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Zoom lenses (sometimes referred to as "true" zoom) are ideally parfocal, in that focus is maintained as the lens is zoomed (i.e., focal length and magnification changed), which is convenient and has the advantage of allowing more accurate focusing at maximal focal length then zooming back to a shorter focal length to compose the image. [1]
Cone of light behind an achromatic doublet objective lens (A) without (red) and with (green) a Barlow lens optical element (B). The Barlow lens, named after Peter Barlow, is a type of diverging lens which, used in series with other optics in an optical system, increases the effective focal length of an optical system as perceived by all components that are after it in the system.
The optical microscope, also referred to as a light microscope, is a type of microscope that commonly uses visible light and a system of lenses to generate magnified images of small objects. Optical microscopes are the oldest design of microscope and were possibly invented in their present compound form in the 17th century.
Axial optical units are more complicated, as there is no simple definition of resolution in the axial direction. There are two forms of the optical unit for the axial direction. For the case of a system with high numerical aperture, the axial optical units in a distance z are given by:
The resolution of a microscope is defined as the minimum separation needed between two objects under examination in order for the microscope to discern them as separate objects. This minimum distance is labelled δ. If two objects are separated by a distance shorter than δ, then they will appear as a single object in the microscope.
A stanhope or stanho-scope is an optical device that enables the viewing of microphotographs without using a microscope. [1] [2] They were invented by René Dagron in 1857. [1] Dagron bypassed the need for an expensive microscope to view the microscopic photographs by attaching the microphotograph at the end of a modified Stanhope lens. [1]
In the Book of Optics, al-Haytham hypothesized the existence of primary and secondary light, with primary light being the stronger or more intense of the two.The book describes how the essential form of light comes from self-luminous bodies and that accidental light comes from objects that obtain and emit light from those self-luminous bodies.
The entrance and exit angles of each ray that passes through an imaging system (grey box) are related. When the imaging system obeys the Abbe sine condition, the ratio of the sines of these angles equal the (lateral absolute) magnification of the system.