Fixed focus describes a camera or lens system in which the focus is permanently set at a predetermined distance and cannot be adjusted by the photographer. Rather than offering the ability to focus on subjects at varying distances, the lens is locked at a fixed point - typically set at or near the hyperfocal distance - which is calculated to provide the greatest possible depth of field and ensure that subjects across a broad range of distances appear acceptably sharp in the final image.
The hyperfocal distance is the closest focusing distance at which a lens can be set while still rendering subjects at infinity acceptably sharp. By fixing the focus at this point, camera manufacturers can maximise the zone of apparent sharpness extending from a relatively close foreground distance all the way through to the far distance, making the camera suitable for a wide variety of everyday shooting situations without any focusing adjustment on the part of the photographer. This approach works most effectively with lenses of shorter focal lengths and smaller apertures, both of which naturally produce greater depth of field.
Fixed focus systems are most commonly found on simple, entry level, and disposable cameras, where ease of use, low manufacturing cost, and compact design are the primary considerations. By eliminating the mechanical complexity of a focusing system, cameras can be made smaller, lighter, and more affordable, while still producing acceptable results for general purpose photography in reasonable lighting conditions. Many early and basic point and shoot cameras, as well as single use disposable cameras, employ fixed focus lenses for precisely these reasons.
While fixed focus cameras lack the versatility and precision of cameras with adjustable focusing systems, they remain effective tools for casual and snapshot photography, and their simplicity makes them particularly well suited to situations where speed and ease of operation are more important than critical focusing accuracy. It is worth noting that fixed focus should not be confused with manual focus or autofocus systems, both of which allow the photographer or camera to actively adjust the point of focus for subjects at different distances.