焦距
jiāo jù · HSK 7
focal length
📷🔍 焦 jiāo (focus/burnt) + 距 jù (distance) = focal length
焦 carries the sense of a burning point where light converges; 距 means distance or gap. Together: the distance to the focusing point, i.e. focal length. The same 焦 appears in 焦点 (focal point).
焦 — bird 隹 over fire 灬
焦 is an associative compound showing a short-tailed bird (隹) above fire (灬), depicting roasting a bird until scorched. The original sense was 'burnt' or 'charred,' which extended to 'scorched, dried out,' and metaphorically to 'anxious, worried' (as in 焦急).
距 — foot radical 足 + 巨 (jù, large/ruler)
距 combines the foot radical 足 with 巨, which provides the sound. Originally it referred to the spur on a rooster's leg, then extended to mean 'distance' or 'to be apart from'—the gap measured between two points, like strides of the foot.