Epson developed ultra-short throw projectors to alleviate issues with standard projectors, which cast the shadow of anyone standing in front of the projector on the screen, produce bothersome glare from the light source, and are often installed in front of viewers, where they can get in the way.

Unlike standard-throw projectors, ultra-short throw projectors can cast a large image even when installed a very short distance from a wall or screen. For example, an ultra-short throw model may be able to cast an 80-inch image on a screen from a distance of 50 cm.

Ultra-short throw projectors offer three main advantages.

• They can be installed close to the projection surface.
• They typically do not cast large shadows.
• They don't get in the way.

When using a standard-throw projector, the presenter often stands in front of the projection surface. The problem with this is that the presenter may cast a shadow on the screen, making the content hard to see. Moreover, the presenter may be bothered by glare from the projector light source.
However, ultra-short throw projectors can be set up closer to the projection surface and forward of where a presenter would stand. Consequently, shadows and glare are less likely to be a problem.

Interactive projectors, which capitalize on this feature of ultra-short-throw systems, have become popular in recent years. Users can annotate and interact with projected images using an interactive pen. They can even operate the PC from a projected image and share projected images with other projectors over a network. Features like these are fueling an expansion of demand in classrooms and business.

There are many other ways to use ultra-short throw projectors. They can project large images even in space-constrained locations such as show windows to bring the space alive.

The projection lens is critical for an ultra-short throw projector. Epson uses two types of ultra-short throw projection lenses in its projectors, ones with folded optics and ones with a concave mirror.

High-lumen models are equipped with lens shift functionality. Lens shift moves the projection lens horizontally and vertically relative to the screen. The screen projection position can be adjusted without tilting the entire projector. However, if you try to shift the lens with a projector equipped with another type of ultra-short throw lens, the projector itself will interfere with the projected light, making it difficult to adjust the screen upwards, as shown in the illustration below.
Therefore, Epson adopted an ultra-short throw lens with folded optics for its high-lumen projectors. By taking advantage of folded optics, Epson minimizes projector interference with the projected light and allows the optical axis of the projection lens to be offset in the projector direction.

A projector with an ultra-short throw lens that has folded optics is advantageous in ceiling mounted applications because it easily projects images over the entire wall even in places where the ceiling is low. These lenses make it possible to reduce the depth of projectors and dramatically improve projector installation and projection freedom. The periscope-like configuration of the lens means projectors can be embedded in ceilings, with all but the head of the projection lens largely concealed and unobtrusive.

Ultra-short throw lenses with folded optics can reduce projector depth and are used not only in high-lumen models but also in home projectors.
Unlike standard projectors, ultra-short throw projectors can be placed near a wall just like a television to cast a large screen. A large-diameter aspherical lens is used as the outermost lens to minimize image distortion. Good focus performance is achieved over a wide range of projection sizes by using an inner focus design.

Another type of Epson ultra-short throw lens uses a concave mirror. This projection lens consists of multiple lenses and a concave aspherical mirror. The concave aspherical mirror reduces image distortion and chromatic aberration, which greatly contributes to the realization of ultra-short focal length lenses. Furthermore, these projection lenses have fewer and smaller optical components, so they are easier to make lighter and thinner, with few protrusions in the thickness direction.

Ultra-short throw lenses with a concave mirror are used in interactive projectors with an integrated whiteboard for education and business. Because they are compact, thin, and lightweight, these projectors have a stylish presence.