Far-infrared camera lens, lens unit, and imaging apparatus
Three lenses formed of ZnS are used in combination. A first lens is a meniscus lens having a middle portion which is convex on an object side. A second lens has a middle portion that is a meniscus, which is concave on an object side and has positive refractive power, and a peripheral portion, which is convex on the object side. The first and second lenses have positive refractive power in combination. A third lens is provided adjacent to the second lens with a distance therebetween 1 mm or less and has a middle portion, which is a convex meniscus on an object side, and a peripheral portion which is concave on the object side. A diffraction surface is formed in either surface of the lens.
1. A far-infrared camera lens comprising:
a first lens that is formed of ZnS and has a middle portion that is a meniscus, which is convex on an object side and concave on an image surface side, and a peripheral portion, which is concave on the object side and convex on the image surface side;
a second lens that is formed of ZnS and has a middle portion that is a meniscus, which is concave on an object side and has positive refractive power, and a peripheral portion, which is convex on the object side; and
a third lens that is formed of ZnS, is provided adjacent to the second lens, and has a middle portion which has a convex meniscus shape on an object side and a peripheral portion which is concave on the object side, wherein
a diffraction surface is formed in either lens surface of at least one of the first lens, the second lens, or the third lens, and
a viewing angle is 50° to 70°.
2. The far-infrared camera lens according to claim 1 , wherein
the third lens is provided adjacent to the second lens with a distance therebetween 1 mm or less.
3. The far-infrared camera lens according to claim 1 , wherein
a total focal distance f is 6 mm to 11 mm, and
a focal distance f 12 of only the first and second lenses is 5 mm to 18 mm.
4. The far-infrared camera lens according to claim 1 , wherein
when the total focal distance of the three lenses is f, the focal distance of only the first and second lenses is f 12 , 0.9≦f 12 /f≦1.6.
5. The far-infrared camera lens according to claim 1 , wherein
the first, second, and third lenses formed of ZnS are manufactured by molding ZnS raw powder by heat compression using a lens-shaped mold.
6. The far-infrared camera lens according to claim 1 , wherein
in all of the first, second, and third lenses,
sag amount<5 mm,
1.5 mm<central thickness<8 mm, and
1 mm<edge thickness<8 mm.
7. A lens unit using the lens according to claim 1 .
8. An imaging apparatus comprising:
the lens unit according to claim 7 ; and
an imaging unit that images an image formed on the lens unit.
9. The far-infrared camera lens according to claim 1 , wherein
the first lens is located at a first distance from an image plane,
the second lens is located at a second distance from the image plane, the second distance being smaller than the first distance, and
the third lens is located at a third distance from the image plane, the third distance being smaller than the second distance.