Catadioptric Research Articles

Adjustment of a catadioptric objective with an eccentric pupil for the infrared spectral range

A method for the adjustment of a wide-angle catadioptric collimating objective for the infrared spectral range with an eccentric pupil designed according to the Cassegrain scheme with a prefocal lens compensator is proposed. The approach combines interference methods for determining the position of the axis of the aspherical main mirror and the position of the secondary mirror with an autocollimating method for the centering of the compensator lenses. All the adjustment procedures are performed in a standard objective housing without reference to the geometric bases of the optical elements. An analysis of the adjustment errors and the testing results of the manufactured objective are presented.

Correction of aberration-induced phase errors in phase measuring deflectometry.

Phase measuring deflectometry is a powerful measuring method of complex optical surfaces that captures the reflected fringe images associated with a displaying screen and calculates the normal vectors of the surface under test (SUT) accordingly. The captured images are usually set conjugate to the SUT, which in turn makes the screen defocused. As a result, the blurring effect caused by the defocus and aberrations of the off-axis catadioptric imaging system can severely degrade the phases solved from the blurred images. In order to correct the phase errors, the space-variant point spread functions (PSFs) are modeled using a skew-normal function. The phase bias is estimated by forward convolution between the captured images and the PSF models. Demonstrated with a highly curved aspheric surface, the measurement accuracy can be improved by three times.

Tim’s Vermeer, Reconsidered

A recent documentary feature film, Tim’s Vermeer, proposes that Johannes Vermeer secretly used a catadioptric telescope and novel mirror–comparator procedure to create his sublime paintings of domestic interiors. How well does that bold hypothesis stand up to analysis?

Aberration calculation of catadioptric combined optical system with oblique incidence

Aberration calculation of catadioptric combined optical system with oblique incidence

Adaptive Phase Correction for Phase Measuring Deflectometry Based on Light Field Modulation

The phase measuring deflectometry is a powerful measuring method for complex optical surfaces, which captures the reflected fringe images associated with a displaying screen and calculates the normal vectors of the surface under test (SUT) accordingly. The captured images are usually set conjugate to the SUT, which in turn makes the screen defocused. As a result, the blurring effect caused by the point spread function (PSF) of the off-axis catadioptric imaging system can bias the solved phases. In order to correct the phase errors, a light field is constructed based on the Fourier compressive sensing method to describe the light transmission between the screen and camera pixels. Fringe modulation is conducted to enhance the robustness against noise, and then, space-variant PSFs can be extracted from the light field. The true phases are obtained by solving a Wiener deconvolution problem, with the merit function adaptively regularized by adjusting the damping parameter. The proposed method can correct adaptively the phase errors induced by the complex aberrations. Compared to the reference measurements, the form accuracy can be improved by four times.

Design of catadioptric panoramic optical imaging system with ultra-large field of view

折反射全景光学成像系统具有平面对称光学系统的成像特性，提出应用光焦度控制方程和超大视场光学系统六阶波像差理论来初步确定系统结构初始参数，在此结构基础上，应用Zemax软件对其进行设计和优化，得到了一款仅由1块偶次非球面反射镜和6块折射透镜组成的折反射全景光学成像系统。该系统工作在可见光波段，全视场角范围为12°～178°，<i>F</i>数为3.5，其像差得到了较理想校正，调制传递函数在空间频率40 lp/mm处均大于0.37，成像性能较好，满足实际应用要求。同时，对设计的系统进行了公差分析。

大相对孔径长焦距同轴折反射式望远物镜设计

大相对孔径长焦距同轴折反射式望远物镜设计

Gas Pipeline Inspection Using Autonomous Robots With Omni-Directional Cameras

Maintenance of pipelines is a major concern for oil and gas companies and millions of dollars are spent on preventive inspections every year. The type of equipment used in carrying out inspections is expensive and very sophisticated requiring very specialized manpower. Here, a novel approach to pipeline inspection is presented using a small mobile robot and a catadioptric omni-directional vision system. The system captures panoramic videos using conical and/or hyperbolic mirrors, which are transmitted to a monitoring station to examine the inner surface of gas pipelines. The videos are prepped, unwrapped, and un-warped to obtain a realistic flat image of the whole inner surface of the pipeline. The Simulated Annealing optimization method is implemented to optimize the system parameters using different mirror shapes and unwrapping and un-warping techniques. Simulations and experimental studies using a mobile robot equipped with a CCD camera and a conical mirror are presented here to demonstrate the viability of this inspection technique. The developed robotic system can be used to visually pre-scan pipelines before using much more expensive tools such as magnetic flux leakage (MFL) or ultrasound (UT) based inspection systems. These latter tools cost tens of thousands of dollars per hour and will be used only after suspicious areas are visually detected. This will reduce the inspection time and cost significantly.

Three-Dimensional Reconstruction of Indoor and Outdoor Environments Using a Stereo Catadioptric System

In this work, we present a panoramic 3D stereo reconstruction system composed of two catadioptric cameras. Each one consists of a CCD camera and a parabolic convex mirror that allows the acquisition of catadioptric images. We describe the calibration approach and propose the improvement of existing deep feature matching methods with epipolar constraints. We show that the improved matching algorithm covers more of the scene than classic feature detectors, yielding broader and denser reconstructions for outdoor environments. Our system can also generate accurate measurements in the wild without large amounts of data used in deep learning-based systems. We demonstrate the system’s feasibility and effectiveness as a practical stereo sensor with real experiments in indoor and outdoor environments.

3D Human Pose Estimation with a Catadioptric Sensor in Unconstrained Environments Using an Annealed Particle Filter.

The purpose of this paper is to investigate the problem of 3D human tracking in complex environments using a particle filter with images captured by a catadioptric vision system. This issue has been widely studied in the literature on RGB images acquired from conventional perspective cameras, while omnidirectional images have seldom been used and published research works in this field remains limited. In this study, the Riemannian varieties was considered in order to compute the gradient on spherical images and generate a robust descriptor used along with an SVM classifier for human detection. Original likelihood functions associated with the particle filter are proposed, using both geodesic distances and overlapping regions between the silhouette detected in the images and the projected 3D human model. Our approach was experimentally evaluated on real data and showed favorable results compared to machine learning based techniques about the 3D pose accuracy. Thus, the Root Mean Square Error (RMSE) was measured by comparing estimated 3D poses and truth data, resulting in a mean error of 0.065 m when walking action was applied.

Catadioptric Stereo Optical Gas Imaging System for Scene Flow Computation of Gas Structures

The need for reducing greenhouse gas emissions from industrial facilities has motivated the development of new and more reliable techniques for gas leak localization and quantification. Optical gas imaging (OGI) systems offer a fast and intuitive approach by exploiting the absorption properties of gases, such as methane, in the infrared range. Based on this, several efforts have been made in the recent years for gaining additional quantitative information from the measurement data, e.g. gas concentration or gas velocity. In this work, a catadioptric stereo OGI system based on four planar mirrors and an OGI camera is proposed for computing spatio-temporal (also referred to as scene flow) information from stereo gas images. The proposed system represents a way to reduce the effects of temporal and radiometric differences and the cost and size of two-camera-based stereo OGI systems and leads to more reliable results under the tested conditions.

Choosing the optical materials for multichannel catadioptric systems with Mangin mirrors in the video cameras of miniature drones

This paper discusses a method of choosing the optical material for multispectral catadioptric systems with Mangin mirrors and ways to computer-model these systems with a (single) and two image planes for the video cameras of miniature drones. The given optical system can operate either with a multichannel radiation detector or with two radiation detectors after the channels are separated by a spectral-splitter mirror.

Omni-Zernike Algorithm for Template Matching in Catadioptric System

Image descriptor have been widely applied in many computer visions and image understanding applications including pattern recognition, robotic, video surveillance, camera calibration and image retrieval, etc. Invariants features are robust when apply several transformations of photometry (illumination, blur, noise, JPEG compression) and transformations of geometry (scaling, rotation, translation and viewpoint change). In this study, we present representation and matching region descriptors. Consequently, a set of region used provided by catadioptric system for evaluation of the performance. These regions are normalized by unit circle form with form and size change. In this contribution, the image descriptors of regions used is Moment's Zernike. They are most suitable invariants in omnidirectional context thanks to the polar coordinates used both omnidirectional geometry and Zernike Moments formulation. The aim is realize a robust matching between object's block by using a measure of distance between Zernike's moment descriptors for optimal similarity. Results shown clearly demonstrate the performance of our method and powerful than most important region descriptors (GLOH, SIFT, PCA-SIFT, complex moments and steerable filters) in term of the ROC curve or precision-recall criterion.

Front Cover

AbstractWe present a 3D printed high‐NA catadioptric lens for forward signal collection in laser‐scanning microscopy. The lens can replace expensive and bulky high‐NA microscope objectives or condensers and is so thin to fit inside top‐stage microscope incubators. The lens is particularly beneficial in Stimulated Raman Scattering (SRS), where a high‐NA beam collection is needed to avoid artefacts due to Cross Phase Modulation.Further details can be found in the article by Andrea Bertoncini, Sergey P. Laptenok, Luca Genchi, Vijayakumar P. Rajamanickam, and Carlo Liberale (e202000219). image

Catadioptric hyperspectral imaging, an unmixing approach

Hyperspectral imaging systems provide dense spectral information on the scene under investigation by collecting data from a high number of contiguous bands of the electromagnetic spectrum. The low spatial resolutions of these sensors frequently give rise to the mixing problem in remote sensing applications. Several unmixing approaches are developed in order to handle the challenging mixing problem on perspective images. On the other hand, omnidirectional imaging systems provide a 360‐degree field of view in a single image at the expense of lower spatial resolution. In this study, we propose a novel imaging system which integrates hyperspectral cameras with mirrors so on to yield catadioptric omnidirectional imaging systems to benefit from the advantages of both modes. Catadioptric images, incorporating a camera with a reflecting device, introduce radial warping depending on the structure of the mirror used in the system. This warping causes a non‐uniformity in the spatial resolution which further complicates the unmixing problem. In this context, a novel spatial–contextual unmixing algorithm specifically for the large field of view of the hyperspectral imaging system is developed. The proposed algorithm is evaluated on various real‐world and simulated cases. The experimental results show that the proposed approach outperforms compared methods.

Catadioptric Optical System Design of 15-Magnitude Star Sensor with Large Entrance Pupil Diameter.

The optical system is one of the core components for star sensors, whose imaging quality directly influences the performance of star sensors for star detection, thereby determining the attitude control accuracy of spacecrafts. Here, we report a new type of optical system with a catadioptric structure and a large entrance pupil diameter for a 15-magnitude star sensor. It consists of an improved Cassegrain system (R-C system), an aperture correction spherical lens group and a field of view correction spherical lens group. By embedding the secondary mirror of the R-C system into the output surface of the negative spherical lens of the aperture correction spherical lens group, the blocking of incident light is eliminated from the secondary mirror holder. After the structure optimization, the catadioptric optical system (COS) had a spectral range of 450 nm–950 nm, an entrance pupil diameter of 250 mm, a half-diagonal field of view of 1.4° and a focal length of 390 mm. By using theoretical calculations and experimental measurements, it was verified that the COS, with the ability to correct astigmatism, lateral color and distortion, can fulfill the detection of 15-magnitude dark stars.

Dual-view catadioptric panoramic system based on even aspheric elements.

We propose a compact catadioptric imaging system based on even aspheric elements to solve some major limitations of conventional panoramic structure, such as field of view, blind spot, resolution, illumination, and less structure is introduced. The design includes a catadioptric front unit that is capable of providing a compression image of a panoramic scene and of relaying high-performance aspheric lenses to a decompression image. It is arranged to project two uncompressed images from two channels on a single sensor. Their optical paths do not interfere with each other, and there is no blind-spot image.

3D‐Printed high‐NA catadioptric thin lens for suppression of XPM background in Stimulated Raman Scattering microscopy

AbstractStimulated Raman Scattering (SRS) is a fast chemical imaging technique with remarkable bioscience applications. Cross Phase Modulation (XPM) is a ubiquitous nonlinear phenomenon that can create spurious background signals that render difficult a high‐contrast imaging in SRS measurements. The XPM‐induced signal is usually suppressed using high numerical aperture (NA) microscope objectives or condensers to collect the transmitted excitation beam. However, these high NA optics feature short working distances, hence they are not compatible with stage‐top incubators, that are necessary to perform live‐cell time‐lapse experiments in controlled environments. Here, we show a 3D printed high NA compact catadioptric lens that fits inside stage‐top incubators and allows the collection of XPM‐free SRS signals. The lens delivers SRS images and spectra with a quality comparable to a signal collection with a high‐NA microscope objective. We also demonstrate the compatibility of the 3D printed lens with other nonlinear microscopies usually associated with SRS in multimodal microscopes.

Design and Performance of a Catadioptric Omnidirectional Zoom Optical System Using a Hybrid Lens for Visible Light

Design and Performance of a Catadioptric Omnidirectional Zoom Optical System Using a Hybrid Lens for Visible Light

On-Chip Terahertz Detector Designed with Inset-Feed Rectangular Patch Antenna and Catadioptric Lens

This study proposes an on-chip terahertz (THz) detector designed with on-chip inset-feed rectangular patch antenna and catadioptric lens. The detector incorporates a dual antenna and dual NMOSFET structure. Radiation efficiency of the antenna reached 89.4% with 6.89 dB gain by optimizing the antenna inset-feed and micro-strip line sizes. Simulated impedance was 85.55 − j19.81 Ω, and the impedance of the antenna with the ZEONEX horn-like catadioptric lens was 117.03 − j20.28 Ω. Maximum analyzed gain of two on-chip antennas with catadioptric lens was 17.14 dB resonating at 267 GHz. Maximum experimental gain of two on-chip patch antennas was 4.5 dB at 260 GHz, increasing to 10.67 dB at 250 GHz with the catadioptric lens. The proposed on-chip rectangular inset-feed patch antenna has a simple structure, compatible with CMOS processing and easily implemented. The horn-like catadioptric lens was integrated into the front end of the detector chip and hence is easily molded and manufactured, and it effectively reduced terahertz power absorption by the chip substrate. This greatly improved the detector responsivity and provided very high gain. Corresponding detector voltage responsivity with and without the lens was 95.67 kV/W with NEP = 12.8 pW/Hz0.5 at 250 GHz, and 19.2 kV/W with NEP = 67.2 pW/Hz0.5 at 260 GHz, respectively.