LCD Projectors Explained - LCD projectors use Liquid Crystal Display (LCD) panels, similar to those found in watches, clocks, games and other display devices. A light source is shone through the LCD panel which is covered in a grid of individually controllable cells (picture elements). Each LCD picture element is equivalent to a pixel in the display resolution, ie. an SVGA resolution LCD projector will have a grid of 800 wide by 600 high individual picture elements. Each individual picture element can be faded between 100% transparent and 100% black, controlling the light level emitted for each particular pixel. All but the cheapest LCD projectors will actually have three of these LCD display units, with the light source being split (using dichroic mirrors) into separate Red, Green & Blue (RGB) streams, each of which is then fed through its own LCD display panel, thereby controlling the amount of red, green & blue light hitting each pixel. By controlling the relative mixes of these three primary colours hitting each pixel all other colours can be created.

Note: This is similar to how a traditional CRT (ie. non flat screen) television works, in as much as they use clusters of three pixels ( one each of red green & blue ) on the screen which are then illuminated to varying levels. As the clusters are small the eye perceives the combined effect of the three which merge to create the colour. Old style Barco (and similar) projectors also used this technology, although they had three separate lenses (one for each colour) on the front which had to be focussed by a technician

Back to LCD projectors - Once we have fed our three primary colours through the LCD display panels, the three light beams are then recombined (once again using mirrors) and focussed through the projector lens giving a full colour image. This image can then be focussed & zoomed using the standard LCD projector lens. These lens are built in and are generally not interchangeable in the way that other projectors (eg Kodak Carousels) are. Typical zoom ratios are 1.7 - 2.1. Digital zoom is also possible in some LCD projector models. There are certain projectors available with interchangeable lenses but these are very specialist and tend to be prohibitively expensive at upwards of £3000 compared with less than £1000 for a unit with a built in lens. If you have specialist projector enquiries then please call Rock at our Edinburgh office on 0131 558 3824.

LCD projector technology has advanced hugely over the past few years. It previously has had drawbacks with a slight "screen-door" effct being visible (ie. the gaps between the LCD picture elements were visible) but this is no longer an issue. LCD projectors are considerably brighter than equivalent rated DLP (Digital Light Processing) projectors and we do not find the improved contrast ratio that DLP projectors offer to be particularly noticeable. LCD projectors are now very compact, light and easy to use. Our current workhorse Mitsubishi SVGA projector is not much bigger than a phone book and not much heavier for that matter. Most decent modern units are plug and play and will autodetect a wide range of input signals and sources. We typically find that customers use laptop computers, DVD players, VHS players & games consoles as video / data sources. Basically, anything which can output a video / data source can be used. Please note that our projectors (like most modern units) are not equipped with speakers suitable for use in public situations being little better than those found on a mobile phone or computer chassis therefore additional sound equipment will be required for applications with audio.

Placement - Optimal placment is for the screen to be placed centrally at a 90 degree angle to the projection device, with the bottom the screen and the lens being level. The distance between the screen & unit should be twice the width of the screen image. It is possible to compensate for situations where the projector & screen bottom are not level using the digital keystone facility. Our XGA units allow for horizontal keystone adjustment if the projector cannot be placed centrally. Keystoning (in case you are unaware) results in the image being distorted and no longer rectangular. eg. If you are projecting from below the screen the image will be wider at the top than at the bottom. Digital keystone allows for the image to be adjusted to restore the desired rectangular shape onscreen.

Projector hire Aberdeen / Renting multimedia equipment / Digital projections from laptop computers