Mylar screens

Factual Questions
21

Yuk, the diagram Mangetout is badly mislabelled. The screen on the floor is not reflective. It is dispersive, it is a simple projection screen. If it were reflective the audience would simply see the projector in the on-stage screen, and the beam of light emanating from the projector’s lens. But with a simple projection screen on the floor, and the mylar screen angled at about 45 degrees, the image on the projection screen is seen vertical and as if it were on the stage.

Choosing a stretched mylar screen is useful for a number of reasons. An important one is that it is very thin. Reflections come from both surfaces of the screen, but since the screen is so thin they are indistinguishable. A glass sheet will have two surfaces, and if you are close enough you will see two images offset very slightly. On stage this will not matter too much, but is a consideration. Mylar also stretches very flat. So much so that you can make an almost perfect mirror stretching aluminised mylar on a frame. Such mirrors are used to reflect light from projectors where you need to fold the optical path to get space use down. Rear projection systems and virtual reality system use them. Getting a glass pane this perfect would be quite difficult. Especially in large sizes. (I have a couple of such mirrors that were originally constructed for VR systems. They are uncanny. What you see in them is utterly real, in comparison an ordinary rear surface silvered glass mirror is so obviously flawed you wonder how you put up with them.)

22

Correct. Also, if the projection onto this is vertical, it needs to pass through the 45 degree mylar sheet (and may cast a reflection onto the backdrop of the stage). But it can probably be contrived to project directly onto the horizontal screen, with a keystone adjustment.

23

Full flight aircraft simulators use this same principle, with the mylar vacuumed tight onto the viewing bowl to give a huge image simulating the field of view from a cockpit. The sense of depth you get from these is uncanny. When the mylar isn’t taut, though, it’s somewhat nauseating to look at.

24

At least as important, though, is that the projection is from (virtual) infinity–just as you’d expect from distant objects. Crappy flight simulators will just have nearby displays, and the difference is quite obvious.

25

Thank you, everyone. Seems we may have a challenge trying to implement this in a small black-box-like theater, but it gives me a starting point to experiment with. Much appreciated!