Black Top Masking is important!

Black Top Masking (BTM) above the image is a critical factor for Stewart Filmscreen retractable screens. Superior flatness, an artifact-free and evenly tensioned surface are two contributing reasons that Stewart’s electrically operated screens are the highest quality available in their size categories.  Stewart achieves this by paying close attention to details and optimizing the side tension, by carefully adding a slight curvature to the screen along the entire length of the fabric.

Proper image height above the finished floor (AFF) is the fundamental factor when computing BTM. The ceiling height, or case installation height is the next consideration when calculating BTM.  Finally, we need to know the total image height. These measurements can be plugged into a simple formula. This quick exercise insures maximum viewing access in the venue, and extended screen life.

The projector location and the presence or absence of projector lens shift capabilities, correlates with the determination of the appropriate BTM.  Consult the projector companies for details.  For example, will a vertical “lens shift” be required or is it possible to align the top of the projector lens with the top of the projection screen and yet align the bottom of the image at 42” AFF?

The BTM is MINIMALLY ADJUSTABLE as a rule. The retractable screen is engineered with a defined amount of BTM. We show 3”, 6”, 9” and 12” in our pricing guide.  But the BTM can be customized to your project's needs. Please note, 12” of BTM is not adjustable to 3” of BTM…” that will cause wrinkling” in the bottom corners of the image. The reason for this is the engineered bowing of the screen sides.  Proper side bowing with the tab-guy wires assures screen flatness. When the BTM is reduced or increased, due to adjustments of the down limit on the retractable roller tube motor, the engineered bowing of the screen is altered.  If altered too much, the screen’s flatness may be less than optimal.

Here is the baseline calculation guide that will determine BTM for your projection screen.