Throw Distance and Throw Ratios Explained

What is projector throw distance?

When you are shopping for a new projector there are several important projector specifications which you will need to take into account when comparing the projectors’ spec sheets. These technical specifications and how they differ will affect the way in which your projector performs, and how well suited it is to the presentation environment you will be using the projector in. One major specification which relates to the projector’s lens, which it is useful to understand, is the projector’s throw distance.

What throw distance is and how it is calculated will affect how you use the projector. This Bamboo AV advice article should give you a detailed understanding of everything to do with throw distance, including short throw distance lenses, long throw distance lenses and applications where shorter and longer throw distances may be required.

Calculating throw distance

A projector’s throw distance is the distance between the projector and the image on the screen (i.e., the distance that the image is “thrown”). Throw distance is calculated by measuring the distance from the projector’s lens to the projection screen that the image is being cast onto. Throw distance is the basis for determining the projection screen size possible for use - a common standard for projector throw distances is one foot (30.5 cm) of projection screen width to every two feet (61 cm) between the projector’s lens and the screen. A smaller throw distance as opposed to a larger throw distance means a smaller possible distance between the projection screen and projector, if the size of the projected image is kept constant.

Calculating throw distance

What is a projector throw ratio?

The throw ratio of a projector is the result of dividing the distance between the projector’s lens and the projection screen by the width of the image being projected, or more simply:

Screen width x Throw ratio = Throw distance

The throw ratio figure provides projector owners with all they need to know when deciding where to place their projector or projection screen. For example, if you know that you want to use a projection screen that is ten feet wide and you know that your projector’s throw ratio is 1.8:1 (which means 1.8 ft of throw distance per foot of screen width) then you should place your projector 18 feet away from the projection screen since 10 multiplied by 1.8 equals 18.

Why are throw distance and throw ratio important?

A projector’s throw distance is vital in determining what size projection screen to use and how far from the projector to place it. By measuring the throw distance you can determine the positional adjustments needed to accommodate a predetermined projection screen size or projector placement. If these alterations aren’t possible (for example, if the projector is being installed in an auditorium and needs to be at the back of the hall) then you may need an extra or different lens to increase or decrease the projector’s throw distance. If the projector is too close to the screen then a short throw lens may be required, otherwise the image may appear pixelated. This can be an issue with interactive whiteboards where the projector is often placed close to the board. On the other hand, if a projector is placed too far from the screen then the projected image may appear unclear if a long throw lens is not installed. Some projectors are specifically designed to have either long or short throws distances, and thus ship pre-installed with specific these specific lenses. However, the majority of projectors will need an external lens to be installed to accommodate projector placements at extreme distances close to the projection screen or very far away from it.

The advantages of short throw distance lenses

A shorter throw distance will result in a bigger picture being projected, if the distance between the projector and the projection screen is kept constant. For further effect a short throw lens can be used to project an even larger image. Some projectors, such as the Hitachi X275, come pre-installed with a short throw lens and can thus project a 48-inch diagonally wide image from only 4 feet way. Projectors with short throw distances are suited to those people that require portability, such as road warriors, or for those people that need to use their projector and screen in smaller environments such as modest home theatre rooms, hotel rooms or small meeting rooms.

The advantages of long throw distance lenses

A longer throw distance allows for smaller, sharper images to be projected from further distances away. A longer throw lens is preferable if you intend to use your projector in large, expansive surroundings such as in large conference rooms or houses of worship where the projector is required to be hidden at the back of the building. In these situations a long throw lens will most likely be required to make sure that the quality of the projected image is maintained while moving the projector further away from the screen.

We hope that this Bamboo AV advice article has been useful to you!

Back to Audio Visual Article Index