1. Introduction

Interactive projectors can be classified by the throw type: Long, Short and Ultra Short.
Long Throw projectors have a Throw Ratio (Distance to Screen/Screen Width) of ~ 1. So if the screen is 1.7m wide, the projector should be place around 1.7 m away. (For a screen ratio of 16:10, this means that the Height is 1.07m and the diagonal is 2m, or 80” wide).
Short Throw projectors have a Throw Ratio of ~0.6. For the same screen described above, the distance to the screen will be ~1m.
Ultra Short Throw projectors have a Throw Ratio of ~0.3. For the same screen described above, the distance to the screen will be ~0.5m.
This article describes the procedures for a ceiling mount installation of a Short Throw projector in a typical classroom or meeting room. The ceiling mount ensures that the presenter has minimum glare issue and the shadow is also minimized, so that the presentation space is maximized.

2. The Goals

The goals of the ceiling mount include:
The projected image should cover most of the screen (e.g. a whiteboard).
The image should be centered.
Note: the bottom of the screen should not be greater than 90cm, if the projector is used in a primary school or a kindergarten; a shorter child may not be able to reach the top of the screen with the Light Pen.

3. Preparation for the installation

Before starting the physical work, you need to determine an optimized point in the air that achieves the goals of the installation. However, classrooms, lecture halls, meeting rooms, or other venues all have individual ceiling height, screen size, building material, power availability, etc. Furthermore, every projector has its own dimensions, and every mounting rack is designed differently. As such every projector installation will have different dimensions and challenges. For a typical classroom or meeting room, we will assume that the ceiling is approx. 2.5m high and some form of attachment from the ceiling is achievable and a power socket is nearby.

We will designate this point with axis X, Y and Z, being distances from the center point, C – the center point on the upper width of the screen.

X – The distance from the lens to the screen.

Y – The distance from the projector to the ceiling.

Z – The distance from the lens to the upper center point of the screen.

Refer to the diagrams:
4. The following steps are for general guidelines only. For specific model, you can refer to the user manual for dimensions and apply the principles in this article.

a)     Calculate the distance X with Throw Ratio formula:
For example, for i-LAN interactive projector model BS-W261i, if the screen size is 1.7m (wide) x 1.06m (height), and your projector output is set to 16:10 screen format, then X = 1.0m.

b)     Workout offset compensation distance. For example, for BS-W261i, 16:10 screen ratio and 80” (2m) diagonal, there is a 12cm offset compensation distance, meaning that the projector needs to be placed 12cm above the center point C. Then, Y = Offset distance + Distance between Ceiling and C.

c)     With the assistance of another person and a ladder, power on the projector and point at the intended screen until the size fits. Then measure the distance from the lens to the screen (X) and the distance from the ceiling to the lens (Y). Measure these lengths and verify with theoretical X and Y.

d)     Define Z by working out the distance between the lens and the center of the mount on the projector. The projector should be mounted such that the lens is in line with C.

e)     With X, Y and Z defined, you can now proceed to arrange for the mounting to be fixed on the ceiling, pending the local conditions (ceiling type vs. the mount structure, etc.)

f)      Consider the wiring requirements (cables for power, HDMI, VGA, US, etc.)

The above procedure is a general guideline for a ceiling mount of a Short Throw interactive projector. It will ensure minimum shadow and glare to the presenters’ eyes.
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