Angular aperture

About: Angular aperture is a research topic. Over the lifetime, 1771 publications have been published within this topic receiving 27257 citations.

Effects of Fresnel number in focusing and imaging

Abstract: The effects of a finite value for Fresnel number in focusing systems are discussed. For an aperture illuminated by a convergent spherical wave, a shift of the maximum intensity towards the aperture results, associated with a coordinate scaling with regions further from the aperture stretched. There is also a dependence on the numerical aperture of the system, the focal shift decreasing with apertures. For high apertures, the focal field can be expressed in terms of a scaled Debye integral. An alternative geometry is that of a focusing system with an aperture stop at an arbitrary position. If the stop is situated in the front focal plane of the lens, the amplitude in the back focal plane is given by the Fourier transform of the aperture amplitude, and the effective Fresnel number is infinite. For positions further from the lens it is negative, so that the maximum in intensity is shifted further from the lens, and the scaling is such that regions closer to the lens are stretched. A high aperture system can be modeled using the concept of the equivalent refractive locus. The field in the front focal plane is transformed into an angular spectrum of plane waves with an appropriate apodization term, so that if the aperture stop is in the front focal plane the effective Fresnel number is infinite.© (1999) COPYRIGHT SPIE--The International Society for Optical Engineering. Downloading of the abstract is permitted for personal use only.

Magneto-optical disc system having an objective lens with a numerical aperture related to the thickness of the protective layer

Abstract: An magneto-optical disc system includes an magneto-optical disc with a light-transmitting cover and an objective lens for bundling or focusing a laser beam on a recording layer of the magneto-optical disc in order to perform recording and/or reproduction. The thickness t 2 of the light-transmitting cover is set to fall within the range of 0.6 to 0.1 mm, the numerical aperture (NA) of the objective lens is set to fall within the range of 0.55 to 0.70 and the wavelength of the light beam is selected to be between 635 and 680 nanometers.

Large aperture zoom lens system

Abstract: A large-aperture zoom lens system comprising a first focusing lens unit having a positive focal length, a second variator lens unit having a negative focal length, a third compensator lens unit having a negative focal length and a fourth relay lens unit, said fourth lens unit consisting of a front subunit comprising at least one negative lens component and a rear subunit comprising at least two positive lens components. Said lens system comprises a small number of lens elements, and has a short total length, a long back focal distance and favorably corrected aberrations.

Four-group great aperture ratio zoom lens

Abstract: A great aperture ratio zoom lens has, in succession from the object side, a first lens group of positive refractive power having a focusing function, a second lens group of negative refractive power having a magnification changing function, a third lens group of positive refractive power having a correcting function for keeping the image plane at a predetermined position, and a fourth lens group of positive refractive power having an imaging function. The first to third lens groups from a substantially a focal magnification changing portion. The fourth lens group includes, in succession from the object side, a forward group comprising a positive meniscus lens component having its convex surface facing the object side, a positive lens components having its surface of sharper curvature facing the image side, and a biconcave lens component, and a rearward group having a negative lens component and a positive lens component. The zoom lens satisfies certain conditions.