Custom Gobos on The Fly

In the right hands, gobo projection from ellipsoidal reflector spots (ERS) can be a very powerful production tool.
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In the right hands, gobo projection from ellipsoidal reflector spots (ERS) can be a very powerful production tool. We have reached that moment in technological evolution where the increasing optical efficiency of ellipsoidal spots and the decreasing light requirements of our camera pickups have finally collided. This development ushers in the realistic possibility of using gobo projection in our everyday work.

The range of ready-made gobo patterns available from the catalogs of GAM (www.gamonline.com), High End (www.highend.com), Lee (www.leefiltersusa.com), Rosco (www.rosco.com) - and many others - is quite extensive, although some of the patterns have been around long enough to have become visual clichés. Although the ready-mades will certainly add a cost-effective dimension to your compositions, sooner or later you will need something that isn't in the book or on the Web site.

Not so many years ago, the only method available for constructing a custom gobo involved using an Exacto knife to cut the desired shapes (or an approximation thereof) from an aluminum pie-pan or a sheet of zinc printer's plate.

A later development, sold as an expensive commercial kit, employed a photo-resist and chemical etching process that was derived from the technology used to prototype printed circuit boards. While this method allowed for the production of more intricate and accurate gobo designs, it was neither simple nor straightforward.

The range of methods currently available for custom gobo production is bewilderingly large. Monochrome choices range from the basic stainless steel plate offered as a special service by several of the ready-made gobo producers, to metal deposited on high temperature glass from the likes of High End Systems.

Full-color multilayered dichroic gobos are also available - such as those using the process developed by Beacon of Sweden and made available through its U.S. licensees, Gobo Express (www.goboexpress.com) and Gobos To Go (www.gobostogo.com).

As all of these methods involve intricate, complex and often toxic photographic and lithographic processes, none of them are well-suited for in-house use. Most of the companies offering custom gobos can provide a fast turnaround and delivery, and many will accept artwork in digital form - allowing you to simply send it in by e-mail.

This improved accuracy and convenience naturally comes at a price, with one-off items ranging from hundreds up to thousands of dollars, depending on production method and urgency.

MODERN ERS

The use of the "cool" dichroic reflector in ETC's Source Four and Altman's Shakespeare spots was a key element in the development of the modern high-efficiency ERS. Among a host of other benefits, the optical gate of these instruments is much cooler than earlier versions of the spot, and thus allows us to use materials less robust than sheet steel for gobos.

Although there is a lot of prior art in the use of dichroic reflectors, the design shared by Altman and ETC was patented, effectively preventing the use of this technology by other manufacturers. Of course this only served as a challenge to other luminaire designers to find a way to build a cool beam ellipsoidal without contravening that patent.

The Pacific ERS, designed by Andrew Nichols and Frank Tornyai at Selecon (www.seleconlight.com) in Auckland, New Zealand, may look slightly awkward at first glance, but the outside-the-square solution produces what is probably the coolest optical gate available. A planar dichroic reflector is used to produce a right-angle bend in the optical path between the lamp house and the gate.

Unlike other designs where a significant proportion of the lamp's output goes directly to the gate without hitting a selective dichroic reflector, all of the Pacific's light goes via the reflector where the infrared content is removed and radiated out, via a waffle-iron shaped heatsink. The Pacific is available here in the United States from Barbizon (www.barbizon.com), Angstrom (www.angstromlighting.com) and AC Lighting (www.aclighting.com).

When the Pacific was initially released, David "Fergo" Ferguson, Selecon's Australian representative, used a dramatic party trick to illustrate the effectiveness of the luminaire's thermal design. Into the gate of a running Pacific, he would insert a design, printed on regular office-grade transparency film. After drawing the appropriate incredulous response from his audience, Ferguson would then quickly remove it to prove that the film was still intact.

FERGOS

Ferguson, when not on the road for Selecon, is a highly respected and very busy lighting designer. He has gone on to develop the production of gobos on transparency film into something much more substantial than a short-term party trick. The Fergo (as the transparency-based gobos have since become known) has been widely adopted by theatrical lighting designers and television lighting directors in Australia and New Zealand.

Ferguson has developed a set of guidelines for the production and projection of custom gobos from the comfort of your keyboard - using materials available in any office - and with a turnaround time of minutes, not days. What follows is a summary of his findings.

The artwork suitable for use as a gobo is limited only by what you can get onto a sheet of film. In effect, any image that can be printed with a computer printer or office copier can become a gobo. Word processing documents, digital photographs, scanned images, spreadsheet graphs, desktop publishing documents, Photoshop images, CAD drawings and even Web pages can be used, if appropriate care is taken with image resolution and color density.

Any device that can print onto transparency film can be used for gobo production, although Ferguson has noticed that some inks and some printing technologies produce better output. As with any medium, the finer the detail on the output, the clearer the projected gobo.

Ferguson's favorite device is the dye sublimation printer found in many design and publications offices (perhaps even in your own graphic arts or art department). Unfortunately the color laser printer that is replacing this technology does not yet produce such clear colors.

When it comes to office printers, Ferguson has a preference for Epson's inkjets. He is very pleased with the results from the portable Canon BJC-55 inkjet printer, which has the added advantage of being compact enough to sit at the production desk during rehearsals to facilitate last-minute production changes. Laser printers - both color and monochrome - produce clear, stable images, although many office laser printers only offer 600 dpi resolution. The color printing and copying service offered at Kinkos is a very convenient and cost-effective alternative.

Depending on the light source and the density of the image, the operational life of a gobo can vary between a couple of hours and a copule of months. The optimum balance between gobo life and light output is obtained by using the 575 W long-life GLA or high-output GLC lamps, checked back to 80-percent output.

A further important precaution is the insertion of a glass UV filter between the lamp and the transparency. As it is UV bleaching of the pigments that causes image fading - not heat damage - this filter can extend the life of the gobo by up to 400 percent. A range of discharge lamp houses is also available for the Pacific. If dimming is not important for your gobo projection, it may be worth checking out the 70 W and 150 W CDM versions. More details are available on the Web at http://www.seleconlight.com/english/support/gobos-desktop.htm.