In a recent Christian youth theater production where I was responsible for video and theatrical lighting support, our team wanted to use the church's video screens as scenic elements. This involved two screens hung over the outer stage left and right edges of the stage, and one center projector that would project onto a semi-circular "window" built into the set piece to project images of the city of Babylon as seen through the window. However, as the play had numerous blackouts, we were concerned about the amount of light the screens would project even when the image was black-in a dark room, even "black" video is very bright.
To solve this issue, we had the opportunity to try out some projector dowsers made by City Theatrical in Carlstadt, N.J. This device is very simple, yet highly effective. A stepper motor in a housing is mounted near the projector lens, and a thin aluminum "flag" is then attached to the motor shaft. The flag will traverse a 90-degree range of motion based on a DMX signal sent over its assigned channel from a lighting console. Optionally, the dowser can also be controlled by a simple contact closure.
Tech volunteers Michael Bynam and Jonathan Walton mounted the dowser on a rented side arm that was attached to the projector-mounting pole coming down from the ceiling. The side arm is basically a piece of pipe with a lighting clamp attached to one end. The dowser mounting plate attaches to the side arm, and the dowser to the mounting plate.
Due to the short distance between the pole and the front of the projector, we needed to use a long side arm and mount the dowser past the end of the projector-turned around 180 degrees-to get the flag close enough to completely block the light output from the projector to the screen. This worked well; we just needed to be careful when attaching the flag to the motor that we understood which way the flag was going to move, so we didn't end up karate chopping the side arm.
The dowsers are powered by a separate power supply sold by City Theatrical (but are also compatible with a variety of color scroller power supplies). The DMX address is set via three 10-digit rotary switches. Standard five-pin DMX is run into the power supply, and four-pin color scroller cable is then run from the power supply to the dowser. Two dowsers can be daisy-chained off one power supply.
Our first two dowsers worked very well right off the bat. On the third, we had some trouble getting going: the LED status lights were indicating that while a DMX signal was present, there were errors in the DMX stream. The manual stated that this could be the cause of a bad cable or failed opto-isolator upstream from the dowser. We ended up moving the power supply closer to the dowser to shorten the four-pin cable run, and then it worked fine. The other two dowsers were working fine with a total of 125 feet of the four-pin cable.
To control the dowsers, we simply added the dowser channels into the appropriate lighting cues to control when any given projector would be visible-very simple.
The dowsers performed very well throughout the week of the play, and greatly augmented the use of video for our production. I would highly recommend them to others wanting to completely black out their video screens when not projecting for an event. The dowser has an MSRP of $575, and each power supply is $150.
Jim Kumorek is owner of Spreading Flames Media, providing video production, photography and writing services to the architectural, A/V/L, and hospitality industries. He has also been an editor at Church Production Magazine and a church technical director responsible for audio, video and lighting systems. He can be contacted at james@spreadingflamesmedia.com.
