Fr.: distance focale
same as → focal length.
Fr.: longueur focale
The distance between the optical center of a lens, or the surface of a mirror, and its focus.
Fr.: plan focal
A plane at right angles to the principal axis of a lens or mirror on which the best image is formed.
Fr.: point focal
Same as → focus.
Fr.: rapport focal
The ratio of the → focal length of a reflecting surface or lens to its effective diameter, i.e. to its → aperture. The smaller the focal ratio, the smaller the image scale and the more luminous the image for a given aperture.
kâhande-ye kânuni, bâzhâzande-ye ~
Fr.: réducteur focal
1) kânun; 2) kânunidan
Fr.: 1) foyer; 2) focaliser
1) (n.) A point where parallel light rays from an object are gathered together by a
lens or a concave mirror. It is the place where the clearest image of a distant object
forms. Also called focal point. See also → focal distance.
From L. focus "hearth, fireplace," of unknown origin,
Kânun "hearth, fireplace."
Of an optical system, being in focus or brought into focus; adjusted to produce a clear image.
Past participle of → focus.
The act of bringing into focus.
Noun of → focus.
A mass or layer of suspended water droplets or ice crystals near the surface of the earth, reducing visibility.
From Dan. fog "spray, shower, snowdrift," related to O.N. fok "snow flurry."
Meh "fog" (variants miq, mož, Tabari miyâ, Lori/Laki (kara) mozy, Ossetic mig/megæ), from Mid.Pers. mēq "cloud, mist," Av. mēγa- "cloud;" cf. Skt. meghá- "cloud, overcast weather;" Gk. omikhle "mist;" Lith. miglà "mist, haze;" PIE base *mighlā- "cloud."
Fr.: arc blanc
A large, faintly colored, circular arc formed by light (usually sunlight) falling on cloud or fog. Also called → cloudbow.
Fr.: équation de Fokker-Planck
A modified form of → Boltzmann's equation allowing for collision terms in an approximate way. It describes the rate of change of a particle's velocity as a result of small-angle collisional deflections.
After Dutch physicist Adriaan Fokker (1887-1972) and the German physicist Max Planck (1858-1947); → equation.
Fr.: gens, les gens
1) Usually, folks. (used with a plural verb) people in general.
M.E.; O.E. folc; cognate with O.Sax., O.Norse folk, O.H.G. folk (Ger. Volk).
Palg, from (Pashto) parrk "group of people," with variants: (Dehxodâ) parré "group of people; a circular disposition of troops for hunting or other purposes; a rank or file of soldiers;" (Lori, Torbart-Heydariye-yi, Qomi) borr "group of people, crowd;" (Qomi) borré; (Laki) berr "group of people;" (Qâyeni) bor "group, flock, herd;" (Kurd. Kurmanji) âpora "crowd;" transformation of -r- into -l- (as por = bol, → poly-) in Tabari bəlik, əllik "herd, flock;" ultimately from Proto-Ir. *paraka-, from *par- "to fill;" cf. Av. pər- "to fill, stuff with," pouru- "full, much, many;" O.Pers. paru- "much, many;" Pers. anbâr "ricks, storehouse," por, bol "full, much, many;" PIE *pel- "to fill;" → population.
The traditional beliefs, legends, customs, etc., of a people; lore of a people (Dictionary.com).
Coined by English scholar and antiquary William John Thoms (1803-1885), from → folk, + lore "traditional knowledge or belief," from M.E., O.E. lar cognate with Du. leer, Ger. Lehre "teaching," E. learn.
Palgvâr, literally "customs of people," from palg, → folk, + vâr "custom, rule, law" (Dehxodâ).
An observation which expands previous observations and aims at obtaining complementary data in particular with other telescopes/instruments.
Follow-up, from follow, from O.E. folgian, fylgan "to follow, pursue," from W.Gmc. *fulg- (cf. O.Fris. folgia, M.Du. volghen, Ger. folgen "to follow") + up, O.E. up, uppe (cf. Du. op, Ger. auf "up, upward"), from PIE base *upo "up from below;" cf. O.Pers./Av. upā; Skt. úpa; Gk. hypo; L. sub, → hypo-; → observation.
Nepâheš, → observation; peygir, from pey "after; step," related to pâ "foot, step, track," → foot, + gir present stem of gereftan "to take, seize" (Mid.Pers. griftan, Av./O.Pers. grab- "to take, seize," cf. Skt. grah-, grabh- "to seize, take," graha "seizing, holding, perceiving," M.L.G. grabben "to grab," from P.Gmc. *grab, E. grab "to take or grasp suddenly;" PIE base *ghrebh- "to seize").
Fr.: tache de queue
Agent noun of follow, from O.E. folgian, fylgan "to follow, pursue," from W.Gmc. *fulg- (cf. O.Fris. folgia, M.Du. volghen, Ger. folgen "to follow").
Laké, → spot; peyrow "follower," from pey "step; after," related to pâ "foot, step, track," → foot, + row "going; which goes," present stem of raftan "to go, walk, proceed," Mid.Pers. raftan, raw-, Proto-Iranian *rab/f- "to go; to attack."
Fomalhaut (α PsA)
famelhut (#), mâhidahân
The brightest star (V = 1.17) in the constellation → Piscis Austrinus. Fomalhaut is a white A3 main-sequence star about 25 light-years away. It is encircled by a dust belt (→ debris disk) of about 25 A.U. wide at a radial distance of about 140 A.U.
From Ar. Fam al-Hut (
Famelhut, from Ar. as above; Mâhidahân, from mâhi "fish," from Mid.Pers. mâhik; Av. masya-; cf. Skt. matsya-, Pali maccha- + dahân "mouth;" Mid.Pers. dahân, from Av. zafan-, zafar- "mouth (of Ahrimanic beings)."
rixtâr (#), font
Fr.: police, fonte
An assortment or set of type or characters all of one style and sometimes one size (Merriam-Webster.com).
From M.Fr. fonte "act of founding, casting," from fondre "to melt," so called because all the letters in a given set were cast at the same time (etymonline.com).
Rixtâr, from rixtan "to cast, to pour," → morphology.
1) The terminal part of the vertebrate leg upon which an individual stands.
M.E., from O.E. fot; cf. O.S. fot, O.N. fotr, Du. voet, O.H.G. fuoz, Ger. Fuß, Goth. fotus "foot;" cognate with Pers. pâ, pây, as below.
Pâ "foot;" Mid.Pers. pâd, pây; Khotanese fad; Av. pad- "foot;" cf. Skt. pat; Gk. pos, genitive podos; L. pes, genitive pedis; E. foot, as above; PIE *pod-/*ped-.
Fr.: effet Forbes
Increased reddening and monochromaticity of light as the path length in the air increases.
After the Scottish physicist James David Forbes (1809-1868); → effect.