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Adaptive optics ophthalmoscopes
Published in Pablo Artal, Handbook of Visual Optics, 2017
All optical systems are affected by optical aberrations that degrade imaging performance. Correcting the lower-order aberrations of the eye’s optics such as defocus and astigmatism provides most people with good vision. However, in order to better understand the function of the normal retina and the pathophysiology of retinal disease, one needs to look into the eye. This can, of course, be accomplished by studying histological preparations ex vivo, but the retina has to be studied in vivo in order to diagnose and monitor retinal disease and evaluate efficacy of medical treatment. This was facilitated by the independent inventions of the ophthalmoscope by Charles Babbage in 1847 and the indirect ophthalmoscope by Hermann von Helmholtz in 1851. The functionality and usability of the ophthalmoscope were greatly advanced by the invention of the handheld direct-illuminating ophthalmoscope by Francis Welch and William Allyn in 1915. Modern-day versions of the Welch–Allyn ophthalmoscope are routinely used in eye examinations today.
Prisms and Refractive Optical Components
Published in Daniel Malacara-Hernández, Brian J. Thompson, Fundamentals and Basic Optical Instruments, 2017
Daniel Malacara-Hernández, Duncan T. Moore
Optical aberrations, such as spherical aberration, coma, and astigmatism, can seriously affect the image quality of an optical system. To eliminate the aberrations, several optical components, lenses, or mirrors have to be used so that the aberration of one element is compensated by the opposite sign of the others. If we do not restrict ourselves to the use of spherical surfaces, but use some aspherical surfaces, a better aberration correction can be achieved with fewer lenses or mirrors.
Recent progress in three-dimensional flexible physical sensors
Published in International Journal of Smart and Nano Materials, 2022
Fan Zhang, Tianqi Jin, Zhaoguo Xue, Yihui Zhang
The eyes of aquatic animals possess exceptional image-sensing characteristics, such as an extremely wide field-of-view, a deep depth-of-field, and a high sensitivity (Figure 3c (I)). Kim et al [110]. demonstrated an aquatic-vision-inspired imager comprising a hemispherical Si nanorod photodetector array with serpentine interconnects and monocentric lens, as presented in Figure 3c (II) and (III). The serpentine interconnects in the photodetector array could minimize the strain induced in the imaging sensor array on the hemispherical substrate (the inset of Figure 3c (III)). Due to the curved shape of the photodetector array, imaging can be performed using a monocentric lens without optical aberration, resulting in a miniaturized design of digital camera. In addition, the hemispherical Si nanorod photodetector array shows an enhanced photo absorption, owing to its nanorod-textured surface, which reduces the surface reflection and transmission. Therefore, even under weak light intensities, the camera can still image very well. The integrated camera also provides a wide field-of-view (120°) and deep depth-of-field (from 20 cm to infinity) without optical aberrations (Figure 3c (IV)).
Extraction and analysis of microscopic traffic data in disordered heterogeneous traffic conditions
Published in Transportation Letters, 2021
R. B. Amrutsamanvar, B. R. Muthurajan, L. D. Vanajakshi
As ideal pinhole camera does not have any optical aberration, the above-mentioned camera matrix in Equation (3) does not account for any lens distortion. However, in reality, cameras have imperfections, which result in different types of radial and tangential lens distortions. These distortions need to be corrected in advance to obtain the idealized planar image, which is a prerequisite for the aforementioned computation. In the present study, Brown-Conrady model (Duane 1971) was used for correcting the radial and tangential distortion. Since this model implies straightforward distortion correction and is reported to be effective in literature for numerous applications (Devernay and Faugeras 2001; Tsai 1987; Zhang 2000), it was selected for the present study. Equation (4) depicts the applied distortion correction using this model, where are radial distortion coefficients, are the tangential distortion coefficients and .
PIV measurements of turbulent flow overlying large, cubic- and hexagonally-packed hemisphere arrays
Published in Journal of Hydraulic Research, 2020
Taehoon Kim, Gianluca Blois, James L. Best, Kenneth T. Christensen
Experiments were conducted in a closed-loop, refractive-index matched (RIM) flume at the University of Notre Dame (Blois et al., 2012). The test section is 2.5 m long and its acrylic cross-section is m2. This flow facility provides developing turbulent boundary layers on all four walls of the test section at the measurement location and enables bulk , where is the bulk velocity and ν is kinematic viscosity) of approximately to be obtained. In the current experiments, the RIM technique was utilized to explore the near-wall flow over various acrylic roughness models to achieve minimal optical aberration and light reflection at the surface. An aqueous solution of sodium iodide (NaI), 63 by weight, served as the working fluid in the RIM flume, with a specific gravity and kinematic viscosity (ν) at ambient temperature of 1.8 and m2 s−1, respectively, and a refractive index (RI) of approximately 1.496 at C (Budwig, 1994). Since the RI of the working fluid is quite sensitive to temperature (Narrow, Yoda, & Abdel-Khalik, 2000), the temperature of the working fluid was controlled using an in-line heat exchanger that allowed fine tuning with a resolution of C.