Home

International Dictionary of Terms in Amateur Telescope Making

Currently 9 languages are supported: English (of course), French, German, Dutch, Portuguese, Spanish, Indonesian, Italian, Russian.

All words are given in English, then they are explained in English, and the translations follow.

→ Jump to: ↑ top [A] B C D E F G H I J K L M N O P Q R S T U V W X Y Z References Acknowledgements

• A •

Abrasive
Sand-like stuff that you need for grinding (the abrasive is harder than the glass, and scrapes the glass when we grind the mirror)
PT: abrasivo
NL: slijppoeder
FR: abrasif
ES: Abrasivo
DE: Schleifpulver, Schleifmaterial
ID: obat asah (abrasif)
IT: abrasivo
RU: Ð?бразивы
Achromat
Sort of refractor, with primary lens corrected for 2 wavelengths.  Most common refractor; suffers from color bleeding with very bright objects (due to dispersion).
NL: achromaat
PT: acromático
FR: objectif achromatique
RU: Ð?хромат
ID: Akromat
Adhese, to
To join 2 pieces of glass by heat treatment without distorsion.
DE: Schweissen ohne Erweichung
RU: Ð¿Ñ€Ð¸ÐºÐ»ÐµÐ¸Ð²Ð°Ð½Ð¸Ðµ
AFoV
Apparent Field of View. This is the field of view that is written on eyepiece specifications. To get the true field of view (FoV), you have to divide the AFoV by the magnification of the optical system (telescope). See also the telescope formulas page.
NL: schijnbaar gezichtsveld
DE: Scheinbares Gesichtsfeld
Airy disk
Center spot of the diffraction pattern caused by a point-like source (star).
NL: buigingsschijfje
FR: tache d'Airy
RU: Ð”иÑ?к Эри
DE: Beugungsscheibchen
ID: Cakram Airy
Alignment
Adjusting the optical axis such that it is coincident with the mechanical axis of the tube.
NL: Mechanisch uitrichten.
FR: alignement
DE: Ausrichtung bez. der optischen Achse
RU: Ð®Ñ?тировка положениÑ? оптичеÑ?кой оÑ?и
PT: alinhamento
ID: Penyesuaian axis optik
ES: Alineamiento, alineación
Aloxite
Brand name for Amaril, which is Aluminium Oxyde (Al2O3).
FR: aloxite
DE: Aloxite
Alt-Az mount
A mount on which one axis moves up and down (altitude) and the other axis moves around to the left and to the right (azimuth).
FR: Monture azimutal
NL: alt-azimuth montering
RU: Ð?льт-азимутальнаÑ? монтировка
DE: Altazimutale Montierung
Aluminizing
Putting an aluminium coating on the optical surface of a mirror, so that it reflects more light.
NL: aluminiseren
FR: aluminiser
PT: aluminizar
DE: Aluminisieren
ID: melapis dengan aluminium
IT: alluminatura
RU: Ð?люминирование
Alundum
Brand name for Amaril, which is Aluminium Oxyde (Al2O3).
FR: alundum
DE: Alundum
Amaril
This rather common mineral consists of Aluminium Oxyde (Al2O3) with inclusions (so-called contaminations) of magnetite (FeO.Fe2O3), hematite (Fe2O3), quartz (SiO2) and other minerals. It commonly serves as (cheap) abrasive, as it reaches 9 on the Mohs scale. It is typically yellowish. Amaril is from the Corundum group of minerals, which also groups Ruby and Sapphire.
FR: amaril
NL: amaril, korund
DE: Amaril, Korund
Annealed
Which has undergone annealing.
FR: recuit
PT: temperada
DE: angelassen
Annealing
Thermal treatment of materials to alleviate or even totally eliminate internal stresses.  The material is heated at a relatively high temperature at which material diffusion occurs at a reasonable speed.  The material is held at that temperature for a certain time, and then is cooled very slowly, to avoid material stresses being reintroduced.
NL: ontlaten, gloeien (behandeling van bvb getrokken of gewalst staal, om het weer te verzachten)
FR: recuire
RU: ÐžÑ‚жиг
DE: anlassen
PT: dar têmpera
Aperture
Diameter of the light inlet of a telescope.
NL: apertuur, opening
FR: ouverture
DE: Ã–ffnung
RU: Ð”иаметр объектива
PT: abertura
ID: Apertur
APO
Apochromat
Sort of refractor, with primary lens corrected for 3 wavelengths. Very expensive, but marvellous images...
NL: apochromaat
FR: objectif apochromatique
PT: apocromático
RU: Ð?похромат
ID: Apokromat
Apparent Field of View
See: AFoV
Appleply
Sort of plywood (strong and lightweight).
Ash
Sort of hardwood, rather coarse grained. Ash tends to be whiter than oak. Both can be quite pretty, but their primary feature is strength. [Peter Brooks]
ATM
Amateur Telescope Making, Amateur Telescope Maker, ...
NL: amateurkijkerbouwer
FR: Constructeur de telescope amateur
ES: Constructor amateur de telescopios
PT: Construtor de telescopios amador
ID: Pembuat Teleskop Amatir
DE: Amateur-Fernrohr-Bauer
IT: Costruzione amatoriale di telescopi
RU: Ð›ÑŽÐ±Ð¸Ñ‚ель телеÑ?копоÑ?троениÑ?
→ Jump to: ↑ top A [B] C D E F G H I J K L M N O P Q R S T U V W X Y Z References Acknowledgements

• B •

Backlash
When you rotate an axis of a gear box, then you will often experiment that when you invert the rotation direction, the output axis does not change immediately its rotation direction.  There is some play on the system, called backlash.  Every mechanic system has backlash, but it only becomes a problem when it becomes noticeable.
NL: terugveren, speling
PT: folga
FR: jeu
DE: Getriebespiel
RU: ÐœÐµÑ€Ñ‚вый ход, люфт
ID: Tendangan balik
Backpacking scope
A telescope that can be "carried on your back", thus a portable telescope.
Baffle
Sort of diaphragm in the light path, used for enhancing the image contrast by reducing the incidence of unwanted scattered light, ...
NL: baffle, lichtscherm
DE: Blende(n)
FR: pare-lumière interne
RU: Ð‘ленда, диафрагма, отÑ?екатель
Ball bearing
Bearing with balls as rolling parts.
NL: kogellager
FR: roulement à billes
Barlow
Optical interface that artifficially lenghtens the focal length of the primary; by doing so the barlow interface increases the magnifying power of the eyepiece. Common barlow interfaces multiply the focal length of the primary by 2 or 3, resulting in 2 or 3 times more power with the same eyepiece.
Barn door mount
Sort of telescope mount, mostly used for photographic cameras.
NL: schuurdeur montering
PT: suporte "porta de celeiro"
Bartelize, to
his verb refers to Mel Bartels' motorized Dobson, and means "motorize the alt-azimuth telescope with steppers and a laptop"  (ATM list, January 14th, 1998 by Ed de la Rie).
Bearing
Interface that allows much smoother rotation of an axis (e.g.: roller bearing)
NL: lager
FR: roulement
ES: Rodamiento
PT: rolamento
ID: bantalan/alas poros
DE: Lager
IT: cuscinetto
RU: ÐŸÐ¾Ð´ÑˆÐ¸Ð¿Ð½Ð¸Ðº
Belt sander
Sander which sands by means of a belt that is driven by means of 2 rollers.
NL: bandschuurmachine.
FR: entraînement à ruban tracté
DE: Bandschleifer
PT: lixadeira de fita
Beral coating
Sort of high reflective, dielectric coating used on mirrors, with very low reflection losses (US brand name)
ID: pelapisan dengan Beral
Bevel
Descr ?
PT: chanfro
Bevel, to
Descr ?
NL: afstompen, afvlakken (?)
FR: biseauter, chanfreiner
DE: abschrägen, fasen
RU: Ð·Ð°Ñ‰Ð¸Ñ‚наÑ? фаÑ?ка
PT: chanfrar
ID: Menumpulkan
Beveled edge
Reason 1: To reduce the stress on the edge of a mirror, beveling of the edge is important. With a beveled edge you reduce the risk of breaking chips of glass, if the mirror touches/hits a harder material (e.g. the mirror cell)
Reason 2: Sharp edges (which are normal in blank production) are dangerous for the hands of the ATM'er. See the ASCII-Drawing: 
  /^^--..__..--^^\     <- Surface of Mirror
 !                !
  \______________/     <- Back of Mirror
The slash and the backslash represent the "Beveled edge". [Detlev Markfort]
Birch
Kind of tree.
NL: berk
FR: bouleau
PT: Vidoeiro
ES: Abedul
DE: Birke
IT: betulla
RU: Ð‘ереза
Bit
Object that is used for making holes (with a drill) or cuts (with a router).
NL: boorpunt
FR: pointe de foreuse, foret, mèche
PT: broca
ES: broca
ID: mata bor / mata roter
IT: punta, scalpello
Blank
Disk of glass (or pyrex, ceramic, metal) before grinding and polishing.
NL: glasschijf
FR: disque miroir
PT: disco espelho
ES: Disco de vidrio
ID: Kaca/gelas
DE: Rohling
Blocking tool
Tool on which optical pieces are placed for making a plaster block
FR: outil à bloquer
RU: Ð½Ð°ÐºÐ»ÐµÐµÑ‡Ð½Ð¸Ðº, приÑ?поÑ?обление длÑ? блокировки деталей
Blueing
Coating a lens with an anti-reflective coating.  Since the reflective losses are minimized at about 550 nanometer (wavelength of green light to which the human eye is the most sensitive), the coated lens appears to be blueish, since the green part of the light is not reflected anymore and hence disappears, leaving only the complementary color(s).
NL: blauwen, ontspiegelen
FR: traîter anti-reflet
Bolt
Cylindrical threaded metal piece (with a head which is in most cases hexagonally shaped) used for joining parts. You can use washers and nuts on them.  You can also make a bolt by means of a threaded rod and two nuts, when you solder one nut at one end of the rod.
NL: bout
FR: boulon
PT: parafuso
ES: perno
DE: Schraube
ID: baut
IT: bullone
RU: Ð±Ð¾Ð»Ñ‚, винт
Brass
Metal alloy of Copper (Cu) and Zinc (Zn), with a yellow appearance.
NL: messing
FR: laiton
ES: latón
Bronze
Metal alloy of Copper (Cu) and Tin (Sn), with a yellow appearance.
NL: Brons
FR: Bronze
DE: Bronze
ES: bronce
Bruiser
Apparatus or container in which you break down abrasive.
FR: brisoir
RU: Ñ?тупка
Bubbles
1. Air balls in glass.
FR: bulles
DE: Blasen
RU: Ð¿ÑƒÐ·Ñ‹Ñ€Ð¸ в Ñ?текле
PT: bolhas
ID: Gelembung udara
2. Bubbles in glass brought to the surface in grinding or polishing.
FR: points crevés
DE: Blasen
3. Bubble, natural in a crystal.
FR: vacuole
DE: Lufteinschluss
RU: Ð³Ð°Ð·Ð¾Ð²Ñ‹Ðµ включениÑ? в еÑ?теÑ?твенных криÑ?таллах
ID: Gelembung di dalam kaca
→ Jump to: ↑ top A B [C] D E F G H I J K L M N O P Q R S T U V W X Y Z References Acknowledgements

• C •

Carborundum
Silicium Carbide (SiC), a very hard grinding agent (almost as hard as diamond). It has a hardness of 9.5 on the Mohs scale.
FR: carborundum
DE: Karborundum
RU: ÐºÐ°Ñ€Ð±Ð¾Ñ€ÑƒÐ½Ð´
Cassegrain Telescope
Sort of catadioptric telescope with a curved secondary.
CAT
Catadioptric
Telescope that combines reflection and light bending (refraction), like Schmidt-Cassegrains, Maksutovs, ...
FR: objectif/téléscope catadioptrique
Cedar
Sort of wood.
FR: cèdre
NL: ceder, cederhout
PT: cedro
Cell
System that supports a mirror or a lens.
NL: spiegelcel of spegelhouder, lensvatting,
FR: Barillet
PT: Suporte do espelho principal, célula
ES: Soporte
ID: penyangga
DE: Zelle
IT: cella, supporto
RU: Ð¾Ð¿Ñ€Ð°Ð²Ð°
CeO2
Cerium Oxide (actually Cerium Dioxide).
Cerium Oxide
Polishing agent (CeO2), sometimes referred to as "cerium".  Doesn't stain like rouge.
NL: Ceriumoxyde
FR: Oxyde de Cérium, rose à polir oxyde de cérium
DE: Ceroxyd
RU: Ð´Ð²ÑƒÐ¾ÐºÐ¸Ñ?ÑŒ цериÑ?
Cervit
Brand-named low expansion glass.
FR: vitro-céramique
NL: vitrokeramisch glas
Chamfer, to
To grind away sharp edges. See also: Bevel, to.
FR: chanfreiner
DE: Kanten brechen, facettieren, fasen
RU: Ð½Ð°Ð½ÐµÑ?ение фаÑ?ок (фаÑ?етировка)
PT: chanfrar
ID: Menumpulkan
Cherry
Sort of wood, hard, with a reddish colour.
PT: cerejeira
NL: kerselaar
FR: cerisier
DE: Kirsche
Chordal stroke
A grinding stroke used during hogging to remove large quantities of glass quickly. In this stroke, you grind mirror on top with the center of the mirror over the edge of the tool. You grind first on one chord, rotate mirror and tool, then on another, and so forth. Picture a stop sign (an octogon) - that's the pattern the center of your mirror will make after you have done a few wets.
FR: courses excentrées
Chrysocal, Chrysocale
Chrysocal (also called Chrysocale) is a common name for Phosporous Bronze, and has the chemical composition of CuSn3 Zn9 . It is often used as blade sring material in electric motors. One interesting application of chrysocal is in astatic mirror cells, where the chrysocal is used as a blade spring.
FR: chrysocal, chrysocale, bronze phosporeux, feuillard bronze
Chuck
? descr ?
FR: mandrin
DE: Bohrfutter
PT: mandril
ES: mandril
Clutch
The thing that you use in a car when changing the gear of a car (1st gear to 2nd gear and so on). More in general, a clutch makes it possible to couple/discouple something to/from a motor.
PT: embreagem
NL: koppeling
FR: embrayage
DE: Kupplung
ID: Kopling
Coating
Layer of metal or dielectric that is applied on a surface.  Most important coatings are optical coatings.  Lense coatings help minimizing the reflection losses at the surfaces, while mirror coatings have enhanced reflective properties and also protect the reflective film against corrosion (as a SiO2 coating atop of a reflective Al coating on mirrors).
NL: coating
FR: revêtement
PT: revestimento
ID: lapisan
DE: Vergütung (bei Linsen), Beschichtung (bei Spiegeln)
IT: rivestimento, mano
RU: Ð½Ð°Ð½ÐµÑ?ение отражающего или проÑ?ветлÑ?ющего покрытиÑ?
ES: revestimiento
Coil spring
Spring made of a wire put in a coil (like a wine-opener)
NL: spiraalveer
FR: ressort à boudin
ES: Resorte espiral
PT: Mola
ID: gulungan pegas
DE: Spiralfeder
IT: molla a spirale
Collimation
Adjusting all optical elements such that they share a single optical axis.
NL: collimatie, uitrichten van de optische elementen
FR: collimation
RU: Ð²Ð·Ð°Ð¸Ð¼Ð½Ð°Ñ? центрировка оптичеÑ?ких деталей телеÑ?копа
PT: colimação
ID: Kolimasi
Colophony
The solid residue after distilation of oil turpentine from crude turpentine. Syn.: Rosin.
FR: colophane
DE: Kolophonium
Computer Aided Telescope
Telescope that is driven with the help of a computer.  Examples are stepper motor driven Alt-Azimuth mounts à la Mel Bartels, . . .
NL: computergestuurde telescoop
FR: téléscope assisté par ordinateur (?)
DE: Computerunterstütztes Fernrohr
Corundum
Aluminium Oxyde (Al2O3), hard polishing stuff, but softer than carborundum.
FR: corindon
DE: Korundum
NL: korund
RU: ÐºÐ¾Ñ€ÑƒÐ½Ð´
Cradle
The part of a mount, special on GEM's, to rest the tube.
NL: wieg, schommeldoos (dobsonmontering).
DE: Wiege
FR: berceau
RU: ÑƒÐ·ÐµÐ» креплениÑ? трубы к оÑ?и Ñ?клонениÑ?
PT: berço
Crayford focuser
Sort of focuser which is based on pure friction.  Very often this focuser design has very little to no backlash.
CT
Cassegrain Telescope (without corrector plate). A reflector.
→ Jump to: ↑ top A B C [D] E F G H I J K L M N O P Q R S T U V W X Y Z References Acknowledgements

• D •

D'Autumne platform
Sort of platform on which you set an alt-az mounted scope, so that it becomes equatorial.  Due to constructional constraints however, the platform can only track for a certain time (up to 2-3 hours max.).
NL: d'Autumne (volg)platform
FR: plateforme de type d'Autumne
RU: Ð¿Ð¾Ð»Ñ?рнаÑ? платформа
Dental plaster
FR: plâtre dentaire
Dental stone
FR: ciment dentaire
Depth gauge
Apparatus for measuring the sagitta.
FR: jauge de profondeur
DE: Tiefenmass
RU: Ñ?ферометр
ID: Pengukur sagitta
Derotator
Engine that compensates for field rotation.
FR: compensateur de rotation de champ
Diagonal
Elliptical secondary mirror tilted at 45 degrees, between the eyepiece and the primary in e.g. Newtonians.
NL: vangspiegel
FR: miroir secondaire diagonal
ES: Diagonal
PT: espelho secundario
ID: cermin sekunder
DE: Fangspiegel, Sekundärspiegel
IT: diagonale, secondario
Diagonal holder
Support to keep the diagonal in place.  It is often attached to a spider.
NL: vangspiegelhouder
FR: support de secondaire
DE: Fangspiegelhalterung
RU: Ð´ÐµÑ€Ð¶Ð°Ñ‚ель диагонального зеркала
ID: Penyangga cermin sekunder
Dig on an optical surface
? Descr ?
FR: Ã©chignures
DE: Grübchen
Dillpickel telescope
An all spherical catadoptric newtonian.
Dispersion
The fact that light with different wavelengths is refracted (bent) differently. Examples where dispersion is shown: light decomposition in a prism, ...
NL: dispersie, kleurschifting
FR: dispersion
PT: dispersão
DE: Dispersion
Dob
Contraction of "Dobsonian"
Dobson, John
Creator of the popular Dobsonian telescope: a very stable alt-azimuth mount with huge bearings.  John Dobson's intention was to build a telescope with "off the shelf" parts at low expenses.
Dobsonian
Term that denotes both the Dobsonian mount (see Dobson, John) and the whole telescope assembly.
Dobsonian mount
Very stable alt-azimuth mount with huge bearings.
NL: dobsonmontering
PT: Suporte de tipo Dobson
ID: penyangga tipe Dobson
FR: monture Dobson
IT: montatura dobsoniana
Dowel
Descr?
ID: pasak kayu
Drill, to
Make a hole in something (with a drill for example)
NL: boren (m.b.v. een boor)
FR: percer, forer (à l'aide d'une perceuse, foreuse)
PT: furar (ou berbequim)
ES: Perforar
ID: bor
DE: bohren (mit einem Borher)
IT: perforare, trapanare
RU: Ñ?верление отверÑ?тий
→ Jump to: ↑ top A B C D [E] F G H I J K L M N O P Q R S T U V W X Y Z References Acknowledgements

• E •

Ebony Star
Sort of laminate with low-friction surface, often used in Dobson bearings. This is a commercial name (a Wilsonart brand laminate)
FR: remplacement pour le formica
Edge, to
??? descr ???
FR: déborder
DE: rundieren
Entrance pupil
Optical aperture of an optical system (telescope, eyepiece, binoculars, . . .), at which the light enters.
NL: intreepupil
DE: Eintrittspupille
FR: pupille d'entrée
IT: pupilla di uscita
RU: Ð²Ñ…одной зрачок
EP
Abbreviation meaning "Eyepiece", sometimes also "Exit Pupil" or "Entrance Pupil" (depending on the context).
Equatorial mount
Most common type of telescope mount (until the Dobson revolution): since one axis is parallel to the rotational axis of the Earth (this axis points to Polaris (Northern hemisphere) or sigma Octantis (Southern hemisphere)), you can follow an object by just counteracting the rotation of the earth.
NL: equatoriale montering
ID: penyangga tipe ekuatorial
PT: suporte equatorial
FR: monture équatoriale
DE: parallaktische Montierung
RU: Ð¿Ð°Ñ€Ð°Ð»Ð»Ð°ÐºÑ‚ичеÑ?каÑ? (Ñ?кваториальнаÑ?) монтировка
Erfle
A wide-field eyepiece.
Exit pupil
Optical aperture of an optical system (telescope, eyepiece, binoculars, . . .), at which the light exits.
NL: uittreepupil
DE: Austrittspupille
FR: pupille de sortie
RU: Ð²Ñ‹Ñ…одной зрачок
Eyepiece
→ see the related page on this site.
Set of lenses the eye will look through.
NL: oculair, ooglens
FR: oculaire
PT: ocular
ES: ocular
DE: Okular
ID: okuler
IT: oculare
RU: Ð¾ÐºÑƒÐ»Ñ?Ñ€
Eye relief
Distance between the eye and the eyepiece.
NL: oogreliëf
DE: Augenrelief
FR: position du cercle oculaire
RU: ÑƒÐ´Ð°Ð»ÐµÐ½Ð¸Ðµ выходного зрачка
→ Jump to: ↑ top A B C D E [F] G H I J K L M N O P Q R S T U V W X Y Z References Acknowledgements

• F •

Feathers
Feather shaped defects within transparent materials.  The term is applied also to collections of bubbles or flecks.
FR: feuillets
DE: Federn
Field derotator
Field of View
See: FoV
Field rotation
Rotation of the field of view in your eyepiece (or on your CCD or camera), due to misalignment of the polar axis in an equatorial munt, or in general due to the fact that your mount is NOT equatorial.  It is easy to visualise when you imagine that Saturn rises, culminates and afterwards sets, but during that motion the orientation of the rings of Saturn change (they follow the ecliptic): tilted to the left at rise time, then horizontal at culmination, then tilted to the right at set time.
NL: veldrotatie
FR: rotation de champ
DE: Feldrotation, Gesichtsfelddrehung
PT: rotação do campo
IT: rotazione di campo
RU: Ð²Ñ€Ð°Ñ‰ÐµÐ½Ð¸Ðµ полÑ? зрениÑ?
Figuring
Bring a certain figure in the surface of the mirror. The final stage of grinding a mirror. At this stage, your mirror is already polished. You use altered stroke patterns, altered laps, or other techniques to turn your sphere into a parabola (assuming you are making a Newtonian or similar design). After this, it's off to the coater.
[1] Altering the shape of a surface to improve definition.
ID: pembentukan (if figuring means parabolizing the blank).
DE: Parabolisieren, retouchieren [1], korrigieren [1]
FR: mise en forme, retoucher [1]
RU: Ñ„игуризациÑ?
File
Tool for scraping off bits of material, in order to flatten an edge, ...
NL: vijl
FR: lime
DE: Feile
RU: ÑˆÐ»Ð¸Ñ„овальный бруÑ?ок
ES: lima
Finder, Finder scope
Small telescope on the side of a bigger one, with a wider field of view, used to help find the object one wants to observe.
NL: zoeker
FR: chercheur
PT: buscador
ES: telescopio mira, buscador
ID: teropong pencari
DE: Sucher, Sucherfernrohr
IT: cercatore
RU: Ð¸Ñ?катель
Fine grinding
The stage of grinding after rough grinding in which you improve your sphere, remove pits, and prepare for polishing. You start with fairly coarse grits like 220 and proceed one by one to the finest grits (5 micron aluminum oxide or so) during this stage.
DE: Feinschliff
FR: doucissage
RU: Ñ‚онкаÑ? шлифовка
ID: Asah halus
First Light
Emotional moment, when the brand new telescope will be seeing the first star light...
FR: première lumière
f-number
See: focal ratio
Focal length
The length at which parallel rays of light are brought into focus for a particular lens or mirror.
NL: brandpuntsafstand
FR: distance focale
PT: distância focal
DE: Brennweite
RU: Ñ„окуÑ?ное раÑ?Ñ?тоÑ?ние
ID: Jarak fokus
Focal ratio, f-ratio, f-number
The ratio F/D of the focal length F and diameter D of a mirror or lens. It is often seen on photographic lenses; you change the focal number by means of a diaphragm (you often find values in the series 5.6, 8, 11, 16, 22). With telescopes, the focal ratio is a constant for every instrument, since we do not use a diafragm (we want to fetch the most light as possible).
NL: openingsverhouding
DE: Ã–ffnungsverhältnis
FR: rapport d'ouverture
RU: Ð¾Ñ‚ноÑ?ительный фокуÑ? (величина, обратнаÑ? отноÑ?ительному отверÑ?тию)
ID: Rasio fokus
Focus
Point at which a parallel incoming beam is converged to after contact with an optical system.
NL: brandpunt
FR: foyer
DE: Brennpunkt
RU: Ñ„окуÑ?
ID: Fokus/titik api
Focuser
Part that alows the image to be seen sharply.
NL: focusseerinrichting
FR: porte-oculaire (focusseur, mise au point)
ES: Porta ocular
PT: porta-ocular
ID: pemfokus
DE: Okularauszug
IT: fuocheggiatore
RU: Ñ„окуÑ?ировочный узел
Formica
Sort of plastic used in plies or sheets for covering wood panels like in kitchen use (laminate). In ATM, formica is often used in combination with teflon for bearings.
FR: formica
IT: formica
NL: formica
ID: Formica
Foucault test
A test of optical surfaces, developed by Leon Foucault, a French optician. The test uses reflection and geometrical optical principles to amplify shadows of defects on the mirror so that they are easily visible.
FR: test de Foucault
NL: Foucault-test
RU: Ñ‚еÑ?Ñ‚ Фуко
ID: Test metode Foucault
FoV
Field of View. This is the angle in which you can see things through an optical instrument (telescope, binocular, photographic camera, ...). Normally we mean "true" field of view when referring to FoV. See also AFoV, and the telescope formulas page.
NL: (waar) gezichtsveld
FR: champ de vision (réel)
DE: Gesichtsfeld
f-ratio
FRP
Construction material, often used in public bathroom wall panelings.  Provides much less friction than Ebony Star or another formica-like laminate.  Since the friction between FRP and teflon is very low, this material is only useful in heavy (large, say 16" and more) dobs.
Fuller's earth
Substance used with rouge in polishing on cloth polisher.
FR: terre à foulon
DE: Fullererde
→ Jump to: ↑ top A B C D E F [G] H I J K L M N O P Q R S T U V W X Y Z References Acknowledgements

• G •

GE 2, GE II
Sort of transparent RTV, sometimes referred to as "bathtub sealer". This is a commercial name of General Electric!  In Europe, it is found as "Rubson" (commercial name) (check this !)
FR: Ã©lastomère de silicone
Gear
1. Wheel with teeth on it (as in a gear box).
NL: tandwiel, rader
FR: roue dentée
DE: Getriebe (rad)
2. In a motorized engine (car, truck, ...) it regulates the output rotational speed and torque in function of the motor speed. E.g., start the car in 1st gear, then go into 2nd gear etc. Normal cars have 4 to 6 gears (plus one rear). The gear is realised by means of "gears". See also: clutch. (1st significance).
NL: versnelling (van een auto: eerste, tweede versnelling, ...).
FR: vitesse (d'un automobile: première vitesse, deuxième vitesse, ...)
DE: Gang (beim Automobil)
GEM
Abbreviation of "German Equatorial Mount".
NL: Duitse parallactische (of: equatoriale) montering.
DE: Deutsche Montierung
PT: suporte equatorial Alemão
FR: monture allemande
RU: Ð½ÐµÐ¼ÐµÑ†ÐºÐ°Ñ? монтировка
ID: Penyangga tipe Jerman
Glare shield
Sort of light shield that is often seen in nose cones of (larger) dobsonians, opposite to the focuser.  This shield blocks eventual light rays that are not originated from the primary via the diagonal; by doing so the contrast is enhanced.
NL: lichtscherm
FR: Ã©cran
ID: Penahan silau
Glass board
See: FRP
Graduated lap
A graduated lap is a lap with varying contact of pitch against the glass.  A common graduated lap consists of the squares of pitch become smaller and the channels become larger as you move towards the edge. Think of flower petals.  You don't have to remove large gobs of pitch - just scrape away the surface a tiny bit to lose the contact. Eventually contact comes back and you scrape some more.  These are very effective laps for parabolizing - don't use them for small slow mirrors. [Mel Bartels]
DE: deformierte Pechhaut
Grinding
First phase of mirror making. Consists of creating a spherical curvature on one side of the future mirror glass by using abrasives and water
NL: slijpen
FR: creusage, ebauchage, meulage [1]
ES: desgastar
DE: schleifen , Schliff [1]
PT: desbaste
ID: mengasah
IT: smerigliatura
RU: ÑˆÐ»Ð¸Ñ„овка
Grit
Small particles of aluminium oxide (Al2O3) or silicon carbide (SiC), graded according to their size, used to grind the mirror. Can be found in ATM specialised stores or abrasive specialised stores. For a conversion chart comparing different size scales, visit Newport Glass Work's site at http://www.newportglass.com/grit.htm.
Also: pitch of the abrasive (size of the particles).
FR: grain
NL: korrel
ID: pasir/kerikil halus
DE: Korn
IT: graniglia
RU: Ð¼Ð¸ÐºÑ€Ð¾Ð¿Ð¾Ñ€Ð¾ÑˆÐºÐ¸
Ground board
Base of a Dobsonian, upon which the rocker box rests.  Between them you find the azimuth axis.
NL: grondbord
DE: Grundplatte
Gypsum
??? descr ??? see plaster
NL: gips
FR: gypse
DE: Gypsum, Gips
PT: gesso
RU: Ð³Ð¸Ð¿Ñ?, алебаÑ?Ñ‚Ñ€
ID: Gips
ES: yeso
→ Jump to: ↑ top A B C D E F G [H] I J K L M N O P Q R S T U V W X Y Z References Acknowledgements

• H •

H
Acronym for "Huygens".
Helical focuser
Focuser that focuses by rotating the eyepiece holder (on which there is a thread).
Hickory
Sort of hardwood, quite tough. Used extensively for implement handles (axe and shovel handles where toughness is essential). [Peter Brooks]
HM
Acronym for "Huygens-Mittenzwey".
Hogging
The initial rough grinding you do to put the initial curve in your mirror. You do not need to worry as much about obtaining the correct figure at this point, just getting your mirror close. Rough grinding will produce the spherical shape you are aiming for.
FR: Ã©bauchage
RU: Ð³Ñ€ÑƒÐ±Ð°Ñ? шлифовка
Hose clamp
Descr ?
DE: Schlauchschelle
Huygens
rand of eyepieces.  The first ones ever made, today only used for solar observations in one single light frequency (thus in combination with solar filters placed in front of the telescope (not in the eyepiece).
Huygens-Mittenzwey
Brand of eyepieces. An enhanced version of the Huygens eyepieces.  Often a very cheap eyepiece found in some cheap telescopes.
→ Jump to: ↑ top A B C D E F G H [I] J K L M N O P Q R S T U V W X Y Z References Acknowledgements

• I •

Idler roller
Descr?
→ Jump to: ↑ top A B C D E F G H I [J] K L M N O P Q R S T U V W X Y Z References Acknowledgements

• J •

Jigsaw
Tool that cuts wood and other material thanks to a small saw blade that goes up and down very fast.
NL: wipzaag, decoupeerzaag, figuurzaag
FR: scie sauteuse
DE: Stichsäge
PT: serra de recorte
IT: sega da traforo
RU: Ð»ÐµÐ½Ñ‚очнаÑ? пила, лобзик
ID: Gergaji listrik
→ Jump to: ↑ top A B C D E F G H I J [K] L M N O P Q R S T U V W X Y Z References Acknowledgements

• K •

Kellner
Brand of eyepieces with a doublet at the eye end.  Becomes a standard in less expensive eyepieces.
Knife Edge
Used in the famous Foucault-Test to "read" the Surface of the Mirror.
DE: Messerschneide
König
Sort of wide-angle eyepiece (an WW II invention).
Kydex
Sort of plastic.
→ Jump to: ↑ top A B C D E F G H I J K [L] M N O P Q R S T U V W X Y Z References Acknowledgements

• L •

Laminate
Thin layer of a plastic, often used for coating wood panels (in kitchens, ...).  Examples: formica, Ebony Star.
NL: laminaat
PT: laminado
DE: Laminat
ID: Laminasi
Lap
See: Pitch lap
NL: pekbodem
Larch
Sort of wood. Larch is a type of pine generally speaking. Good pieces have a very close grain like old slow growing pine has. Its most common use is wooden utility poles! The English call it "Spar Pine". When they landed on this side of the Atlantic, they were amazed at the tall straight trees that grew near the Virginia coast that could be used for spars, masts, yardams, etc. on their ships. [Daniel Fundo]
NL: lork ?
FR: mélèze ?
Lathe
Machine that makes circular symmetrical machining of material possible, by turning
NL: draaibank
DE: Drehbank
PT: torno
ES: torno
FR: tour
→ Jump to: ↑ top A B C D E F G H I J K L [M] N O P Q R S T U V W X Y Z References Acknowledgements

• M •

MA
Acronym for "Modified Achromat", a brand of eyepieces of Meade.
ma, m.a.
Minor axis.
MacDOB, MacDOBS
Term invented by the Macintosh using ATMer. Since the most common way to computerize a Dobson is by means of a parallel port interface (e.g., Mel Bartel's page on motorized Dobsonians), which doesn't exist on a Macintosh PC. Instead, the MacDOB works with a serial interface.
Mahogany
Sort of hardwood.
PT: mogno
NL: mahonie
FR: mahonia
Maple
Sort of wood, dense and generally quite strong. Good for clamping pieces. Can be used for bearings. [Peter Brooks]
NL: esdoorn
FR: Ã©rable
Microfacet
Small "facets" added to a pitch lap by pressing a netting (plastic window screening, vegetable-bag netting, bath-type scrubby, etc.) material into the lap.
FR: microfacette(s)
NL: microfacet(ten)
Mill
A mill is a large machine, looking somewhat like an oversized drill press. It has a table which can be moved in two directions (the X and Y axes) very precisely (generally to .001" or so). The spindle, which holds the cutting tool, can be moved up and down (the Z axis), also in fairly precise increments. The cutting tool turns at speeds from about 500 rpm to --- say --- 2000 rpm (rough figures here, on both ends of the speed range). Mills tend to be very expensive. (see also: router) [Dan Brown]
The most common is the "Bridgport" (brand name) type vertical mill, there is also a benchtop mill-drill, usually made in Taiwan or China. Weighs about 300kg. Smaller and less capable than the big boy, but more affordable. [Peter Brooks]
PT: fresa
DE: Fräsbank
Millies-Lacroix
Adrien Millies-LaCroix. Usually refers to a a graphical method of interpreting Foucault test data.
RU: Ð¼ÐµÑ‚од Миллье-Лакруа
Minor axis
The minor axis is the smallest diameter of an ellipse.  With diagonals in Newtonians, the m.a. is also the diameter of the obstruction caused by the diagonal (circular appearance of the diagonal when tilted at 45°).
NL: korte as
PT: eixo menor
DE: kleine Achse
FR: petit axe
RU: Ð¼Ð°Ð»Ð°Ñ? оÑ?ÑŒ диагонального зеркала
Mirror box
Box-like part of a truss tube Dobsonian, in which the mirror is mounted. It rests in the rocker box.
NL: spiegeldoos
Mohs scale
The Mohs scale is a scale of mineral hardness. It was introduced in 1812 by the German mineralogist Frederich Mohs (1773-1839), who selected the ten minerals because they were common or readily available. The scale is not a linear scale, but somewhat arbitrary. The ten minerals and their hardness on the Mohs scale between brackets are: Talc (1), Gypsum (2), Calcite (3), Fluorite (4), Apatite (5), Orthoclase (6), Quartz (7), Topaz (8), Corundum (9) and Diamond (10).
NL: (hardheids)schaal van Mohs
PT: escala (de dureza) de Mohs
FR: Ã©chelle (de dureté) de Mohs
Monocentric eyepiece
Sort of Eyepiece, in witch all radii of the lenses fall on the same point, like the "Steinheil"-Type [Detlev Markfort]
NL: monocentrisch oculair
DE: Monozentrisches Okular
MOT
Mirror On Top
FR: Miroir dessus
NL: spiegel boven
ES: Espejo encima
PT: Espelho em cima
ID: Kaca Di Atas
DE: Spiegel oben
IT: specchio sopra
RU: Ð»Ð¸Ñ†ÐµÐ²Ð°Ñ? Ñ?торона зеркала
Mount
Construction that supports the telescope.
NL: montering
Muffin fan
Sort of fan (actually a brand name) that you encounter in power supplies and some computers (cooling fans).  In ATM we use such a small fan for helping the primary to cool down to the ambient temperature, and sometimes to avoid turbulences in the light path (?).
NL: ventilatortje
FR: petit ventilateur
PT: pequeno ventilador
ID: kipas angin
DE: Ventilator
IT: ventolina di raffreddamento
RU: Ð²ÐµÐ½Ñ‚илÑ?тор
→ Jump to: ↑ top A B C D E F G H I J K L M [N] O P Q R S T U V W X Y Z References Acknowledgements

• N •

Nagler
Brand of eyepieces with a very wide apparent field of view (82°). Brand name from TeleVue. Excellent eyepiece.
Needle bearing
Bearing with needles as rolling parts.
NL: naaldlager
FR: roulement à aiguilles
Newt
Contraction of "Newtonian telescope"
ID: Newtonian
DE: Newton
Newtonian Telescope
A reflecting telescope that uses a large mirror (the primary) which reflects light to a smaller mirror (the secondary) which reflects light out the side of the tube to the eyepiece.
NL: Newtonkijker
PT: telescópio Newtoniano
FR: newtonien
RU: Ð?ьютон
DE: Fernrohr nach Newton
ID: Teleskop Newtonian
Nose cone
Part of a truss tube dobsonian where you find the focuser and spider (plus diagonal).
NL: neuskegel, lichtkooi [en niet lichtekooi (vrouw van lichte zeden)].
Null test
???
FR: Null test
RU: Ð½ÑƒÐ»ÑŒ-теÑ?Ñ‚
Nut
Most of the times hexagonally shaped metal part with a threaded hole in the middle (use it on a bolt or a threaded rod).
FR: Ã©crou
NL: moer
DE: Mutter
PT: porca
ID: Mur
IT: dado
RU: Ð³Ð°Ð¹ÐºÐ°
ES: tuerca
→ Jump to: ↑ top A B C D E F G H I J K L M N [O] P Q R S T U V W X Y Z References Acknowledgements

• O •

Oak
Sort of hardwood, rather coarse grained, quite strong. Ash tends to be whiter than oak. Both can be quite pretty, but their primary feature is strength. [Peter Brooks]
FR: chêne, bois de chêne
NL: eik, eikehout
PT: carvalho
DE: Eiche, Eichenholz
ES: roble
Objective
Lens (or mirror) which receives the light from the object at which we point the telescope.
NL: objectief
FR: objectif
ES: objetivo
PT: objetivo
ID: Obyektif
DE: Objektiv
IT: obiettivo
RU: Ð¾Ð±ÑŠÐµÐºÑ‚ив
Orthoscopic
Brand of eyepieces corrected for 1st order aberrations.  Also called "Abbe eyepiece" or "aplanar eyepiece", due to the design.  Good eyepiece (compare with Kellner).
FR: orthoscopique
RU: Ð¾Ñ€Ñ‚оÑ?копичеÑ?кий окулÑ?Ñ€
OTA
Optical Tube Assembly (the tube part of the telescope, without mount).
NL: kijkerbuis, buis met optiek
PT: tubo óptico de um telescópio
FR: tube optique
RU: Ñ‚руба в Ñ?боре Ñ? оптикой
ID: Tabung Teleskop
→ Jump to: ↑ top A B C D E F G H I J K L M N O [P] Q R S T U V W X Y Z References Acknowledgements

• P •

PanOptic
Brand of eyepieces with a large field of view (68°).  Brand of TeleVue.  Almost comparable to the Nagler eyepieces.
PEC
Acronym for "Periodic Error Correction".
Periodic Error Correction
Gears are repetitive systems (one tooth of a gear returns to its initial state after every revolution). Since most gears are not perfect, they induce errors, that come back with a repetitive pattern (reprats after every revolution). So does a system built with gears, like a gear box.  Then you will have to take into account all gears.
FR: correction d'erreurs périodiques (→ correcteur d'erreurs périodiques)
RU: ÐºÐ¾Ñ€Ñ€ÐµÐºÑ†Ð¸Ñ? периодичеÑ?кой ошибки привода
ID: Koreksi Kesalahan Periodik
Pickering scale
Scale devised by John Pickering for expressing the seeing conditions.
NL: Pickering-schaal (voor seeing)
FR: Échelle de Pickering
Pickering scope
Telescope used by John Pickering, which he used to make a magnitude scale for seeing.
Pine
Sort of wood
PT: pinho
NL: den
FR: pin, sapin
ES: pino
Pit
Small hole in mirror/blank. This can happen when the grit is contaminated with coarse particles.
NL: putje
DE: Pore(n), Grübchen
PT: pequeno furo, buraquinho
FR: piqûre
RU: Ð²Ñ‹ÐºÐ¾Ð»ÐºÐ°, точка
ID: Lubang
Pitch
Black syrup-like substance (heaviest fraction of the destillation of petroleum, also derived from tree sap), used for polishing.  Actually, you make a pitch lap, and then the abrasive (rouge, CeO, ...) sticks on the lap. The optical pitch comes from trees!
ES: Brea, resina de pino
NL: pek, polijstpek
FR: poix, poix optique
PT: pixe (substância feita a partir de pixe ou resina de pinheiro)
ID: ter (?)
DE: Pech
IT: pece
RU: Ð¿Ð¾Ð»Ð¸Ñ€Ð¾Ð²Ð¾Ñ‡Ð½Ð°Ñ? Ñ?мола
Pitch lap
Sort of cushion made from pitch, used for polishing.
ES: Pulidor
NL: pekbodem
FR: Polissoir
PT: Polidor
DE: Pechhaut
IT: mola di pece
RU: Ð¿Ð¾Ð»Ð¸Ñ€Ð¾Ð²Ð°Ð»ÑŒÐ½Ð¸Ðº
Plaster
TROUBLES: there are TWO substances, one called "plâtre" and another called "gipse" in French (gypsum?).  The later has a chemical formula CaSO4.nH2O (without H2O it's called "anhydrite", and is blueish).  If you know more about it, please let me know!
Plaster is made of gypsum which is heated at very high temperature in a special oven, in order to extract one water molecule.  If the gypsum is heated too much, or for a too long time, then all the water molecules of the gypsum are extracted, and what we get is anhydrite, a blueish to grey substance, which is very slow in absorbing water again.
When cooled, and mixed with water, a cristallisation occurs, and plaster hardens.
White variety is named plâtre de Paris. He is very quick, hard, and white. More rough ones are greyish ore bluish, and are maore often used in construction.
NL: plaaster
FR: plâtre
PT: gesso
ES: yeso
DE: Gips
IT: gesso
Plaster of Paris
White stuff used for covering interior walls and making molds and sculptures. Sort of plaster (see: Plaster).
FR: plâtre de Paris
ES: Yeso Paris
NL: plaaster, gips ???
PT: gesso
DE: Gips
IT: solfato di calcio
Plaster tool
Grinding or polishing tool made of plaster instead of glass/pitch.
FR: outil en plâtre
IT: utensile in gesso
Plate glass
Sort of glass (window glass) commonly used for mirrors. Plate glass has a green color, and needs to be annealed to eliminate stresses in the material.
FR: verre àglace
RU: Ð»Ð¸Ñ?товое Ñ?текло
PT: vidro de tampo de mesa
ID: Kaca biasa
Plössl
Brand of eyepieces. Consists of two doublets, modified Plössls also incorporate an intermediate lens in between the doublets. Very good eyepiece; it seems that this design will become the all-round eyepiece.
Plywood
Sort of wood made of thin layers of wood glued together at different directions of the wood fibres, in order to strenghten the wood.
NL: multiplex
FR: contre-plaqué, multipli
PT: contraplacado (Portugal); compensado (Brasil)
ES: Enchapado, contrachapado
DE: Sperrholz
ID: kayu lapis
IT: legno compensato
Polisher
Tool with which the polishing takes place.  See: pitch lap.
FR: polissoir
DE: Polierschale, Polierwerkzeug
ES: pulidor
Polishing
Last action in making a mirror.  The polishing consists in the smoothening of the figure of the mirror by means of a very fine grit (CeO, rouge, ...).
NL: polijsten
FR: polissage
ID: pemolesan
DE: polieren
PT: polimento
RU: Ð¿Ð¾Ð»Ð¸Ñ€Ð¾Ð²ÐºÐ°
Poncet mount
?? descr ??
FR: monture Poncet
NL: Poncet-montering
ID: Penyangga tipe Poncet
Poncet platform
Sort of platform used to guide an alt-az mounted scope (mostly a Dob) for a certain amount of time.
FR: plateforme de type Poncet.
ID: Platform Poncet
NL: Poncet platform
P-P
Contraction of "Peak-to-Peak" error of an optical surface. The peaks are the errors "above" the desired value, the valleys are the errors "below" the desired value. For calculating the P-P error, the maximum of the peaks and valleys is considered. This value is then multiplied by 2 to obtain the P-P value. This is an upper bound for the maximal error. See also: P-V.
Primary
Contraction of "primary mirror" - Largest mirror, used as a converging lens in reflectors. Syn.: objective.
NL: hoofdspiegel
FR: Miroir principal, primaire
PT: Espelho principal
ES: primario
ID: Cermin Primer
DE: Hauptspiegel
IT: primario
RU: Ð³Ð»Ð°Ð²Ð½Ð¾Ðµ зеркало
Pulley
Descr?
Pumice powder
Powder made from pumice (the porous stone that comes from a volcano).
NL: puimsteenpoeder
FR: ponce, poudre de pierre ponce
DE: Bimssteinpulver
Putty powder
Tin-oxide.
FR: potée d'étain
DE: Zinnoxyd, Zinnasche
NL: tinas, tinoxyde
P-V
Contraction of "Peak-to-Valley" error of an optical surface. The peaks are the errors "above" the desired value, the valleys are the errors "below" the desired value. For calculating the P-V error, only the maximum of the peaks and valleys are considered. Both error values can differ. This is the maximal error.
RU: Ð²ÐµÐ»Ð¸Ñ‡Ð¸Ð½Ð° полной ошибки формы поверхноÑ?ти зеркала (ее размах)
Pyrex
A type of glass with a lower coefficient of expansion (also harder) than plate glass.  Generally colourless.
FR: pyrex
NL: pyrex
RU: Ð¿Ð¸Ñ€ÐµÐºÑ?
→ Jump to: ↑ top A B C D E F G H I J K L M N O P [Q] R S T U V W X Y Z References Acknowledgements

• Q •

→ Jump to: ↑ top A B C D E F G H I J K L M N O P Q [R] S T U V W X Y Z References Acknowledgements

• R •

Rack and Pinion Focuser
Focuser with a sliding eyepiece holder on which a pinion is mounted.  Focusing is achieved by turning on a knob.
FR: porte-oculaire àcrémaillère (???)
NL: focusseerinrichting met tandheugelsysteem
DE: Okularauszug mit Zahnstangenantrieb
PT: focalizador de coroa e pinhão
Reflector
Telescope with a primary that reflects (acts like a mirror) the incoming light, like Newtonians, Cassegrains, ...
NL: reflector, spiegelkijker
DE: Reflektor, Spiegelteleskop
FR: téléscope, téléscope réflecteur, téléscope àmiroir
RU: Ñ€ÐµÑ„лектор
ID: Reflektor / Pemantul
Refractor
telescope with a primary that bends (refracts, like a lens) the incoming light, thus where the light passes through the optical system (glass, ...).
Due to dispersion, a refractor needs to be corrected for color shift: see achromats and apochromats.
NL: lenzenkijker
DE: Refraktor, Linsenteleskop
FR: lunette, téléscope réfracteur, téléscope à lentille
RU: Ñ€ÐµÑ„рактор
ID: Refraktor / Pembias
RFT
Acronym for "Rich Field Telescope".  This is a kind of telescope used with low power in order to obtain a large field of view, often exceeding 1°.
NL: rich-field telescoop
FR: téléscope à grand champ de vision
PT: telescópio de grande campo de visão
RU: ÐºÐ¾Ð¼ÐµÑ‚оиÑ?катель
ID: Teleskop Sudut Lebar
Rifle Scope
Small finder which is often mounted on a rifle for aiming. Has a very big eye relief and oversized exit pupil.
NL: geweerzoeker, vizier
FR: lunette de fusil
DE: Zielfernrohr
RU: Ð¾Ð¿Ñ‚ичеÑ?кий прицел
RMS
Abbreviation of "Root Mean Square" error of the optical surface. This is an average value, smaller than the P-V (Peak-to-Valley) error. The RMS value is obtained by taking the square root of the quadratic "distance" (= error) of the desired values and the true value (actually, this is done by a discrete sum of such values obtained from measurings).
RU: Ñ?реднеквадратичеÑ?каÑ? ошибка поверхноÑ?ти
ROC
Radius of curvature (of the mirror).  The ROC is defined as the radius of the spherical surface of the mirror.  It is about twice the focal length.
NL: kromtestraal
PT: raio de curvatura
FR: rayon de courbure
DE: Krümmungsradius
RU: Ñ€Ð°Ð´Ð¸ÑƒÑ? кривизны Ñ?феричеÑ?кой поверхноÑ?ти
ID: Radius Kurva
ES: radio de curvatura
Rocker box
Box-like part of a Dobsonian in which rests the mirror box.  The rocker box rests on the ground board.
NL: schommeldoos
Rod
Cylindrical (metal) piece.
NL: staaf
FR: tige
PT: haste, barra
ES: Barra, vastago
DE: Stange
ID: batang
IT: barra
RU: Ð²Ð¸Ð½Ñ‚, шпилька
Roller
Cylindrical object which typically rotates around its axis, like in old-fadhion roller skates (not the roller blades), and the roller bearings.
FR: rouleau, roulette
NL: rol
DE: Rolle
IT: rullo
Roller bearing
Bearing with rollers as rolling parts.
NL: rollager
FR: roulement à rouleaux
DE: Rollenlager
IT: cuscinetto a rulli
RU: Ñ€Ð¾Ð»Ð¸ÐºÐ¾Ð²Ñ‹Ð¹ подшипник
Ronchi grating
Grating used in the ronchi test.
NL: Ronchi rooster
FR: trame de Ronchi