How is focal length related to working distance and magnification?
Focal length is the distance from the center of the lens (or lens system) to the viewed object when in focus. Working distance is measured from the lowest protruding portion of the magnifier below the lens usually, the bottom of the shade or shade housing, to the object when it appears in focus. As a general rule of thumb, as magnification increases, focal length and working distance both decrease. As points of reference, for an illuminated magnifier with a 3-diopter lens, the typical focal length is 13″ and the typical working distance is between 11-1/2″ and 12-1/2″. For an illuminated magnifier with a 5-diopter lens, the typical focal length is 8″ and the typical working distance is between 6-1/2″ and 7-1/2″. Choosing the right illuminated magnifier is often a balancing act between level of magnification, field of view, focal length and working distances. Assembly and rework applications tend to need greater working distances as space is needed for tools and maneuverability. Because
