Design and analysis of a compact wide-field unobscured zoom mirror system (original) (raw)

Unobscured reflective zoom systems

Zoom Lenses, 1995

All-reflective telescopes have found significant utilization in the astronomical community, government, and industry. Until recently, the concept of an all-reflective zoom telescope, particularly having an unobscured pupil, with meaningful capabilities was unknown. Several designs of unobscured-pupil zoom telescopes comprising only three mirrors are presented. The designs discussed have fields-of-view up to 3° by 3°, F/#s as low as 3 and zoom ratios of up to 4:1. The RMS geometric blur diameter for one zoom telescope,having a 4:1 zooming range, was found to be 45 jradians in the wide FOV condition (2° by 2° and F/4).

All-reflective four-element zoom telescope: design and analysis

1990 Intl Lens Design Conf, 1991

The design process for an all-reflective zoom telescope is presented. Special consideration is given to the development of the starting configuration and the subsequent optimization proce. The non-traditional optimization route utilized as a result of the unusual pupil characteristics of such an all-reflective zoom system is examined. Results of the design are presented.

Development of Linear Astigmatism Free—Three Mirror System (LAF-TMS)

Publications of the Astronomical Society of the Pacific, 2020

We present the development of Linear Astigmatism Free-Three Mirror System (LAF-TMS). This is a prototype of an off-axis telescope that enables very wide field of view (FoV) infrared satellites that can observe Paschen-α emission, zodiacal light, integrated star light, and other infrared sources. It has the entrance pupil diameter of 150 mm, the focal length of 500 mm, and the FoV of 5.5°× 4.1°. LAF-TMS is an obscuration-free off-axis system with minimal out-of-field baffling and no optical support structure diffraction. This optical design is analytically optimized to remove linear astigmatism and to reduce high-order aberrations. Sensitivity analysis and Monte-Carlo simulation reveal that tilt errors are the most sensitive alignment parameters that allow ∼1. Optomechanical structure accurately mounts aluminum mirrors, and withstands satellite-level vibration environments. LAF-TMS shows

Step-zoom dual-field-of-view infrared telescope

Applied Optics, 2003

The design of a dual-field-of-view telescope for an 8 -12-m imaging waveband is described. Preliminary calculations are made to determine the first-order parameters of the narrow-and the wide-field modes. To achieve a switchable dual-field-of-view system, one uses an optical configuration based on the axial motion of a single lens group along the optical axis. The same lens is also used for focusing at near objects and for athermalization by small axial movement. A total of six lenses with one conic surface are used in the design, making the telescope cost effective and lightweight. The final optical design is presented, along with the aberrations curves and modulation transfer function plots, showing excellent performance in both fields of view.

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

Journal of Optics

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.

A wide-field near-infrared camera and spectrograph for the Mt. Abu 1.2 m telescope

Ground-based and Airborne Instrumentation for Astronomy II, 2008

We describe the design and optimization of a wide-field near-infrared camera and spectrograph (NICAS) for Mt Abu 1.2 m, f/13 Cassegrain telescope of Physical Research Laboratory. The principal science goals include photometric mapping of star forming regions and medium resolution spectroscopy of Young Stellar Objects, evolved stars and transient sources. The design goals are to achieve seeing-limited angular resolution in an un-vignetted field of view of ~ 8'x8' with 0.5′′ per pixel (of 18.5 µm) on a HgCdTe 1024x1024 infrared array, requiring a two-fold Cassegrain focal reduction. In addition to the imaging, the instrument is required to have spectroscopic capability with a resolving power of 10 3 in the 0.85 -2.5 µm region, needing a dispersion of 1 nm per pixel. Finally, since our telescope has a moderate aperture, the throughput losses need to be minimized. The specifications are achieved by an optical design using 9 singlet lenses. Only those lens materials are chosen for which measured values are available for refractive indices at 77 K (detector operating temperature), changes of indices with temperature, and thermal coefficients of expansion. The design is optimized to give sharpest images at 77 K. The optical path is folded by 90° after collimation by a fold-mirror and reimaged on the detector. The fold-mirror is replaced by a diffraction grating for spectrograph mode. In order to minimize the reflection losses, all the lenses will be anti-reflection coated for the full operating wavelength range. Details of the design are presented.

Proto-Model of an Infrared Wide-Field Off-Axis Telescope

Journal of The Korean Astronomical Society, 2010

We develop a proto-model of an off-axis reflective telescope for infrared wide-field observations based on the design of Schwarzschild-Chang type telescope. With only two mirrors, this design achieves an entrance pupil diameter of 50 mm and an effective focal length of 100 mm. We can apply this design to a mid-infrared telescope with a field of view of 8 • × 8 •. In spite of the substantial advantages of off-axis telescopes in the infrared compared to refractive or on-axis reflective telescopes, it is known to be difficult to align the mirrors in off-axis systems because of their asymmetric structures. Off-axis mirrors of our telescope are manufactured at the Korea Basic Science Institute (KBSI). We analyze the fabricated mirror surfaces by fitting polynomial functions to the measured data. We accomplish alignment of this two-mirror off-axis system using a ray tracing method. A simple imaging test is performed to compare a pinhole image with a simulated prediction.

High Performance FOV Switching Mechanism Design for an Infrared Zoom Lens

International Journal of Automation and Smart Technology, 2011

This paper presents the design and implementation of a prototype dual FOV (field-of-view) zoom lens mechanism. The infrared zoom lens uses a permanent magnet DC motor for the motion driver and a microcontroller as the controller. Through the cooperation of two major sensor signals, a shaft encoder and a position sensor, the FOV switching mechanism can achieve both high-speed and high-precision alignment. Experimental results showed an alignment accuracy average of 0.155 mrads and less than 0.5 second alignment settling time. Despite the influence of the non-zero backlash and the A/D uncertainty on the infrared zoom lens, the goal of alignment can be reached by the cooperation between the two major sensors and the controller. The control strategy for switching control was also proposed to help reaching the high-speed precision design specifications.

DESIGN AND ANALYSISA ZOOM CASSEGRAIN TELESCOPE COVER MIDDLE IR REGION USING ZEMAX PROGRAM

The goal of the project is to find an optimal design of zoom-Cassegrain telescope which is popular for amateur astronomers. Also,the objective function of the optical design is to reduce the aberrations to provide aclear image. Cassegrain telescope has been designing and analysis by using (Zemax) software. The full field of view of the objective lens angle to 0.383°, the focal length to 747,748,750 and751mm, Back focal distance BFD 41 mmand Entrance pupil diameter 218.The system consists of a fixed focal length of the objective lens, zoom eyepiece. The eyepiece continuous zoom the zoom telescope system especially Cassegrain the zoom telescope system applications a wide range of zoom optical system .Wide range of wavelength extends from (3.2-4.2μm) and diffraction limited over a large field of angles with F/#3.4 also studied. We find that less aberration that hasbeenreached in the design values are(±0.5 to ±2.2) µm.