Long-wave infrared (LWIR) objective lenses are typically utilized in conjunction with uncooled detectors. With the continual advancement of uncooled detectors in recent years, the cost-effectiveness of LWIR imaging systems has steadily improved. Currently, LWIR objective lenses hold the largest market share among infrared objective lenses, particularly in civilian applications. Given the proliferation of long-wave infrared imaging systems in civilian spheres, cost control becomes a significant consideration in LWIR objective lens design. Presented herein is an LWIR objective lens boasting a large field of view and aperture:
| Spec | Value |
|---|---|
| Focal length | 6mm |
| F# | 1 |
| Wavelength | 8-12um |
| FOV | 127° |
| Sensor | 1024×768,12um |
| Athermalization | -32℃—65℃ |
Given the typical pairing of LWIR lenses with uncooled detectors, lenses are designed with a high F-number, typically ranging between 1 and 2, to enhance sensitivity to temperature differentials and minimize stray light interference. This particular lens features an F-number of 1, indicative of a large relative aperture. As infrared detectors increase in size and pixel density, so do the demands placed upon lens field of view and resolution. The 1024×768, 12µm detector employed in conjunction with this lens represents a sizable array detector.
While an objective lens with a large aperture and field of view facilitates expansive scene imaging while upholding image quality, it also presents challenges in lens design and fabrication. Increasing optical system complexity is one approach to enhancing performance. However, for infrared objective lenses, which often employ costly infrared crystal materials, overly intricate lens structures may hinder market adoption. The judicious integration of aspherical lenses can maintain performance while streamlining structure. This lens incorporates a high-order aspherical lens element to achieve superior imaging performance, as evidenced by the following modulation transfer function (MTF) and spot metrics:
Comprising a total of seven lenses, this lens boasts a relatively straightforward structure, with an MTF exceeding 20% at 40 line pairs per millimeter, thereby meeting the requirements of the 1024×768, 12µm detector.
Athermalization
Infrared optical systems may operate under significant temperature variations, necessitating athermalization to maintain consistent imaging performance. Temperature fluctuations can alter lens parameters such as refractive index, curvature, and air spacing, consequently affecting focal length and image quality. Athermalized infrared objective lenses, also known as non-thermal treatment lenses, mitigate these effects.
This lens employs a combination of diverse infrared materials to achieve athermalization across a temperature range spanning from -32°C to 65°C. Imaging performance remains consistent across varying temperatures, obviating the need for re-focusing.
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