Short focal length projection
It’s a video projector’s focal length or ‘throw’ that determines the distance between the projector and the screen.
There are 4 types of focal length: Ultra-short, short, classic and long.
Also called ‘wide-angle’ or ‘short throw’, short focal length projection makes it possible to project large images with the projector only a short distance from the screen.
➡ Video projectors with a short focal length can be installed on a table for temporary operation, or fixed to the ceiling, or placed above the projection surface. Some are compatible with 3D or can include a TNT decoder.
Comparing short focal length and ultra-short focal length projectors
The lower the projection ratio, the shorter the focal length. Video projectors with an ultra-short focal length (‘ultra-short throw’) are so close to the screen that they’re practically touching it.
– Ultra-short focal length: Projection ratio less than 0.3
– Short focal length: Projection ratio approximately 1.
➡ The projection ratio is the relationship between the size of the image and the distance between the projector and the screen. It’s the distance between the projector and the fabric, divided by the size of the screen.
The projection ratio can be used to determine the position of the video projector depending on the desired image size (or vice versa). Suppliers of video projectors state the minimum and maximum projection ratios. You can find the appropriate projection ratio using calculation tables.
What is short focal length projection for?
This type of video projector is ideal for professional use, making it possible to have a large image in a relatively small venue such as a boardroom or classroom.
Also, because the distance between the projection surface and the video projector is short, the speaker will not be dazzled while addressing the audience, and will not block the beam of light if he or she moves.
It is also suitable for personal use in a home environment.
The pros and cons of short focal length projection
The advantages of short focal length projection:
– Easy to install, and very practical (can be placed alongside electronic equipment such as an amplifier or a Blu-Ray player)
– Can be used in small rooms
– Better light yield because the projector is located next to the screen. It is quite possible to watch films during the day or with the lights on.
– Reduction of shadows, because the short distance between the video projector and the screen means there is little risk of anything getting in the way
– No intrusive noise, because the projector is further away from the viewers.
– Better than a television, with excellent display technologies
– Because the video projector light source is very close to the screen, there is less risk that children will look at it, so it’s safer.
– One of the few disadvantages is a higher price than for a standard video projector. The main reason for this is that a better optical system is required for good image quality.
– With ultra-short focal lengths, parallax correction combined with tangential projection will cause distortion to the image unless the screen is absolutely flat.
What types of screen can be used with models with short focal length?
The entire ORAY range can be used with these projectors.
What types of screen can be used with models with ultra-short focal length?
Basically, screens with fixed frames. Roll-up screens, even if flat, will inevitably cause distortion of the image at the edges. A partial solution to this problem is to use tensioned screens. However, this will never be more than an acceptable compromise, and may sometimes prove unacceptable for very demanding viewers or applications.
➡ It is therefore important to choose a suitable screen, which will ensure good image quality in the long term.
The two types of screen that work best with ultra-short focal lengths are:
– Screens on a fixed frame, which keep the screen perfectly taut in the long term.
– Roll-up screens that are tensioned to keep the projection surface flatter.
ORAY offers many projection screens that are suitable for ultra-short focal length projectors:
|Orion in-ceiling tensioned||Roll-up||Acceptable|
|Cinevision 1||Fixed frame||Recommended|
|Cinevision 2||Fixed frame||Recommended|
|Le Mask||Fixed frame||Recommended|
|Cadre HC||Fixed frame||Recommended|
|Special video||Fixed frame||Recommended|