How to make a Movie projector make front projector to rear facing?

Answer 1

Conventional projection uses a projector in front of the screen, hence the term "front projection". It is also possible to project from the rear of a translucent screen, "rear projection". The problem with rear projection is that the image will be reversed left to right.

Video projectors all have a menu setting that allows the image to be reversed before it is projected so the resulting screen image will be seen the right way round.

The question mentions movie projectors suggesting a film projector rather than a video projector. Because a film projector is fully optical there are no electronic methods to reverse the image but it can still be done. Most projectors allow alternative lenses to be fitted. Using a specialist reversing lens will correct the image orientation but they are expensive. The image can also be reversed using a mirror in the light path. The mirror needs to be a front silvered mirror, one that has the reflective coating on the front rather than the rear as this avoids double images. This is much the same process as a reversing lens which has a mirror or prism inside the lens housing.

Front projection distances tend to be large, with the projector being at the rear of a room. Rear projection rooms or cabinets are generally much shorter so wide angle lenses are often used to produce a large image from a short distance. A movie projector should have a short focus lens to reduce the required projection distance if possible. However, by using a mirror, the projection distance can be extended as the effective distance is the sum of the distance from the projector to the mirror and the mirror to the screen. Careful positioning of the projector and mirror will be needed and this is not as simple as it first appears. It may well be worth looking at dedicated mirror mounts to get the right result.