Digital projection systems come in two different varieties: LCD & DLP.Modern LCD projectors use 3 screens, usually about 0.9-1.5" diagonal, to project the three primary light colours (red, green and blue). The light source (lamp) is separated into the primary colours using prisms, the resultant light is then passed through the LCD panels which are made up of thousands of individually controllable panels which can either block the light, let is pass through or partially close to allow some of the light through. Each panel corresponds to a pixel on the projection, so each pixel is made up of three panels (one from each screen). After passing through the screens, the light is recombined using another prism then passes through the projection lens to form an image.
DLP projectors work on a slightly different principal. A single panel of thousands of hinged mirrors which are individually controllable is placed in alignment with the light source. The mirrors are rotated to allow different amounts of light through. Colour is added by having a rotating three coloured disk in front of the mirror panel, the mirrors aligning themselves to allow light through at the appropriate time.
Which to choose? In terms of data projection performance the LCD system wins every time but if your projecting video (for example home cinema) then not quite perfectly crisp image that DLP gives is the better option. DLP projectors also tend to be cheaper than LCD.
Modern projectors fall into 3 categories of resolution. Which you choose depends on the application and the resolution of the computer equipment you use. If you're using Windows then you can see the resolutions by right clicking on the desktop, selecting properties then settings. The resolution is shown in the bottom right hand corner of the settings window as 2 figures. These are the horizontal and vertical resolution and will usually be one of the following:
800 x 600 - SVGA (Super Video Graphics Array)
1024 x 768 - XGA (eXtended Graphics Array)
1280 x 1024 - SXGA (Super eXtended Graphics Array)
Choose a projector which matches the resolution you want to use. Note that on laptops there is a "native" (built in) resolution which the laptop is best at displaying, other resolutions will use compression and expansion. Choose a projector which matches your laptops native resolution. Bear in mind the resolution that your presenation was designed in. If it was designed at 1024 * 768 then it should be displayed in the same resolution.
How bright does it need to be?
There are two major considerations when looking at the brightness of a projector (measured in ANSI lumens).
i) The ambient light prevalent when you are actually giving your presentation. This should be as dark as possible but bear in mind that your audience may well be taking notes so cinema light levels will be too low. Artificial light is always less invasive than natural light so you're better off closing the curtains and switching the lights on if possible.
ii) Throw distance. This is the distance from the center of the projector lens to the screen. The further away the projector, the larger the image and the more the set amount of light emitting from the projector is dispersed. If you double the projectors distance from the screen, you get an image four times bigger (twice as wide and twice as high) and only 1 quarter the brightness. As a guide, projectors of around 500 ANSI lumens are good for a small presentation to half a dozen people, 700 for 20-25 people and 1000 upwards for larger groups. Remember, the larger the audience, the larger the room, the larger the screen and so the further away and brighter the projector will need to be.
If you take the average portable computer as being about 2.5-3kg then the definition of portable as far as projector manufacturers are concerned is a bit subjective (anything up to about 8kg). Add the case, cables and accessories and you'll soon find a "portable" projector becomes an exercise in stamina over any distance. This is something to consider if you envisage having to carry the projector for any period of time. Most hard cases are available with wheels on one edge (like a golf bag) but remember that these are very delicate machines and therefore the use of wheeled cases should be restricted to relatively smooth surfaces.
Today, all projectors come with extensive sets of leads allowing you to connect up to virtually any source including computer, video, DVD etc. If you are upgrading, you no longer need to specify, and pay extra for, cables to connect to your source.
Can I take it abroad, what about power requirements?
Modern projectors allow you to connect to virtually any mains power source in the world, they can automatically adjust from 100-250V and 50-60Hz. At most you may need to purchase an adapter to connect to the available power source. This has come about mainly because it's no longer economically viable to manufacture different models for different countries although you do still get cosmetic and model number differences around the world.
What sort of screen do I need?
The advantage, above all else, of modern projectors is the high light output. This means that in practical terms, virtually any screen will do, even a white wall can give good results in the right lighting conditions. That said, a decent screen can make all the difference to your presentation and make your image look that much more professional. So how do you choose? First and foremost is audience size. A small screen is better for small audiences as there is a limit to how much the eye can see at once and a smaller image will be brighter as there is less light dispersion, you don't want to make your presentation less personal by having everyone sit thirty feet from the screen. Be wary of high gain screens, the rule is, the higher the gain, the narrower the viewing angle so if your audience is somewhat spread out, use a normal gain screen. Unfortunately, screen size is all a bit subjective and there's no set formula for the ideal screen to audience size.
If you're on the move, make sure your screen is easily portable.There's no point in a ten foot screen if it won't fit in your car and you don't want to look foolish fumbling about with a screen you need a winch to erect.
Some projectors come with a zoom lens which allows a little more leeway in how far a projector is placed from a screen to project a given sized image. This can be very useful for the projector on the move, so is worth considering. These zoom features are, however, limited to quite a small range. The reason for this is the added complication in the mechanics of the projector and the reduction in performance. The mechanical side is simply the fact that the projection lens has to move in order to zoom in and out. Because the lens needs to be very accurately aligned, the more movement allowed, the more the risk of lateral movement which causes focus problems and distortion. Also, the ideal shape of a lens changes as focal length changes (which is why zoom lenses are not considered to be as good as fixed focal length in camera circles) and so there is always a compromise with zoom lenses. Lastly all lenses have a single point in front of them at which they are in focus. The area in front of and behind that point which is so close to being perfectly focused that it looks focused is called the depth of field (you can see the effect by looking at a photo of someone which is focused on the person but everything behind them is out of focus). This depth of field decreases as the focal length increases, which makes focusing harder. You needn't worry about this as these built in limits in projectors mean that you'd never notice any picture degradation anyway.The performance is just a case of the further the lens is from the light source (the projectors lamp) the less light gets through. So, the longer the distance, the dimmer the image. Again, because of the limited zoom, there's no perceptible loss of brightness.
Make sure your office/company insurance covers you while transporting, setting up and using equipment outside the office, bearing in mind that many insurance policies have clauses requiring you to inform the insurer of any equipment you own or use over a certain value.
So the specs. to look for:
- Resolution - Try to match the computer resolution and design you presentations with this in mind.
- Brightness - How large is you audience and what are the lighting conditions.
- Portability - Are you going to be travelling with the projector? If so, choose a light one.
In accordance with normal business practice you should inspect the equipment on receipt and be sure of its condition before signing for it.