35mm slides are a type of photographic reversal film produced from a 35mm roll of film. Each side contains an image on a transparent base, surrounded by a paper or cardboard frame that allows the user to handle the slide without smudging its image with fingerprints or dirt.
Slides are typically viewed using a device called a slide projector; the slide is inserted into the projector, which casts a bright string of light through the transparency.
This projects an enlarged form of the slide’s image onto a wall or a screen mounted for this purpose. Slides may also be viewed with a small, hand-held magnifying device; some of these contain their own light source, while others require use of a back-lit slide board.
35mm slides may be produced from both color and black-and-white film, although the black-and-white slides have always been rather uncommon. Slides were once very popular for use in lectures and presentations; the slides would contain photographs or lecture outlines, and allow large numbers of students or attendees to view the image simultaneously.
However, in photography, slides have now been almost entirely replaced in this capacity by overhead projectors and computerized slide software, both of which are considered easier to use and less likely to experience mechanical failure. 35mm slides have become increasingly rare in modern times; they have been supplanted by digital media that is less likely to become damaged, corrupted, or misplaced.
The tiny size of 35mm slides made losing single slides a real risk, and lengthy slide presentations could be ruined if the slides were placed out of order in the projection device.
Historical enthusiasts who still enjoy using 35mm slides may choose to take advantage of slide-creation services, offered by several reputable companies, that will create slides from digital photographs. This can also be done at home via any number of available slide converters. These slides may also be created from computer-generated graphics, scanned documents, telescope images, and microscope images.
Several different types of slide projectors and slide viewers are available; most projectors allow an extensive series of slides to be placed in a specific order within the projector, usually in a round plastic or metal carousel containing individual slots for each slide.
The carousel is then advanced within the projection machine either by pressing a button on the machine itself, or by using a remote controller connected to the projector by a cord. When purchasing a slide projection machine, it is important to check all components to ensure that they still work; a machine with mechanical defects will not work reliably and may irreparably damage the slides placed inside of it.