China
Africa
Explore chapters and articles related to this topic
Practical microscopy
Published in William Bolton, R.A. Higgins, Materials for Engineers and Technicians, 2020
The optical system of the microscope consists essentially of two lenses, the objective O and the eyepiece E. The former is the more important and expensive of the two lenses, since it must resolve fine detail of the object under examination. Good-quality objectives, like camera lenses, must be of compound construction. However, at magnifications of ×1000 or so, one is dealing with dimensions comparable with the wavelength of light itself, and further improvements in the magnification of the lens would produce no corresponding improvements in the sharpness of the image. The magnification given by an objective depends upon its focal length – the shorter the focal length, the higher the magnification obtainable. It is calculated by dividing the tube length of the microscope (200 mm for most instruments) by the focal length of the objective lens.
Machine Vision System Components
Published in Sheila Anand, L. Priya, A Guide for Machine Vision in Quality Control, 2019
To do a recap, selecting a lens appropriate to the camera is essential for obtaining a good-quality image. Lens resolution must fit/match that of the sensor resolution. For a high-resolution camera, the magnification required by lens is less that for a low-resolution camera, which requires a lens with a longer focal length. Focal length also has to be selected based on the working distance available for imaging the required object/scene. Lenses with a shorter focal length provide a wider field of view of the object than lenses with longer focal length, which provide greater magnification. Aperture size is determined based on the available lighting conditions. Aperture must be wider or larger for low-lighting conditions. The DoF is based on the working distance over which the object must be in focus. To get a wide DoF, a lens with a smaller aperture and a shorter focal length is used. Finally, to obtain a complete image, the size of the lens must be equal to or greater in size to match the circle size of the sensor.
Understanding Optics
Published in Barat Ken, Laser Safety Tools and Training, 2017
Even though the rays are traveling in the same direction, they strike the first surface at different incidence angles because that surface is curved. The ray in the center enters the lens at normal incidence, and therefore it does not bend at all. The rays farther from the center enter at larger angles the farther they are from the center and therefore bend more. At the flat surface of the lens, the rays bend again when they go from the glass back into air. As a result of these two refractions, the rays that come from the point source traveling in the same direction converge after passing through the lens. In fact, they converge in just such a way that they intersect at a single point called the focal point of the lens. The distance from the lens to the focal point is called the focal length of the lens.
Experimental investigation of a box-type solar cooker incorporated with Fresnel lens magnifier
Published in Energy Sources, Part A: Recovery, Utilization, and Environmental Effects, 2020
Gulsavin Guruprasad Engoor, S. Shanmugam, AR. Veerappan
The focal length of the lens may be defined as the distance from the lens to the point where the incoming input beam of light converges. It is mainly represented by the simple lens equation