backfocusing

Backfocusing is a focusing error in which the autofocus system places the plane of critical sharpness behind the intended subject. In practice, the part of the scene you want to be in focus remains softer than objects behind it, or the subject looks blurred at the chosen focus distance. It is the counterpart to front focusing, where the focus lands in front of the subject.

Causes of backfocusing can include calibration issues between lens and camera body, especially on systems with lens-specific focus adjustments. It may also arise from a misaligned lens mount, a faulty AF module, or changes in equipment after service or replacement. Some lenses exhibit focus shift with changing aperture or focal length, though that is a separate phenomenon from persistent back focusing. In cameras with separate AF sensors, miscalibration or firmware limitations can contribute as well.

Diagnosis typically involves controlled testing. Use a focus test chart or a ruler at a fixed distance, and shoot with a single AF point on the target under good light. Compare results across lenses and bodies, and verify by switching to manual focus. Testing in different focus modes (phase-detection vs. contrast-detection, if available) and updating firmware can help. If the issue occurs with many lenses, the body may be miscalibrated; if it occurs with a single lens, the lens may require service or recalibration.

Remedies range from lens-specific calibration or exchange to body adjustments such as AF microadjustment (where supported) or professional service for sensor or mount alignment. In some cases, a manufacturer repair is required to restore accurate autofocus.