A full-frame DSLR is a digital single-lens reflex camera (DSLR) with a 35 mm image sensor format (36 mm × 24 mm). Historically, 35 mm was one of the standard film formats, alongside larger ones, such as medium format and large format. The full-frame DSLR is in contrast to full-frame mirrorless interchangeable-lens cameras, and DSLR and mirrorless cameras with smaller sensors (for instance, those with a size equivalent to APS-C-size film), much smaller than a full 35 mm frame. Many digital cameras, both compact and SLR models, use a smaller-than-35 mm frame as it is easier and cheaper to manufacture imaging sensors at a smaller size. Historically, the earliest digital SLR models, such as the Nikon NASA F4 or Kodak DCS 100, also used a smaller sensor.

Kodak states that 35 mm film (note: in "Academy format", 21.0 mm × 15.2 mm) has the equivalent of 6K horizontal resolution, according to a senior vice president of IMAX. This equates to 10K horizontal resolution in full-frame size.