scholarly journals A Giant Meridian Circle - Reflector

1995 ◽  
Vol 166 ◽  
pp. 360-360
Author(s):  
V.N. Yershov
Keyword(s):  
Focal Plane ◽  
Optical Axis ◽  
Focal Length ◽  
Vertical Plane ◽  
Optical Scheme ◽  
Infrared Observations ◽  
Secondary Mirror ◽  
Axis Position ◽  
Reference Grid ◽  
Reading System

A 1.5 m reflector is proposed for infrared and optical meridian observations in order to extend the fundamental coordinate system to faintest objects and to the K-infrared waveband. Classical meridian circles are unfit for the infrared observations because their lens objectives do not give good images in the infrared. But reflectors are almost never used as meridian circles due to uncertainties in their optical axis position. The main problem is that the secondary mirror is not connected with the micrometer and the circle reading system. In order to overcome this difficulty the author proposes to use an intermediary focal plane between the primary and the secondary mirrors where a luminous reference grid of wires might be placed. The Gregory optical scheme has such a focal plane, and its secondary mirror forms images of a star and the grid at the micrometer's detecting area. At the same time a special champher around the primary's central hole forms anautocollimated image of the grid near the grid itself. The micrometer measures the star image coordinates relative to two images of the reference grid. So, observations will not be affected by displacements of the secondary mirror and by those of the micrometer. The telescope's equivalent focal length has been chosen as 3 m, and the optical system has been transformed into an aplanatic Mersenne combined with an aplanatic focal reducer corrector (Popov, 1988). A new autocollimated circle reading system is chosen for the instrument (Yershov and Nemiro, 1994). The observations will be linked to the fixed optical axis of two long-focus collimators placed at the prime vertical plane.

scholarly journals PbS and CCD Array Autocollimation Micrometers for the Infrared Meridian Circle

1995 ◽  
Vol 167 ◽  
pp. 337-338
Author(s):  
V. N. Yershov
Keyword(s):  
Focal Plane ◽  
Optical Axis ◽  
Meridian Circle ◽  
Pulkovo Observatory ◽  
Primary Mirror ◽  
Small Constant ◽  
Ccd Array ◽  
Secondary Mirror ◽  
Axis Position ◽  
Optical Unit

A new infrared meridian instrument is being developed at Pulkovo Observatory. The main purpose of the instrument is to extend the fundamental coordinate system to the K-infrared waveband and to faint stars at visual and I-wavebands. The instrument has a 30-cm primary mirror made from astrositall. An intermediate focal plane is used to introduce luminous reference marks. One can obtain autocollimated images of the marks at the intermediate focal plane with the use of a polished chamber located around the central hole of the primary mirror. The secondary mirror of the telescope forms images of the marks and of their autocollimated counterparts and passes them to the plane of a photodetector (Fig. 1.). The luminous marks give a reference frame for the measurements. These measurements are not affected by displacements of any optical unit placed after the intermediate focal plane or by displacements of the detector. The measurements are done relative to the coordinates of the average between positions of the luminous mark and its autocollimated image. Any small constant difference between the center of curvature and the optical axis position can be determined in the laboratory.

scholarly journals An Autocollimation Circle Reading System for the Infrared Meridian Instrument

1995 ◽  
Vol 166 ◽  
pp. 361-361
Author(s):  
V.N. Yershov ◽  
A.A. Nemiro
Keyword(s):  
Optical Axis ◽  
Angular Position ◽  
Optical Center ◽  
Meridian Circle ◽  
Primary Mirror ◽  
Axis Position ◽  
Spherical Mirrors ◽  
Reading System ◽  
Zero Points ◽  
New System

A new autocollimation circle reading system is proposed for the reflector meridian circle (Nemiro and Streletsky, 1988). The instrument will be used for observations in the K-infrared waveband. Instead of the divided circle fixed to the instrument tube the new system has small spherical mirrors polished at the lateral surfaces of the primary mirror. The primary mirror is made from sitall and has an autocollimation system aimed at monitoring its optical axis position. The small spherical mirrors of the circle reading system link the circle readings with the primary's optical axis. The divided circles are fixed unmovable opposite to both lateral surfaces of the primary's optical block. Both surfaces have four spherical mirrors. The distance between the divided circles and the mirrors is equal to the mirrors' radii of curvature. The scales of each circle are illuminated from outside (where the measuring microscopes are placed). The mirrors form autocollimated images of the divisions at the plane of the divisions itself. Averaged coordinates of a division and its autocollimated image give the position of the mirror's optical center, and the semi-difference of the coordinates gives the angular position of the telescope. So, the measurements of the circle positions are differential ones, and any displacements of the microscope zero-points are not critical. The precision of measurements is estimated to be better then 0.05″ (random) and 0.005″ (systematical). The work was supported by the Russian Foundation of Fundamental Investigations (the project's code is 93-02-17095).

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

Sensors ◽  
2020 ◽  
Vol 20 (19) ◽  
pp. 5501
Author(s):  
Yang Bai ◽  
Jianlin Li ◽  
Rongwei Zha ◽  
Ying Wang ◽  
Guangzhi Lei
Keyword(s):  
Optical System ◽  
Attitude Control ◽  
Pupil Diameter ◽  
Focal Length ◽  
Field Of View ◽  
Star Sensor ◽  
Spherical Lens ◽  
Entrance Pupil ◽  
Secondary Mirror ◽  
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.

scholarly journals DoF-Dependent and Equal-Partition Based Lens Distortion Modeling and Calibration Method for Close-Range Photogrammetry

Sensors ◽  
2020 ◽  
Vol 20 (20) ◽  
pp. 5934
Author(s):  
Xiao Li ◽  
Wei Li ◽  
Xin’an Yuan ◽  
Xiaokang Yin ◽  
Xin Ma
Keyword(s):  
Optical Axis ◽  
Focal Length ◽  
Calibration Method ◽  
Depth Of Field ◽  
Model Parameters ◽  
Lens Distortion ◽  
Camera Model ◽  
Distortion Model ◽  
Manual Adjustment ◽  
Close Range

Lens distortion is closely related to the spatial position of depth of field (DoF), especially in close-range photography. The accurate characterization and precise calibration of DoF-dependent distortion are very important to improve the accuracy of close-range vision measurements. In this paper, to meet the need of short-distance and small-focal-length photography, a DoF-dependent and equal-partition based lens distortion modeling and calibration method is proposed. Firstly, considering the direction along the optical axis, a DoF-dependent yet focusing-state-independent distortion model is proposed. By this method, manual adjustment of the focus and zoom rings is avoided, thus eliminating human errors. Secondly, considering the direction perpendicular to the optical axis, to solve the problem of insufficient distortion representations caused by using only one set of coefficients, a 2D-to-3D equal-increment partitioning method for lens distortion is proposed. Accurate characterization of DoF-dependent distortion is thus realized by fusing the distortion partitioning method and the DoF distortion model. Lastly, a calibration control field is designed. After extracting line segments within a partition, the de-coupling calibration of distortion parameters and other camera model parameters is realized. Experiment results shows that the maximum/average projection and angular reconstruction errors of equal-increment partition based DoF distortion model are 0.11 pixels/0.05 pixels and 0.013°/0.011°, respectively. This demonstrates the validity of the lens distortion model and calibration method proposed in this paper.

Diffraction ring pattern at the focal plane of a spherical lens – axicon doublet

1976 ◽  
Vol 54 (17) ◽  
pp. 1774-1780 ◽  
Author(s):  
Pierre-André Bélanger ◽  
Marc Rioux
Keyword(s):  
Plane Wave ◽  
Laser Beam ◽  
Optical System ◽  
Focal Plane ◽  
Focal Length ◽  
Spherical Lens ◽  
Diffraction Ring ◽  
Fresnel Integral ◽  
Drill Holes

A spherical lens and an axicon are combined to form an optical system producing a ring-shaped focalization pattern. The diameter of the ring in the focal plane depends on the angle of the axicon, on its dielectric index, and on the focal length of the spherical lens. The diffractional analysis of the lens–axicon combination, when illuminated by a plane wave, is presented. In particular, we show that, when the aperture is large, the Kirchhoff–Fresnel integral can be reduced to a known function. A close examination of the function reveals that the diffractional width of the ring is equal to approximately twice the width of the Airy pattern of the lens alone. This type of focalization is well suited for a system where a laser beam is used to drill holes.

Coulomb wave functions in the theory of the circular paraboloidal waveguide

1988 ◽  
Vol 66 (3) ◽  
pp. 212-227 ◽  
Author(s):  
J. LoVetri ◽  
M. Hamid
Keyword(s):  
Electromagnetic Fields ◽  
Focal Plane ◽  
Focal Length ◽  
Coulomb Field ◽  
Wave Functions ◽  
Field Pattern ◽  
Current Loop ◽  
Far Field ◽  
Far Field Pattern ◽  
A Current

In this paper it is shown how the Coulomb wave functions, commonly used in the description of a Coulomb field surrounding a nucleus, can be used in the description of electromagnetic fields that are symmetric with respect of [Formula: see text] inside a paraboloidal waveguide. The Abraham potentials Q and U, which are useful in describing fields with rational symmetry, are used to simplify the problem. It is shown that these potentials must satisfy a partial differential equation that when separated yields the Coulomb wave equation of order L = 0. Electromagnetic fields due to simple source distributions inside the paraboloid are expanded in terms of these functions. Specifically, solutions for current-loop sources located in the focal plane of the paraboloid are obtained. The case where the wall of the paraboloidal waveguide is assumed to be perfectly conducting is treated as well as the case where the wall has finite impedance. The finite paraboloid is also considered, and the far field is formulated using Huygen's principle. It is found that for the finite surface-impedance case, the far-field pattern due to a current loop operating at 100 MHz in the focal plane of a paraboloidal reflector of 1 m focal length is different from the perfectly conducting case. Specifically, the pattern seems to be more omnidirectional for the impedance case than for the perfectly conducting case. Numerical results are presented for relevant aspects of the problem.

DESIGN AND PERFORMANCE OF TRISH, A BINOCULAR ROBOT HEAD WITH TORSIONAL EYE MOVEMENTS

1993 ◽  
Vol 07 (01) ◽  
pp. 51-68 ◽  
Author(s):  
EVANGELOS MILIOS ◽  
MICHAEL JENKIN ◽  
JOHN TSOTSOS
Keyword(s):  
Optical Axis ◽  
Automatic Gain Control ◽  
Focal Length ◽  
Vertical Component ◽  
Gain Control ◽  
Vertical Axis ◽  
Stereo Pair ◽  
Robot Head ◽  
And Performance ◽  
Stereo Processing

We present the design of a controllable stereo vision head. TRISH (The Toronto IRIS Stereo Head) is a binocular camera mount, consisting of two fixed focal length color cameras with automatic gain control forming a verging stereo pair. TRISH is capable of version (rotation of the eyes about the vertical axis so as to maintain a constant disparity), vergence (rotation of each eye about the vertical axis so as to change the disparity), pan (rotation of the entire head about the vertical axis), and tilt (rotation of each eye about the horizontal axis). One novel characteristic of the design is that each camera can rotate about its own optical axis (torsion). Torsional movement makes it possible to minimize the vertical component of the two-dimensional search which is associated with stereo processing in verging stereo systems.

The eye of the soldier beetle Chauliognathus pulchellus (Cantharidae)

1979 ◽  
Vol 203 (1153) ◽  
pp. 361-378 ◽  
Keyword(s):  
Cross Section ◽  
Focal Plane ◽  
Optical Axis ◽  
Field Size ◽  
Acceptance Angle ◽  
Corneal Surface ◽  
Physiological Properties ◽  
Cone Cells ◽  
Optical Pathway ◽  
Surface Calculation

The soldier beetle eye is unusual in having large optically isotropic corneal cones which project inwards from a thick isotropic cornea. Refraction is mainly at the corneal surface. Calculation shows that the first focal plane is near the tip of the cone, from which the optical pathway continues as a crystalline tract. At the distal end of the crystalline tract, 3 µm in diameter, the four cone cells enclose the proximal tip of the corneal cone; at the proximal end they enclose the distal tip of a long fused rhabdom rod. The eye is remarkable in that there are two classes of retinula cells; four cells contribute to the long thin axial rhabdom, 2 µm in diameter and 120 µm long, and the other four cells form two rounded rhabdoms, 10 x 4 µm in cross-section and 20 µm deep, which lie to one side of the optical axis. The physiological properties of individual retinula cells were measured by intracellular recording. The retinula cells are of three spectral types with peaks near 360, 450 and 520–530 nm. Except by the criterion of spectral sensitivity, the retinula cells sampled could not be sorted into more than one class. The measured value of the acceptance angle, near 3° in the dark-adapted state, is consistent with the hypothesis that all sampled cells were of the anatomical type that participate in the central rhabdom rod. A calculation of the theoretical field size of individual retinula cells from measurements of refractive index and lens dimensions predicts that cells which participate in the central rhabdom will have acceptance angles near 3°. The conclusion, therefore, is that only one anatomical type of cell has so far been sampled.

scholarly journals Study on Concentrating Characteristics of a Solar Parabolic Dish Concentrator within High Radiation Flux

2015 ◽  
Vol 2015 ◽  
pp. 1-7 ◽  
Author(s):  
Qianjun Mao ◽  
Liya Zhang ◽  
Hongjun Wu
Keyword(s):  
Focal Plane ◽  
Flux Distribution ◽  
Radiation Flux ◽  
Focal Length ◽  
Thermal Conversion ◽  
High Radiation ◽  
Equal Area ◽  
Future Design ◽  
Parabolic Dish ◽  
Parabolic Dish Concentrator

Concentrating characteristics of the sunlight have an important effect on the optical-thermal conversion efficiency of solar concentrator and the application of the receiver. In this paper, radiation flux in the focal plane and the receiver with three focal lengths has been investigated based on Monte Carlo ray-tracing method. At the same time, based on the equal area-height and equal area-diameter methods to design four different shape receivers and numerical simulation of radiation flux distribution characteristics have also been investigated. The results show that the radiation flux in the focal plane increases with decreasing of the focal length and the diameter of the light spot increases with increasing of the focal length. The function of the position with a maximum of radiation flux has been obtained according to the numerical results. The results also show that the radiation flux distribution of cylindrical receiver has the best performance in all four receivers. The results can provide a reference for future design and application of concentrating solar power.

scholarly journals Focus-Adjustable Head Mounted Display with Off-Axis System

2020 ◽  
Vol 10 (21) ◽  
pp. 7931
Author(s):  
So Hyun Seo ◽  
Jae Myung Ryu ◽  
Hojong Choi
Keyword(s):  
Optical System ◽  
Optical Axis ◽  
Focal Length ◽  
Normal Vector ◽  
Effective Focal Length ◽  
Head Mounted Display ◽  
Conventional Methods ◽  
Angle Of Reflection

An off-axis system refers to an optical system in which the optical axis and the normal vector at the vertex of each surface do not match. An off-axis optical system can be applied in order to construct a thin and light optical system. In particular, the optical system used for a see-through head-mounted display (HMD) must be designed asymmetrically, with respect to the optical axis. Because the vision of a human is different for each individual, HMD requires focus adjustment. The effective focal length (EFL) of the optical system must be calculated to obtain the focus adjustment. However, the off-axis optical system cannot be calculated by conventional methods. In this study, the EFL was calculated by rotating the coordinates of the rays near the optical axis by the angle of reflection or refraction at the intersection of each surface, with the rays coinciding with the optical axis. The magnitude of movement of the micro-display for focus adjustment was obtained from the calculated EFL, for a see-through type HMD.

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