Zoom lens are lenses whose focal distance or magnification change continuously by changes in position between lenses.

In order change the size of a subject with a single lens, you can change the distance between the object and the lens, but also formed image position is changed. However, if you combine two lensed and move, you can change the size of the subject while 

maintaining its focus.

Enable to inspect the subjects in various magnification according to zoom ratio.

L-Fusion Optics designs and provides custom ordered lenses.