In view of the problem that the imaging quality of the large-aperture and long-focal length infrared optical system is sensitive to temperature changes. In this paper, we propose an idea of combining athermalization design with catadioptric optical system, and a large-aperture long-focal length catadioptric infrared optical system is designed by this idea. According to the influence of each parameter by environmental changes, the system optical power is allocated reasonably. Select the appropriate infrared lens material and reflector base material for the system so that the image plane deviation caused by the environmental changes of the components cancel each other out. The design method and idea proposed in this paper have important reference value for the realization of heat dissipation of catadioptric optical system. The working band of the system is 8~14μⅿ,the focal length is 250ⅿⅿ, F-number is 1, and the three infrared materials used in the system are HWS2, HWS9 and IRG22. The design results show that the system can maintain high imaging quality in the temperature range of -40°C~+60°C, with the modulation transfer function (MTF) curves close to the diffraction limit at the cutoff frequency. The design methods and ideas proposed in this paper have significant reference value for realizing athermalization of catadioptric optical systems.
In view of urgent demand high resolution and large field of view on three-line array airborne mapping camera, the paper proposes an airborne mapping camera optical system with large field of view and high resolution, which consists of single telecentric lens, RGB multispectral prism and field splicing prism. In order to solve RGB multispectral splitting problem in system, a new multispectral splitting prism based on a close distance confocal plane linear array sensor is proposed, which successfully solves RGB multispectral splitting problem of confocal plane linear array sensor with a close distance (B band and G band are only 4 pixels apart, and G band and R band are 2.2mm apart). The telecentric optical system is designed, focal length is 130mm, field of view (FOV) is 77° (working field of view is 60°), and image elecentricity is less than 0.1° across full field of view. There are four multispectral bands which are panchromatic, R, G, B band. The optical system has excellent imaging quality and compact structure.
In view of the urgent demand high resolution and large field of view on three-line array airborne mapping camera, the paper proposes a new idea which applies monocentric multiscale principle to three-line array airborne mapping camera with high resolution and large field of view (FOV), and gives the design method and design process of optical system. monocentric multiscale optical system is designed, focal length is 70mm, resolution is 0.1m@2Km, and there are four multispectral bands which are panchromatic、R、G、B band. The Base to Height ratio (B/H) is 0.83. The FOV of monocentric multiscale optical system is 80°, and working FOV is 60° which can be extended to 105°. The optical system has excellent imaging quality and successfully solved contradiction between large FOV and high resolution.
KEYWORDS: Cameras, Modulation transfer functions, Optical engineering, Temperature metrology, Monochromatic aberrations, Picosecond phenomena, Thermal effects, Satellites, Signal to noise ratio
Thermal design is highly related to the performance of space cameras as temperature changes cause thermal displacements of the cameras’ optical and mechanical systems, consequently affecting imaging quality. However, most existing thermal design methods for space cameras focus on several thermal design parameters without a comprehensive and quantitative analysis. Therefore, we proposed an optimization thermal design method for space cameras based on thermo-optical analysis and the Taguchi method. We first established the thermal balance equations of space cameras, and by analyzing the thermal design parameters in the equations, we identified the key parameters that affect the temperature field, thermal displacements, and imaging quality of the camera. Furthermore, we evaluated the influence of each thermal design parameter on imaging quality based on the integrated thermo-optical analysis. Thereafter, we applied the Taguchi method to quantitatively calculate the effect of each thermal design parameter on imaging quality. Finally, we implemented an optimal thermal control scheme for space cameras based on the results of the Taguchi method. The experimental results demonstrated that the proposed method is reliable and efficient and would be beneficial to researchers working on the thermal design of optical instruments.
The relationship between the illumination of the stray light and the modulation transfer function (MTF) of the optical imaging system is deducted by the manuscript. With the analysis, an experiment has been designed to confirm the analysis. The experiment result shows that: the exist of stray light will lead to the optical imaging system MTF reduce, the new imaging MTF is related to the MTF in ideal condition, object contrast, the illumination of the object and stray light.
With the limit of optical materials, it is difficult to design zoom optical systems which have long focal length by refractive systems with a simple configuration. All-reflective zoom optical systems could be lightweighted, compact and free of chromatic aberrations, and reflective optical systems can be unobscured by off-axis mirrors and have very good application foreground. In this paper, an all-reflective zoom optical system was designed, the all-reflective zoom optical system worked in the band of 400~1000nm, the diameter of the pupil was 100mm, the F number was 6~15, focal length varied from 600~1500mm, field of view (FOV) was 2°×0.8°~0.8°×0.48°. The pixel size of detector was 10×10μm. The result showed that MTF was higher than 0.3 at 50lp/mm and the quality of the optical system approached the diffraction limit, which met the design demand.
As the space remote sensing technology progresses, the developing trend of telescope is larger and larger aperture, higher and higher resolution. An Optical system with the relative aperture of 1:2 is introduced. The primary optical properties are: focal length of 120mm, F number of 2, field angle of 7.4°. It has the advantages of large high resolution, small size and excellent image quality. Several kinds of aberration curves and the MTF curve are given. Its imaging quality is nearly diffraction limited so that the spatial frequency is greater than 70lp/mm when its modulated transfer function (MTF) value of the optical system is equal to 0.8,and the optical system distortion is less than 1%. At last, the stray light is analyzed and the baffle of the telescope is designed. The solid model of the Optical system was constructed in Tracepro software, the point sources transmittance (PST) cure was given at different off-axis angle between 7.4°~80°,the analysis result indicates that the PST values are less than 10-6 when off-axis angle are larger than soar critical angle. So the system is suitable for observation or photography of deep sky objects.
With the development of the digital airborne photo-grammetry technology, the more performances of the optical system for airborne mapping camera are required, such as the longer focal, the wider field of view (FOV), at the same time, the secondary spectrum correction becomes more important and difficult for the optical system design. A high performance optical system of airborne mapping camera with 200mm focus and2ω=60°FOV is designed in this paper. The range of work wavelength is from 430nm to 885nm. A two-layer HDOE with negative dispersive characteristic is used to eliminate the secondary spectrum in the process of optical system design. The diffraction efficiency of the designed two-layer HDOE is up to 90%. From the result of design, the MTFs in whole fields are over 0.5 at 90lp/mm, which shows that the system has a great image quality. Meantime, the thermal analysis is done at the temperature range between -20°C and 40°C, and the MTF curves of the system at-20°C ~40°C show that a great image quality is kept, which meets the design requirements.
Bad pixels and response non-uniformity are the primary obstacles when IRFPA is used in different thermal imaging systems. The bad pixels of IRFPA include fixed bad pixels and random bad pixels. The former is caused by material or manufacture defect and their positions are always fixed, the latter is caused by temperature drift and their positions are always changing. Traditional radiometric calibration-based bad pixel detection and compensation algorithm is only valid to the fixed bad pixels. Scene-based bad pixel correction algorithm is the effective way to eliminate these two kinds of bad pixels. Currently, the most used scene-based bad pixel correction algorithm is based on adaptive median filter (AMF). In this algorithm, bad pixels are regarded as image noise and then be replaced by filtered value. However, missed correction and false correction often happens when AMF is used to handle complex infrared scenes. To solve this problem, a new adaptive bad pixel correction algorithm based on pulse coupled neural networks (PCNN) is proposed. Potential bad pixels are detected by PCNN in the first step, then image sequences are used periodically to confirm the real bad pixels and exclude the false one, finally bad pixels are replaced by the filtered result. With the real infrared images obtained from a camera, the experiment results show the effectiveness of the proposed algorithm.
Due to the extra wide field of view, fisheye optical systems are appropriately applied in space camera for scouting large-scale objects with near-distance. At the same time, because of the violent sunlight linger within the field of view more than other optical system and more stray light occur during the period, to design proper lens-hood can effectively reduce the sunshine time. Another distinct characteristic of fisheye optical system is the first protrude lens, which is contrived with negative focus to trace the ray with angle about even above 90 degree of incidence. Consequently, the first lens is in danger of damaging by scratching when operating the camera during the ground experiments without lens-hood. Whereas on account of the huge distortion which is the third mainly characteristic of fisheye optical system, to design appropriate lens-hood is a tough work comparing with other low-distortion optical system, especially for those whose half diagonal field is more than 90°. In this paper, an research carried out on the design lens-hood for fisheye is proposed. In the way of reverse ray-tracing, the location on the first lens and point-vector for each incident ray can be accurately calculated. Thus the incident ray intersecting the first lens corresponds to the boundary of the image sensor form the effective object space. According to the figure of the lens and the incident rays, the lens-hood can be confirmed. In the proposed method, a space fisheye lens is presented as a typical lens, whose horizontal field and vertical field are 134°, diagonal field is up to 192°, respectively. The results of design for the lens-hood show that the lingering time of sunshine is shorten because of obstructing some redundant sunlight, and the first outstanding lens are protected in the most degree.
This paper designs a compact apochromatic lens with long focal length, which operates over very-broad spectrum from 400nm to 900nm for high resolution image application. The focal length is 290mm, and F-number is 4.5.In order to match CCD sensor, lens resolution must be higher than 100lp/mm. It is a significant challenge to correct secondary spectrum over very-broad spectrum for this application. The paper firstly pays much attention on dispersion characteristic of optical materials over this very-broad spectrum, and dispersion characteristic of glasses is analyzed. After properly glasses combinations and optimal lens structure selected, this compact apochromatic lens is designed. The lens described in this paper comprises fewer lenses, most of them are ordinary optical materials, and only one special flint type TF3 with anomalous dispersion properties is used for secondary spectrum correction. Finally, the paper shows MTF and aberration curve for performance evaluation. It can be seen that MTF of the designed lens nearly reach diffraction limit at Nyquist frequency 100lp/mm, and residual secondary spectrum is greatly reduced to less than 0.03mm (in the lines 550nm and 787.5nm). The overall length of this compact apochromatic lens is just 0.76 times its focal length, and because of fewer lenses and ordinary optical materials widely used, production cost is also greatly reduced.
Following with the “high-resolution upsurge” appeared in many counties in recent few years, it is an inevitable trend to increase the size of the Optical Telescope. However, because of the volume constrains of space-borne astronomical instruments, segmented reflector is thought as the main measure of future astro-physical missions by many scientists. In this paper, a coaxial three-mirror anastigmatic system (TMA) with a segmented primary mirror is modeled in optical software. The optical system, which has 2.4m aperture, 48m focal length and the field-view angle of 0.3°×0.06°, works in the 450nm~900nm wave band. The ‘1+6’ aperture-stiching model is applied. Firstly, the initial structure of the system is inputted to the CODEV, and a certain constraint functions are set, and then the system automatically optimizes. Finally, designing results show that the Modulation Transfer Function (MTF) is really very near to the limit of diffraction. We get a good image quality of the optical system design results.
KEYWORDS: Clocks, Charge-coupled devices, CCD image sensors, Image processing, Cameras, Field programmable gate arrays, High speed cameras, Digital signal processing, Data transmission, Analog electronics
We present a field-programmable gate array (FPGA)-based hardware architecture for high-speed camera which have fast
auto-exposure control and colour filter array (CFA) demosaicing. The proposed hardware architecture includes the
design of charge coupled devices (CCD) drive circuits, image processing circuits, and power supply circuits. CCD drive
circuits transfer the TTL (Transistor-Transistor-Logic) level timing Sequences which is produced by image processing
circuits to the timing Sequences under which CCD image sensor can output analog image signals. Image processing
circuits convert the analog signals to digital signals which is processing subsequently, and the TTL timing, auto-exposure
control, CFA demosaicing, and gamma correction is accomplished in this module. Power supply circuits provide the
power for the whole system, which is very important for image quality. Power noises effect image quality directly, and
we reduce power noises by hardware way, which is very effective. In this system, the CCD is KAI-0340 which is can
output 210 full resolution frame-per-second, and our camera can work outstandingly in this mode. The speed of
traditional auto-exposure control algorithms to reach a proper exposure level is so slow that it is necessary to develop a
fast auto-exposure control method. We present a new auto-exposure algorithm which is fit high-speed camera. Color
demosaicing is critical for digital cameras, because it converts a Bayer sensor mosaic output to a full color image, which
determines the output image quality of the camera. Complexity algorithm can acquire high quality but cannot implement
in hardware. An low-complexity demosaicing method is presented which can implement in hardware and satisfy the
demand of quality. The experiment results are given in this paper in last.
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