SLR

SLR stands for single-lens reflex camera, a type of camera that uses a movable reflex mirror and a viewing system to present through-the-lens framing. Light from the scene passes through the lens and is reflected by a reflex mirror up to a viewfinder formed by a pentaprism or pentamirror. When the shutter is released, the mirror flips up, the shutter opens, and light reaches the film or digital sensor, capturing the image. This arrangement allows the photographer to see exactly what will be photographed, through-the-lens metering and autofocus in many models.

Most SLRs use interchangeable lenses and standardized mounts, enabling a wide range of focal lengths and accessories. They were the dominant format for 35 mm photography from the 1950s into the 1990s, with notable milestones such as the Nikon F system, which helped establish professional lens ecosystems. In addition to 35 mm, there have been medium format SLRs and other formats that employed the same basic reflex mechanism.

With the advent of digital imaging, SLR designs were adapted to digital sensors, giving rise to the digital single-lens reflex (DSLR). These cameras retained the reflex viewing path and many of the same lens ecosystems as their film predecessors, while replacing film with electronic sensors and digital storage. In the late 2000s and 2010s, mirrorless cameras—lacking the reflex mirror—gained popularity by offering lighter bodies and electronic viewfinders, leading to a shift in some market segments.

Today, the term SLR is often used to refer to both film and digital single-lens reflex cameras, though many have moved to mirrorless systems. SLRs remain valued for optical viewing, rugged builds, and extensive lens lineups, particularly among long-time enthusiasts and professionals.