May Issue - Stage Directions Magazine

May Issue - Stage Directions Magazine

Light On The Subject

By Andy Ciddor

The Right


Why are profile spots so different in the U.S.

as opposed to the rest of the world?

One of North America’s most widely used ellipsoidal

spots is the basic fixed focus Altman 360Q.

Selecon’s Rama 150 PC is an example

of a spot fixture that’s popular abroad.

The ETC Source Four is another very popular

ellipsoidal spot used in North America.

Globalization has been bulldozing its inexorable path

through the world of theatre since Genghis Kahn decided

to take his European vacation. Wandering about

backstage in any vaguely modern performance space anywhere

in the world, most of the equipment will seem familiar to you.

But only at first glance.

You may well see your favorite brands of dimmers, consoles

and luminaires, but look more closely — you are likely to find

some surprising differences. Some of the ellipsoidal reflector

spots (known in other parts of the English speaking world as

profile spots) may have a zoom focus knob on the lens barrel,

and some of the Fresnel spots may actually have smooth (plano

convex) lenses rather than the stepped lens you were expecting.

While not entirely absent from North American equipment

inventories, these variations are not very common in the U.S.

In Historical Context

The plano-convex spot (known in some places as a focus

spot) was in common worldwide use in the early 20th century.

Like today’s Fresnel spots, these luminaires used a spherical

reflector to capture some of the light from the lamp and send

it forward through a lens that allowed the beam to be focused

onto the stage. At that time, the lens was a simple plano-convex

lump of moderately heat-resistant glass, and the lamp was likely

to have a cage or drum-shaped filament.

The combination of the comparatively crudely made lens

with a filament that lay anywhere but on the focal plane of the

optics produced a vaguely rectangular blob of light with dark

and light bands due to the structure of the filament. Moving

the lamp and reflector within the fixture enabled some variation

in the size of the beam and the sharpness of the striations.

The uneven output pattern from these plano-convex (PC) spots

made them particularly difficult to blend together to get an

even stage wash.

It should come as no surprise to learn that the lighting industry

was anxious to find a better instrument than the PC spot.

Developments took two directions. The first approach, taken by

Levy and Kook, was to build a more efficient and accurate optical

system using an ellipsoidal reflector and a grid filament lamp,

which provided a more even beam of light through the PC lens.

The beam was sufficiently flat that it projected a crude profile

of any object placed at the right point in the beam. Thus arose

the Leko ellipsoidal reflector spot (ERS), or profile spot, whose

descendents would be fitted with shutters, irises and gobos.

The other tactic for dealing with the PC spot’s main imperfection

was to use a fuzzier and less accurate lens to remedy

the uneven beam. The Fresnel lens, with its molded-in “imperfections”

and its inaccurate focus due to the stepped rings,

turned out to be ideal. The more diffuse beam was less striated

and much easier to blend into even coverage. The shorter

focal length of the Fresnel lenses also brought with it a wider

range of beam angles. Although cost was initially a barrier to

its widespread adoption, once manufacturing processes were

improved, the Fresnel spot drove the PC spot to virtual extinction

by the middle of last century. The archeologically inclined

reader may be able to find a few dead PC spots (usually with a

big crack in the lens) buried in the equipment graveyards under

the stages and in the back corners of the equipment stores in

older performing spaces.

The States Versus Abroad

Since its introduction, the ERS has been the subject of much

research and development effort. The reflector system has been

redesigned several times to collect more light and to focus it

more sharply. A variety of lamps, featuring higher outputs and

better filament arrangements, have been developed. In different

efforts, the lens system has been both simplified for higher

efficiency and made more complex by introducing zoom focus.

The projection capabilities have been vastly improved through

the addition of condenser optics before the gate, while the

gate itself has been fitted with a vast variety of shutter systems,

including a second set of offset blades to allow for both soft

and hard focused edges. Despite all of these possibilities, North

America’s most widely used ellipsoidal spots remain the basic

fixed focus Altman 360Q and the fixed focus models of the ETC

Source Four.

The situation in the 200V+ regions (i.e., Asia, Africa and

Europe) has been almost the complete reverse. Since the CCT

Silhouette, a zoom-focusing quartz-halogen powered profile

spot, first appeared in the UK in the early 1970s, there has been

almost no interest in the fixed focus variety. So little interest, that

even the world’s most popular ellipsoidal, the ETC Source Four,

only became popular in the 200V+ regions after a range of zoom

focusing models were introduced.

16 May 2007 •

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