diafilm

Diafilm is a term used for photographic film designed to produce positive transparency images, or slides, for projection with a slide projector. The standard format is 35mm film; each frame yields a positive image on a transparent base after reversal processing. The finished frames are mounted in small slide mounts and viewed in a projector or slide carousel.

Historically, diafilm saw widespread use from the mid-20th century onward, especially in German-speaking countries where the word diafilm is commonly used for slides rather than camera negatives. Photographers would shoot with 35mm cameras, have the film developed into color or black-and-white positives, and present a sequence of slides in educational, home, or business settings. Carousels and diaprojectors allowed automated projection of many slides in order.

Most diafilms were color reversal (positive) films yielding bright, saturated transparencies, though black-and-white transparency film existed as well. The 35mm format produced a 24x36 mm image, and slides were mounted in standard frames compatible with common slide projectors.

With the rise of digital photography and multimedia projectors, the use of diafilm declined markedly in the late 20th and early 21st centuries. A niche remains among enthusiasts and archivists, and some manufacturers still supply reversal film and slide projectors for historical or artistic use.