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SHORT THROW PROJECTORS

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Projector throw distance

When researching DLP or LCD projectors,  you will most likely have seen the "throw distance" quoted on the projector specification sheet. A projector's throw distance refers to the length between the projector's lens and the projection screen -- i.e. from how far away the image can be projected while still staying in focus.  You may also have seen projectors referred to specifically as short throw projectors" or "long throw projectors".

Throw distance can be determined by simply measuring the distance between the projector and the screen it is projecting on to. A typical projector throw distance -- to ensure an optimal image size -- is one foot of screen width for every two feet (2') between the projection screen and the projector.

The lens that the projector uses can alter this ratio substantially as projector lenses can be tailored to render small images over long distances, or big image projections over a comparatively small distance.

This ProjectorSourceCanda.ca article considers the second of these two examples -- projecting an image onto a screen or surface from a very short distance away. This is what is known as a short throw projector lens.  Projector Source Canada will explain how short throw projectors work, provide ideas on how they can be used to add flexibility to your multimedia presentations.

What is a short throw projector?

A short throw projector is a special type of projector that has been specifically designed to project larger images when there is only a very small distance between the projector and the projection screen.  The reason for this could be for cosmetic reasons such as wanting to hide the projector, or could be due simply to the room size constraint.

While standard projectors can be adapted for short throw purposes by installing an external short throw lens, specific short throw projectors are manufactured with the short throw lenses already installed. These are considered to be the best option for short throw projection.

There are several examples of dedicated short throw projectors on the market and specifications can be found on projectorsourcecanda.ca. These projectors have been specifically designed to project images from close to the projection screen. By using an extremely short throw lens and a special short throw optical system, these short throw projectors can project a 60-inch wide (diagonal) image from only five feet away.

The image below shows the difference in positioning between a regular projector in the top image, and a short throw projector in the bottom image. Note than for the regular projector, the projector has to be placed back in the audience, which can cause problems with shadows being cast on the screen. The short throw projector is able to project the same size image tough it can be placed in front of the entire audience.


 

How does a short throw projector work?

Short throw projectors function in much the same way as any other projector although the optical system in a short throw projector may be tweaked slightly in some models which may have an ultra-short throw optical system and a free shaped lens and mirror.

The difference, and what allows a short throw projector to project high quality images from an extremely short distance from the screen, is the magnifying qualities of the short throw lens being used. These magnifying qualities are determined by the short throw lens's shape.

What is the difference between short throw and long throw lenses?

The physical shape of the projector lens is what differentiates short throw and long throw lenses.  The lens's shape fundamentally alters the size of the image projected.  A long throw lens can keep the projected image small and tight when the projector is placed away from the screen.  

This type of lens is applicable in situations where the projector needs to be placed hidden away at the back of the building such as in a large room, church or similar room layout.  If this type of lens were not used then the projected image would appear too large and too unclear.  Similarly, if a short throw lens were not implemented in situations where the projector is placed close the screen then the image would appear too small to be read clearly.  In a short throw projector, the lens is slightly bent to allow an image of a greater size to be projected.

Limitations of regular projectors

Standard projectors are hindered by their ability to adjust to varying room sizes and changing presentation situations.  Problems will arise if the projector is not positioned at a set distance and a set angle to the screen. 
While it is sometimes possible to use lens shift and zoom lens capabilities to try to remedy these problems, in situations where the projector is close or far away the image may not be optimal.

Where are short throw projectors beneficial?
There are numerous benefits from using a short throw projector. The primary advantage is the flexibility it provides users when placing projectors in a small room since a short throw projector can project a large image from a short distance. They are particularly suitable for schools, small businesses or any other intimate environment.  This includes:
  • Smaller sized classrooms
  • Home theatres with limited space
  • Small conference rooms, such as those often found in hotels
  • Advertising stands and booths at exhibitions
  • Small home theaters
A particular advantage for individuals that frequently use projectors is short throw projectors help eliminate any eyestrain as the light shining from the projector does not shine directly into the presenter's eyes. This is a big plus for teachers who might use projectors all day long!

A further benefit is that since the image has to travel a shorter distance, the effect of light ambiance is lessened, thus resulting in a much brighter image.

Short throw projector pricing

It is possible to turn any standard projector into a short throw projector by purchasing and installing an external short throw lens.  Price can vary from $1,000 to $6,000 per lens depending on the quality of the short throw lens and the projector model that the lens is made for. Generally, the more expensive the lens, the larger the output and sharper the image that can be projected from a shorter distance from the projection screen.

Installing an external lens can potentially void the warranty on your projector, and that not every projector can accept external short throw lenses. Therefore, when possible purchasing a dedicated short throw projector is advisable.

Short throw projectors prices range from $500 to $5000. The more expensive short throw projectors usually offer a better quality lenses and thus a bigger, better quality image when closer to the screen. A good guideline is that as price increases, you can move the projector closer to the screen without reducing the quality of the projected image.

We hope you enjoyed this article by Projector Source Canada.  For more information or to purchase a display and projector for your business or home, visit us online at http://www.projectorsourcecanada.ca

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