Throw Distance and Image Geometry
Unlike a television, which has a fixed size, a projector's image size is determined by its distance from the screen. This is known as the Throw Distance. Every projector has a specific 'Throw Ratio' based on its internal lens optics, which dictates how large the image will be at a given distance.
Understanding Throw Ratio
The Throw Ratio is expressed as Distance / Width.
- Long Throw (1.8+): Common in commercial cinemas or large auditoriums where the projector is mounted at the back of the room.
- Standard Throw (1.2 to 1.5): The most common for home theaters; the projector usually sits on a ceiling mount about 10-12 feet from the screen.
- Short Throw (0.4 to 1.0): Can create a 100" image from just a few feet away.
- Ultra Short Throw (0.1 to 0.3): Sits directly against the wall, projecting upward at a steep angle.
The Formula
Throw Distance = Screen Width * Throw Ratio
Where:
Screen Width=
The physical width (not diagonal) of the projector screenThrow Ratio=
The specific lens constant provided by the manufacturerLens Shift and Zoom
High-end projectors feature Optical Zoom, which allows you to adjust the image size without moving the projector. They may also feature Lens Shift, which allows you to move the image up, down, or sideways without tilting the projector, preventing 'Keystone' distortion (where the image looks like a trapezoid).