Focal Length Position Research Articles

Design of an optical passive semi-athermalization zoom lens

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.

Design of IR zoom lens system for long-range detection in uncooled LWIR camera

A new compact optical zoom lens system with variable focal length 100–200 mm for uncooled LWIR (8–12 μm) camera is designed. It is used for long-range detection. The optimized IR zoom lens consists of four group elements. The F/# of the zoom system is F/1.4 at all zoom positions. Its performance reaches the diffraction limit at each focal length position. Moreover, optical design and image quality are calculated by ZEMAX optical software. The imaging quality performance is steady during zoom process. In addition to the above benefits, the optimized IR zoom lens is light and compact (200 mm) with 4 lenses and only one of them has diffractive surface to lower production cost. Upon applying anti-reflection coating, the total transmittance of the optical system is enhanced from 2 to 99% at λ = 10 µm.

Offner型连续变焦中波红外光谱成像系统设计

In order to adapt to the application requirements of different field of view spectrometers, a continuous zoom medium-wave infrared spectrum imaging system based on offner scheme was designed. The front zoom system to achieve continuous zoom in the range of 60-300 mm was introduced in the system, and a grating-type offner concentric structure was used for spectral splitting and imaging. The working band was 3-5 m, the cooled medium-wave infrared detector was used, the F#=4.0 in this system. According to the object image exchange principle and the power distribution principle, the initial structure of the front zoom system and the relay system were calculated, and the zemax software was used to optimize each subsystem to meet the design parameters. The modulation transfer function of the final continuous zoom medium-wave infrared spectrum imaging system based on offner scheme was close to the diffraction limit at a spatial frequency of 33 lp/mm, and the root mean square radius of the spot was smaller than one pixel. The design results show that the system structure is simple, and the image quality is good and meets the design indicator requirements at each focal length position and each spectral segment.