Choosing the Right Projector
Quick Links:
 Video Projectors Terms and Information
 Overhead Projectors Terms and Information
 Visual Presenter Terms and Information

The cost of projectors can vary significantly from model to model. With features ranging from simple to advanced, how do you find out which one will best suit your needs and your budget? You also don't want to worry about service issues or having to replace a lamp that may soon be obsolete. That's why it's important to buy from an experienced dealer who knows about the model, the manufacturer, its features and capabilities.

The terms and features described below will provide you with some very basic education about the technology found on today's projectors. Although technology can change by the minute, we hope this information is helpful to you. Also, you may email us at info@longselectronics.com with any questions you may have.

Video Projectors (LCD and DLP™)
LCD stands for Liquid Crystal Display. LCD produces digital images for viewing through three separate LCD glass panels, on each for Red, Green, and Blue. DLP™ stands for Digital Light Processing™. DLP™ reproduces images using a single chip made up of millions of microscopic mirrors, each with its own color wheel of Red, Green and Blue.

Both have advantages and disadvantages. LCD projectors are less expensive, yet sometimes bulky. They generally perform best where color reproduction is critical. However, they focus so precisely on each pixel that this causes disadvantages with viewing video. DLP™ projectors are more expensive, yet extremely lightweight and portable. They are most preferred for their cinema-like quality and lamp efficiency.

Key terms and definitions for video projectors:

1. Brightness - Also known as "Lumens." Lumens measure the intensity of light, or as stated in The American Heritage® Dictionary of the English Language:

Lumen - The unit of luminous flux in the International System of Units, that is equal to the amount of light given out through a solid angle by a source of one candela intensity radiating equally in all directions.
The American Heritage® Dictionary of the English Language, Fourth Edition Copyright © 2000 by Houghton Mifflin Company. Published by Houghton Mifflin Company. All rights reserved

The Lumen rating tells you several things about a projector. One with a lower lumen rating will work best in a room that is typically dark (i.e., no bright windows or ambient light to cause your image to look "washed out" and hard to see). A projector with a higher lumen rating will project bright enough for you to leave the majority of the lights on without sacrificing your image clarity or color. As far as performance and legibility are concerned, a projector that's bright enough to leave most of your lights on (especially in classrooms) can also help you make sure everyone is paying attention.

Consider the room you will use your projector in most. However, the higher lumen rating the better for projectors that will be traveling from room to room with different lighting situations.

2. Resolution - the maximum number of pixels that can be displayed, usually expressed as (number of horizontal pixels) x (number of vertical pixels). Multiply these two numbers together and that's the maximum number of pixels that projector has to display your images.

Some of the more common resolutions available today are:
VGA - 640 x 480
SVGA - 800 x 600
XGA - 1024 x 768
SXGA - 1280 x 1024
UXGA - 1600 x 1200
QXGA - 2048 x 1536

The resolution you need depends on the type of images you'll be projecting. For large fonts and graphics, an SVGA projector will work fine. However, if you're projecting video, background images with text, or detailed charts, a projector with XGA resolution or higher will make sure your message comes across legibly.

3. Contrast ratio - The ratio between black and white. Usually listed anywhere from 300:1 (300 to 1) up to 3,000:1 (3000 to 1) and anywhere in between. The contrast ratio tells you how many more times darker the color black will appear than the white. A low contrast ratio means that a true black may appear gray instead, especially in brighter rooms.

The difference in performance between a low and high contrast ratio also depends a lot on the human eye, the amount of ambient light, and the type of material that will be projected.

4. Aspect ratio - This is the ratio between the width of a picture and the height. This is listed as 4:3 (standard) or 16:9 (widescreen or "letterbox" style).

5. Throw distance - Tells you how far away or how close you can be from your projection screen. Make sure the projector won't require more distance to the screen than your room will allow. If you're not sure, the links provided below can help you out through the use of a "throw distance calculator."

6. Image size - How large or small the images can be, or how large a screen can the projector fill.

7. Keystone correction - When your projector or projection screen is at the wrong angle, images will appear "crooked", distorted and out of focus. Since it's not always possible to situate your projector perpendicularly to the screen, most are equipped with keystone correction. This correction can be digital, optical, vertical, vertical/horizontal, one or two-dimensional and manual or automatic depending on the make.

Overhead Projectors
Overhead projectors are stand-alone electrical/optical devices that allow you to present images onto a screen through transparencies. Light shines through the images and the optics of the projector focus it up on screen. However, they can not display opaque or solid images, such as pages from a book.

Key terms and definitions for overhead projectors:

1. Fresnel lens - A specially constructed lens that produces a soft-edged concentration of light. The Fresnel lens is about 1" below the surface of the stage glass.

2. Stage Glass - The glass surface where the transparencies are placed, between the light source and the optics.

3. Lens - Part of the optics that focuses the image for projection. There are three lens types:
a. Singlet - one lens
b. Doublet - two lenses
c. Triplet - three lenses

4. Head Assembly - The combination of the optics and mirrors. There are two head types:
a. Open Head - uncovered open optics, brighter image
b. Closed Head - covered, enclosed optics, stays cleaner

5. Thermal Switch - A temperature sensitive switch that senses heat build-up and removes power from the lamp if cooling fan fails.

6. Safety Interlock Switch - A switch that removes power to the overhead projector if the unit is opened. Prevents danger of being electrocuted.

7. Focal Length - The minimum distance from the stage glass to the lens. The focal length will determine the size of the projection at a given distance. A short focal length (about 11") will be a wide-angle projection requiring the projector to be fairly close to the screen. A standard focal length (about 14") will have a narrower projection, so the unit may be further away.

8. Throw Distance - The distance from the head to the projection screen.

Some additional features found on most overhead projectors today include a quick lamp changing system and a hi/low switch for lamp brightness. The lamp change feature allows you to keep a spare lamp inside. Should one go out during the middle of your presentation, you can simply flip a switch and change lamps without interruption. A hi/low switch not only reduces or increases lamp brightness; continued use of the low setting can extend lamp life!

Visual Presenters and Document Cameras
Unlike those big and bulky opaque projectors from years past, visual presenters are extremely flexible and highly powerful and presentation tools. They offer much value and affordability and they're much smaller and compact too.

You can display any solid object; printed/opaque documents or book pages, small 3D objects, photos, slides, negative and positive film, and even X-Rays! Examine the tiniest of objects in minute detail as if through a microscope, except everyone else in the room will be able to see it at the same time. A presenter with a zoom feature allows even closer inspection.

Visual presenters offer a color or black and white camera mounted on a moveable arm that you position over your document or object. Most include flexible lights for illumination. The base, or stage, usually has side or bottom lights.

Types of Visual Presenters/Document Cameras
There are two types of visual presenters: analog and digital. Depending on the type of input connections provided, you can display objects anywhere from a computer screen, TV monitor, plasma panel,or through a data/video projector.

Analog visual presenters produce images in NTSC video format (same as a standard VCR). They will connect to a TV or VCR where images can even be displayed and even recorded onto a VHS tape for later viewing.

Digital visual presenters use the same technology found in most digital cameras. They will typically have a color CCD (Charged Coupling Device) image sensor for better quality. Most plug directly into a data/video projector. Some can be connected through a computer. A digital-based image shown on a computer can be saved as a file (much like from high resolution scanner). Some have a built-in memory to store and capture images internally for later viewing.

Digital presenters can often produce a rapid series of images to form a short movie. Unlike real-time video recording through a camcorder, presenters are capable of producing a series of images in fps (frames per second-a.k.a. frame rate). This tells you how smoothly each frame will transition from one to another. Therefore, the larger this number is, the smoother movements will be.

Copyright © 2005 by Long's Electronics. All rights reserved.