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Projection Lenses

Is your projector's standard lens right for your application?

Video or data projectors only give a limited projection screen image size. By exchanging the unit's lens (LCD or DLP) for an ancillary lens the projector can be placed further or closer to the projection screen. The advantage of this is that the size of the image can be kept within the confines of your screen from a greater distance while putting the data/video projector in a more convenient position at the rear of the room. Or, the projector can be placed closer to the screen to provide a larger image area in a smaller room. If your projector does not give you the image size you really want then you may need a new lens.

Create large images in tight spaces

You may have heard about throw distance, but what does it mean to you? A common throw distance is one foot of screen for every two feet of space between projector and screen. That is a general rule for projectors with a standard lens. Projectors with short throw lenses are able to create larger images with less distance between projector and screen.

When is a short throw lens beneficial?

A short throw lens (wide-angle lens) allows users to create the big picture they want, in a tight space. Short throw lenses are commonly used in environments such as small conference rooms, small classrooms, trade show booths, and small home theaters.

What is the difference between a short throw and long throw lens?

While short throw lenses help create larger pictures from shorter distances; long throw lenses help create smaller, more viewable images from greater distances. A long throw lens is advantageous in large venues, particularly in fixed installations. Churches often require long throw lenses for worship spaces, because the projector is often mounted far away from the screen, behind the congregation. Without a long throw lens, the image would be too large.

What about zoom lenses?

Manual or digital zoom is a feature on many standard, long, or short throw lenses. Without a zoom lens, the only way to adjust the picture size is to move the projector forward or backward. The zoom feature allows for larger or smaller images from the same distance, much like a zoom lens on a 35mm camera. If your projector will always stay a fixed distance from the screen, a zoom lens may not be necessary.

How do I calculate what size lens I require?

First you will need to know the following information:

1. Projection distance in inches (measured from the front of the video projector housing to the screen).
2. Projector LCD panel size in inches (diagonal or width).
3. Screen size in inches (diagonal or width).

Next, use the following formula to determine your required lens focal length:

NOTE: It is very important that you be consistent. If you use the diagonal screen size measurement, then you must also use the diagonal measurement for the projector LCD panel size. If using screen width, then use the LCD panel size width. Also, if you are working in inches, then you need to do all of your calculations in inches. You can convert the lens size to millimeters at the end. Please note the following information:

Screen Diagonal x 0.8 = Screen Width
LCD Diagonal x 0.8 = LCD Width
1 Foot = 12 Inches
1 Inch = 25.4 Millimeters