An approach to design a dual-channel two-focal-length lens based on the panoramic annular lens (PAL) structure is presented in this paper. The method of establishing the second channel to eliminate the blind area has been explored in some documents, and mostly it is achieved by utilizing the front surface of the PAL block. But in this paper, we modified the PAL block and divided it into two channels according to their different azimuth direction. These two channels have different focal lengths. Thus, by rotating the system around its axis, optical step-zoom effect can be obtained. Finally, a dual-channel system with a radial zoom ratio of 3× is designed, of which the wide-angle channel has a field-of-view (FOV) of 60° (radial) ×60° (azimuthal) and the long focal length channel has a FOV of 20° (radial)×20° (azimuthal). These two channels share the same stop surface, relay lens, and the image sensor. And a thin glass plate with diffractive structure is placed before the image plane to further correct aberration and obtain a common back focal length for the two channels. This system may have applications in many fields, such as surveillance, robot vision, and foveal imaging.
To meet the requirements of the current projection display system. This paper present an ultra-short throw catadioptric projection lens with a freeform mirror. This catadioptric structure consists of two parts. The first part is a set of rotationally symmetrical refractive lenses and the second part is a freeform mirror. In our design, Texas Instruments's Digital Light Processing (DLP) is chosen as the image source. A 0.65inch DMD is employed as the spatial light modulator. The two parts of system are firstly designed respectively, and then they are combined for final design. And a three-dimensional direct design method is firstly employed to design the freeform mirror. The final designed projection lens composes of nine lenses and a XY polynomial mirror, of which the F number is 3.5, the focal length is 6.05mm, and the screen size is 60inch. The designed system achieves projected the display screen with a projection distance of 440mm, which the throw ratio is 0.29. Results show that the MTF of all the FOVs are over 30% at 66lp/mm. The maximum distortion is less than 4%. Due to the high optical performance and compact structure, this designed projection lens is suitable for household and educational applications.
This paper presents an optical design for the all-reflective dual-channel imaging system based on freeform surfaces. This system may be useful in remote sensing where coarse searching and fine observation are both needed. For this system, an off-axis three-mirror system with a middle image is chosen to design and the uniform stop is placed before the first optical surface. Meanwhile, beam splitter can be placed between secondary mirror and the location of the middle image to obtain multiple paths and the different curvatures of the tertiary mirrors can be used to differentiate the focal lengths of two channels and then get a zoom ratio of this system. One channel with a wide FOV of 3×1.5° but a small focal length of 700 mm can be used for searching, while the other one with a long focal length of 1480 mm but a narrow FOV of 0.5×0.5° can be used for fine reconnaissance. Furthermore, An XY polynomial, established as an even function of x, was employed to improve imaging quality, so we obtained a system of the symmetry about the YOZ plane, which can bring considerable convenience to alignment and testing for the system. The modulation transfer function curves of both channels are above 0.3 at 50 line pairs per millimeter, which indicates a good imaging quality.
The panoramic lenses are getting more and more popular in recent years. However, these lenses have the drawback of obscuring the rays of the coaxial fields, thus cause blind area in the center field of vision. We present a novel panoramic system consisting of two optical channels to overcome this issue, the system has a field of view (FOV) reaching 200 in vertical and 360 in horizontal direction without blindness area. The two channels have different focal lengths, providing design flexibility to meet application requirements where the center FOV or the marginal FOV is of more interest. The system has no half-reflecting surfaces to ensure high transmission ratio, but this feature greatly increase the design difficulty. The distortion of the novel lens is much smaller than traditional panoramic lenses since the distortion has two node points. Due to the ability of information acquisition in real-time and wide-angle, the novel panoramic lens would be very useful for a variety of real-world applications such as surveillance, short-throw projector and pilotless automobile.
A tool is developed with the macro capability of CODE V for optical design with off-the-shelf catalog lenses, which can greatly reduce the fabrication costs for an optical system and shorten its development cycle. This tool automatically replaces current elements in the system by stock lenses in the database, and gets the system optimized at the same time. Major aspects of the tool, including the preparation of the stock lens database, the optimization strategy and the replacement method are discussed in detail. Three examples are designed to demonstrate the effectiveness of the replacement tool, and the results show that acceptable performance can be achieved by this tool. Finally, limitations and applications of this tool are discussed. Our tool can effectively replace elements in a system with stock lenses, and it can also improve optical performance of a system already composed of stock lenses by further replacing and optimization.
Fundus camera is a complex optical system for retinal photography, involving illumination and imaging of the retina.
Stray light is one of the most significant problems of fundus camera because the retina is so minimally reflective that
back reflections from the cornea and any other optical surface are likely to be significantly greater than the light reflected
from the retina. To provide maximum illumination to the retina while eliminating back reflections, a novel design of
illumination system used in portable fundus camera is proposed. Internal illumination, in which eyepiece is shared by
both the illumination system and the imaging system but the condenser and the objective are separated by a beam splitter,
is adopted for its high efficiency. To eliminate the strong stray light caused by corneal center and make full use of light
energy, the annular stop in conventional illumination systems is replaced by a fiber-coupled, ring-shaped light source
that forms an annular beam. Parameters including size and divergence angle of the light source are specially designed.
To weaken the stray light, a polarized light source is used, and an analyzer plate is placed after beam splitter in the
imaging system. Simulation results show that the illumination uniformity at the fundus exceeds 90%, and the stray light
is within 1%. Finally, a proof-of-concept prototype is developed and retinal photos of an ophthalmophantom are captured.
The experimental results show that ghost images and stray light have been greatly reduced to a level that professional
diagnostic will not be interfered with.
Two types of fisheye lenses for automobile navigation are designed with slope-constrained Q-type aspheres. Special
requirements have been considered in the design process, and Q-type surfaces are introduced by converted from other
kinds of aspheric description with only coefficients of low-order terms retained. A possible problem of imaging the first surface onto the sensor has also been analyzed. As a result, as for the six-element fisheye lens, MTF is greater than 0.3 at
45lp/mm, f-θ distortion is less than 0.03 when the focal length is calibrated, field of view is 230° and full field relative
illumination is greater than 0.4. For the four-element fisheye lens, MTF is greater than 0.4 at 45lp/mm, f-θ distortion is
less than 0.16 , field of view is 190° and full field relative illumination is greater than 0.6. The design results show that the Q-type surfaces employed in fisheye lenses can make the system more compact, lightweighted and easier to