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The Ellipsoidal Reflector Spotlight, or ERS, is the most common and most powerful of the array of fixtures available to the lighting designer. It is also sometimes called a Leko (the Strand Leko was a popular fixture in the 70s and 80s and this has in some places become the generic name for an ERS).
All ERS fixtures, regardless of manufacturer, have a few things in common:
Because of the considerable control that the lighting designer has over the shape of the light, this is the go-to fixture in a theatrical lighting rig. |
This diagram of an ERS shows all of the inner workings of the instrument. The 'Focus Knob' loosens up the lens tube to change the relationship of the lenses and the lamp. Much like focusing a camera, this either sharpens or fuzzes out the edge of the beam. The shutters and the template (gobo) slot are right next to each other, because this is the place within the optics that allows a very sharp focused edge. Color media is placed in the gel frame in front of the lens.
Diagram from: technical information for Harvard's Loeb Drama Center: link |
Fixed Angle ERSThe Source 4 is the most common Ellipsoidal Reflector Spotlight (ERS) in the marketplace today. This one is a fixed angle instrument. The most common field angles for the Source 4 are 19°, 26°, 36°, and 50°, though a narrower 14° is becoming more available and very narrow 10° and 5° angle lenses are available.
The Altman Shakespeare instrument is a very similar fixture- just manufactured by a different company. |
Lens Tube or 'Barrel'Modern fixed angle Ellipsoidals like ETC Source 4, Altman Shakespeare, S6 and Phoenix have the ability to change the field angle of the light simply by swapping out the lens tube. Usually, the angle is on a decal on the side of the lens tube, and the most common angle lenses are 50°, 36°/40°, 26°/30° and 19°/20°. This is a rough approximation of the field angle. See the Photometrics section for more specific information on this.
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Long Throw ERSIt seems counter-intuitive that in order to get a narrower beam the light would need this massive lens assembly- but that's how the physics work. A 5° lens assembly will create a 10' pool of light from a distance of about 70'.
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Zoom ERSZoom Spotlights allow on site adjustment of the field angle without the need to swap out lenses. By adjusting the position of the lenses, the instrument can be focused anywhere within a given range. The Altman Zoom units that we have in the C of C inventory can be adjusted from 15° to 35°, or from 30°-55°.
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PhotometricsPhotometrics are the measurable aspects of light. In short, how big is the pool of light, and how bright is it? When the designer is choosing lights for the design, it is important to know that the instruments will do what they need to do. Go to the Photometrics page to learn more about the science of measuring light output.
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GobosShort for "Goes Before Optics", a Gobo is a steel or glass template that is placed in the gate of the unit. By running the edge of the beam sharp or soft, the designer either gets a very specific pattern of light and shadow, or a fuzzy breakup of the light. More details on the Gobo page.
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ALTMAN 360QFor many years the Altman 360Q fixed beam ellipsoidal was an industry standard. Altman has just recently stopped manufacturing them but you will still find them in many theatres (including ours). These instruments do not have interchangeable lens assemblies like the Source 4 or Shakespeare. The naming convention also does not mimic the approximate beam spread- it is a combination of the lens diameter and the focal length. The most common are- from wide to narrow: 4.5x6 (approximately equivalent to a 50° instrument), 6x9 (36° or 40°), 6x12 (26° or 30°) and 6x16 (19° or 20°) .
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What about leds?LED lighting instruments have been used as wash fixtures for several years now, but the ERS equivalent is relatively new. In order to get the lighting instruments bright enough to compete with tungsten fixtures, manufacturers have had to use multiple LED chips, which led to difficulty in building the optics so that ERS fixtures can do what ERS fixtures do- specifically have sharp edged beams, shutters and gobos. In the last few years LED brightness has increased, and the engineering of the optics in the instruments have allowed these challenges to be largely solved. The instruments typically have multiple color engines, reducing or eliminating the need for colored gel. LEDs are much more expensive than traditional instruments, but despite the cost we are seeing more of them in the marketplace. They are operated by DMX rather than traditional dimming systems. See the DMX page for more information on this.
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Because of how the optics work inside the instrument, when gobos and shutters are used, they appear in a 'mirror image' when they finally come out of the instrument. For instance, when you push in the shutter on the physical bottom of the lighting fixture, the top of the beam of light is cut off on the stage. Gobos that have a specific 'up' and 'down' orientation must be installed 'upside down' into the instrument in order to project correctly on the stage.
Modern ERS lighting instruments also have the ability to 'rotate the barrel' or twist the gate and lens tube in either direction. Sometimes the angle at which the light is hung does not allow the electrician to make the angle shutter cut that is necessary. In this case, rotating the entire lens tube (including the 'gate') will allow the proper cut to be made. This also helps when trying to get a gobo to properly line up. |
Additional InfoSome instrument manufacturers:
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