The lens bent the light to stack these images. When all the images overlapped completely, the slide was in focus. You will find convex lenses in telescopes, microscopes, magnifying glasses, cameras, slide and movie projectors, and other instruments that use light to create an image. Though each slide projector is a little different all projectors have a few basic components. The light bulb and reflector.
Every projector has some light source.
In some projectors the reflector and the bulb are one unit. You may have to remove the bulb to take a close look at the filament, the coiled wire, which glows when the bulb is on. If you do touch it, don't worry, just clean the bulb with a facial tissue and some rubbing alcohol. Between the light bulb and the slide you may find a thick piece of greenish glass. This glass prevents much of the heat produced by the bulb from reaching the slide.