scholarly journals Scaling the Retinal Image of the Wide-Angle Eye Using the Nodal Point

Photonics ◽  
2021 ◽  
Vol 8 (7) ◽  
pp. 284
Author(s):  
Michael Simpson
Keyword(s):  
Linear Relationship ◽  
Retinal Image ◽  
Nodal Point ◽  
Axial Distance ◽  
Actual Behavior ◽  
Wide Angle ◽  
Angular Range ◽  
Exit Pupil

Angles subtended at the second nodal point of the eye (NP2) are approximately the same as input visual angles over a very large angular range, despite the nodal point being a paraxial lens property. Raytracing using an average pseudophakic eye showed that the angular nodal point criterion was only valid up to about 10°, and that the linear relationship was due instead to the cornea and lens initially creating chief ray angles at the exit pupil that are about 0.83 times input values for this particular eye, and then by the retina curving around to meet the rays in a manner that compensates for increasing angle. This linear relationship is then also maintained when retinal intersections are calculated relative to other axial points, with angles rescaled approximately using the equation R/(R + delta), where delta is the axial distance from the center of a spherical retina of radius R. Angles at NP2 approximately match the input angles, but the terminology is misleading because this is not a paraxial property of the eye. Chief rays are used with finite raytracing to determine the actual behavior.

scholarly journals Wide-angle Reconfigurable Refraction by Silicon Fourier Metasurfaces

2021 ◽  
Vol 2015 (1) ◽  
pp. 012005
Author(s):  
A A Antonov ◽  
M V Gorkunov
Keyword(s):  
Analytical Approach ◽  
Numerical Solutions ◽  
Full Scale ◽  
Silicon Films ◽  
Angle Of Incidence ◽  
Wide Angle ◽  
Angular Range ◽  
Optical Setup ◽  
Fourier Harmonics ◽  
Rayleigh Hypothesis

Abstract We design metasurfaces based on silicon films with smooth relief described by several Fourier harmonics and study their ability to redirect the refracted light over a wide angular range controlled by subtle variations of the optical setup. We use semi-analytical approach based on the Rayleigh hypothesis as well as full-scale numerical solutions to optimize the relief shape. To illustrate the reconfigurability potential, we design metasurfaces efficiently redirecting the refracted light from 83° to −73° with respect to the normal, when the angle of incidence is varied from 0° to 2°, and from 80° to −74°, when the substrate permittivity is altered from 2.3 to 2.2.

Comparison of Narrow-angle and Wide-angle Digital Breast Tomosynthesis Systems in Clinical Practice

2021 ◽  
Author(s):  
Andrea M Winter ◽  
Linda Moy ◽  
Yiming Gao ◽  
Debbie L Bennett
Keyword(s):  
Clinical Practice ◽  
Three Dimensional ◽  
Digital Breast Tomosynthesis ◽  
Variable Number ◽  
Architectural Distortion ◽  
Wide Angle ◽  
Angular Range ◽  
Breast Tomosynthesis ◽  
Narrow Angle ◽  
Scan Time

Abstract Digital breast tomosynthesis (DBT) is a pseudo three-dimensional mammography imaging technique that has become widespread since gaining Food and Drug Administration approval in 2011. With this technology, a variable number of tomosynthesis projection images are obtained over an angular range between 15° and 50° for currently available clinical DBT systems. The angular range impacts various aspects of clinical imaging, such as radiation dose, scan time, and image quality, including visualization of calcifications, masses, and architectural distortion. This review presents an overview of the differences between narrow- and wide-angle DBT systems, with an emphasis on their applications in clinical practice. Comparison examples of patients imaged on both narrow- and wide-angle DBT systems illustrate these differences. Understanding the potential variable appearance of imaging findings with narrow- and wide-angle DBT systems is important for radiologists, particularly when comparison images have been obtained on a different DBT system. Furthermore, knowledge about the comparative strengths and limitations of DBT systems is needed for appropriate equipment selection.

The Design of a Hybrid Diffractive-Refractive Wide-Angle Eyepiece with a Large Exit Pupil Distance

2013 ◽  
Vol 710 ◽  
pp. 469-473
Author(s):  
Feng Wang ◽  
Jian Zhong Cao ◽  
En Shi Qu ◽  
Deng Qun Yu ◽  
A Qi Yan ◽  
...  
Keyword(s):  
Image Quality ◽  
Optical System ◽  
Focal Length ◽  
Optical Design ◽  
Random Phase ◽  
Optical Element ◽  
Wide Angle ◽  
Optical Elements ◽  
Exit Pupil ◽  
Design Software

The diffractive optical elements, with the negative dispersive characteristic and the random phase distributing to realize random phase modulation for wave-front, are not only helpful to simplify the optical system, but also improve the image quality, while putting it into the optical system. It can decrease the element numbers of the system and obtain a compact configuration that introducing diffractive optical element into the design of eyepiece. A hybrid diffractive-refractive wide-angle eyepiece, with a big exit pupil distance, is designed by using the Code V Optical Design Software. The features of the wide-angle eyepiece are 30mm effective focal length, 60°whole field-of-view (FOV), 30mm exit pupil distance and 6mm exit pupil diameter, and which consists of four lens and two diffractive elements. From the result of design, the MTF in the center field of the wide-angle eyepiece is over 0.55at 60lp/mm, at the same time, the MTFs in all fields are over 0.3 at 50lp/mm, which show that this wide-angle eyepiece has a great image quality.

scholarly journals Tunable Reflectarray Cell for Wide Angle Beam-Steering Radar Applications

2013 ◽  
Vol 2013 ◽  
pp. 1-7 ◽  
Author(s):  
F. Venneri ◽  
S. Costanzo ◽  
G. Di Massa
Keyword(s):  
Phase Shifter ◽  
Tuning Range ◽  
Beam Steering ◽  
Wide Angle ◽  
Angular Range ◽  
Angular Region ◽  
Antenna Beam ◽  
Phase Tuning ◽  
Radar Applications ◽  
Electronically Tunable

An electronically tunable reflectarray element is proposed in this work to design beam-steering antennas useful for radar applications. A reduced size reflectarray unit cell is properly synthesized in order to extend the antenna beam scanning capabilities within a wider angular region. The radiating structure is accurately optimized to provide a full phase tuning range by adopting a single varactor load as phase shifter element. A 0.46λ-reflectarray cell is designed at the frequency of 11.5 GHz, obtaining a phase agility of about 330°. The cell is successfully adopted for the design of a21 × 21reconfigurable reflectarray. The antenna is numerically tested for different configurations of the varactors capacitance values, and good beam-steering performances are demonstrated within a wide angular range.

CBED Shadow Images and Cs:Aberration Measurement

1982 ◽  
Vol 40 ◽  
pp. 696-697
Author(s):  
R. W. Carpenter ◽  
I.Y.T. Chan ◽  
J. M. Cowley
Keyword(s):  
Focal Point ◽  
Spherical Aberration ◽  
Optic Axis ◽  
Wide Angle ◽  
Caustic Surface ◽  
Convergent Beam

Wide-angle convergent beam shadow images(CBSI) exhibit several characteristic distortions resulting from spherical aberration. The most prominent is a circle of infinite magnification resulting from rays having equal values of a forming a cross-over on the optic axis at some distance before reaching the paraxial focal point. This distortion is called the tangential circle of infinite magnification; it can be used to align and stigmate a STEM and to determine Cs for the probe forming lens. A second distortion, the radial circle of infinite magnification, results from a cross-over on the lens caustic surface of rays with differing values of ∝a, also before the paraxial focal point of the lens.

A linearity test for thick specimens imaged by HVEM over a 180° angular range

1991 ◽  
Vol 49 ◽  
pp. 552-553
Author(s):  
Yu Liu
Keyword(s):  
Phase Contrast ◽  
Three Dimensional ◽  
Angular Range ◽  
Two Dimensional ◽  
Back Projection ◽  
Line Integral ◽  
Exponential Law ◽  
Transmission Electron ◽  
Absorption Law ◽  
Linearity Test

The image obtained in a transmission electron microscope is the two-dimensional projection of a three-dimensional (3D) object. The 3D reconstruction of the object can be calculated from a series of projections by back-projection, but this algorithm assumes that the image is linearly related to a line integral of the object function. However, there are two kinds of contrast in electron microscopy, scattering and phase contrast, of which only the latter is linear with the optical density (OD) in the micrograph. Therefore the OD can be used as a measure of the projection only for thin specimens where phase contrast dominates the image. For thick specimens, where scattering contrast predominates, an exponential absorption law holds, and a logarithm of OD must be used. However, for large thicknesses, the simple exponential law might break down due to multiple and inelastic scattering.

Mosaic Mapping: A Means of Tiling Images to Shorten Acquisition Speed for Lower - Magnification SEM Images and Wavelength Dispersive Spectrometers (WDS) X-Ray Maps

1996 ◽  
Vol 54 ◽  
pp. 438-439
Author(s):  
J.D. Geller ◽  
C.R. Herrington
Keyword(s):  
Limiting Factors ◽  
X Rays ◽  
Angular Range ◽  
Acceptance Angle ◽  
Sem Images ◽  
Worst Case ◽  
X Ray ◽  
Focusing Distance ◽  
Layered Crystals ◽  
Working Distance

The minimum magnification for which an image can be acquired is determined by the design and implementation of the electron optical column and the scanning and display electronics. It is also a function of the working distance and, possibly, the accelerating voltage. For secondary and backscattered electron images there are usually no other limiting factors. However, for x-ray maps there are further considerations. The energy-dispersive x-ray spectrometers (EDS) have a much larger solid angle of detection that for WDS. They also do not suffer from Bragg’s Law focusing effects which limit the angular range and focusing distance from the diffracting crystal. In practical terms EDS maps can be acquired at the lowest magnification of the SEM, assuming the collimator does not cutoff the x-ray signal. For WDS the focusing properties of the crystal limits the angular range of acceptance of the incident x-radiation. The range is dependent upon the 2d spacing of the crystal, with the acceptance angle increasing with 2d spacing. The natural line width of the x-ray also plays a role. For the metal layered crystals used to diffract soft x-rays, such as Be - O, the minimum magnification is approximately 100X. In the worst case, for the LEF crystal which diffracts Ti - Zn, ˜1000X is the minimum.

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