When you buy a camera, you want to know what kind of lens it has and what kinds of lenses you can get to enhance your picture-taking ability. With today's projectors, Zoom lenses are pretty standard. The important question is how much a lens's f-number — the smaller the number, the more light - changes at different zoom settings. If the change is minimal your image will remain uniformly bright regardless of lens position.
Types of Lenses
Glass is the optimal filter for projecting images and will give you a clearer picture. However, glass is heavier than the lightweight plastic lenses that are now being manufactured, so pick plastic if you are going to be on the road a lot.
Optional lenses are also available through some manufacturers and resellers. If your conference room machine will be called upon to project at different positions, angles, and brightnesses, you should ask about interchangeable lenses.
Zoom Lens - Most projectors have a zoom lens. This allows for the adjustment of the image size without the need to move the projector. The type of zoom lens varies from projector to projector. Some zoom lenses are manually operated. Power zooms are motorized. This is a nice feature if you wish to work remotely from the projector. Optional lenses allow you to choose the specific focal length of lens. Without a zoom lens, the only way to adjust the picture size is move the projector forward or back.
HELPFUL HINT: Many of the micro-portables have zoom lenses with limited range. A unit with a zoom factor of 1.2x will only let you adjust picture size by 20%. You can often move the projector a foot or two either way and accomplish the same adjustment. Nevertheless, if you have a fixed screen size you are trying to fill, even a limited range zoom will make it easier to fine-tune the image size to the screen.
No Zoom - No zoom may be necessary if your projector will always stay a fixed length from the screen.
Manual Zoom - Some zoom lenses are operated manually, which require you to be near the projector as you adjust the image.
Power Zoom - Power, or motorized, zoom lenses let you adjust the image remotely.
Digital Zoom - Magnifies an image through digital interpolation of the pixels. This magnification technology is less vivid than the magnification abilities of an optical (multi-focal length) zoom lens.
Optional Lenses - With optional lenses, you can choose the specific focal length that suits your needs.