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Microscopes
Published in Daniel Malacara-Hernández, Zacarías Malacara-Hernández, Handbook of OPTICAL DESIGN, 2017
Daniel Malacara-Hernández, Zacarías Malacara-Hernández
A microscope with an eyepiece without a field lens has the disadvantage that the exit pupil of the microscope is far from the eyepiece, making the observation uncomfortable. A field lens may be introduced, as shown in Figure 16.1, at the plane where the intermediate real image is formed. If the field lens is very thin and exactly at the real image plane, no aberrations are introduced (with the exception of Petzval curvature). Only the exit pupil is moved closer to the eyepiece. Another more important reason for introducing the field lens is the correction of some aberrations. The system formed by the eyepiece and the field lens is simply called an eyepiece. The effective focal length of the eyepiece is then obtained from Equation 3.46. If the field lens is exactly at the plane of the observed image, we may easily see that the effective focal length is equal to the focal length of the lens closer to the eye, without any influence from the field lens. However, in general, the field lens is not at the plane of the observed image.
Lenses, Prisms, and Mirrors
Published in Toru Yoshizawa, Handbook of Optical Metrology, 2015
Figure 2.15a shows a series of relay lenses. Clearly, as the light is relayed, less of it is caught by the second lens. Simply relaying the image plane was not sufficient. In Figure 2.15b we see a system in which an extra lens at the intermediate image plane relays the image of the lens aperture. That is, we now have two interleaved relay systems, one relaying the image and the other relaying the lens aperture. It requires no further explanation to appreciate the advantage of adding the second set of lenses. A lens placed at an image plane to relay the aperture is known as a field lens. Incidentally, the surfaces of a field lens should not be quite in the image plane, because any scratches or dust will be in focus and will be added to the scene. The lens should therefore be close to, but not actually at, the image plane.
Study on the crack propagation behaviour of eccentric uncoupled blasting in a deep-level rock mass
Published in International Journal of Mining, Reclamation and Environment, 2023
Fei Zhang, Liyun Yang, Huanning Hu, Chen Huang, Siyu Chen
The experimental system is shown in Figure 6. It mainly includes three parts: laser light path, initial stress field loading, and image acquisition. The laser transmitter emits a green laser beam. From the knowledge of optics, light rays can form a parallel beam between the two field lenses through the action of the beam expander lens and field lens. The initial stress field is realised by the self-designed simulation ground stress loading device in Figure 6. The high-speed camera collects image information during the fracture process of the specimen. The shooting frame rate is 131 250 fps, the shooting area is 128 × 264 pixels, and the image resolution is 96 ppi.