noun
back focus; focus behind the subject
Photography term: the lens is focused on a point behind the intended subject, leaving the subject itself out of focus. Contrasts with 前ピン (front focus).
See also: ピント
この写真は後ピンで、人物がぼけている。
This photo has back focus, so the person is blurred.
後ピンを直すには、フォーカスを手前に調整してください。
To fix back focus, adjust the focus forward.
General term for focus or focal point. 後ピン specifically describes a focusing error where the focal plane is behind the subject.
Compound of 後 (あと, 'behind') and ピン, a clipping of ピント ('focus'). The term likely arose in photography circles to describe a common focusing mistake.