Ellipsoidal reflector spotlight (abbreviated to ERS, or colloquially ellipsoidal, ellipse or leko) is the name for a type of stage lighting instrument, named for the ellipsoidal reflector used to collect & direct the light through a barrel that contains a lens or lens train lens. The optics of an ERS instrument are roughly similar to those of a 35 mm slide projector. There are many types of ERS that are designed for the myriad of applications found in the entertainment industry. ERS instruments come in all shapes and sizes. Each particular model of ERS has its own set of characteristics. Generally, ERS instruments are the most varied and utilized type of stage lighting instrument. ERS may also be referred to as Profile Spotlights (especially in Europe) because the beam can be shaped to the profile of an object. Ellipsoidal reflectors are used for their strong, well-defined light and their versatility. Leko and Source Four are brand names which may occasionally be used to refer to any sort of ellipsoidal.
Characteristics of an ellipsoidal lighting unit include:
- An ellipsoidal reflector
- A lens or lens train
- An adjustable barrel, allowing a lighting designer to change the focus (softness) of the light thrown by the unit by changing the distance between the reflector and the lens train. "Zoom" ERS instruments can vary the size of beam as well as the focus.
- ERS fixtures are also characterized by the use of two PC (Plano-Convex) lenses in the barrel which face Convex sides together. The distance between these lenses along with the size of the lens determines how wide the output beam of light is. For example a 6x9 (6" Lens -by- 9" focal length) produces 37-degrees
- A set of brackets on the end of the barrel for the insertion of gel frames or a colour changer unit to alter the colour of the light as with almost all stage light instruments
- A series of shutters at the base of the barrel for shaping and narrowing the light beam is usually present, some ERS have an iris to narrow the beam in shape of a circle and some instruments have or can be made to have both
- A slot in the body of the unit for the insertion of metal gobos to change the pattern of the light in most cases is present, this slot can also hold a glass gobo, dichroic colour roundel or an effects unit
The lamps are loaded from the rear (in most cases), and either mounted axially, or radially with the base either up or down (the orientation is important when mounting the instrument as using the light upside down will shorten lamp life) at a 45-degree angle or some times at a 90 degree angle. The filament of the lamp is at one focal point of the ellipsoidal reflector and the gate with the shutters and gobo are at the other focal point.
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Field Angle
Ellipsoidals are supplied with a certain size lens or lenses that determines the field angle, anywhere from five to ninety degrees. Field angle is the angle of the beam of light where it reaches 10% of the intensity of the center of the beam. Most manufacturers now use field angle to indicate the fixture's spread typically in this series (5°, 10°, 15°, 26°, 36°, 50°, 75°, 90°). Older fixtures are described by the width of the lens x focal length of the instrument. For example, a 6x9 ellipsoidal would have a 6" diameter lens and a focal length of 9". 6x9 Instruments have a field angle of approximately 37°. 6x12 instruments have a field angle of approximately 27°. As the field angle narrows, the instrument can be used further from the stage. Variable focus (zoom) instruments with two lenses that move in and out from the lamp housing are also available, allowing the user to manually adjust to the desired focal length within a certain range.[1]
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Updates to the Design
The ETC Source Four, created in 1992, updated the traditional ERS design. The company took advantage of advances in lamp and reflector technology to increase luminous output with less wattage. The Source four is the first fixture to allow for interchangeable lens tubes, which allows for the same body of the fixture to be used for multiple beam field angles, ranging from 5 to 90 degrees.
Most Recent Developments
Since the release of the Source four, other lighing manufacturers have since revised their products to competed in the market share aside the ETC. The Selecon Pacific, an L shaped ERS has an irregular shape due to an integrated dichroic cold mirror, which has a heat sink to draw heat from the instrument. This keeps the beam of the fixture cool allowing for the use of plastic gobos. This cool beam also improves shutter, gobo and color gel life, and also can improve the temperature on stage.[2] The Altman shakespeake, is also intended to compete with the Source four by having similar features. The patents for some components in this unit have been licensed from ETC's Source Four.
See also
References
- ^ Gillette, J. Michael (2003). Designing With Light: An Introduction to Stage Lighting, Fourth Edition". McGraw Hill. p. 60. ISBN 0-7674-2733-5.
- ^ Gillette, J. Michael (November 10, 2004). Theatrical Design and Production: An Introduction to Scene Design and Construction, Lighting, Sound, Costume, and Makeup. McGraw Hill. p. 365. ISBN 0-07-256262-5.
External links
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