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  Lens type & Zoom


Different projectors use different lenses and have various zoom ratios.
When choosing a projector, you should have an idea of where you can install it and what size image you would like to achieve. So you need to ensure the projector you buy is able to achieve this.

Lens throw ratio

There are many different lenses used in different projectors. The main difference between them being the throw ratio
The throw ratio is the ratio between the throw distance and the image width, with the throw distance being the distance between the lens and the projection screen.

Throw ratio

For example a projector with a throw ratio of 2.0:1 would need 2 meters of throw distance for 1 meter of image width. For an image 2m wide, the projector would need to be 4m away from the screen.

Types of lenses

  • Standard throw lenses: there is no absolute standard ratio but the most common ratio available on projectors is around 2.0:1. As explained above, this means that you need to place the projector 4m away to get a 2m wide image.

  • Short throw lenses: short throw lenses allow you to place the projector much closer to the screen. For example a 0.8:1 short throw lens allows you to place the projector 1.6m away to achieve a 2m image.
  • Ultra short throw lenses: some projectors have ultra short throw lenses allowing them to be installed on the wall just above the screen or interactive whiteboard. The throw ratio can be as low as 0.1:1. This means the lens only needs to be 18cm away from a 77" diagonal interactive whiteboard.
    This is useful in classrooms for example because the teacher can stand in front of the board to write or interact without causing a shadow.
  • Long throw lenses: long throw lenses allow you to place the projector further away from the screen. With throw ratios of around 2.5:1 up to 9.0:1 or more, they are useful in large venues such as theatres or conference rooms.


Examples of throw distance for a given throw ratio - To achieve a 2m wide image

Throw Ratio Lens Type Throw distance

Ultra Short Throw


Short Throw

Short Throw


Long Throw

Long Throw

Ultra Long Throw


Optional lenses

If you have specific requirements regarding the throw distance and image size, you may need a projector capable of using optional lenses.

While the majority of "standard" projectors are suitable for most applications, there are situations where the projector needs to be installed closer or further away from the screen while retaining a specific image size.
In these situations, you can choose to buy a projector with an optional lens.

Optional lenses as their name suggest can be installed and de-installed from the projector.
Projectors that take optional lenses usually have a choice of 3, 5 or more lenses with a variety of throw ratios, so you can usually find a lens that will allow you to install the projector exactly where you want it.



You probably are already familiar with zoom from owning a digital camera or camcorder. It basically allows you to increase the size of the object on camera without you moving.

With projectors the principle is the same, except it's the projected image size that you can increase without moving the projector.

Most projectors have zoom lenses, giving you some flexibility. The exception being short throw and ultra short throw projectors: they usually have fixed lenses where you need to move the projector forward or back to achieve a given image size.

Why is a zoom lens useful?

The main reason a zoom lens is useful is because it gives some flexibility in where the projector can be installed. Once you have installed a projector at the point it needs to be, you can tweak the image size to fit the screen exactly without having to worry about moving the projector 1cm back or forward.

In mobile applications, the zoom allows you to adapt quickly to different venues where the screen size may be different or when you can't predict how far back the projector can be placed.

Zoom ratios can vary depending on the projector but the most common is 1.2:1 (or 1.2x). A 1.2x zoom allows you to vary the image size by 20%


Examples of image height with a projector with 1.2x zoom at various throw distances


Digital or optical zoom?

An optical zoom lens physically extends to magnify the image while a digital zoom lens will digitally crop the image and enlarge the result of the cropping.

An optical zoom will not affect the quality of the image but a digital zoom will because to make the cropped area bigger, the process involves interpolating (creating) pixels to complete the image.
This can affect the quality of the image so it is always preferable to use optical zoom rather than digital zoom.

Manual and powered/motorised zoom

Some projectors offer manual zoom while other offer powered or motorised zoom.

On a manual zoom lens, you will have to manually adjust the lens by either rotating a zoom ring on the lens or adjusting a lever.
On a motorised zoom lens, you can adjust the zoom from the projector remote control or by pressing a button on the projector itself.