초록 ▼

A compact objective lens is disclosed which is particularly suitable for infrared optical systems. The lens features a simple design with only two lens elements, namely a first lens element receiving incident radiation and having front and rear surfaces, and a second lens element receiving incident

A compact objective lens is disclosed which is particularly suitable for infrared optical systems. The lens features a simple design with only two lens elements, namely a first lens element receiving incident radiation and having front and rear surfaces, and a second lens element receiving incident radiation from the first element and having front and rear surfaces. The lens forms an image of a scene on a focal plane. At least three of the four surfaces of the elements are aspheric surfaces. The lens has an f-number less than about 2, a field-of-view less than about 30 degrees, and an effective focal length less than about 6 inches. The elements are made from a material selected to pass radiation in the infrared band of the electromagnetic spectrum, e.g., germanium. The lens is suitable for use as an objective lens for a long-wave infrared sight for small arms, e.g., rifle or shoulder-launched surface to air missile launching system, i.e., a lens optimized for operating in the electromagnetic spectrum between about 7.5 and about 15 micrometers.

대표청구항 ▼

I claim: 1. A two-element objective lens for an: infrared optical system, the lens consisting of: a) a first lens element receiving incident radiation and having front and rear surfaces, and b) a second lens element receiving incident radiation from the first lens element and having front and rear

I claim: 1. A two-element objective lens for an: infrared optical system, the lens consisting of: a) a first lens element receiving incident radiation and having front and rear surfaces, and b) a second lens element receiving incident radiation from the first lens element and having front and rear surfaces, the first and second lens elements forming an image on a focal plane; and c) an aperture stop placed adjacent to the first lens element and between the first and second lens elements; wherein at least three of said surfaces of the first and second lens elements comprise aspheric surfaces; the lens has an f-number less than about 2; the lens has a field-of-view less than about 30 degrees; the lens has an effective focal length less than about 6 inches; and the first and second lens elements are made from a material selected to pass radiation in the infrared band of the electromagnetic spectrum; and wherein the lens features diffraction-limited performance, in which the modulation transfer function approximately matches a diffraction limit of the lens. 2. The lens of claim 1, wherein the lens has an effective focal length between two and four inches. 3. The lens of claim 1, wherein the lens has an effective focal length of between one and two inches. 4. The lens of claim 1, wherein all four surfaces comprise aspheric surfaces and wherein the first and second lens elements are constructed from a material selected from the group of materials consisting of germanium, gallium arsenide, zinc selenide and zinc sulfide. 5. The lens of claim 1, wherein the lens exhibits a maximum radial field of between five and fifteen degrees. 6. The lens of claim 4, wherein the lens exhibits an f-number of less than 2. 7. Gunnery apparatus comprising: a weapon; and a long-wave infrared sight mounted to the weapon; wherein the sight includes an objective lens as claimed in claim 1. 8. The apparatus of claim 7, wherein the weapon comprises a rifle. 9. The lens of claim 1, wherein the first and second lens elements are made from a material selected to pass radiation in a single band in the infrared portion of the electromagnetic spectrum. 10. The lens of claim 9 wherein the single band comprises the long-wave infrared band. 11. A long-wave infrared sight for weapon comprising: a detector for detecting infrared radiation; and a two-element objective lens consisting of a) a first lens element receiving incident radiation and having front and rear surfaces, and b) a second lens element receiving incident radiation from the first element and having front and rear surfaces and directing light onto a detector, the detector located at a focal plane of the objective lens; and an aperture stop placed adjacent to the first lens element and between the first and second lens elements; wherein at least three of said surfaces of the first and second lens elements comprise aspheric surfaces; the lens has an f-number less than about 2; the lens has a field-of-view less than about 30 degrees; the lens has an effective focal length less than about 6 inches; and the first and second lens elements are made from a material selected to pass radiation in the infrared band of the electromagnetic spectrum; and wherein the lens features diffraction-limited performance, in which the modulation transfer function approximately matches a diffraction limit of the lens. 12. The sight as claimed in claim 11, wherein the lens has an effective focal length of between two and four inches. 13. The sight as claimed in claim 11, wherein the lens has an effective focal length of between one and two inches. 14. The sight as claimed in claim 11, wherein all four surfaces comprise aspheric surfaces and wherein the first and second lens elements are constructed from a material selected from the group of materials consisting of germanium, gallium arsenide, zinc selenide and zinc sulfide. 15. The sight as claimed in claim 11, wherein the lens exhibits a maximum radial field of between five and fifteen degrees. 16. The sight as claimed in claim 15, wherein the lens exhibits an f-number of less than 2. 17. The sight of claim 11, wherein the weapon comprises a small arms weapon.