The 'pst-lens' package A PSTricks package for lens
Denis Girou, Manuel García Luque · 2006
This package defines a lens which can be used in various contexts to simulate the effect of a lens, using the unique macro \PstLens, with some customization parameters. It is also a good example of the great power and flexibility of PSTricks, as in fact it is a very short program (it body, without considering the various customizations, is only 7 lines long!) but nevertheless powerful. And last, it is also a good pedagogical example of how to design and program high level graphic objects above PSTricks own ones. pst-lens uses the extended version of the keyval interface. Be sure, that you have installed the xkeyval package. Otherwise get it from CTAN.