Super wide angle lens arrangement for infrared applications
More particularly, a wide-angle optical assembly for an IR camera is described, comprising a lens system consisting of an object-side lens ( 2 ) and an image-side lens ( 3 ), and an aperture stop ( 1 ) on the object-side of the assembly, wherein: the object-side lens ( 2 ) and the image-side lens ( 3 ) are positive meniscus lenses; all centers of vertex radii of the lens surfaces are oriented towards the object-side, defining for each lens a concave surface and a convex surface; the thickness ( 8 ) of the object-side lens ( 2 ) is larger than 0.60 EFL; the thickness ( 9 ) of the image-side lens ( 3 ) is between 0.30 EFL and 0.70 EFL; 0.95<BFL/EFL<1.2; and, the EFL amounts to between 55% and 75% of the image plane diagonal.
1. A wide-angle optical assembly for an IR camera, comprising a lens system comprising an object-side lens, an image-side lens, and an aperture stop on an object-side of the assembly, wherein:
the object-side lens and the image-side lens are positive meniscus lenses;
all centers of vertex radii of the surfaces of the lenses are oriented towards the object-side, defining for each lens a concave surface and a convex surface;
a thickness of the object-side lens is larger than 0.60 EFL;
a thickness of the image-side lens is between 0.30 EFL and 0.70 EFL;
0.95<BFL/EFL<1.2; and,
the EFL is between 55% and 75% of the image plane diagonal; and where EFL is the effective focal length of the optical assembly and BFL is the back focal length of the optical assembly.
2. The optical assembly of claim 1 , wherein one or more surfaces of the lenses are aspherical.
3. The optical system of claim 2 , wherein:
a curvature of the concave surface of the object-side lens increases with the lens height;
a curvature of the convex surface of the object-side lens decreases with the lens height;
a curvature of the concave surface of the image-side lens decreases with the lens height; and,
a curvature of the convex surface of the image-side lens decreases with the lens height.
4. The optical assembly of claim 1 , wherein at least one lens is provided with a diffractive structure.
5. The optical assembly of claim 1 , wherein the lenses comprise IR transparent material with a refraction index of more than 2.1.
6. The optical assembly of claim 1 , further comprising one or more optically flat and IR-transparent window(s) for protection of the assembly.