Infrared imaging lens and infrared camera
An infrared imaging lens ( 1 ) includes a plurality of lenses (L 1 to L 3 ) which are disposed in respective positions, the plurality of lenses each being made of glass having a refractive index of 2.8 to 4.0 measured at a wavelength of 10 μm, the infrared imaging lens having an image circle having a diameter which is 0.7 times to 1.3 times a focal length of the infrared imaging lens.
1 . An infrared imaging lens, comprising a plurality of lenses which are disposed in respective positions,
the plurality of lenses each being made of glass having a refractive index of 2.8 to 4.0 measured at a wavelength of 10 μm, wherein
a first lens,
a second lens, and
a third lens are disposed in this order from an object side to an image surface side, the third lens has positive power and a meniscus shape that is convex to the image surface side, and
the infrared imaging lens has an image circle on an image surface, the image circle having a diameter which is 0.7 time to 1.3 times a focal length of the infrared imaging lens.
2 . The infrared imaging lens as set forth in claim 1 , wherein the infrared imaging lens has, in the image circle, a modulation transfer function of not less than 0.17 in a wavelength range of 7 μm to 14 μm at a spatial frequency of 41.7 cycles/mm.
3 . An infrared imaging lens, comprising a plurality of lenses which are disposed in respective positions,
the plurality of lenses each being made of glass having a refractive index of 2.8 to 4.0 measured at a wavelength of 10 μm,
the infrared imaging lens having, in the image circle, a modulation transfer function of not less than 0.17 in a wavelength range of 7 μm to 14 μm at a spatial frequency of 41.7 cycles/mm.
4 . The infrared imaging lens as set forth in claim 1 , wherein the first lens has positive power and a meniscus shape that is convex to the object side.
5 . The infrared imaging lens as set forth in claim 4 , wherein a focal length f1 of the first lens and a focal length f of the infrared imaging lens satisfy the following relational expression:
1.0 ≤f 1 /f≤ 2.9.
6 . The infrared imaging lens as set forth in claim 4 , wherein an effective diameter of an object-side surface of the first lens serves as an aperture of the infrared imaging lens.
7 . The infrared imaging lens as set forth in claim 4 , wherein the second lens has positive power.
8 . The infrared imaging lens as set forth in claim 7 , wherein
the third lens has a highest power among the first lens, the second lens, and the third lens.
9 . The infrared imaging lens as set forth in claim 4 , wherein the second lens has a meniscus shape that is convex to the image surface side.
10 . The infrared imaging lens as set forth in claim 4 , wherein at least one of an image surface-side surface of the second lens and an object-side surface of the third lens is a diffractive surface.
11 . The infrared imaging lens as set forth in claim 4 , wherein a focal length f3 of the third lens and a focal length f of the infrared imaging lens satisfy the following relational expression:
0.8 ≤f 3 /f≤ 1.2.
12 . The infrared imaging lens as set forth in claim 1 , wherein the infrared imaging lens has a half angle of view of 21° to 36°.
13 . The infrared imaging lens as set forth in claim 1 , wherein the infrared imaging lens has, in the image circle, a modulation transfer function of not less than 0.50 in a wavelength range of 7 μm to 14 μm at a spatial frequency of 20.85 cycles/mm.
14 . The infrared imaging lens as set forth in claim 1 , wherein the infrared imaging lens has a relative illuminance of not less than 40% on the image surface in the image circle.
15 . The infrared imaging lens as set forth in claim 1 , wherein the glass is chalcogenide glass.
16 . The infrared imaging lens as set forth in claim 15 , wherein the chalcogenide glass has an infrared absorption edge wavelength of not less than 18 μm at which the chalcogenide glass has a light transmittance of 20% measured at a thickness of 2 mm.
17 . The infrared imaging lens as set forth in claim 1 , wherein the infrared imaging lens has an F-number of 1.0 to 1.2.
18 . The infrared imaging lens as set forth in claim 1 , wherein the infrared imaging lens has a focal length of 7 mm to 12 mm.
19 . The infrared imaging lens as set forth in claim 1 , wherein the infrared imaging lens has a total lens length of not more than 30 mm.
20 . An infrared camera, comprising:
an infrared imaging lens recited in claim 1 ; and
an infrared image sensor.