Think your big TV is impressive for home cinema? A projector can create a picture that's measured in feet, not inches, and be every bit as sharp and colourful as an LCD screen. Plus, on a summer's evening, you can take it outside for outdoor movie viewing with friends.
How does a projector work?
There are two different types of projector, LCD and DLP. They work in slightly different ways.
LCD projectors - Liquid Crystal Display projectors work by splitting light from a powerful lamp into its red, green and blue elements using a prism. Each colour is then sent through an LCD filter to create that colour channel for a frame, and the image is recombined through another prism before passing through a large magnifying lens to beam it out of the front of the projector.
DLP projectors - Digital Light Processing technology is substantially different from LCD technology. In a DLP projector, the image for each frame is broken down into the colours red, green and blue before processing. Light is shone into the project through a 'colour wheel', which spins between red, green and blue fast enough so that each colour is displayed at least once per frame displayed. This light is then focused on to an array of tiny mirrors, one for each pixel in a picture. The mirrors are synchronised to move with the colour wheel, so that the entire green picture is displayed through the front lens, then the blue one and so on. The images change so quickly that the human eye composites them into a single, full colour picture.
What's the rainbow effect?
The rainbow effect is well documented, but relatively rare. It happens to some people using DLP projectors where the colours don't change quickly enough to keep up with the on-screen motion, and red, green or blue halos can be seen around objects on screen. The rainbow effect is less obvious in newer DLP projectors than in old ones, because the colour wheel spins incredibly fast, showing each colour up to 10 times per frame.
Do I need a screen to use a projector?
It's a good idea to use a screen, or paint the wall you're planning to use in a special paint. The picture quality from a projector depends on the colour of the surface it's being shone on to, so anything remotely off-white will affect the overall look.
What resolution do I need?
Projector resolution can be confusing, since it's often referred to in terms of pixels, such as 1280x800, or in the older notation for computer monitors, like VGA, WXGA and so on. Increasingly, though, most projectors are following the HDTV standard, and support resolutions up to 1920x1080, otherwise known as 1080p.
Are replacement bulbs expensive?
It's worth looking into the cost of replacement bulbs before buying a projector, as the specially designed filaments can be costly.
It's worth noting that projector bulbs get very hot during use, and often need to be cooled with fans. Look into specific reviews for a projector you're interested in to make sure it's quiet enough to use for home movies.
If the projector is not positioned absolutely straight on to the wall or screen it's facing, even the slightest incorrect angle will be magnified and show up once it's turned on. Most often this shows up as 'keystoning', when the sides of an image begin to converge at the top or bottom.
Most projectors have a lens that can be adjusted to overcome this, and many can detect keystoning and automatically correct for it. The best place to put a projector is on the ceiling.
A special mount that fixes a projector to the ceiling will not only get you the best picture quality, but also keep it out of the way when you're not using it. If you do plan on this, it's worth investing in a projector with a remote control.
DVI - Digital Video Interface is the standard link between a PC and a monitor, and is often found on projectors too. Also look for projectors with HDMI inputs, or VGA ports.
SVGA - this common resolution equates to 800x600 pixels. Other common resolutions are VGA (640x480) and UVGA (1024x768). The best projectors use the HD standard of 1920x1200 pixels, also known as WXGA. It's worth nothing that because the LCD screen or DLP mirrors in a projector are so tiny, even low resolution projectors can appear sharper than they do on TVs or monitors with the same number of pixels but smaller actual displays.