The optical diagrams we have described provide explanations which allow a better understanding of calculus. They also improve and complete the non-standard method given by Abraham Robinson: they are necessary tools for it, both from the psychological (didactic) and the epistemological point of view, because they propose a good - and mathematically justified - mental representation of the behavior of a real function in many ``critical'' situation (at small neighborhoods, at infinity, by looking at infinitesimally small details ...).
Moreover: i) the role of optical diagrams in a calculus teaching environment seems relevant. We are preparing experimental research on the calculus students at the University of Pavia (mathematics and engineering curricula) devoted to detecting the details of the didactic effects and the learning improvements; ii) we are convinced they can be exploited in other everyday non-mathematical applications (finding routes, road signs, buildings maps, for example), in connection to various zooming effects of spatial reasoning; iii) we think the activity of magnification of optical diagrams can be studied in other areas of model-based reasoning, such as the ones involving creative, analogical, and spatial inferences, both in science and everyday situations so that this can extend the psychological theory.