| The Right Profile |
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| Contributed by Andy Ciddor | |
| May 01, 2007 |
; "Image") Why are profile spots so different in the U.S. as opposed to the rest of the world?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. Why the Difference? There has been much gnashing of teeth and pounding of café tables and bars over why these differences have arisen. The fixed focus fanatics base their fervor on the higher output and sharper focus possible with the simpler optics of their favored fixture. The zoom focus acolytes believe that the additional flexibility offered by the wider range of beam angles justifies the marginal light loss, the higher weight and higher price of their choice. One particularly hurtful (but valid) comment from the fixed beam camp is that, in many installations, the front-ofhouse rig is immutable because of a venue’s structure, and so nullifies any possible benefit from zoom optics. There may be other, less clearly identified forces at work, however. In most of the world, a luminaire is seen as a long-term investment that may not be replaced for 15 to 25 years, so buying the most flexible unit possible is seen as a measure of futureproofing the investment. Equipment upgrade and replacement cycles tend to be much shorter than this in the U.S., particularly when the inventory belongs to a commercial enterprise. In the same way that continental drift has separated the continents and allowed differing evolutionary paths for related species of animals and plants; so, too, has supply voltage difference isolated the two branches of luminaire development. Ohm’s law makes it quite clear that if you halve the voltage to a device (230V to 110V), you will need twice the current to produce the same amount of power (approximately 4 amps per kilowatt at 230V and 8 amps per kilowatt at 110V). What Ohm’s law doesn’t tell you is that a 100V+ lamp is almost 10 percent more efficient than its 200V+ equivalent, due to increased heating efficiencies in the heavier filament. It also neglects to mention that the thinner filament is much more fragile or that the insulation required for 200V+ devices is substantially heavier and more expensive than that required for 100V+. There may be 200V+ and 100V+ versions of many lamps, but they are by no means equivalents in terms of filament size, robustness or efficiency. It was only quite recently, when voltage- independent switching power supplies became standard on some moving lights, that it was possible to make a luminaire that would work wherever in the world it was plugged in. The Altman 360Q probably didn’t make it in the 200V+ regions because there was no decent lamp available for it and because it came with 110V insulation that could not be approved by electrical authorities. Similarly, CCT was so busy building Silhouette luminaires to run at 200V+ that no effort was made to develop a 100V+ version. Even in this time of galloping globalization, only a handful of theatrical luminaire manufacturers set out to build products that can work across the entire voltage and regulatory spectrum. While one evolutionary branch of the plano convex spot may have become the Fresnel spot in most of the world, in Europe in the early 1980s, Fresnel lens technology was used to craft a hybrid lens. This is a kind of back-cross between the original ground and polished plano-convex lens and the molded Fresnel lens. Variously known as a prism convex or pebble convex lens, this variation has some knobby features molded onto what was previously the flat surface of the PC lens. The intention is to remove the unevenness of the original PC’s beam without losing its sharp focus. The result lies somewhere between an ellipsoidal and a Fresnel spot. Some less charitable critics of the result have observed that it combines the worst characteristics of both. While many LDs will use this luminaire for specific applications, such as tight stage pools, their use in the professional industry is not widespread. Nevertheless, most 200V+ theatrical Fresnel manufacturers also offer a PC variant of their products. Nigel Levings, the 2003 Tony Award-winning lighting designer (La Boheme) who works in venues and productions on both sides of the Atlantic, gets to have the final to say on the subject. “From time to time, I have been forced to use PCs in repertory rigs, but I don’t like them much, “ he admits. “I see them as a lazy substitute for those who can’t calculate beam coverage. My rigs these days are mostly S4 fixed beam profiles (ERS) with various frosts and PAR cans.” I guess that this argument will probably continue in the bar after tonight’s show. Andy Ciddor has been involved in lighting for nearly four decades as a practitioner, teacher and technical writer. Don't get Stage Directions? Click here to subscribe now!
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