Traditional zoom lenses cannot clearly image during the entire zoom process when the ambient temperature changes and needs to focus frequently at middle focal length positions. An innovative design method called the optical passive semi-athermalization (OPSA) design for zoom optical systems is proposed which, based on the difference in the focusing sensitivity of the focusing group at short and long focal length positions, seeks out sensitive groups that have a greater impact on the imaging quality at the short focal position. By changing the temperature characteristics of the temperature-sensitive lenses in these groups, an OPSA zoom optical system can be realized, which exhibits a compact structure and excellent imaging quality. Under the ambient temperature of -40∘ C to +60∘ C, the OPSA zoom lens needs to refocus only once at the long focal length position, which can ensure an image clearly during the entire zoom process. Remarkably, this innovative method not only mitigates the frequent focusing challenges in traditional zoom lenses, but also contributes to the diminutive size.
Addressing the urgent need for long-distance dim target detection with a wide field-of-view and high sensitivity, this paper proposes a visible and short-infrared dual-band common-aperture optical system characterized by a broad field and extended focal length. To achieve system miniaturization and high-sensitivity target detection, the visible and infrared optical systems share a Ritchey-Chretien primary and secondary mirror. The primary optical path is segmented into visible light (0.45-0.75 µm) and short-wave infrared (SWIR) (2-3 µm) bands by a dichroic spectral splitter prism. The SWIR optical system utilizes four short-wave cooled infrared detectors, and wide-field stitching is achieved using a field-of-view divider. While ensuring the high cold-shield efficiency of cooled infrared detectors, this common-aperture optical system delivers visible and SWIR dual-band images with expansive fields, elongated focal lengths, and sizable apertures. The visible-light optical system has a focal length of 277 mm, a field-of-view of 2.3∘×2.3∘, and an entrance pupil diameter of 130 mm. Meanwhile, the SWIR optical system features a focal length of 480 mm, a field-of-view of 2.26∘×1.8∘ and an entrance pupil diameter of 160 mm. The design outcomes suggest that the imaging quality of the optical system approaches the diffraction limit. This visible/SWIR common-aperture optical system exhibits high sensitivity, a large field-of-view, compact structure, and excellent imaging quality, thereby meeting the requirements for long-distance dim target detection and imaging.
