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The Petzval field curvature is equal to the Petzval sum over an optical system, where is the radius of the i th surface and the n s are the indices of refraction on the first and second side of the surface. [4] Petzval curvature of a spherical mirror is double of its curvature and Petzval radius of a mirror is equal to its focal length.
Adjustable focus lenses, like single-focus lenses, also reduce image-jump and spatial distortion in the field of view associated with traditional multi-focal lenses. Additionally, the ideal near-vision correction can be achieved with precision, because the variable lenses emulate the focusing action of the youthful (non-presbyopic) eye.
Bharat Electronics Limited was founded in Bangalore, Karnataka, India in 1954. [4] Starting with the manufacture of a few communication equipment in 1956, BEL started manufacturing receiving valves in 1961, germanium semiconductors in 1962, and radio transmitters for AIR in 1964 with help from the Soviet Union.
Junayd ibn Abd al-Rahman al-Murri (723 – 726 CE) recaptured Sindh, conquered Gujarat and parts of Rajasthan, however, Arab forces invading Malwa and achieved victory. [5] The fourth Umayyad campaign was launched after Arabs lost control of Sindh and conquered territories of Rajasthan and Gujarat under Tamim ibn Zayd al-Utbi (726 – 731 CE).
Corrective lens. A pair of contact lenses, positioned with the concave side facing upward. A corrective lens is a transmissive optical device that is worn on the eye to improve visual perception. The most common use is to treat refractive errors: myopia, hypermetropia, astigmatism, and presbyopia.
The Nikon F2 is an all-metal, mechanically-controlled (springs, gears, levers), manual focus SLR with manual exposure control. The camera itself needed no batteries, though the prism light meter did (and the motor drive if added). The F2 replaced the Nikon F, adding many new features (a faster 1/2000-second maximum shutter speed, a swing open ...
English Wikipedia (marked blue in the graph) is the most-read version of Wikipedia, accounting for 48% of the website's global traffic as of 2021. The English Wikipedia is the most edited Wikipedia's language version of all time. The English Wikipedia reached 4,000,000 registered user accounts on 1 April 2007, [23] over a year since the ...
The economy of India has transitioned from a mixed planned economy to a mixed middle-income developing social market economy with notable public sector in strategic sectors. It is the world's fifth-largest economy by nominal GDP and the third-largest by purchasing power parity (PPP); on a per capita income basis, India ranked 136th by GDP (nominal) and 125th by GDP (PPP).