When discussing the throw capabilities of a projector, the “short vs long” code is referring to the amount of distance you’ll need to “throw” an image between the projector itself and the screen to get the display size you desire. Simply put, the lens and mirror assembly built into a projector determine its throw distance capability. While most projectors send light onto the screen directly through the lens, Ultra Short Throw projectors direct the emitting lens light away from the screen — reflecting from a mirror of specific angle to direct the image on the screen. This is how they achieve the narrow distance from the installation point to the screen. Regardless of brand, these are categorized by how much distance the projector needs from the screen to create a 100″ image.
Why Go Short?
A big reason for schools, and even the home theatre crowd, opt for short or ultra short throw projectors in the clarity of picture, sans annoying shadows. No longer will “little bunny Foo-Foo” hop across the algebra equations, thanks to Johnny in the front row. And Uncle Mike crossing the room for a popcorn refill won’t inadvertently black out the screen just as the culprit in the evening’s who-dun-it is revealed. The close placement of the projector to the wall or whiteboard relieves any disturbance of the picture.
For teachers, this is far more than an annoyance. For years, they were relegated to the back of the classroom both to run the projector or slide machine. Not only would it be distracting for students for an educator to stroll front and center (with a face sporting the Doppler effect or periodic table) but the light shining in the eyes inhibits connecting with students to gauge their interest or understanding. Standing in front of the class not only allows teachers to authoritatively impart lessons or lectures, but it allows them to engage fully with the class, using the screen and media behind them to enhance their session.
For some schools lacking room in the budget for interactive whiteboards, the inclusion of a short throw or ultra short throw projector can turn any surface into this engaging tech. Because of a lack of shadow distortion, finger points can be distinguished for group work. The projector can even be ceiling mounted with the ability to point downward, turning a group table into a giant display for students to gather and learn. This can offer a more inclusive experience for students with mobility issues or disabilities. Many interactive projectors recognize multiple contact points, letting as many as 20 students work together on group projects. Clearly, for some — this makes going short the “smart” choice.
The Shortcomings
So why would any school opt for traditional long throw projectors? Even with all the benefits, a few drawbacks have some schools wavering. For many ultra short throw projectors, the tech does not include a zoom capability. This means the projector must be physically positioned to match the screen size. Another issue along those lines is a lack of autofocus on some models, which could be a problem if the mobile cart, table or floor mounted tech gets bumped. In a classroom of young students, this could mean frequent disruptions as the teacher resets the alignment of the picture.
The bottom line also can have an effect on throw choice. Long throw lenses are generally less expensive due to the quality of glass in the lens. They also work perfectly well for large halls, auditoriums or exhibition spaces. The surface the image or video is being displayed upon gets more important, the shorter the throw. For ultra throw either a light reflecting screen, tension-enable screen or whiteboard is best. All of these can represent pricy hits if they aren’t already in place. Because of the extreme angle of the light stream, distortions/bumps/cracks/building material patterns on a wall will be exaggerated and ripples in a cheaper non-tension rod pull down screen would mar the picture.
Here are the typical breakdowns of projector-to-screen distance:
