或參考這一篇, "Depth of field - what it is and what affects it" "Depth of field is the amount of subject matter in front of and behind your plane of focus that appears to be in focus." 留意其中用字 Plane of focus. 當你在用對焦點對焦時其實是在這點上的相等距離造成一個平面. 在此平面前方或後方的物體都會失焦.
接下來也說了, 影響depth of field的因素有f/stop - 光圈, the focal length of the lens - 鏡頭焦段, the distance to the subject - 被攝主題之距離. 對焦點根本不是決定在同一平面上物體模糊的原因. http://www.uscoles.com/depthoffield.html