The lens should be designed around the detector's active area, pixel pitch, resolution, spectral response, and required image circle. Focal length and F/# should also be selected according to the required FOV, spatial resolution, sensitivity, and system geometry. Matching lens performance to detector resolution helps avoid over- or under-specifying the optical system.

Different infrared bands require different combinations of optical materials, coatings, detector technologies, and thermal considerations. The required spectral range should therefore be defined early in the design process, particularly for systems operating across multiple bands or under changing environmental conditions.

Athermalization should be considered when the system must maintain focus and imaging performance across a significant operating-temperature range. Temperature changes can affect material refractive index, optical element dimensions, housing dimensions, and focal position. Depending on the system requirements, passive optical/mechanical compensation or active focus control may be used.

Important parameters include detector format and pixel pitch, spectral band, focal length, F/#, FOV, MTF, transmission, distortion, operating temperature, and focus mechanism. For cooled systems, the detector's cold-stop geometry and system pupil requirements may also need to be considered during optical design.

A custom IR lens is appropriate when an existing configuration cannot meet the required spectral range, detector format, FOV, focal length, F/#, image quality, temperature range, packaging, or mechanical interface. Customization may also be required for athermalized, multi-band, motorized-focus, or specialized OEM imaging systems.

Material selection depends on the operating wavelength, refractive properties, dispersion, thermal behavior, environmental durability, manufacturability, and system requirements. Anti-reflection coatings should be optimized for the required spectral band, AOI, substrate materials, and operating environment to minimize reflection losses and maximize system transmission.

For an efficient engineering review, provide the spectral range, detector model or detector format and pixel pitch, focal length or required FOV, F/#, working distance, operating-temperature range, image-quality requirements, focus method, mechanical envelope, environmental requirements, and quantity. Detector specifications, mechanical drawings, target MTF, or an existing optical prescription can also be provided when available.