Projector throw ratio refers to the ratio of light that projects out of the projector compared to the amount of light reflected back on to a surface that is near the projector”.
Why do this? The projectors used in modern classrooms are placed at a distance from students. The goal is for as much light as possible to project on to the walls and ceiling. This makes it impossible for most students in these classrooms, even those sitting right next to the projector, not be able to see projected material. This creates an embarrassing situation- students can’t see what’s happening on screen and are forced into awkward interactions with each other or with their teacher.
A way around this is to project the computer screen directly into the ceiling or wall. This requires a projector with an optical axis that is aligned parallel to the surface of the ceiling, wall, or other surface that it is projected on. This makes it easier to see if you are in an environment where light reflection from walls and ceilings will be a problem for students.
Also read: What is contrast ratio in projector?
The lens size of a typical projector can be adjusted to achieve this same effect (“throw ratio”) for any given distance depending on how far the image needs to project. The farther out from the center of the lens, the more light reflects back at students and/or faculty. The closer the lens sits to the surface, the less light reflects back.
Thinking back to high school physics, think of it like this: An object traveling in a straight line will reflect and refract off of surfaces. The angle at which it leaves is determined by how far away the surface is from its center. The angle at which it reflects off of the surface is determined by the angle at which the object hit the surface. If you imagine this scenario with a line of students sitting in a straight line and in their seating position (as most people do in high school physics class), then the farthest away students will see the screen first, followed in order by those more closely to them.
Typically, a lens will have to be adjusted toward and away from light sources for most of its travel through space. Most lenses will have some amount of flexiity when it is adjusted because any optical property has an upper and lower limit.
The key here is to find the point on the lens where its maximum distance away from a light source is the closest to the projector (without getting too close and causing distortion). This is what we call the “throw ratio”.
Read more: What is a good lumens for a projector?
It is also important to look at how near an image can be projected onto a surface. If you remember from your physics classes, when something travels in a straight line away from you, it appears smaller and smaller. There’s some difference between how far away you can project onto a surface without making it appear distorted and how far away it can be projected while still being able to see anything.
These two concepts are opposite of each other, and so it’s best to start moving the lens away from a light source closer to where you want the image projected. The throw ratio is the farthest point on the lens from a light source that produces good results.
When using this method in modern classrooms, teachers will often have problems with desks blocking the path of students who sit too close to a projector. Thus, it’s important to make sure that desks are either moved or that students sit in an appropriate distance from where you want your image projected onto your walls and ceiling.
In the end, this isn’t a perfect method, but it’s one of our best options for minimizing light reflectance onto students and teachers in modern classrooms.
Relevant reading: What is a good contrast ratio for a projector?
Why is my projector dim?
A projector is said to be too dim when it does not project a clear or bright enough image on the screen. This means that your audience will have trouble viewing your presentation, which can have a negative effect on any speaking engagements.
There can be several causes for a projector to be too dim, many of which are completely out of your control, and some of which you may be able to do something about:
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