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33 Cards in this Set

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optics
ref. to optical features of a stage lighting instrument-- the reflector and lenses
specular reflection
light reflection off a shiny surface.
angle of incidence=angle of reflection
dichroic reflector
in theatrical SPOTLIGHT, a glass reflector with dichroic coating which allows some wavelengths of light to pass through while reflecting others
focal point of reflectors
specific point at which a light source must be placed in relationship to the reflector in order to achieve desired reflective pattern ie when light was most focused, not blurry, during demo
spherical reflector
reflector cast in shape of part of a sphere, returns light back to its focal point which is located in the exact center-- found in fresnel spotlights.
parabolic reflector
reflector cast in shape of part of a parabola; reflects light in parallel rays-- found in PAR fixtures
ellipsoidal reflector
reflector cast in shape of part of an ellipsoid; reflects light back to its secondary focal point-- found in ellipsoidal reflector spotlights
primary focal point in ellipsoidal
point nearest the reflector; if light source is positioned here, rays striking reflector are redirected to converge at conjugate focal point
conjugate focal point in ellipsoidal
the more distant focal point
refraction
the bending of light rays as they pass through mediums with different densities
law of refraction
when a ray of light passes into a denser medium (ie air 2 glass) it is bent toward a perpendicular drawn to the surface at the point of entry. when it reemerges into the less dense medium, it is bent away from a perp. drawn at that point
plano-convex lens
a lens with one flat [plano] side and one outwardly curved convex side-- found in ellipsoidal reflector spotlights
focal point of lenses
pt. at which parallel rays of light converge after passing through a lens-- if source of light is placed at the focal point, parallel rays will result. moving source of light away from focal point causes rays to diverge or converge
focal length
the distance from the focal point to the center of the lens; measured in in. or mm.
ellipsoidal reflector spotlight (ERS)
uses ellipsoidal reflector; creates concentrated sharp light and has built-in beam shaping capability (shutters, iris, gobos)
C-clamp
clamp used to attach a lighting instrument to a pipe
yoke
the U-shaped part that holds the C-clamp and allows instrument to tilt
gate
in ERS, position at which shutters, iris, and gobos are located; close to reflector's secondary focal point where light rays cross
shutters
metal moveable plates, inserted at gate of ERS, that allows beam to be shaped in linear manner from any of four directions
iris
device, located at gate of ERS, makes the beam's circumference larger or smaller
zoom ellipsoidal
ERS with moveable lenses that provide adjustable beam diameter
fixed lens (ERS)
allows adjustment in beam edge but not spread; older ellipsoidals use two plano-convex lenses belly to belly in a barrel
interchangeable lens (ERS)
usu. provides 3 dif. beam spreads; allows for movement of lenses in relationship to one another or substitution of one lens for another
zoom lens (ERS)
provides variable beam spread within fixed range;rear plano convex, front bi convex lens slide toward or away from each other
beam edge
in spotlight beam, where light drops off to 50% of maximum intensity
field edge
in spotlight beam, where light drops off to 10% of max intensity
Fresnel spotlight
named after inventor of the lens; has spherical reflector and ability to change beam size
flood focus
when lamp is moved all the way forward, light beam achieves its largest diameter
spot focus
when lamp is moved all the way back away from the lens, light beam becomes narrowest
barn door
accessory for fresnel that attaches to color frame holder and allows for linear beam shaping from four sides-- external equivalent of ellipsoidal shutters
top hat (snoot)
fresnel accessory that attaches to color frame holder and reduces spill and glare from instrument's lens; shape of a tincan
PARcan fixture
Parabolic Alluminized Reflector
douser
mechanical device. commonly found in followspots, used to dim the light