Zoom lens

A zoom lens gives you the ability to set the projector at a convenient location, and adjust the projected image size. This allows the same adjustment that you get by moving a projector closer and further away from a screen, without actually moving it

Zoom Lens Specification

Zoom Lens capability is detailed as a ratio between its standard size and its maximum size. E.g. 1.2:1 details a maximum of 20% zoom from the original size. Zoom lenses range from 1.1:1 up to 2.0:1 or more.

Contrast Ratio

Contrast is the ratio between the brightest and darkest areas of the image. The two types of technology LCD and DLP have very different maximum contrast ratio's.

Contrast ratios should be high (1500:1 or higher) to get the best video or photo image. For computer graphics and data presentation, 400:1 is usually ample.

LCD tend to be around 400:1 whilst a dlp can achieve 2000:1.

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Screen Size Matters

The larger the screen the more power your projector will need. A small screen of say 50cm may require a 2000 lumen projector whereas a 100cm may require 3000 or 4000 lumens.

Standard Types of Projector

The standard two types of technology used in projectors are LCD and DLP.

LCD - Liquid Crystal Display is a thin, flat display device made up of any number of colour or monochrome pixels arrayed in front of a light source or reflector

DLP - Digital Light Processing is a technology used in projectors and video projectors.

LCOS - Liquid Crystal On Silicon

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Projector Resolution

The resolution of a projector is the amount of detail that a projector may show. The larger the numbers the greater the potential definition of the image. Different dimensions of resolution are given abbreviated names

Standard Screen Projector Dimensions (4:3 ratio)

• SVGA 800 x 600
• XGA 1024 x 768

Home Cinema Projector Dimensions (16:9 raitio)

• WVGA 854 x 480
• WSVGA 1024 x 576
• WXGA 1280 x 720

Wireless projectors

Wireless projectors are catching on fast. No more messy cables, quicker set-up and the ability to switch between presentations on different laptops on the fly are all appealing prospects.

Progressive Scan

A Progressive Scan converter takes an Interlaced Scan formatted signal, and converts it to a superior signal where the complete picture is drawn from top to bottom in one pass. This results in less flicker and smoother motion.

Most TV signals are sent in an "Interlaced Scan" format. First the display device (TV or projector) displays the image's odd lines, one at a time from top to bottom. This takes about one sixtieth of a second. It then fills in the even lines, taking another one sixtieth of a second. So the full picture is first drawn with half its information missing, which is then filled in. In all the process takes 1/30 of a second per complete frame.

Some DVD players have progressive scan converters built in, and may have the option to output in either progressive or interlaced scan modes. Some projectors (in particular the specialist home cinema projectors) also have progressive scan converters built in. Alternatively, it is possible to purchase an inexpensive progressive scan converter as a separate unit which can convert your TV and DVD signals.

Multiple Computer Ports

If you want to connect multiple computers or video sources to the projector simultaneously, you will need multiple input jacks to accommodate this. For example, you may want to connect a notebook computer and a desktop computer to support two consecutive presentations, or two different presenters. If your projector only has one computer source, you'll have to unplug the notebook and plug in the desktop between presentations. Check to make sure the projector has enough connections to support your typical use.

Video Signal Standards:

Most business projectors accept composite video, S-video, and computer/RGB signals as three types of signal transmission.

Most projectors also recognize YPbPr/YCbCr component video as well. However, there are two all-digital standards known as DVI and HDMI. Many new computer video cards feature DVI or HDMI output, which allow the user to keep the signal in the digital domain and eliminate analog to digital conversions.

If you are interested in optimizing video performance and you have a video source that offers DVI or HDMI output, check to see which of the projectors on your list possess a digital input. The spec sheet may say HDMI, DVI-I, or DVI-D.

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