| 摘要 |
A wide-angle lens 1 for infrared radiation, suitable for use in a cooled infrared camera, has two lens element groups 2, 3 arranged along an optical axis A. The groups have a plurality of lens elements 22, 24, 26, 28, 32, 34 and there is also a detector unit 4 which may consist of a Focal Plane Array (FPA), filter, cold-light diaphragm and window. The lens element group nearest the object 2 has a negative refractive power and the lens element group nearest the image 3 has a positive refractive power. The quotient of the back focal length s' and the focal length f is greater than 3.5 and may be less than 4.5. The quotient of the distance L from the first lens element 22 closest to an object to the image plane and the focal length f is less than 15 and may be greater than 12. The lens element closest to the object may consist of silicon or sapphire and may also have spherical shaping. The object-side element group may consist only of lenses with a negative refractive power and the image-side element group may consist only of lenses with a positive refractive power. |
