The Projector

Projector Installation

Most slide and overhead projectors project a wide beam and so should be positioned at a height approximately half the height of the screen (See illustration projector wide/table). Most digital projectors are tabletop projectors. Because they are designed to project their beam from a conference table, optics are designed to reach a screen that will be higher than the projector (See illustration projector normal/table.). If your installation needs demand a different orientation of beam, you can change the beam by widening the lens’ focal length with a zoom lens or an interchangeable lens. Many digital projectors can also be installed from a ceiling; in this case, the beam is reversed and angles downward. (See illustration projector normal/ceiling.) Most digital projectors also allow for rear projection, when using a translucent screen. In this case, the electronic controls will reverse the image. If the image is not reversed electronically (or in previous editing), it would be seen backwards. The most important thing is to make sure you have the right relationship between the projector and the projection surface.

illustration projector wide/table: R. Modrak. Beam from slide and overhead projectors and digital projector with wide lens.

illustration projector normal/table: R. Modrak. Beam from digital projector with normal lens.

illustration projector normal/ceiling: R. Modrak. Beam from digital projector with normal lens, reversed for ceiling installation.

Enlarging and Diminishing the Image Size

Manufacturers sometimes provide one-line specs about projection distance; for example, that a projector can “project image sizes from 5 to 50’.” Unfortunately, this number doesn’t tell you how far the projector itself needs to be from the terminal point, a significant factor in installation. More helpful are distance and screen size charts such as Epson’s chart, below, which shows that their PowerLite S1+ LCD projector will project a 300” image when the projector is 30-38’ from the screen.

The flexibility to move the projector closer or further from the projection surface will vary in each installation, room, or site. Each lens has a different focal length or range of focal lengths; this determines how close to or far from the screen the projector will focus. A projector outfitted with a fixed focal length lens must be moved closer or farther from the viewing screen in order to enlarge the image size. If the projector has a zoom lens, the focal length can be changed (from normal focal length to wide angle, for example) in order to change the beam or image size without moving the projector. The wider the focal length, the larger the image.

: Courtesy of Epson America, Inc. Projection distance and screen size chart.

Keystone Correction

A beam of light will be symmetrical if it hits a surface from straight on. For example, if you pointed a flashlight directly in front of you, the beam that hits the wall will be circular. As you lift the flashlight over your head, angling the light at the same point on the wall, the beam will take on an oval shape. This is the phenomenon of keystoning.

Aspect Ratio

The aspect ratio refers to the dimensions of the rectangular shape of a video picture. Any given television set or projector comes in its own native format--typically either 4:3, the standard television proportion, or 16:9, the wide screen proportion. However, as there is no universal standard, no matter which format projector you get, either 4:3 or 16:9, it will not fit all the video material you will want to watch in its native frame. There is no perfect solution, but the simplest way to set up your system is by matching a native 4:3 projector with a 4:3 screen or a native 16:9 projector with a 16:9 screen.

Projector Noise

Most projectors are cooled by a fan, whose operation may be loud enough to disrupt presentations or performances. Be aware of the noise your projector will make. Noise is measured with a dB (deci Bel) rating. The Epson PowerLite  S1+ LCD projector claims to have a “Whisper-Quiet Fan” at 33dB.

Image Quality and Image Resolution

With this same logic, still images being projected should be sized depending upon whether you want to fill the screen completely or partially. Projectors scale up smaller images and scale down larger ones to fit into the area of the native resolution. Rescaled images lose clarity and sharpness. Therefore, size the image according to pixel dimension rather than dpi. For example, if you want an image to fill the screen when viewed at 100%, size it around 1024 x 768 pixels to match the display monitor’s native resolution of 1024 x 768. If you want it to fill half the screen, size it roughly around 500 x 375.

A computer’s need for resolution is lower than a print’s. The standard monitor resolution is 72 dpi. When viewing images from a computer monitor, resolution determines image size, not quality. (This is the opposite of how resolution affects printed images wherein resolution does determine image quality, but not size.) When projecting images, dpi only matters in terms of file size: too high a dpi resolution will make the file harder to process and can delay transitions between images. Usually 72 dpi, saved in JPEG format, is sufficient, unless the image is very small -- postage stamp size -- in which 300 dpi may be necessary for a sharp image.