A slide projector is a specialized projector which has been designed to be used with slides. Slides are small transparencies mounted in sturdy frames which are ideally suited to magnification and projection, since they have a very high resolution and a resultingly high image quality. The use of slide projectors is in decline, as other projection methods have become more popular.
There are several different components to a slide projector, starting with a slot where slides can be inserted. Many slide projectors are designed to work with carousels, circular racks of slides which can be rotated to allow a sequential projection of images which may be automatic, or controlled with a button or remote operated by the user.
The rack for slides is surrounded by a light source and focusing lenses which ensure that the light passes through the slide, and allows for focusing so that the slides will appear crisply on the projection screen. Slide projectors can be adjusted to project at a variety of distances, with the use of focusing tools. The device also classically includes a fan to ensure that the workings of the slide projector do not get too hot, as heat can damage the slides.
At one time, the slide projector was the presentation method of choice when visual media needed to be presented to a large group. Travelers often took photographs on slide film for the express purpose of holding slide shows of their trips when they returned, and slides could also be prepared for business and educational presentations. In an art history course, for example, the teacher might use slides of famous works of art to display examples for discussion.
Slides are actually a great presentation tool, because of the very high image quality. However, slide projectors can be difficult to work with, especially in the case of carousel projectors, which can become recalcitrant with time. It is also difficult to remember to insert the slides properly so that the images are not reversed or inverted, and to organize the slides in order. As many people who have made presentations with a slide projector know, one of the worst things which can happen is dropping the carousel on the way to the presentation podium, causing all the slides to fall out.
Because slides can be difficult to work with, other projection methods such as projectors designed to link to computers or read presentations from CDs and DVDs have become more commonplace. These projectors may be of lower quality, but they are simple enough for almost anyone to operate.