Optical Design of COLIBRÍ: A Fast Follow-up Telescope for Transient Events

2020 ◽  
Vol 09 (01) ◽  
pp. 2050001 ◽  
Author(s):  
J. Fuentes-Fernández ◽  
A. M. Watson ◽  
S. Cuevas ◽  
S. Basa ◽  
J. Floriot ◽  
...  
Keyword(s):  
Image Quality ◽  
Ambient Temperature ◽  
Focal Plane ◽  
Near Infrared ◽  
Optical Design ◽  
Field Of View ◽  
The Future ◽  
Transient Events

COLIBRÍ will be a Franco-Mexican 1.3-m telescope and imager for observing the visible and near infrared counterparts of transient events detected by the future SVOM mission. The imager is divided into two instruments: DDRAGO, with two 4k[Formula: see text][Formula: see text][Formula: see text]4k CCDs observing in [Formula: see text] and [Formula: see text], respectively, and CAGIRE, with one 2k[Formula: see text][Formula: see text][Formula: see text]2k LYNRED or H2RG detector observing in [Formula: see text]. DDRAGO will directly image the telescope focal plane with a field of view (FoV) of 26[Formula: see text][Formula: see text][Formula: see text]26 arcmin. CAGIRE will reimage the focal plane to make a pupil image available for a cold stop and adjust the plate scale to deliver a similar FoV. CAGIRE will not use a conventional collimator-camera configuration but rather an arrangement of lenses that sends the pupil image close to the focal plane after all of the reimaging optics. This allows most of the optics, including the infrared filters, to be at ambient temperature and avoids the complexity of having mechanisms and powered optics within the cryostat (CR). We present here the optical design of the system and a thorough analysis on the expected image quality of the instruments and the telescope.

Apochromatic Collimator Objective Lens Design with Big Field of View

2013 ◽  
Vol 710 ◽  
pp. 413-418
Author(s):  
Fei Guo ◽  
Mei Zhao ◽  
Mai Yu Zhou ◽  
Ming Quan Yang ◽  
Shan Shan Cong
Keyword(s):  
Image Quality ◽  
Structural Parameters ◽  
Optical Design ◽  
Field Of View ◽  
Practical Significance ◽  
Large Field ◽  
Objective Lens ◽  
Initial Structure ◽  
Core Part

Objective lens is the core part of a collimator, its quality has a direct impact on the collimators quality. Due to the small field of view and low image quality requirement, general collimator objective lens is difficult to achieve the requirement of testing an aerial camera s performance. So designing a large field of view, apochromatic collimator objective lens has an important practical significance. In this paper, the major qualifications were first proposed to design the collimator objective lens,according to which the initial configuration was confirmed. Then we used the ZEMAX optical design software to optimize the initial structure and normalized the optimized structural parameters. Finally the image quality of collimator objective lens was evaluated to make it achieve the requirement of qualifications.

scholarly journals Okayama Astrophysical Observatory Wide-Field Camera

2019 ◽  
Vol 71 (6) ◽  
Author(s):  
Kenshi Yanagisawa ◽  
Yasuhiro Shimizu ◽  
Kiichi Okita ◽  
Daisuke Kuroda ◽  
Hironori Tsutsui ◽  
...  
Keyword(s):  
Focal Plane ◽  
Near Infrared ◽  
Galactic Plane ◽  
Focal Plane Array ◽  
Variable Stars ◽  
Field Of View ◽  
Wide Field

Abstract We report on the development of a wide-field near-infrared (0.9–2.5$\, \mu$m) camera built as a renewal of the existing classical Cassegrain 0.91 m telescope at Okayama Astrophysical Observatory. The optics system was replaced with fast hybrid optics (f/2.5) composed of forward Cassegrain optics and quasi-Schmidt optics, which results in an effective image circle of 52 mm diameter on the focal plane. The new camera, called the Okayama Astrophysical Observatory Wide-Field Camera (OAOWFC), has imaging capabilities in the $Y$, $J$, $H$, and $K_{\rm s}$ bands over a field of view of $0.^{\!\!\!\circ }47 \times 0.^{\!\!\!\circ }47$ with a HAWAII-1 HgCdTe PACE focal plane array. The primary purpose of OAOWFC is to search for variability in the Galactic plane in the $K_{\rm s}$ band and to promptly follow up transients. We have demonstrated a photometric repeatability of 2% in the densest field in the northern Galactic plane and successfully discovered previously unreported variable stars. The observations of OAOWFC are fully autonomous, and we started scientific operations in 2015 April.

scholarly journals Calibration of the island effect: Experimental validation of closed-loop focal plane wavefront control on Subaru/SCExAO

2018 ◽  
Vol 610 ◽  
pp. A18 ◽  
Author(s):  
M. N’Diaye ◽  
F. Martinache ◽  
N. Jovanovic ◽  
J. Lozi ◽  
O. Guyon ◽  
...  
Keyword(s):  
Image Quality ◽  
Focal Plane ◽  
Closed Loop ◽  
Near Infrared ◽  
Experimental Tests ◽  
Relative Increase ◽  
Visible Range ◽  
Wavefront Control ◽  
Island Effect ◽  
Plane Wavefront

Context. Island effect (IE) aberrations are induced by differential pistons, tips, and tilts between neighboring pupil segments on ground-based telescopes, which severely limit the observations of circumstellar environments on the recently deployed exoplanet imagers (e.g., VLT/SPHERE, Gemini/GPI, Subaru/SCExAO) during the best observing conditions. Caused by air temperature gradients at the level of the telescope spiders, these aberrations were recently diagnosed with success on VLT/SPHERE, but so far no complete calibration has been performed to overcome this issue. Aims. We propose closed-loop focal plane wavefront control based on the asymmetric Fourier pupil wavefront sensor (APF-WFS) to calibrate these aberrations and improve the image quality of exoplanet high-contrast instruments in the presence of the IE. Methods. Assuming the archetypal four-quadrant aperture geometry in 8 m class telescopes, we describe these aberrations as a sum of the independent modes of piston, tip, and tilt that are distributed in each quadrant of the telescope pupil. We calibrate these modes with the APF-WFS before introducing our wavefront control for closed-loop operation. We perform numerical simulations and then experimental tests on a real system using Subaru/SCExAO to validate our control loop in the laboratory and on-sky. Results. Closed-loop operation with the APF-WFS enables the compensation for the IE in simulations and in the laboratory for the small aberration regime. Based on a calibration in the near infrared, we observe an improvement of the image quality in the visible range on the SCExAO/VAMPIRES module with a relative increase in the image Strehl ratio of 37%. Conclusions. Our first IE calibration paves the way for maximizing the science operations of the current exoplanet imagers. Such an approach and its results prove also very promising in light of the Extremely Large Telescopes (ELTs) and the presence of similar artifacts with their complex aperture geometry.

scholarly journals PENINGKATAN KUALITAS FOKUS CITRA IMAGER MULTISPEKTRAL SATELIT LAPAN-A3 (IMAGE-FOCUSING QUALITY IMPROVEMENT ON LAPAN-A3 SATELLITE MULTISPECTRAL IMAGER)

2018 ◽  
Vol 14 (1) ◽  
pp. 37
Author(s):  
Andi Mukhtar Tahir ◽  
Patria Rachman Hakim ◽  
A. Hadi Syafruddin
Keyword(s):  
Image Quality ◽  
Transfer Function ◽  
Modulation Transfer Function ◽  
Near Infrared ◽  
Beam Splitter ◽  
Modulation Transfer ◽  
Color Channel ◽  
Multispectral Imager ◽  
Image Focus

LAPAN-A3 satellite brings a multispectral imager as main payload which has four color channel, i.e.: red, green, blue and near-infrared. The imager optics system uses beam-splitter mechanism, which divides the incoming light passing lens system into each color channel detector. Since each channel detector has different position and orientation with respect to lens center, then images produced by each channel detector will have different image focus quality. Such factor could reduce the quality of image produced. This research aims to improve the composite image quality of LAPAN-A3 satellite multispectral imager by ensuring that every channel detector will have uniform focus setting. The method used in this research consists of taking series of observation of object with zebra-cross pattern, then processed them by using Imatest software. The determination of the quality of each image focus are based on Modulation Transfer Function (MTF) calculation in particular spatial frequency. After several observations and calculation, image focus level of each channel detector can be successfully uniformed by controlling the distance of each detector to the center of lens. Furthermore, the experiment also able to reduce distortion caused by channel co-registration in horizontal axes. As a result, image quality of LAPAN-A3 satellite multispectral imager can be improved significantly. These results can be used as reference on the actual LAPAN-A3 sattelite ground station operation, and to support the development of experimental multispectral imager that is prepared for the next LAPAN-A4 sattelite. ABSTRAKSatelit LAPAN-A3 membawa imager multispektral sebagai muatan utama, yang memiliki empat kanal warna yaitu merah, hijau, biru, dan near-infrared. Sistem optik imager dirancang dengan menggunakan beam-splitter yang akan membagi cahaya yang melewati sistem lensa menuju detektor masing-masing kanal warna. Karena setiap detektor memiliki posisi dan juga orientasi yang berbeda terhadap pusat lensa, maka akan terjadi ketidakseragaman derajat kefokusan untuk setiap citra yang dihasilkan oleh masing-masing kanal warna, yang dapat mengurangi kualitas citra komposit yang dihasilkan. Penelitian ini bertujuan untuk meningkatkan kualitas citra komposit imager multispektral satelit LAPAN-A3 dengan cara memastikan agar setiap kanal warna akan menghasilkan citra dengan derajat kefokusan yang seragam. Metode yang digunakan yaitu dengan mengambil sejumlah data pengamatan terhadap obyek dengan pola geometri zebra-cross, dan kemudian diolah dengan menggunakan perangkat lunak Imatest. Penentuan kualitas fokus citra dilakukan dengan mengukur Modulation Transfer Function (MTF) pada frekuensi spasial tertentu. Berdasarkan sejumlah pengamatan dan perhitungan yang dilakukan, derajat kefokusan citra yang dihasilkan masing-masing detektor dapat diseragamkan dengan mengatur jarak detektor tersebut terhadap pusat lensa. Selain itu, percobaan yang dilakukan juga dapat mengurangi distorsi ko-registrasi kanal yang terjadi pada sumbu horisontal. Kedua hasil tersebut secara signifikan dapat meningkatkan kualitas citra imager multispektral satelit LAPAN-A3, terutama dalam aspek geometri. Hasil penelitian ini diharapkan dapat digunakan sebagai panduan dalam proses operasional satelit LAPAN-A3 selanjutnya dan juga dapat mendukung pengembangan imager multispektral eksperimen yang sedang dikembangkan untuk satelit LAPAN-A4.

scholarly journals SPHERICAL PRIMARY MIRROR IN TELESCOPES WITH COMPLEX (MULTI-ELEMENT) OPTICAL DESIGNS

2021 ◽  
Vol 34 ◽  
pp. 81-84
Author(s):  
S.V. Podlesnyak ◽  
N.N. Fashchevsky ◽  
Yu.N. Bondarenko ◽  
S.M. Andrievsky
Keyword(s):  
Wave Front ◽  
Focal Plane ◽  
Optical Design ◽  
Effective Field ◽  
Field Of View ◽  
Spherical Mirror ◽  
Primary Mirror ◽  
Reflected Wave ◽  
Aperture Ratio

An optical design for telescope with spherical primary mirror, planoidal surface and two-lens corrector is discussed. The spherical mirror hasn aperture ratio 1/2.69. After reflection from the spherical mirror, the wave front falls on a planoidal surface and “forms” the reflected wave front from a virtual mirror with e 2 = 1.576. After passing the two-lens corrector, the light is collected in the focal plane. A dot diagram in the focal plane shows that all three-order aberrations are successfully corrected. The effective field of view is 2 degrees. The aperture ratio is 1/2.28.

scholarly journals PENINGKATAN KUALITAS FOKUS CITRA IMAGER MULTISPEKTRAL SATELIT LAPAN-A3

2016 ◽  
Vol 14 (1) ◽  
pp. 37 ◽  
Author(s):  
Andi Mukhtar Tahir ◽  
Patria Rachman Hakim ◽  
A. Hadi Syafruddin
Keyword(s):  
Image Quality ◽  
Transfer Function ◽  
Modulation Transfer Function ◽  
Near Infrared ◽  
Beam Splitter ◽  
Modulation Transfer ◽  
Color Channel ◽  
Multispectral Imager ◽  
Image Focus

LAPAN-A3 satellite brings a multispectral imager as main payload which has four color channel, i.e.: red, green, blue and near-infrared. The imager optics system uses beam-splitter mechanism, which divides the incoming light passing lens system into each color channel detector. Since each channel detector has different position and orientation with respect to lens center, then images produced by each channel detector will have different image focus quality. Such factor could reduce the quality of image produced. This research aims to improve the composite image quality of LAPAN-A3 satellite multispectral imager by ensuring that every channel detector will have uniform focus setting. The method used in this research consists of taking series of observation of object with zebra-cross pattern, then processed them by using Imatest software. The determination of the quality of each image focus are based on Modulation Transfer Function (MTF) calculation in particular spatial frequency. After several observations and calculation, image focus level of each channel detector can be successfully uniformed by controlling the distance of each detector to the center of lens. Furthermore, the experiment also able to reduce distortion caused by channel co-registration in horizontal axes. As a result, image quality of LAPAN-A3 satellite multispectral imager can be improved significantly. These results can be used as reference on the actual LAPAN-A3 sattelite ground station operation, and to support the development of experimental multispectral imager that is prepared for the next LAPAN-A4 sattelite. Abstrak Satelit LAPAN-A3 membawa imager multispektral sebagai muatan utama, yang memiliki empat kanal warna yaitu merah, hijau, biru, dan near-infrared. Sistem optik imager dirancang dengan menggunakan beam-splitter yang akan membagi cahaya yang melewati sistem lensa menuju detektor masing-masing kanal warna. Karena setiap detektor memiliki posisi dan juga orientasi yang berbeda terhadap pusat lensa, maka akan terjadi ketidakseragaman derajat kefokusan untuk setiap citra yang dihasilkan oleh masing-masing kanal warna, yang dapat mengurangi kualitas citra komposit yang dihasilkan. Penelitian ini bertujuan untuk meningkatkan kualitas citra komposit imager multispektral satelit LAPAN-A3 dengan cara memastikan agar setiap kanal warna akan menghasilkan citra dengan derajat kefokusan yang seragam. Metode yang digunakan yaitu dengan mengambil sejumlah data pengamatan terhadap obyek dengan pola geometri zebra-cross, dan kemudian diolah dengan menggunakan perangkat lunak Imatest. Penentuan kualitas fokus citra dilakukan dengan mengukur Modulation Transfer Function (MTF) pada frekuensi spasial tertentu. Berdasarkan sejumlah pengamatan dan perhitungan yang dilakukan, derajat kefokusan citra yang dihasilkan masing-masing detektor dapat diseragamkan dengan mengatur jarak detektor tersebut terhadap pusat lensa. Selain itu, percobaan yang dilakukan juga dapat mengurangi distorsi ko-registrasi kanal yang terjadi pada sumbu horisontal. Kedua hasil tersebut secara signifikan dapat meningkatkan kualitas citra imager multispektral satelit LAPAN-A3, terutama dalam aspek geometri. Hasil penelitian ini diharapkan dapat digunakan sebagai panduan dalam proses operasional satelit LAPAN-A3 selanjutnya dan juga dapat mendukung pengembangan imager multispektral eksperimen yang sedang dikembangkan untuk satelit LAPAN-A4.

scholarly journals Learning curve evaluation upskilling retinal imaging using smartphones

2021 ◽  
Vol 11 (1) ◽  
Author(s):  
Linus G. Jansen ◽  
Payal Shah ◽  
Bettina Wabbels ◽  
Frank G. Holz ◽  
Robert P. Finger ◽  
...  
Keyword(s):  
Image Quality ◽  
Low Cost ◽  
Field Studies ◽  
Field Of View ◽  
Retinal Images ◽  
Fundus Imaging ◽  
Resource Limited ◽  
Examination Time ◽  
Significant Difference

AbstractSmartphone-based fundus imaging (SBFI) is a low-cost approach for screening of various ophthalmic diseases and particularly suited to resource limited settings. Thus, we assessed how best to upskill alternative healthcare cadres in SBFI and whether quality of obtained images is comparable to ophthalmologists. Ophthalmic assistants and ophthalmologists received a standardized training to SBFI (Heine iC2 combined with an iPhone 6) and 10 training examinations for capturing central retinal images. Examination time, total number of images, image alignment, usable field-of-view, and image quality (sharpness/focus, reflex artifacts, contrast/illumination) were analyzed. Thirty examiners (14 ophthalmic assistants and 16 ophthalmologists) and 14 volunteer test subjects were included. Mean examination time (1st and 10th training, respectively: 2.17 ± 1.54 and 0.56 ± 0.51 min, p < .0001), usable field-of-view (92 ± 16% and 98 ± 6.0%, p = .003) and image quality in terms of sharpness/focus (p = .002) improved by the training. Examination time was significantly shorter for ophthalmologists compared to ophthalmic assistants (10th training: 0.35 ± 0.21 and 0.79 ± 0.65 min, p = .011), but there was no significant difference in usable field-of-view and image quality. This study demonstrates the high learnability of SBFI with a relatively short training and mostly comparable results across healthcare cadres. The results will aid implementing and planning further SBFI field studies.

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