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Existing optical see-through (OST) head-mounted displays (HMDs) generally utilize plane mirrors with partial transmission to merge the virtual and real-world scenes, which inducing the vignetting effect to result in small field of view (FOV). Accordingly, this paper proposes an OST-HMD system in which a rotationally-symmetric eyepiece with a wide FOV of ±30 degrees is coupled with a dihedral corner reflector array (DCRA) to achieve a sufficient relief distance to project all of the exit rays of the eyepiece into the pupil. The feasibility of the proposed system is evaluated by means of numerical simulations based on optical models of the HMD lens, DCRA and human eye. The simulation results show that the eye can receive the display information in the wide FOV with a sufficient relief distance through this kind of the OST-HMD development.

Chemiluminescence (CL) is a dominant technology in clinical diagnosis. In order to meet the increasing demand for the sensitive and simultaneous detection of chemiluminescence from multiple samples, the development of multiplex analysis on a single chip is highly desired. However, most chemiluminescence detection systems for multiple samples are still simple lens-based optical imaging systems, and a compromise must always be made between a large aperture (required by the weak chemiluminescence) and a large field of view (required by the size of the sample array). In this paper, we report a fiber bundle-based chemiluminescence detection system for the simultaneous and efficient detection of multiple chemiluminescent samples. In this system, one side of the fiber bundle is directly coupled to the optically active surface of a charge-coupled device (CCD), while the other end is divided into many sub-bundles that are aligned above the samples in a chemiluminescence array to collect their chemiluminescence. Taking advantage of the large numerical aperture and high transmittance of optical fibers, this system shows about a 50 times increase in chemiluminescence collection efficiency over the lens-based imaging system. Moreover, it shows no vignetting effect that is inevitable in a lens-based imaging system with a large field of view. This work provides a promising method for multiple sample chemiluminescence detection, and should find application in bioassays.

Conventional wide-field-of-view cameras consist of multi-lens optics and flat image sensor arrays, which makes them bulky and heavy. As a result, they are poorly suited to advanced mobile applications such as drones and autonomous vehicles. In nature, the eyes of aquatic animals consist of a single spherical lens and a highly sensitive hemispherical retina, an approach that could be beneficial in the development of synthetic wide-field-of-view imaging systems. Here, we report an aquatic-vision-inspired camera that consists of a single monocentric lens and a hemispherical silicon nanorod photodiode array. The imaging system features a wide field of view, miniaturized design, low optical aberration, deep depth of field and simple visual accommodation. Furthermore, under vignetting, the photodiode array enables high-quality panoramic imaging due to the enhanced photodetection properties of the silicon nanorod photodiodes. By integrating a single monocentric lens with a hemispherical silicon nanorod photodiode array, a wide-field-of-view camera is created that offers low optical aberration, deep depth of field and simple visual accommodation.

We quantitatively investigate multiple algorithms for microlens array grid estimation for microlens array-based light field cameras. Explicitly taking into account natural and mechanical vignetting effects, we propose a new method for microlens array grid estimation that outperforms the ones previously discussed in the literature. To quantify the performance of the algorithms, we propose an evaluation pipeline utilizing application-specific ray-traced white images with known microlens positions. Using a large dataset of synthesized white images, we thoroughly compare the performance of the different estimation algorithms. As an example, we apply our results to the decoding and calibration of light fields taken with a Lytro Illum camera. We observe that decoding as well as calibration benefit from a more accurate, vignetting-aware grid estimation, especially in peripheral subapertures of the light field., \copyright 2020 IEEE. Personal use of this material is permitted. Permission from IEEE must be obtained for all other uses, in any current or future media, including reprinting/republishing this material for advertising or promotional purposes, creating new collective works, for resale or redistribution to servers or lists, or reuse of any copyrighted component of this work in other works

In standard photography, vignetting is considered mainly as a radiometric effect because it results in a darkening of the edges of the captured image. In this paper, we demonstrate that for light field cameras, vignetting is more than just a radiometric effect. It modifies the properties of the acquired light field and renders most of the calibration procedures from the literature inadequate. We address the problem by describing a model and camera-agnostic method to evaluate vignetting in phase space. This enables the synthesis of vignetted pixel values, which applied to a range of pixels yield images corresponding to the white images that are customarily recorded for calibrating light field cameras. We show that the commonly assumed reference points for microlens-based systems are incorrect approximations to the true optical reference, i.e., the image of the center of the exit pupil. We introduce a novel calibration procedure to determine this optically correct reference point from experimental white images. We describe the changes vignetting imposes on the light field sampling patterns and, therefore, the optical properties of the corresponding virtual cameras using the equivalent camera array model [L. Mignard-Debise, J. Restrepo, and I. Ihrke, “A unifying first-order model for light-field cameras: The equivalent camera array,” IEEE Trans. Comput. Imag. , vol. 3, no. 4, pp. 798–810, Dec. 2017] and apply these insights to a custom-built light field microscope.

The lens design problem for the 2021 IODC is to design a 100 mm focal length lens where if the lens is flipped end-to-end but the radii are not reversed in sign, the lens has to perform the same as in its original form. The lens is used monochromatically. The goal of the problem is to maximize the product of the entrance pupil diameter and the semi-field of view while holding the RMS wavefront error to ≤ 0.070 wave within the field of view. There were 43 entries from 13 different countries. Three different commercial lens design programs were used, along with four in-house programs. The winning entry from Damien Gawron has an entrance pupil diameter of 198.4083 mm and a semi-field of view of 90° for a merit function product of 17,857 out of a maximum possible 18,000.

The filter-ratio technique to remotely measure electron temperature and speed using four color filters in visible light and a polarization camera was described in detail in previous works, in which we quantified the systematic error associated with using models of a symmetric corona to interpret results from an asymmetric corona. We also showed the criteria applied to select the bandwidths of filters and the pros and cons of replacing the traditional linear polarizer with a polarization camera to measure pB. What started in the 1990s by ground experiments conducted during total solar eclipses that lasted for a few minutes led to a balloon-borne experiment lasting eight hours in 2019 and will blossom into a space experiment on the International Space Station in 2023. Due to constraints on the bandwidths of the four filters, a successful mission requires quantification of the statistical error using Monte Carlo simulations to generate two feasibility profiles, which are unique to the design parameters of the coronagraph, to comprehend the feasibility to measure temperature and speed within the desired temporal and spatial resolutions. For the statistical error analysis, we use modeled K- and F-corona profiles, representative theoretical diffraction, scattering, and vignetting profiles, assumed efficiencies for lenses, mirrors, and polarizers, assumed detector properties on quantum efficiency, full-well depth, dark noise, and read noise, and assumed instrument properties on aperture diameter, solid angle, and pixel resolution.

Metis is a multi-wavelength coronagraph onboard the European Space Agency (ESA) Solar Orbiter mission. The instrument features an innovative instrument design conceived for simultaneously imaging the Sun's corona in the visible and ultraviolet range. The Metis visible channel employs broad-band, polarized imaging of the visible K-corona, while the UV one uses narrow-band imaging at the HI Ly 􀄮, i.e. 121.6 nm. During the commissioning different acquisitions and activities, performed with both the Metis channels, have been carried out with the aim to check the functioning and the performance of the instrument. In particular, specific observations of stars have been devised to assess the optical alignment of the telescope and to derive the instrument optical parameters such as focal length, PSF and possibly check the optical distortion and the vignetting function. In this paper, the preliminary results obtained for the PSF of both channels and the determination of the scale for the visible channel will be described and discussed. The in-flight obtained data will be compared to those obtained on-ground during the calibration campaign.

Background. Parametric synthesis of zoom-afocal optical systems for zoom lenses. Development of an algorithm for dimensional calculation of three-component zoom-afocal systems when accounting overall limitations, providing the desired range of changes in the angular magnification and field of view of the zoom lens, the allowable vignetting of the extreme beams of light when the field of view changes over the entire specified range. Synthesis of an afocal system for a stationary lens, the entrance pupil of which is located behind the afocal system. Objective. The purpose of the paper is to create a universal analytical and suitable for computer automation algorithm for calculation of the optical and overall parameters of the components of zoom-local three-component zoom systems. Methods. The zoom-afocal system is represented by subtle components. A system of equations is compiled in which the distances between the components are unknown. From the equations, the values of these distances are recovered, which provide the necessary values of the angular magnification and zero optical power of the afocal system. In this case, the magnitudes of the optical powers of the components and their ratios should ensure positive values of the distances between them. Using the formulae of the angles and heights of the zero rays on the components of the system, taking into account the permissible vignetting of the beam of rays from the edge of the field of view, the required light diameters of the components are determined. Results. The obtained analytical dependences allow us to determine the focal distances of the afocal system components and their mutual location over the entire required range of changes in the angular magnification using the original data on the allowable longitudinal and transverse dimensions of the afocal system. It is shown that afocal systems have a maximum axial length with the angular increase of one. The largest light diameter has the first component. The diameter of this component reaches its greatest value as the value of the angular increase is close to one. Conclusions. The obtained results allow analytically performing parametric synthesis of three-component zoom-afocal systems, taking into account the requirements for their dimensions, the range of changes in the angular magnification and permissible vignetting of beams of rays from the edge of the visual field.

This paper proposes a low-cost and portable polycamera system and accompanying methods for capturing and synthesizing stereoscopic 360° panoramas. The polycamera consists of only four cameras with fisheye lenses. Synthesizing panoramas from only four views is challenging because the cameras view very differently and the captured images have significant distortions and color degradation including vignetting, contrast loss, and blurriness. For coping with these challenges, this paper proposes methods for rectifying the polyview images, estimating depth of the scene, and synthesizing stereoscopic panoramas. The proposed camera is compact in size, light in weight, and inexpensive. The proposed methods allow the synthesis of visually pleasing stereoscopic 360° panoramas using the images captured with the proposed polycamera. We have built a prototype of the polycamera and tested it on a set of scenes with different characteristics of depth ranges and depth variations. The experiments show that the proposed camera and methods are effective in generating stereoscopic 360° panoramas that can be viewed on popular virtual reality displays.

Because the optical surfaces inside a simultaneous polarization imaging system and the vignetting of the edge field change the polarization state of incident light, the polarization information reconstructed by the system can be inaccurate. We propose a point-by-point instrument matrix calibration method considering the edge field with an integrating sphere plus a rotating polarizer as a polarization-controlled light source, and we carry out a non-contact detection experiment of the tilt angle of flat glass using a simultaneous image polarimetry with double separate Wollaston prism. The experimental results indicate that the degree of linear polarization, angle of polarization, and angle of incidence can be reconstructed more accurately by the system calibrated with the point-by-point instrument matrix. It improves the detection accuracy of the polarization state of the transparent medium surface and lays the theoretical foundation for the research of polarization imaging and the application of quantitative detection.

The GZIII.18/18-ZQ is a spherical three generation image intensifier, whose cathodic sensitivity and signal-to-noise ratio index are significantly improved compared to the second generation, which can improve the night detection capability and observation effect of the microlight night vision. According to the spectra of three generation image intensifier spectral response, sensitivity, signal-to-noise ratio and other parameters, combined with the system requirements of the field of view, resolution and other technical indicators, a low level light system is designed with a focal length of 20.00mm, F number 1.29 and the field of view of 50 degrees. The system uses four lenses, the total length of the total objective is less than 60mm, and the weight is less than 100g. Using a free-surface prism to achieve optical circuit rotation, the performance is improved. Finally, we get the off-axis MTF curve in 40lp/mm greater than 0.5, the whole field of view distortion is less than 4% without vignetting , the transmission rate is greater than 83%.

Metis coronagraph is one of the remote-sensing instruments of the Solar Orbiter mission launched at the begin of 2020. The mission profile will allow for the first time the remote-sensing observation of the Sun from a very close distance and increasing the latitude with respect to the ecliptic plane. In particular, Metis is aimed at the overall characterization and study of the solar corona and solar wind. Metis instrument acquires images of the solar corona in two different wavelengths simultaneously; ultraviolet (UV) and visible-light (VL). The VL channel includes a polarimeter with an electro-optically modulating Liquid Crystal Variable Retarder (LCVR) to measure the linearly polarized brighness pB) of the K-corona. This paper presents part of the in-flight calibration results for both wavelength channels together with a comparison with on-ground calibrations. The orientation of the K-corona linear polarization was used for the in-flight calibration of the Metis polarimeter. This paper describes the correction of the on-ground VL vignetting function after the in-flight adjustment of the internal occulter. The same vignetting function was adaptated to the UV channel.

This is an Open Access article distributed under the terms of the Creative Commons Attribution License (http://creativecommons.org/licenses/by/4.0/), which permits unrestricted reuse, distribution, and reproduction in any medium, provided the original work is properly cited., Nighttime images taken with DSLR cameras from the International Space Station (ISS) can provide valuable information on the spatial and temporal variation of artificial nighttime lighting on Earth. In particular, this is the only source of historical and current visible multispectral data across the world (DMSP/OLS and SNPP/VIIRS-DNB data are panchromatic and multispectral in the infrared but not at visible wavelengths). The ISS images require substantial processing and proper calibration to exploit intensities and ratios from the RGB channels. Here we describe the different calibration steps, addressing in turn Decodification, Linearity correction (ISO dependent), Flat field/Vignetting, Spectral characterization of the channels, Astrometric calibration/georeferencing, Photometric calibration (stars)/Radiometric correction (settings correction - by exposure time, ISO, lens transmittance, etc) and Transmittance correction (window transmittance, atmospheric correction). We provide an example of the application of this processing method to an image of Spain. © 2021 The Author(s)., This work was supported by the EMISSI@N project (NERC grant NE/P01156X/1), Fonds de Recherche du Québec: Nature et Technologies (FRQNT), COST (European Cooperation in Science and Technology) Action ES1204 LoNNe (Loss of the Night Network), the ORISON project (H2020-INFRASUPP-2015-2), the Cities at Night project, FPU grant from the Ministerio de Ciencia y Tecnologia and F. Sánchez de Miguel. Cameras were tested at Laboratorio de Investigaciónn Científica Avanzada (LICA), a facility of UCM-UPM funded by the Spanish program of International Campus of Excellence Moncloa (CEI). We acknowledge the support of the Spanish Network for Light Pollution Studies (MINECO AYA2011-15808-E) and also from STARS4ALL, a project funded by the European Union H2020-ICT-2015-688135. This work has been partially funded by the Spanish MICINN, (AyA2018-RTI-096188-B-I00), and by the Madrid Regional Government through the TEC2SPACE-CM Project (P2018/NMT-4291), Miniesterio de Ciencia y Tecnología (H2020)., With funding from the Spanish government through the Severo Ochoa Centre of Excellence accreditation SEV-2017-0709.

Significance: To expand our understanding of the roles of astrocytes in neural circuits, there is a need to develop optical tools tailored specifically to capture their complex spatiotemporal Ca2+ dynamics. This interest is not limited to 2D, but to multiple depths. Aim: The focus of our work was to design and evaluate the optical performance of an enhanced version of a two-photon (2P) microscope with the addition of a deformable mirror (DM)-based axial scanning system for live mammalian brain imaging. Approach: We used a DM to manipulate the beam wavefront by applying different defocus terms to cause a controlled axial shift of the image plane. The optical design and performance were evaluated by an analysis of the optical model, followed by an experimental characterization of the implemented instrument. Results: Key questions related to this instrument were addressed, including impact of the DM curvature change on vignetting, field of view size, image plane flatness, wavefront error, and point spread function. The instrument was used for imaging several neurobiological samples at different depths, including fixed brain slices and in vivo mouse cerebral cortex. Conclusions: Our implemented instrument was capable of recording z-stacks of 53 μm in depth with a fine step size, parameters that make it useful for astrocyte biology research. Future work includes adaptive optics and intensity normalization.

The first light instrument on the Thirty Meter Telescope (TMT) project will be the InfraRed Imaging Spectrograph (IRIS). The IRIS On-Instrument Wavefront Sensor (OIWFS) provides diffraction limited wavefront sensing – in both tip/tilt and tip/tilt/focus modes – to NFIRAOS (Narrow Field InfraRed Adaptive Optics System). As part of the final design phase, we have further developed the optical and mechanical designs. We present recent changes to the optical design and the resulting performance and tolerance analysis. Changes include decreasing the field of view to 1.5×1.5 arcseconds (square) and moving the field lens to reduce vignetting of the science image. The mechanical design is being updated with more detail for the optical mounts. We present here example mounts and associated analyses and our plans for future prototyping., Adaptive Optics Systems VII, December 14-18, 2020, Online Only, United States, Series: Proceedings of SPIE

Results of a conceptual design study of ULTAIMTE-Wide Field Imager (WFI) is presented. ULTIMATE-WFI is a near-infrared wide-field imager for the ground-layer adaptive optics system of the Subaru telescope (ULTIMATESubaru) which realizes a 0. 002 seeing size over 200diameter at the Cassegrain focus utilizing a deformable 2ndry mirror. WFI has a 15. 07×15. 07 FoV with a wavelength coverage of 0.9–2.5µm. The FoV is covered by four identical optics, each having a square field lens with 226mm on a side. Its effective FoV is 7. 02 on a side, and is covered by a HAWAII-4RG array detector with a pixel scale of 0. 0011/pix. Effective FoV will be 14. 04×14. 04 or 2070 in total. Spot sizes at a detector plane are less than 0. 001 over the wavelength coverage. Due to the large FoV, vignetting by the telescope structure occurs and an additional cold stop is necessary to block their thermal emission, which causes ~80% vignetting at the edge of the FoV. All the optics are contained in a cylindrical structure to be installed on the Cassegrain focus of the telescope, and kept under cryogenic temperature except for the field lenses. Gravitational deformation will be smaller than 1mm, and may have negligible impact on the final image quality., Ground-based and Airborne Instrumentation for Astronomy VIII, December 14-18, 2020, Online Only, United States, Series: Proceedings of SPIE

The 3-concentric-spherical-mirror, object-centered, unit-magnification catoptric relay designed by Abe Offner combines excellent aberration correction with extreme optical simplicity. A drawback of the design for some applications is that for telecentric objects the pupil is located at the secondary mirror and for near-telecentric objects (such as are commonly produced by astronomical telescopes) the pupil lies in the confusion of rays near to the secondary mirror. Recently it has been “re-discovered” that the Offner design is a special case of a more general family of designs, all sharing exactly the same imaging characteristics and optical correction of 3rd and 5th order aberrations. We say “re-discovered” because Offner presented exactly this information in his 1973 patent, but this fact seems to have generally eluded the optical design community. The “generalized Offner” solutions differ from the well-known Offner relay in that the primary and tertiary mirrors have different radii, and there is no limitation in the ratio of these radii, other than that Petzval curvature be corrected. New relays constructed of monocentric triplets of object-centred mirrors are presented for which pupils are accessible without vignetting.

The paper reports an overview of the preliminary optical design for the MICADO Relay Optics (RO) to enable early science observations of the instrument at the Extremely Large Telescope (ELT) with single-conjugate adaptive optics (SCAO). MICADO, the Multi-AO Imaging Camera for Deep Observations, is a first light imager, astrometric camera and spectrograph operating between 0.8 µm and 2.4 µm. The RO are based on a six mirror (6M) optical assembly that relays the telescope focal plane to an accessible position for the MICADO cryostat. The system includes three powered mirrors in a three-mirror-anastigmat configuration and three piston and tip- tilt flat mirrors for the alignment and the beam folding at the interfaces with the ELT and MICADO. This design represents an interesting example of optical performance optimization to achieve high performances optics both for the direct imaging channel and the pupil interface towards MICADO and the SCAO. The RO performances are analyzed and verified at a design level showing the compliance with the requirement specifications and the reliability of the design is assessed with an extended tolerance study and a minimization of the vignetting factor at the MICADO cold stop. The manuscript also contains a demonstration of the optical alignability of a 6M system in terms of pupil and focal plane steering that are essential to cope with the interface tolerances of the next generation of instrument at the foci of the extremely large telescopes.

The anti-vignetting glass (AVG) is the key material for super-second and third-generation low-light image intensifiers. With the development of low-light night vision technology, the requirements of high precision and low damage are put forward to AVG. However, traditional measurement methods, such as vernier calipers, micrometers, dial indicators, etc., are all contact measurement, which will inevitably cause damage to AVG during the measurement process. They cannot meet the technical requirements for low damage. Non-contact measurement technology is a non-destructive testing method that realizes the geometric measurement of AVG by writing measurement programs and setting measurement parameters. However, due to the special structure of AVG, the non-contact measurement technology has measurement errors and cannot meet the high-precision measurement requirements. In this paper systematically analyzes the causes of errors in non-contact measurement technology by studying the characteristics of the light source, the difference in light intensity, and the way of grabbing contour edges. Through the error correction technology, the error of the non-contact measurement technology is eliminated, the AVG high-precision and low-damage non-destructive testing is realized.

Light field cameras have been employed in myriad applications thanks to their 3D imaging capability. By placing a microlens array in front of a conventional camera, one can measure both the spatial and angular information of incoming light rays and reconstruct a depth map. The unique optical architecture of light field cameras poses new challenges on controlling aberrations and vignetting in lens design process. The results of our study show that field curvature can be numerically corrected for by digital refocusing, and vignetting must be minimized because it reduces the depth reconstruction accuracy. To address this unmet need, we herein present an optical design pipeline for light field cameras and demonstrated its implementation in a light field endoscope.

This work is framed within the general objective of helping to reduce the cost of telepathology in developing countries and rural areas with no access to automated whole slide imaging (WSI) scanners. We present an automated software pipeline to the problem of mosaicing images acquired with a smartphone, attached to a portable, low-cost, robotic microscopic scanner fabricated using 3D printing technology. To achieve this goal, we propose a robust and automatic workflow, which solves all necessary steps to obtain a stitched image, covering the area of interest, from a set of initial 2D grid of overlapping images, including vignetting correction, lens distortion correction, registration and blending. Optimized solutions, like Voronoi cells and Laplacian blending strategies, are adapted to the low-cost optics and scanner device, and solve imperfections caused using smartphone camera optics. The presented solution can obtain histopathological virtual slides with diagnostic value using a low-cost portable device.

Curved sensors are a disruptive technology which allow improvement of the image quality and substantial simplification of optical designs. Both bring to the reduction of the volume and mass of the instruments, while improving their performance. The field of curvature is an optical aberration, present in every single optical system, describing the fact that the light going through optics produces an image on a portion of a sphere. The impact of this aberration is seen mostly on the edges of an image by the presence of vignetting and distortion. Current solutions are applied to correct the images, but they imply a growing complexity of the instruments and the increase of their volume. Curved detectors correct this optical aberration directly at the focal surface. Our recent research has demonstrated that curved detectors allow to remove many lenses and release constraints in optical systems, simultaneously making them more compact without performance impairments. The CNRS-LAM has developed a nondestructive, high quality curving process. A full electro-optical characterization performed at LAM on prototypes demonstrates that there is no significant difference among curved and flat sensors. The study and achievement of the association of a wide-angle lens with a curved sensor have proven that it is possible to reduce by a factor of two the number of lenses in the optical system. Moreover, a significant improvement of the sharpness can be noticed, just like the fact that there is no more distortion or vignetting, all until the edges of the image. Curved sensors bring significant improvement of the image quality in trans-disciplinary applications. The team is currently developing new optical concept including a curved focal surface for projects going from bio medical application to space imaging. In this talk I will present our work and results in the frame of freeform CMOS development, optical concept for a wide field imager for an ESA Earth’s aurora monitoring mission and discuss the impact of curved sensors on imaging systems.

In this paper, we present beam pattern tests performed on the SWIPE multi-mode bolometric detector pixel assembly. A 20-mm-aperture horn is coupled to a large detector absorber (10 mm diameter) with a TES sensor located on the side. The pixel assembly has been tested at the bolometer base temperature of 340 mK, inside a custom cryogenic test bed, looking at a Gunn oscillator (128 GHz) located in the far field. We developed a custom cryogenic neoprene absorber, in addition to the stack of standard metal meshes low-pass filters, to reduce the background on the detector at a level similar to the one expected in flight, allowing to measure the main beam of the pixel assembly. The measured FWHM is 21$$^{\circ }$$, slightly narrower than the expected one (24$$^{\circ }$$), due to vignetting produced by the filters stack.

The Transient Double-beam Spectrograph (TDS) is designed for optical low-resolution observations of non-stationary and extragalactic sources with the 2.5-m telescope of Caucasus Mountain Observatory of the Sternberg Astronomical Institute. It operates simultaneously in a short-wavelength (360--577 nm, reciprocal dispersion 1.21 A/pixel, resolving power R=1300 with a 1 arcsec slit) and long-wavelength (567--746 nm, 0.87 A/pixel, R=2500) channels. The light is split by a dichroic mirror with a 50% transmission at 574 nm. In the "blue" channel, the automatic replacement of the grating by a grism with a double resolving power is possible. Two CCD-cameras use E2V 42-10 detectors cooled down to $-70^\circ$C with a readout noise of 3 $e-$ at a readout rate of 50 kHz. The spectrograph is equipped with a back slit viewer camera and a calibration unit allowing to record a comparison spectrum from a hollow cathode lamp for wavelength calibration or from an LED source with a continuous spectrum (the "flat field") to take into account the vignetting and uneven slit illumination. The throughput of the entire optical path without slit loss is 20% at the zenith in the "blue" and 35% in the "red" channel. Excluding the atmosphere and the telescope, the efficiency of the TDS itself reaches a maximum of 47% and 65% respectively. The spectrograph is permanently mounted in the Cassegrain focus of the 2.5-m telescope of CMO SAI MSU sharing the port with a wide-field photometric CCD-camera. The spectrograph is fed by the light from a folding mirror introduced into the optical path. Since November 2019, TDS has been used for regular observations of non-stationary stars and extragalactic sources up to 20-th mag in a 2-h exposure with a signal-to-noise ratio >5 per pixel., 18 pages, 11 figures, 1 table. Accepted in Astronomy Letters

We present a number of example studies of telescope optics using the latest version of the AstroX add on toolbox for McXtrace. Among which are first, a benchmark study of effective area and vignetting for the Chandra X-ray Observatory which we find to match well with literature. Second, a convenient way of building a telescope model (in this case NuSTAR) with many similar optical elements scripted using python module. This lends itself well to be included in online notebooks and/or for teaching. Third, we show a new AstroX module for lobster eye optics, and fourth, a study of the proposed solar axion telescope BabyIAXO.

Electroluminescence (EL) imaging is affected by off-axis illumination together with sensor and lens imperfections. The images’ spatial intensity distribution is mainly determined by the vignetting effect. For quantitative EL imaging, its correction is essential. If neglected, intensities can vary significantly (>50%) across the image. This paper introduces and tests four vignetting measurement methods. The quantitative comparison of different methods shows that vignetting should be characterized preferably in plane by the source of the same type as the photovoltaic (PV) device to be tested. A direct PV-based measurement in short distance with spatial inhomogeneity correction is proposed for general-purpose vignetting characterization. For precise vignetting characterization, vignetting-object separation using pattern recognition is proposed. The use of non-PV light sources for vignetting characterization can cause vignetting overcorrection and can even decrease the quality of the vignetting-corrected images.

Depth estimation for the lense-array type cameras is a challenging problem because of sensor noise and radiometric distortion which is a global brightness change between sub-aperture images caused by a vignetting effect of the micro-lenses. We propose a depth map estimation method which has robustness against the sensor noise and the radiometric distortion. Our method first binarizes sub-aperture images by applying the census transform. Next, the binarized images are matched by computing the majority operations between corresponding bits and summing up the Hamming distance. An initial map obtained by matching has ambiguity caused by extremely short baselines among sub-aperture images. We refine an initial map by the optimization which uses the assumption that the variations of the depth values in the depth map and of the pixel values in the texture-less objects are similar. Experiments show that our method outperforms the conventional methods.

High Dynamic Range (HDR) imaging using a fisheye lens has provided new opportunities to evaluate the luminous environment in visual comfort research. For glare analysis, strict calibration is necessary to extract accurate luminous maps to achieve reliable glare results. Most studies have focused on correcting the vignetting effect in HDR imaging during post-calibration. However, the lens projection also contributes to luminous map errors because of its inherent distortion. To date, there is no simple method to correct this distortion phenomenon for glare analysis. This paper presents a parametric-based methodology to correct the projection distortion from fisheye lenses for the specific use in glare analysis. HDR images were captured to examine two devices: a 190&deg, equisolid SIGMA 8 mm F3.5 EX DG fisheye lens mounted on a Canon 5D camera, and a 195&deg, fisheye commercial lens with an unknown projection, mounted on the rear camera of a Samsung Galaxy S7. A mathematical and geometrical model was developed to remap each pixel to correct the projection distortion using Grasshopper and MATLAB. The parametric-based method was validated using Radiance and MATLAB through checking the accuracy of pixel remapping and measuring color distortion with Structural Similarity Index (SSIM). Glare scores were used to compare the results between both devices, which validates the use of mobile phones in photometric research. The results showed that this method can be used to correct HDR images projection distortion for more accurate evaluation of the luminous environment in glare research.

This paper starts with a description of the usability and the optical layout of an Abbe or Telescope type surgical microscope for stereo optical and stereo digital imaging. Most important optical characteristics for stereoscopic image aquisition are emphasized. Afocal Galilei-type optical zooms are the heart of all modern stereo microscopes for industrial, bioscience and surgical applications. Two type of such zooms are described: Type 1: two separate optical channels, one for each stereoscopic view and. Type 2: one common optical channel for both stereoscopic views each guided off-axis. Type 1 zooms have the advantage of compact size and high optical quality. Their downside are tight tolerances and adjustment of optical members required for a good binocular performance. Type 2 zooms are always good at binocular even for standard tolerances but suffer from magnification dependency of the stereoscopic perception and from nonsymmetrical vignetting. Design examples are provided and some important aspects of aberration correction are discussed. As a vignetting-free system, one afocal commom optical channel Kepler-type zoom design example is proposed. Finally, some advanced surgical microscope setups suitable for two stereoscopic observers in one microscope having different stereoscopic perspectives on the magnified object are shown. The Type 2 common optical channel zoom of Galilei or Kepler type is the best choice if a variable rotation position of a stereoscopic co-observer is required.

We are developing an innovative compact coronagraph for studying the physical conditions in the solar wind acceleration region. This paper presents the new development of the compact coronagraph for the investigation of temperature and speed of electrons in the solar corona. The proposed compact coronagraph is a one stage externally occulted coronagraph without internal occulter or Lyot stop mask. The key of the new idea is to set the inner field cutoff at the External Occulter (EO) much smaller than the specified inner field cutoff. A second occulter on the surface of the detector array removes the remaining diffraction. The occulter on the detector surface functions similar to an internal occulter with the Inner Field of View Cutoff (IFoVC) exactly the same as specified. For BITSE, the desired inner field cutoff is 3 R, but the cutoff at EO is only 1.5 R☉. The diffraction analysis shows that in the sensor plane, the diffraction intensity at the 3 R☉ is not sensitive to the EO cutoff, either at 1.5 R☉ or close to 3 R☉. The advantage of having a smaller EO cutoff is that the vignetting decreased for the Field of View (FoV) near 3 R☉, therefore, the signal increases. Meanwhile, the diffraction of Point Spread Function is much less in the radial direction, which not only increases the image quality around 3 R☉, but also increases the encircled energy and signal to noise ratio. In other words, the data is useful right at 3 R☉! The BITSE optical design and diffraction analysis will be presented in detail. The simulation shows the signal to noise ratio obtained from the diffraction and vignetting data enables corona temperature and speed measurement.

Multiphoton microscopy provides a suitable technique for imaging biological tissues with submicrometer resolution. Usually a Gaussian beam (GB) is used for illumination, leading to a reduced power efficiency in the multiphoton response and vignetting for a square-shaped imaging area. A flat-top beam (FTB) provides a uniform spatial intensity distribution that equalizes the probability of a multiphoton effect across the imaging area. We employ a customized widefield multiphoton microscope to compare the performance of a square-shaped FTB illumination with that based on using a GB, for both two-photon fluorescence (TPF) and second-harmonic generation (SHG) imaging. The variation in signal-to-noise ratio across TPF images of fluorescent dyes spans ∼5.6 dB for the GB and ∼1.2 dB for the FTB illumination, respectively. For the GB modality, TPF images of mouse colon and Convallaria root, and SHG images of chicken tendon and human breast biopsy tissue showcase ∼20% area that are not imaged due to either insufficient or lack of illumination. For quantitative analysis that depends on the illuminated area, this effect can potentially lead to inaccuracies. This work emphasizes the applicability of FTB illumination to multiphoton applications.

Full-disk solar chromospheric and photospheric images are widely used to monitor solar activity. Flat-fielding is a basic step during scientific data production. Here, a Gaussian-type diffuser is used to measure the flat-field of full-disk solar chromospheric and photospheric images. The effectiveness of the method is verified by theoretical simulation and practical measurement. First, the uniformity of the light source generated by the Gaussian diffuser and the sunlight, with a field of view the same as the full-disk solar image, is calculated. The full width at half maximum (FWHM) of the scatter angle of the Gaussian diffuser is one degree, such that the light source presents a Gaussian distribution. After the correction of the Gaussian background, the uniformity of the area light source is 99.6%, which can be regarded as a uniform area light source. Second, experiments are conducted on full-disk solar telescopes at Huairou solar observing station and Yangbajing station. The diffuser covers the entire entrance aperture when taking flat-field frames. Through qualitative and quantitative analysis of experimental results, it is confirmed that a revised flat-field frame can modify uniformity caused by various aspects of the telescope, including vignetting, non-uniformities of filters, and contamination of optical components.

Currently for the European Space Agency (ESA) ATHENA [1,2] mission Silicon Pore Optic (SPO) [3-8] Mirror Modules (MM) with a focal length of f = 12 m, are being developed and tested. The SPO MMs are also the baseline optic for the NASA medium explorer high-resolution spectroscopy mission Arcus [9-10] with f = 12 m that is currently undergoing a phase A study. SPOs are currently being tested at both the PTB laboratory of the BESSY synchrotron facility in Berlin using an X-ray pencil beam and the PANTER X-ray test facility in Neuried of the Max-Planck-Institut fur extraterrestrische Physik, Garching using a long vacuum beamline (distance source to optic ~120 m). The different types of measurements performed at PANTER to characterise the ATHENA and Arcus optics will be discussed. This will be done on the level of an X-ray optical unit (XOU) composed of both a primary and secondary High Performance Optic (HPO) stack, a mirror module (MM) composed of two XOUs, small (

As a tool for investigating the adaptive correction of turbulent distortions of optical radiation in the Shack – Hartmann wavefront sensor, wavefront reconstruction is used based on the approximation of the wave function by a set of Zernike polynomials. The accuracy of the reconstruction of the phase distribution of the light field arriving at the entrance aperture of the system is determined by the information about the light field formed in the plane of the video camera in the form of a Hartmann pattern. A number of external factors, such as the design features of the optoelectronic system, expressed by the vignetting of the lens raster, the round shape of the entrance aperture of the system, and the presence of “strong” turbulence on the optical propagation path affect the filling of the hartmanogram with focal spots and its representation in the recording plane. On the basis of numerical experiments, studies were performed evaluating the accuracy of reconstructing the phase distribution of the light field depending on the intensity of turbulent distortion of optical radiation, taking into account the identified external factors.

Small-sized designs are essential due to the development of the technology for sensors and electronic devices, including general electronic devices as well as missile systems, which are performance-critical. The shutter position from the front of optics (external shutter) to between the optics and the detector (internal shutter) must be changed to reduce the system size. To achieve it with minimum loss, the existing shutter non-uniformity-correction (NUC) algorithm should be improved to consider the effects of lens, particularly the vignetting effect. Therefore, the vignetting effect should be modeled similar to the actual lens effect to improve the uniformity after the suggested shutter NUC (modeled internal shutter). This study presents the details of a modeling method for vignetting and improves the shutter NUC algorithm that applies the modeled vignetting effect to a captured image of the internal shutter. The improved shutter NUC algorithm is validated with the modeling data generated with the conditions of the actual design parameter of a missile system.

Spectral cameras with integrated thin-film Fabry-Perot filters have become increasingly important in many applications. These applications often require the detection of spectral features at specific wavelengths or to quantify small variations in the spectrum. This can be challenging since thin-film filters are sensitive to the angle of incidence of the light. In prior work, we modeled and corrected for the distribution of incident angles for an ideal finite aperture. Many real lenses, however, experience vignetting. Therefore, in this paper, we generalize our model to the more common case of a vignetted aperture, which changes the distribution of incident angles. We propose a practical method to estimate the model parameters and correct undesired shifts in measured spectra. This is experimentally validated for a lens mounted on a visible-to-near-infrared spectral camera. ispartof: APPLIED OPTICS vol:58 issue:7 pages:1789-1799 ispartof: location:United States status: published

To achieve extremely low wavefront error and high throughput with vignetting-free reflective relay optics, a new design approach, "co-axis double three-mirror anastigmat," is proposed. This approach enables the elimination of rotationally asymmetric aberrations that becomes a problem for vignetting-free off-axis reflective optics by utilizing two components of on-axis telescopes and placing the central axis of the two components in parallel. The validity of the proposed approach has been confirmed by a next-generation astronomical instrument.

The Echelle spectrograph operating at Vainu Bappu Telescope (VBT), India, is a general purpose instrument used for many high-resolution spectroscopic observations. A concerted effort is being made to expand the scientific capability of the instrument in emerging areas of observational astronomy. The present study is aimed at evaluating the feasibility of the spectrograph to carry out precision Radial Velocity (RV) measurements. In the current design, major factors limiting the RV precision of the spectrograph arise from the movable grating and slit; optical aberrations; positional uncertainty associated with optomechanical mounts and environmental and thermal instabilities in the spectrograph room. RV instabilities due to temperature and pressure variations in the environment are estimated to vary around 120 $ \textrm{ms}^{-1} $ and 400 $ \textrm{ms}^{-1} $ respectively. The positional uncertainty of the grating in the spectrograph could induce a spectral shift $\sim1.4\,\textrm{kms}^{-1} $ across the Echelle orders. A Zemax model is used to overcome the uncertainty in the zero-positioning and lack of repeatability of the moving components. We propose to obtain the ThAr lamp observations and using the Zemax model as the reference, predict the drifts in the positions of the optical components. The perturbations of the optical components from the nominal position are corrected at the beginning of the observational run. After a good match is obtained between the model and the observations, we propose to use a Zemax model to improve the wavelength calibration solution. We could match the observations and model within $\pm$~1 pixels accuracy after the model parameters were perturbed in a real-time setup of the spectrograph. In this paper, we present the estimation of the perturbations of optical components and the effect on the RV obtained.

Lens Vignetting is a common distortion in imaging systems where the intensity of the image decreases gradually away from the image center. Incorrect compensation of this luminance degradation often results in a more disturbing artifact called color shading, where the resulting image is left with shades of different colors. This paper presents a novel adaptive technique to compensate for lens Vignetting, while preserving color saturation and eliminating the need for per-unit calibration. As a consequence, the performance of automatic white balance algorithms have also been improved. The proposed algorithm is lightweight and realizable on FPGA architecture for real time Vignetting correction. The experimental results indicate a significant improvement in the quality of the corrected images. It is expected that the proposed algorithm will be implemented on mobile Image Signal Processors (ISPs) in the near future.

The vignetting effect in the Soft X-ray Telescope (SXT) onboard Yohkoh is studied using a two-dimensional distribution of the effective area in the field of view taken from a pre-launch experiment. Our initial estimation of the vignetting in SXT was carried out by fitting the data with a second-order polynomial function. The results show that a two-dimensional vignetting effect in SXT is not rotationally symmetric, particularly in the $y$ - (north–south) direction, which is probably due to the offset of SXT’s optical center from the location of its CCD center. We adopted a combined functional form consisting of a second-order polynomial function and a Gaussian function to take this asymmetric distribution of the effective area into account. We also considered the steep gradient of the effective area variation at the region near the vignetting center for the case of higher photon energy with this form. We completed a two-dimensional description of the vignetting effect in SXT by a spline surface fit using the “cleaned” effective area data whose noise was reduced satisfactorily by the fitting of our combined function.

In this paper, we present an electronic interface created for the Nikon 6B/6D visual autocollimator that allows for an increase in the final resolution of measurements and a reduction in the vignetting and distortion effects produced by this optical instrument’s lenses. The electronic interface consists of a Basler ACE high-definition camera and its positioning devices and a computer with a subpixel digital image processing package. The latter includes two main procedures: one for scale calibration and the other for determining the position of crosshair lines. Both procedures work at subpixel level. The feasibility of the measurement method was verified. The resolution obtained for the measurement of angular displacements is about 0.019 s of arc, 25 times better than the one registered by the original visual system. Its overall performance was compared against an electronic level with internationally traceable certification.

Optical Coherence Tomography (OCT) is a technology capable of producing 3-D volumes of microscopic structures with micron-scale resolution. Its main area of application remains ophthalmology and in particular retinal imaging. The quality and usability of the images depends upon the frame rate and the properties of the light being used. Swept source OCT (SS-OCT) can offer a speed advantage; variants using polygon mirrors (PMs) as spectral filters in SS-OCT have resulted in a variety of different arrangements. Although their application has been successfully demonstrated, a more detailed study of the particular aspects and requirements of beam propagation through the filter and their overall impact on the system performance have not been reported. Examining aspects related to vignetting at the PM facet leads to maximizing light throughput and system performance, which is the aim of this work. A swept source spectral filter consisting of a transmission grating, a two-lens telescope, an off-axis PM, and an end reflector mirror has been evaluated in terms of the beam width at the PM facet and how this parameter varies across the entire width of the spectrum at the input of the spectral filter.

One of the core applications of light field imaging is depth estimation. To acquire a depth map, existing approaches apply a single photo-consistency measure to an entire light field. However, this is not an optimal choice because of the non-uniform light field degradations produced by limitations in the hardware design. In this paper, we introduce a pipeline that automatically determines the best configuration for photo-consistency measure, which leads to the most reliable depth label from the light field. We analyzed the practical factors affecting degradation in lenslet light field cameras, and designed a learning based framework that can retrieve the best cost measure and optimal depth label. To enhance the reliability of our method, we augmented an existing light field benchmark to simulate realistic source dependent noise, aberrations, and vignetting artifacts. The augmented dataset was used for the training and validation of the proposed approach. Our method was competitive with several state-of-the-art methods for the benchmark and real-world light field datasets.

We present the optical design of the ELT polarimeter in the context of the Phase-A study for HIRES. It is well known that in order to reduce the instrumental polarization and cross-talk, the optimal position for a polarimeter along the optical path of a telescope is the rotationally symmetric focus. In the particular case of ELT this is represented by the intermediate focus (IF) below M4 which is not directly accessible and needs therefore a reimaging to a safety distance of at least 500 mm. The design of a transfer optics unit for such location is challenging due to the constraint of having an allowed vignetting area of maximum 5 arc min. We focus in our paper on two optical design solutions. The first one is deploying a double Cassegrain system to reimage the IF, which includes the polarization optics and feeds the other ELT mirrors, redirecting the ordinary and extraordinary beams to the front end module (FE) onto the Nasmyth focus. This module comprises components for sky derotation, atmospheric dispersion correction (ADC), wavelength splitting in two bands (UBVRI, zYJH), field stabilization and conversion to f/20, dispatching the light into two pairs of fiber bundles to feed the HIRES spectrograph. The other solution considers a fiber based compact IF module, using a Schwarzschild Collimator with Foster prism, ADC and beam splitters for the two spectral bands. The two polarized beams are sent by pupil imaging through four separate long fibers to the fiber link module of the spectrograph. There we convert the output fiber f ratio from f/2.5 to f/20.

SWIMS-IFU is an image-slicer integral field unit designed for Simultaneous-color Wide-field Infrared Multi-object Spectrograph (SWIMS) of the University of Tokyo Atacama observatory 6.5m telescope. Its field-of-view, slice width and slice number are 17.2 ′′ × 12.8 ′′, 0.4 ′′ and 26, respectively. Due to the space limitation inside SWIMS, the IFU should fit in the dimension of 60mm×170mm×220mm. After finishing development of optical design, we have conducted tolerance analysis. The results show that the probability of vignetting of less than 5% is ∼90%, although at a slice of one side it drops to 50%. We plan to fabricate the mirror arrays monolithically by a ball-end milling with an ultra-high precision machine tool, and have conducted a demonstration process to prove its feasibility. Our requirement for shape error is less than 100 nm P-V and that for surface roughness is less than 10 nm r.m.s. Results of the latest demonstration satisfies the requirement. We will fabricate the mirror arrays and the support structures in 2018, and the IFU will be installed into SWIMS in 2019.

This contribution is focused on the innovative aspects of the design of the Laser Guide Star (LGS) Facility for the Gran Telescopio Canarias (GTC) Adaptive Optics (GTCAO) System [6]. After a trade-off process considering different alternatives, a preliminary opto-mechanical design was defined, based on a “TOPTICA SodiumStar” laser to be launched on-axis. To maximize throughput, different novelties around the optical, and mechanical design of the Laser Launch System, including the Laser Head, the Beam Transfer Optics and the Launch Telescope are emphasized in this paper. In particular, all the elements of the Laser Launch System have been compacted to be placed at the backside envelope of the GTC M2 mechatronics. To fit in that envelope the thermal enclosure of the Laser Head had to be redefined to avoid mechanical interferences and science beam vignetting. An innovative closed-loop Laser Head cooling approach was defined to be also arranged at the backside of GTC M2. Performance simulations running in parallel to the on-axis LGS design could not determine any difference in performance between the on-axis and the off-axis launch. Hence, considering the higher packaging and maintenance complexity required by the on-axis launch, GTC decided to define the off-axis configuration as the new baseline approach. All the solutions already defined for the on-axis approach that were applicable to the new off-axis baseline were reused. To reduce the cost of future upgrades, the LGS design allows generating and launching several LGS with just one launch telescope splitting the light from the Laser Head. In parallel with keeping the volume of the facility to a minimum, an effort to keep its maintenance as simple as possible has been also made to avoid the impact on the telescope operational costs.

Precision in the Radial Velocity (RV) measurements depends upon the efficiency of the technique to remove instrumental artifacts from stellar measurements. Iodine absorption cell technique is being implemented for high precision studies with the Echelle spectrograph operating at Vainu Bappu Telescope (VBT), Kavalur, India. Since the star spectrum is convolved with the PSF of the spectrograph, the asymmetries in the PSF are imposed on the stellar spectral lines. The fiber fed Echelle spectrograph is a general purpose instrument, designed for high resolution (R = 60,000) spectroscopic observations. The asymmetries in the Point Spread Function (PSF) arise due to the off-axis launching of the stellar beam into the collimator and vignetting across the field. Apart from this, due to usage constraints, the grating of the spectrograph is a movable component. The impact on the Doppler shift calculations due to the movable components in the spectrograph is to be estimated. For upgrading the spectrograph for precision studies, the component level sensitivity for RV is to be analyzed. Thus, instrument design asymmetries and component induced PSF variations are analyzed to estimate the limitations of the spectrograph for precision studies. We have developed Zemax based optical design of the spectrograph to estimate the PSF variations and design limitations on the RV studies. Here, we present a model developed in Zemax and a preliminary analysis on RV sensitivity and the PSF asymmetries of the spectrograph. These instrument variations are to be taken as input during RV data reduction for precision measurements.

The Mid-Infrared Multi-field Imager for gaZing at the UnKnown Universe (MIMIZUKU) is a mid-infrared camera and spectrograph developed as a first-generation instrument on the University of Tokyo Atacama Observatory (TAO) 6.5-m telescope. MIMIZUKU covers a wide wavelength range from 2 to 38 μm and has a unique optical device called Field Stacker which realizes accurate calibration of variable atmospheric transmittance with a few percent accuracy. By utilizing these capabilities, MIMIZUKU realizes mid-infrared long-term monitoring, which has not been challenged well. MIMIZUKU has three optical channels, called NIR, MIR-S, and MIR-L, to realize the wide wavelength coverage. The MIR-S channel, which covers 6.8–26 μm, has been completed by now. We are planning to perform engineering observations with this channel at the Subaru telescope before the completion of the TAO 6.5-m telescope. In this paper, we report the results of the laboratory tests to evaluate the optical and detector performances of the MIR-S channel. As a result, we confirmed a pixel scale of 0.12 arcsec/pix and a vignetting- free field of view of 2./0 1./8. The instrument throughputs for imaging modes are measured to be 20–30%. Those for N - and Q -band spectroscopy modes are 17 and 5%, respectively. As for the detector performance, we derived the quantum efficiency to be 40–50% in the mid-infrared wavelength region and measured the readout noise to be 3000–6000 electrons, which are larger than the spec value. It was found that this large readout noise degrades the sensitivity of MIMIZUKU by a factor of two.