Choosing a Hand Lens. Four factors effect the performance of hand
lenses: (1) magnification power, (2) width of field, (3) depth of field
and (4) focal length. For purposes here, magnification power is a
measure of image enlargement. Width of field is a measure of the area
that can be seen through the lens. Depth of field is the range of
distance through the lens within which an object remains in focus. Focal
length refers to the distance from an object at which a magnifier must
be held to achieve clear focus and maximum magnification.
Higher powered magnifiers give greater image enlargement. However,
they have greater light requirements, narrower width of field, shallower
depth of field, and shorter focal length. Three lens (triplet)
construction provides high clarification at edges of lens. Two lens
construction provides a lesser measure of clarification.