Building a Scroller Projector Douser
There are many advantages to a douser, specifically when used with projectors that do not contain an internal iris. Even if your projector does have an iris, the idea of dousing with a "wipe" or a "dissolve" is still an appealing one. For a wipe effect, a standard "flapper douser" can be utilized, but for a smoother wipe with more of a feathered edge, a scroller douser is quite appealing. These units were used in conjunction with 9 projectors on a back wall, meshed to create one large image. The design of the gels seen here and the general design of the unit and wall was created by Peter Nigrini's video shop for the production of "Far from Heaven" at Playwright's Horizon's, with engineering by David Bengali and my company, Lucid Design.
What you'll need:
A scroller casing with operational drums, motors and DMX control*
(*RDM scrollers are not recommended as they are harder to manually control.)
A gel with the desired fade pattern printed on it.
Silver tape
Gaff tape
1 3/4" J-Lar tape
Foamcore & Black foil tape (for shutter cuts, if desired)
C-Clamp
L-Bracket (used for mounting strip lights)
Plywood shims (cut to size as needed.)
8 - 10 Drywall screws
Electric Drill
Bit extender
A fresh Xacto blade
A clean, dust free cutting surface
Gentle, acid-free cleaning solution (1 part dishsoap to 10 parts water works well)
Latex or thin cotton gloves
Prepping the scroll:
*When handling gel, always wear gloves to keep the oil from your skin off the gel. The cleaner the gel before you mount it, the smoother your fade will be. Oil reflects light in a unique way, and will show as an artifact on slower fade sequences.*
On the far side of the scroll, a window needs to be cut that allows the projector beam to shine through without distortion or loss of light. This hole should be cut approx. 2" wider than the space from drum to drum inside the scroller unit, and the tops and bottoms of the hole are reinforced with J-Lar to prevent tearing.
*Make sure that you tape wider than the hole you cut so that the reinforcement distributes the full strain of the scroll when it starts to turn. Only one side is necessary.*
!IMPORTANT! - NEVER CUT A CORNER INTO GEL, ALWAYS USE ROUNDED EDGES. (Any small tear made while cutting your window will snap the gel material when it is in use.)
Place your first piece of Silver tape on the bottom corner of the furthest side of the window, this provides the stopping point for the sensor on the scroller housing. This piece of silver tape should be anywhere from 2 - 3" in length since the scroller registers this end at a high speed. Only use completely transparent scotch tape when moving this silver tape around, and DO NOT put it under the J-LAR. You will most likely be adjusting it's location once you've loaded your gel into the scroller.
Building your frame:
Cut your plywood into three pieces, one will be the width of the scroller unit, and the other two will serve as extension arms that will allow you to adjust the scroller right or left from a pipe for a more precise focus.
(Note: the above configuration was utilized successfully for three projectors vertically on a wall with a pipe installed for the urpose of holding these scroller mounts. It will likely be necessary for a different mounting method to be devised for each show's needs, but the mounting mechanics should still be the same.)
After the wood is cut, affix the l-bracket to the C-Clamp and attach the plywood as shown below.
Once the arm is prepped, attach the two arms to the scroller housing (this part is tricky because of the drums, and a bit extender was required to reach the vents used to mount the screws.) Be sure to use only one screw for this as it will likely want to rotate on the point you use, but be sure to tighten the screw enough that it holds the housing against the shim firmly.
*Do NOT perform this step with the gel loaded on the drums, pictures below are of a disassembly*
After this is secured, go ahead and attach the c-clamp and adjust left or right as needed. We already adjusted the distance from the pipe on the shim below and it needed to go closer for this particular projector.
Loading the scroll:
This is the perfect time to clean your scroll of any fingerprints you may have put on it (they will show.) Using the gentle cleaning solution, remove any tape residue or oil on the gel before mounting.
note: the right hand drum is the one furthest from the light tape sensor in this model.
Now, carefully rotate the gel onto the scroller drum until you reach the end. (It helps to have a second person on hand with this part to hold the gel in place while you tape.) To affix the scroll properly, you have to look up the tension tables for your particular scroller. For us, we had to wind the left drum 5 times due to the length of our scroll. It may be more or less depending on what brand scroller you obtain, but finding how many gels your scroll print represents and adjusting tension appropriately is important to keep your scroll from tearing or bunching up while under operation. If you have trouble with this part, review your instruction manual's directions for loading a scroll as each brand describes it a little differently. The only difference with a scroll you print yourself is that it is likely shorter than an average scroll designed to provide many different colors.
Calibrating your scroll:
This part will change depending on what software you are using to control your scroller, but the MIN and MAX values are determined by the location of the silver tape you place on your scroll. A shorter piece of silver tape should be placed on the far side of your scroll before the solid black runs out, this will stop it from scrolling back into the clear section. Attaching the scroller to a PSU at your test table before mounting will verify that your MIN and MAX values are set correctly. Adjust the tape as needed before mounting the scroller in place.
Masking your scroller: (optional)
Another desirable function of the scroller unit is the ability to mask your beam due to its proximity to the lens. Cutting foam core and using black foil tape will ensure this masking does not fall off. (The vents on the unit will remove regular gaff tape after a few days.) Make sure when taping that you don't cover all of the motor vent ports since this will overheat the scroller's internal components.
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