Front Focus
A calibration error in which a lens consistently focuses slightly nearer than the intended subject.
Measured in
mm
In depth
Front focus was a chronic problem of DSLR phase-detect modules, which measured focus at a separate sensor that could be misaligned with the imaging plane. It is consistent and repeatable, which distinguishes it from a random miss, and it is corrected by microadjustment. Mirrorless cameras that focus on the sensor itself cannot suffer from it.
Examples in practice
A test chart shot at f/1.4 shows the sharpest ruler markings two centimetres in front of the point focused on.