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Free-space Optics
Published in Chunlei Guo, Subhash Chandra Singh, Handbook of Laser Technology and Applications, 2021
In the following sections, we describe how to calculate the position and dimensions of laser beam waists when transformed by lenses. In geometrical optics, an object (loosely something that can be imaged) is considered to be the point of origin of a spherical wavefront, the radius of which equals the distance from the object. Given a lens (or, more generally, an optical imaging system) of focal length f, object (s) and image (s΄) distances from the (thin) lens is given by the well-known ‘lens formula’ [9]:1/s+1/s'=1/f
Basic Optics Techniques and Hardware
Published in Walter Fox Smith, Experimental Physics, 2020
The “power” of a lens is defined as the inverse of the focal length, and has units of diopters, where one diopter equals an inverse meter. If one lens is positioned just after another (so that the two are “in series”), the total power is approximately equal to the sum of the individual powers.
Lenses
Published in Roshan L. Aggarwal, Kambiz Alavi, Introduction to Optical Components, 2018
Roshan L. Aggarwal, Kambiz Alavi
Camera lenses have either fixed focal length or zoom lenses that have adjustable focal lengths. The dedicated digital camera lenses are required to cover a relatively large area in the focal plane of the lens. Therefore, camera lenses have numerous lens elements, including aspheric elements to correct for the chromatic and monochromatic aberrations. Depth of field (DOF) of a camera lens is the distance between the farthest and nearest objects in the scene that appear sharp in the image. DOF is given by () DOF≈2(f#)δ(sof)2
Steering light in fiber-optic medical devices: a patent review
Published in Expert Review of Medical Devices, 2022
Merle S. Losch, Famke Kardux, Jenny Dankelman, Benno H. W. Hendriks
Another optical component that can be added outside the optical fiber to steer a light beam is a lens, as described in twelve patents [26,33,57–66]. A lens redirects a light beam due to refraction, changing its angular distribution. Lenses can be divided into converging and diverging lenses. In six devices, the distal tip includes a converging lens [26,33,57–60]. These converging lenses can be semi-spherical [57,58] or convex lenses [26,33,58–60]. In most standard designs, a converging lens focuses a light beam on a specific tissue area [26,33,57–60], see Figure 2j. The same converging lens can also collect light from this specific tissue area to one or more collecting fibers [33,57]. Smith [60] describes a special design including a converging lens and a faceted surface. The faceted surface receives light from the optical fiber and refracts it into different beam elements, which are then focused into multi-spots by a convex lens. In six devices, the distal tip includes a diverging lens [61–66]. This can be a semi-spherical [61–63], gradient-index [64], or concave [65] lens. Diverging lenses illuminate a wide area in the tissue. Nagale et al. [66] describe a special type of diverging lens, which is a triangular prism. The distal tip of this device consists solely of a prism that is directly coupled to the optical fiber. A light beam entering the prism refracts at the first face and then refracts again at the second face. As a result, light is emitted radially with a wide angular distribution. The prism can also rotate, allowing light to be emitted into the tissue in a 360° range, see Figure 2k.
On the behavior of inhaled fibers in a replica of the first airway bifurcation under steady flow conditions
Published in Aerosol Science and Technology, 2022
Frantisek Lizal, Matous Cabalka, Milan Maly, Jakub Elcner, Miloslav Belka, Elena Lizalova Sujanska, Arpad Farkas, Pavel Starha, Ondrej Pech, Ondrej Misik, Jan Jedelsky, Miroslav Jicha
The precise evaluation of length of fibers is limited by the depth of field. Fibers out of the optimal focus appear shorter. The depth of field is determined by the subject distance, the lens focal length, and the lens relative aperture. For the given camera sensor size (20,48 × 20,48 mm) and the required image spatial resolution (1,3 µm/pix), the depth of field can be controlled only by changing the lens aperture. However, reducing the lens aperture (increasing f-number) reduces the amount of collected light, which severely reduces the contrast of fibers in the image. Moreover, very small apertures are likely to produce diffraction and reduce image overall sharpness. The optical setup used here was a carefully chosen compromise between depth of field, image brightness and sharpness
Liquid crystal technology for vergence-accommodation conflicts in augmented reality and virtual reality systems: a review
Published in Liquid Crystals Reviews, 2021
where k is the wave number (), f is the focal length; n and d are the refractive index and thickness of the optical medium, respectively. Based on Equation (5), we can infer that the focal length of a lens is related to the refractive index and the thickness of the optical medium. Table 3 lists optical elements with tunable focal lengths in the AR and VR systems [22–24,27,28,39–72]. In simplistic terms, the optical power (lens power) of a lens is defined as the reciprocal of its focal length (i.e. lens power = 1/focal length), where the unit of the optical lens power is diopter (D or m−1). For example, a lens power of 2 D is has a focal length of 0.5 m, and a lens power of 0 D indicates infinite focal length.