and the first surface, th is the lens thickness, bf is the backfocus amount between the second surface and the Gaussian image plane (I G ), r 1 is the radius of curvature of the first surface, r 2 is the radius of curvature of the second surface, n is the refractive index of a vitric material of the lens at a wavelength of 10 µm, and f is the focal length. The expressions (1), (2), and (3) show conditions needed to obtain a necessary angle of view, height of image, and optical characteristics such as MTF and peripheral light-quantity ratio. Further, satisfaction of the condition (4) allows comatic aberration to be suppressed from occurring at the second surface, which enables the lens to obtain better optical characteristics. Also, when the lower limit of the condition (5) is met, assembling adjustment with an infrared detector is facilitated. Similarly, when the upper limit of the condition (5) is met, the entire optical system can be reduced in size. Furthermore, when the lower limit of the condition (6) is met, the edge thickness of the lens becomes greater, facilitating the machining process of the lens. Similarly, when the upper limit thereof is met, the influence of infrared absorption by the vitric material is reduced, allowing to obtain a sufficient quantity of light. Moreover, use of the infrared wide-angle single lens and an infrared detector in combination achieves to provide a non-contact temperature measuring device which is made small in size and low in price. Still further, use of the non-contact temperature measuring device of the present invention allows realization of an air conditioner system made small in size and low in cost which can offer optimum air-conditioning by using measurement results of detecting position of a human body and measuring temperatures of individual ranges in a room, without deteriorating the appearance of the air conditioner system. BRIEF DESCRIPTION OF THE DRAWINGS These and other objects and features of the present invention will become apparent from the following description taken in conjunction with the preferred embodiment thereof with reference to the accompanying drawings, in which: Fig. 1 is a schematic view showing a configuration of an infrared wide-angle single lens according to the present invention; Fig. 2 is a schematic view of a non-contact temperature measuring device according to the present invention; Fig. 3 is a schematic constitutional view of an air-conditioner according to the present invention; and Figs. 4 (a), (b), (c), (d-1), (d-2), (d-3), (d-4) and (d-5) are graphs showing aberration views of the infrared wide-angle single lens of the present invention. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS The following describes embodiments of the present invention with reference to the accompanying drawings. Fig. 1 shows a configuration of an infrared wide-angle single lens according to an embodiment of the present invention. The infrared wide-angle single lens 1 has a figure of a positive meniscus lens having a first surface A1 made concave facing toward an object plane O as an infrared light source and a second surface A2 made convex facing toward an imaging plane of the lens. An aperture stop S is disposed between the object plane O and the first surface A1. The examples 1 through 4 of the infrared wide-angle single lens are shown with concrete physical numeric values listed in Tables 1 through 4 respectively under the condition that silicon is used as a vitric material of the lens. It is to be noted here that other materials than silicon may be used as a vitric material of the lens so long as the condition (3) is satisfied. In Tables 1 through 4, reference character d denotes the distance between the aperture stop S and the first surface A1 on the axis; th denotes the lens thickness; bf denotes the backfocus representing the distance between the second surface and the Gaussian image plane I G ; r 1 denotes the radius of curvature of the first surface; r 2 the radius of curvature of the second surface A2; n the refractive index of the vitric material of the lens at a wavelength of 10 µm; f the focal length; def the defocusing amount representing the distance between the proximate-axis image forming position (the Gaussian image plane I G ) and the real image plane I R as shown in Fig. 1; F denotes the F number; and w the half angle of view. The first through fourth Examples of the infrared wide-angle single lens of the present invention constructed as shown in Tables 1 through 4 meet optical performance requirements that MTF of the lens is 50% or more (5 lp/mm) and that a peripheral light-quantity ratio is 85% or more over the entire range of a half angle of view of 35 degrees, despite being a single lens. Aberration views of, e.g., the first Example shown in Table 1 are given in Figs. 4(a) through 4(c) and 4(d-1) through 4(d-5). In the first Example, Fig. 4(a) shows a spherical aberration (mm) indicated by a real line and a sine condition indicated by a broken line where the horizontal axis represents the spherical aberration and the vertical axis represents the height of light rays, Fig. 4(b) shows an astigmatism (mm) of the lens where a real line indicates the case of meridional rays and a broken line indicates the case of sagittal rays, and Fig. 4(c) shows a distortion aberration (%). Figs. 4(d-1) through 4(d-5) show ray aberrations (mm) of the lens, where real lines indicate the case of meridional rays and broken lines indicate the case of sagittal rays, where the horizontal axis represents the height of light rays and FA denotes a field angle. Similarly, the second through fourth Examples shown in Tables 2 through 4 also satisfy the requirements of optical performance as mentioned before. Fig. 2 shows an arrangement of a non-contact temperature measuring device when the infrared wide-angle single lens of the present embodiment is used therein. In Fig. 2, reference numeral 1 denotes an infrared wide-angle single lens of the present invention; 2 an aperture stop; 3 a pyroelectric infrared detector arranged longitudinally (vertically in the figure) to form an eight-element array; 4 a chopper for intermittently shielding an infrared ray; and 5 a motor for rotating the entire unit for scanning an object in the lateral direction. Referring next to the operation of the non-contact temperature measuring device of Fig. 2, the incident infrared ray emitted from an object is intermittently shielded by the chopper 4 and passed through the aperture stop 2, and an image of the object is formed on the pyroelectric infrared detector 3 through the infrared wide-angle single lens 1, whereby one-dimensional infrared images of longitudinally 8-divided ranges are detected. Further, by scanning in the lateral (horizontal in the figure) direction by the motor 5, two-dimensional infrared images are detected. It is also possible to detect a position of a human body from variations in measured temperatures of the individual ranges. In this way, according to the present embodiment, using an infrared detector in combination with an infrared wide-angle single lens of the present embodiment, it becomes possible to measure temperatures of the individual measurement ranges, which allows to realize a small-sized, low-priced non-contact temperature measuring device. Fig. 3 shows an arrangement of an air-conditioner using a non-contact temperature measuring device of the present embodiment. Referring to Fig. 3, reference numeral 31 denotes a non-contact temperature measuring device of the present invention; 32 denotes a data forming unit for forming temperature data of individual ranges from signals generated by the non-contact temperature measuring device 31; 33 denotes a control signal forming unit for forming an air-conditioning control signal based on the data obtained from the data forming unit 32; 34 denotes an air-conditioning control unit for controlling air-blow force, direction of wind, temperature of emission wind of an air-conditioner; 35 denotes a main body of the air-conditioner; and 36 denotes a blowoff port. As described above, by using the non-contact temperature measuring device of the present embodiment in an air-conditioner, it becomes possible to realize an air-conditioner of a small size and low cost which can offer optimum air-conditioning depending on the measurement results of detecting position of a human body and measuring temperatures of individual ranges in a room, without deteriorating the system appearance. Although the present invention has been fully described by way of example with reference to the accompanying drawings, it is to be noted here that various changes and modifications will be apparent to those skilled in the art. Therefore, unless otherwise such changes and modifications depart from the scope of the present invention as defined by the appended claims, they should be construed as included therein. F = 1.4 f = 3.1 (mm) w = 35 (deg) n = 3.4177 d 1.11 r 1 -17.7 th 2.2 r 2 - 5.7 bf 3.37 def -0.45 (Unit: mm) F = 1.4 f = 3.1 (mm) w = 35 (deg) n = 3.4177 d 1.03 r 1 -18.2 th 2.5 r 2 - 5.8 bf 3.40 def -0.45 (Unit: mm) F = 1.4 f = 2.9 (mm) w = 37.5 (deg) n = 3.4177 d 1.03 r 1 -14.6 th 2.0 r 2 - 5.2 bf 2.91 def -0.45 (Unit: mm) F = 1.4 f = 2.93 (mm) w = 37.5 (deg) n = 3.4177 d 1.11 r 1 -21.8 th 2.85 r 2 - 5.8 bf 3.20 def -0.45 (Unit: mm)

Claims: An infrared wide-angle optical system comprising a single lens (1) which is a positive meniscus lens having a first surface (A1) made concave facing toward an object plane (O) and a second surface (A2) made convex, and an aperture stop (S), characterized in that said single lens (1) satisfies the following conditional expressions (1) to (6): (1) -50.0 th < r 1 < -3.5 th (2) -5 th < r 2 < -1.1 th (3) 2 < n < 4.5 (4) 0.1 f < d < 0.8 f (5) 0.5 f < bf < 1.5 f (6) 0.5 f < th < 2f where th is the lens thickness, r 1 is the radius of curvature of the first surface (A1), r 2 is the radius of curvature of the second surface (A2), n is the refractive index of a vitric material of the lens at a wavelength of 10 µm, the aperture stop (S) is disposed between the object plane (O) and the first surface (A1), d is the distance between the aperture stop (S) and the first surface (A1), f is the focal length of the lens (1), and bf is the backfocus. The infrared wide-angle single lens as claimed in claim 1, wherein the vitric material of the lens is silicon. A non-contact temperature measuring device comprising an infrared wide-angle single lens (1) as claimed in claim 1 or 2 and an infrared detector (3). The non-contact temperature measuring device as claimed in claim 3, further comprising a chopper (4) for intermittently shielding an infrared ray and rotating means (5) for rotating the entire unit for scanning in a direction orthogonal to the array of the infrared detector to form a two-dimensional infrared image. The non-contact temperature measuring device as claimed in claim 3 or 4, wherein the infrared detector is a pyroelectric detector. An air-conditioner comprising: a non-contact temperature measuring device (31) as claimed in anyone of the claims 3 to 5; data forming means (32) for forming temperature data of individual ranges based on a signal fed from said non-contact temperature measuring device (31); control signal forming means (33) for forming an air-conditioning control signal based on the data obtained from said data forming means (32); and air-conditioning control means (34) for controlling the air-conditioning based on the air-conditioning control signal obtained from said control signal forming means (33).

Inventors: YAMAMOTO YOSHIHARU, YOSHIKAWA MOTONOBU, YAMAMOTO, YOSHIHARU, YOSHIKAWA, MOTONOBU
Applicants: MATSUSHITA ELECTRIC IND CO LTD, MATSUSHITA ELECTRIC INDUSTRIAL CO., LTD.
Application year: 1993
Main classification: G02B13
IPC codes: G08B13, G02B1, G01J5, G02B13