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Periscopes permit view outside of the vehicle without needing to cut these weaker vision openings in the front and side armour, better protecting the vehicle and occupants. A protectoscope is a related periscopic vision device designed to provide a window in armoured plate, similar to a direct vision slit.
The angle of incidence, in geometric optics, is the angle between a ray incident on a surface and the line perpendicular (at 90 degree angle) to the surface at the point of incidence, called the normal. The ray can be formed by any waves, such as optical, acoustic, microwave, and X-ray. In the figure below, the line representing a ray makes an ...
The principal ray or chief ray (sometimes known as the b ray) in an optical system is the meridional ray that starts at an edge of an object and passes through the center of the aperture stop. [ 5 ] [ 8 ] [ 7 ] The distance between the chief ray (or an extension of it for a virtual image) and the optical axis at an image location defines the ...
A ray tracing diagram for a converging lens A device that produces converging or diverging light rays due to refraction is known as a lens . Lenses are characterized by their focal length : a converging lens has positive focal length, while a diverging lens has negative focal length.
For a (reflecting) mirror, the real image is on the same side as the object while the virtual image is on the opposite side of, or "behind", the mirror. In diagrams of optical systems, virtual rays (forming virtual images) are conventionally represented by dotted lines, to contrast with the solid lines of real rays.
Relay lenses are found in refracting telescopes, endoscopes, and periscopes to optically manipulate the light path, extend the length of the whole optical system, and usually serve the purpose of inverting the image.
Schematic of a conventional and a periscope zoom lens A smartphone with a 5x optical zoom periscope lens camera, recognizable by the rectangular shape of its lens. A periscope lens, sometimes called a folded lens, is a mechanical assembly of lens elements that uses a prism or mirror to redirect the light through the lenses with a 90° angle to the optical axis, as in a periscope.
The diagram on the right shows an observer's eye looking at a frontal extent (the vertical arrow) that has a linear size , located in the distance from point . For present purposes, point O {\displaystyle O} can represent the eye's nodal points at about the center of the lens, and also represent the center of the eye's entrance pupil that is ...