A variable magnification optical system consists of, in order from an object side to an image side, a first lens group, a second lens group, and a subsequent lens group. The variable magnification optical system satisfies a predetermined conditional expression for a partial dispersion ratio related to F line, C line, and a wavelength of 1970.09 nm, a d-line back focus of the variable magnification optical system at a telephoto end, a back focus in any one wavelength from a wavelength of 1300 nm to a wavelength of 2325.42 nm at the telephoto end, and a d-line focal length of the variable magnification optical system at the telephoto end.

A variable magnification optical system consists of, in order from an object side to an image side, a first lens group, a second lens group, and a subsequent lens group. The variable magnification optical system satisfies a predetermined conditional expression for a partial dispersion ratio related to F line, C line, and a wavelength of 1970.09 nm, a d-line back focus of the variable magnification optical system at a telephoto end, a back focus in any one wavelength from a wavelength of 1300 nm to a wavelength of 2325.42 nm at the telephoto end, and a d-line focal length of the variable magnification optical system at the telephoto end.

A three-piece infrared single wavelength projection lens system, in order from an image side to an image source side: a stop; a first lens element with a positive refractive power having an image-side surface being convex near an optical axis and an image source-side surface being concave near the optical axis; a second lens element with a negative refractive power having an image source-side surface being concave near the optical axis; and a third lens element with a positive refractive power having an image-side surface being concave near the optical axis and an image source-side surface being convex near the optical axis. Such arrangements can provide a three-piece infrared single wavelength projection lens system with better image sensing function.

A three-piece infrared single wavelength projection lens system, in order from an image side to an image source side: a stop; a first lens element with a positive refractive power having an image-side surface being convex near an optical axis and an image source-side surface being concave near the optical axis; a second lens element with a negative refractive power having an image source-side surface being concave near the optical axis; and a third lens element with a positive refractive power having an image-side surface being concave near the optical axis and an image source-side surface being convex near the optical axis. Such arrangements can provide a three-piece infrared single wavelength projection lens system with better image sensing function.

A freeform varifocal optical assembly includes at least three optical modules including a first plurality of optical elements including Pancharatnam-Berry phase (PBP) lenses, polarization sensitive hologram (PSH) lenses, metamaterials, or combinations thereof. The plurality of optical elements of each optical module include a property associated with a Zernike polynomial. Each of the first and the three optical modules are configurable between a plurality of optical powers. The freeform varifocal optical assembly is configurable to output a predetermined wavefront in response to an input wavefront.

A diamond lens (3) configured for use in a multispectral imaging system (1). The diamond lens (3) has a largest linear dimension of at least 10 mm and is formed from diamond material having a birefringence An of greater than 1×10.sup.−4, measured over a specified area of at least 4 mm by 4 mm through a maximum thickness of at least 400 μm. A multispectral imaging system (1) comprising the diamond lens (3) and a component (2) comprising the diamond lens are also described.

An optical lens assembly includes, in order from the object side to the image side: a stop, a first lens element, a second lens element, a third lens element, and an infrared bandpass filter. An entrance pupil diameter of the optical lens assembly is EPD, a half of a maximum field of view of the optical lens assembly is HFOV, and the following condition is satisfied: 0.59<EPD/tan(HFOV)<1.33.

An optical lens assembly includes four lens elements which are, in order from an object side to an image side along an imaging optical path: a first lens element, a second lens element, a third lens element and a fourth lens element. The first lens element has positive refractive power. The second lens element has an image-side surface being concave in a paraxial region thereof. The third lens element has an object-side surface being concave in a paraxial region thereof. The fourth lens element with negative refractive power has an object-side surface being convex in a paraxial region thereof and an image-side surface being concave in a paraxial region thereof, and at least one of the object-side surface and the image-side surface of the fourth lens element has at least one inflection point in an off-axis region thereof.

A Mid-Wave Infrared (MWIR) objective and relay lens system has an F# of 3.33 and angular field of view of 15.28°. It is deployed, with a focal plane and scanning system, on airborne platforms for wide area motion imagery. It is corrected for monochromatic and chromatic aberrations over of 3.3 to 5.1 micrometers. Effective focal length is 20 inches, and the overall length is 40.70 inches. The lens has, from object to image, two groups of optical elements with a cold shield/aperture stop 6 inches from the image plane. Group 1 acts as an objective lens with a positive power and three elements, Group 2 acts as a relay lens has a positive power and four elements. The lens is made of Germanium and Silicon. It used in a scanning system in a pre-objective configuration where the fast scan mirror is located in front of the lens system.

A Mid-Wave Infrared (MWIR) objective and relay lens system has an F# of 3.33 and angular field of view of 15.28°. It is deployed, with a focal plane and scanning system, on airborne platforms for wide area motion imagery. It is corrected for monochromatic and chromatic aberrations over of 3.3 to 5.1 micrometers. Effective focal length is 20 inches, and the overall length is 40.70 inches. The lens has, from object to image, two groups of optical elements with a cold shield/aperture stop 6 inches from the image plane. Group 1 acts as an objective lens with a positive power and three elements, Group 2 acts as a relay lens has a positive power and four elements. The lens is made of Germanium and Silicon. It used in a scanning system in a pre-objective configuration where the fast scan mirror is located in front of the lens system.