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How Zoomspot Profiles Work

 
Zoomspot Optical System Lamp In Base Down Orientation

Zoomspot With Base Down Lamp

The diagram on the left shows the optical system of a zoomspot that utilises a base-down lamp position. The lamp filament is centred in the ellipsoidal reflector while the lamp base is located through the bottom of the reflector. The centreline of the lamp and the optical system are at ninety degrees to each other. Some older models used different angles.

The ellipsoidal reflector operates slightly less efficiently in base down designs compared with axial designs (shown below) but it does make the design of lamp itself easier, particularly with large heavy 240V filaments. Early axial 240V lamps were prone to premature failures.

Zoomspot Optical System Lamp In Axial Orientation

Zoomspot With Axial Lamp

This diagram shows the optical system of a zoomspot with an axial lamp position. In this arrangement the lamp filament is centred in the reflector while the lamp base is located through the centre of the reflector. The centreline of the lamp and the optical system are both on the same axis.

Axial designs provide the most efficient way to collect the available light. Advanced technology and engineering of the lamps and luminaires have greatly improved the reliability of modern axial luminaires making the more energy efficient axial designs the more popular choice.

Zoomspot Optical System Lamp In Axial Base Down Orientation

Zoomspot With Base Down Axial Lamp

This diagram shows the optical system of a zoomspot with a base down lamp position that is still an axial design.

In this arrangement the lamp filament is centred in the reflector with the lamp base located through the centre of the reflector as with any axial design but the lamp and reflector are mounted in the luminaire with the lamp and reflector axis at ninety degrees to the axis of the lens system. A special 'cold mirror' is built into the optical system to intercept the light from lamp and reflect it into the lens system.

Although this is a more complex design, its advantages are substantial. The cold mirror can have special dichroic coatings that reflect the wanted visible light through the lens system while allowing the unwanted infrared (heat) and ultraviolet wavelengths to pass through the mirror into a heatsink where they are safely dissipated.

Zoomspots are profile luminaires that utilise a precision optical system that comprises of an ellipsoidal reflector and two or more lenses to provide a light beam that can be focused to a soft or hard edge, zoomed from a wide flood to a narrow spot, and accurately shaped by framing shutters inserted into the gate. In a zoomspot two lenses are adjustable in relation to the lamp and to each other to enable the beam width and focus to be adjusted. The beam width is at its widest when the lenses are closest together and at its narrowest when they are at their furthest apart.

Fixed beam profile spots usually have only one lens, although some designs use two lenses, but in either case only the beam focus is adjustable and the lenses are optimised for the specified beam width.

Most profile luminaires provide a slot to allow a gobo holder to be inserted into the gate adjacent to the framing shutters so that gobo patterns can be projected onto the stage. The ability to function as a pattern projector is one of the benefits the precision optical system provides.

Profile spots are often called ellipsoids, because of the ellipsoidal shape of the reflector, or simply referred to by their model name such as as Acclaim Zoomspot. Overseas they are commonly referred to as ERS (Ellipsoidal Reflector Spotlights). The ellipsoidal reflector is a critical component in the optical system of profile luminaires. Ellipsoidal reflectors are designed to focus the light from the lamp into the focal point of the optical system, and they do so very efficiently.

The position of the lamp in the reflector is usually adjustable to provide light distribution across the beam width that is either even from edge to edge (flat) or brighter in the centre of the beam (peak). Peak distribution allows the beams of adjacent profiles to be overlapped without creating 'hot spots' whereas a flat setting is best for projection of gobo patterns.

Zoomspots vs Fixed Beam Profiles

Zoomspots allow the size of the light beam to be readily set to the size needed for any particular purpose, minimising the light and energy wastage that may otherwise result from large shutter cuts. This also eliminates the need for lighting designers to calculate the exact beam angles required for each luminaire so the appropriate luminaires can be rigged for each show. The down-side is that the extra lenses and variable beam width makes zoomspots a little less efficient. The wider the zoom range the less optimal the optical system becomes. This is why manufacturers make a series of zoom lens systems with limited zoom ranges rather than a single lens system that zooms all the way from pin spot to wide flood. When luminaires are routinely moved to different positions within a theatre, or toured to different theatres, the versatility of zoomspots makes them the obvious and popular choice for multi-purpose venues and repertory theatres.

Fixed beam luminaires allow the manufacturer to optimise the optical system to achieve the best performance from the luminaire, at the specified beam width, to provide a more efficient luminaire with superior light beam characteristics that is simpler to use. When the luminaires are permanently rigged at the same positions in a theatre the need to calculate beam angles from one show to another is largely eliminated making it practical to select luminaires based more on efficiency and light quality than versatility.

Given that modern engineering has reduced the performance and efficiency differences between zoomspots and fixed beam profiles to a minimum, much of the choice also comes down to personal preference.

Typical Uses

Profile spots are mainly used to light the front areas of the stage from Front of House (FOH) spot bars above the auditorium and for lighting upstage areas when maximum control of the light beam is desired. In addition they are often used when tightly focused specials are required, particularly from FOH positions, and for pattern projection.