noun
depth of focus
Technical term in optics and photography; refers to the range in front of and behind the focal plane where the image appears acceptably sharp.
このレンズは焦点深度が浅いので、ピント合わせが難しい。
This lens has a shallow depth of focus, so focusing is difficult.
被写界深度 (depth of field) is the range of subject distances that appear acceptably sharp, while 焦点深度 (depth of focus) is the range at the image plane. They are related but measured on opposite sides of the lens.
Compound of 焦点 (focus) and 深度 (depth). A straightforward technical term with no obscure historical derivation.