What is the purpose of such a black frame? Now the question arises why the screens are masked with a black marginal frame. Here, it is to be mentioned that there are also some light screens that do not have such a black frame in which the size of the screen is equal to the size of the image, as for example a Tripod screen. We immediately recognize that the screen size differs from the image size by a black frame that is also described as masking or marginal frame.
The blue arrow heads measure the actual screen size the red arrow heads measure the actual image size. Let us look at the adjoining image where the measures are drawn in. Finally, one wants to know the size of the image that is finally seen on the screen, and on the other side, it is also important to know how much space the screen will need on the wall for assembling it. Both sizes are important to consider when buying a screen. For example, those who buy a screen will often get two size indications: the screen size and the actual size for the image that is projected on it.
In this chapter, we will first clarify some few important terms related to the size of the screen.
In the following chapters, by means of many practical examples it is explained what is seen on the screen by using a certain combination of projector and screen format. The choice of the screen format mainly depends on the planned application (slide-show, computer screen presentation, normal TV, watching DVD) and of course also from the applied projector (slide projector, 4:3-beamer, 16:9-beamer). There are screens with a square aspect ratio of 1:1, with an aspect ratio of 4:3 as it is the case of the TV's and a widescreen-aspect ratio of 16:9. The referring screen height results from the screen format, which selection is certainly not an easy matter. Most of the times when purchasing a screen, the question about the screen width is at least answered by the spacial conditions and the seat arrangement in the room.
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