Arts. The working of a slide projector or a movie projector is shown in the figure given below:
The light source is placed at the centre of curvature of a converging or a concave mirror. The concave mirror is used to reflect light back in fairly parallel rays. The condenser is made up of 2 converging lenses that refract the light so all parts of the slide are illuminated with parallel rays. The projection or converging lens provides a real, large and inverted image. It must be real to be projected on a screen. The slide (object) must be placed between F and 2F of projection lens so as to produce a real, large, and inverted image. Because the image is inverted, the slide must be placed upside down and laterally inverted so we can see the image properly.