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Objective and Camera Lenses
Published in Robert J. Parelli, Principles of Fluoroscopic Image Intensification and Television Systems, 2020
In a simple lens, focal length is usually of most importance. This is a characteristic of all lenses and is generally used to identify a lens since it is a measure of the refracting power of the lens. Refraction is defined as the bending of a beam of light energy when it passes across an interface of materials with different indices of refraction. Focal length is simply the distance measured from the lens to a focal point. The focal point is, by definition, that point at which light incident upon a lens from an infinitely distant object is brought to a focus. The importance of focal length lies in the fact that this is the determining factor in the magnification at which a scene is an image on the television camera tube. Lens characteristics are shown in Figure 2.2
Sources of Ultrasonic Exposure
Published in Marvin C. Ziskin, Peter A. Lewin, Ultrasonic Exposimetry, 2020
A focused ultrasonic beam pattern is usually characterized by the two parameters shown in Figure 3: the focal length and the focal zone. The focal length is the depth to the maximum intensity and minimum beamwidth (focal point). The focal zone is the region of axial distance (depth) in which the beamwidth is sufficiently narrow to produce minimum lateral blur in the image.
Telescopes for Inner Space: Fiber Optics and Endoscopes
Published in Suzanne Amador Kane, Boris A. Gelman, Introduction to Physics in Modern Medicine, 2020
Suzanne Amador Kane, Boris A. Gelman
As you can see from Figure 2.9b,c, the image is often not the same size as the original object. In fact, depending upon the position of the object and the lens’ focal length, the image formed can be larger or smaller than the original object. The ratio of the image's size, hi, to that of the original object, ho, is called the magnification, M = hi/ho. In our example, it is possible to show, using trigonometry, that M = di/do. (This is true because the ray through the center of the lens travels without deflection, so it makes the same angle with the lens axis on either side of the lens. Because the angles are similar, we can conclude that hi/di = ho/do. Rearranging this last relation, we can find that di/do = hi/ho, and hence M = di/do. We see here how geometrical properties of lines and angles combine with laws of reflection and refraction for ray tracing in geometrical optics.) The rules described above for ray tracing can be extended to cover multiple lenses. This framework allows the construction of optical imaging systems used to create the images formed in endoscopy.
Ocular Rigidity and Current Therapy
Published in Current Eye Research, 2023
Axial myopia is characterized by an eye that is too long for its focal length. Excessive axial elongation can result in pathologic myopia which is defined as eyes having chorioretinal atrophy equal to or more severe than diffuse atrophy.96 The mechanisms regulating eye growth and influencing refractive development are starting to be understood, and are thought to be multifactorial. Visual cues have been shown to play a critical role in modulating eye growth, including image sharpness at the fovea and peripheral retinal defocus.97–106 In response to image quality, or blur, the retina sends biochemical signals to the fibroblasts of the sclera to alter its composition and allow it to stretch.97–102,107–109 It is now known that axial elongation results from connective tissue remodeling as opposed to tissue growth.108,110–112 It is hence inevitable that the biomechanical properties of the sclera are involved in axial elongation,67,108,113 however, the extent to which a more compliant sclera might pre-dispose to myopia development remains unclear.
Multivesicular liposomal depot system for sustained delivery of risperidone: development, characterization, and toxicity assessment
Published in Drug Development and Industrial Pharmacy, 2021
Sonia Alavi, Mohammad A. Mahjoob, Azadeh Haeri, Farshad H. Shirazi, Zahra Abbasian, Simin Dadashzadeh
The shape and surface topography of optimized RSP-MVLs were visualized via an inverted-light microscope (Optika, Italy) connected to a digital camera. A drop (20 μL) of the formulation was transferred to a glass slide, covered by a coverslip, and then photomicrographs were captured at 1000× magnification. Volumetric particle size and distribution of the liposomes were determined based on the laser light diffraction technique by a MasterSizer 2000 (Malvern Instruments, UK) equipped with a low-power helium-neon laser. The measurements were conducted by a 100 mm focal length lens, capable of measuring particles within a size range of 0.5–180 μm. The particle size distribution was investigated by the span value according to the following equation (Equation 1): Dn (n = 10, 50, and 90) denotes the volume percentage of MVLs possessing diameter below of Dn, and n is the %. The smaller span value demonstrates the narrower particle size distribution.
Non-Orthogonal Refractive Lenses for Non-Orthogonal Astigmatic Eyes
Published in Current Eye Research, 2019
Ahmed Abass, Bernardo T. Lopes, Steve Jones, Lynn White, John Clamp, Ahmed Elsheikh
The design method is based on the fact that a surface with a certain power 5 Each meridian was constructed by a series of nodes that were equally spaced along the meridian length. At these nodes, the optical powers of the Back-surface were Figure 3) and the corresponding focal lengths were Figure 4(Aa)). The design is then completed by moving the corresponding meridian nodes on the front-surface outwards until the focal lengths at all nodes were equal to the desired focal length Figure 4(Ab)). An optimisation process was then carried out to reposition the front meridian nodes in the anterior-posterior direction such that most of the refracted light rays fall on the desired focal point. In case the designer needed to create the back-surface of the lens by setting its radius of curvature Equation 2.