  Optical cloaking consists in hiding from sight an object by properly
deviating the light that comes from it. An optical cloaking device (OCD) is an
artifact that hides the object and, at the same time, its presence is not (or
should not be) noticeable for the observer, who will have the impression of
being looking through it. At the level of paraxial geometrical optics, suitable
for undergraduate courses, simple OCDs can be built by combining a series of
lenses. With this motivation, here we present an analysis of a simple
projective OCD arrangement. First, a simple theoretical account in terms of the
transfer matrix method is provided, and then the outcomes from a series of
teaching experiments carried out with this device, easy to conduct in the
classroom, are discussed. In particular, the performance of such an OCD is
investigated by determining the effect of the hidden object, role here played
by the opaque zone of an iris-type diaphragm, on the projected image of an
illuminated transparent slide (test object). That is, cloaking is analyzed in
terms of the optimal position and opening diameter of a diaphragm that still
warrants an almost unaffected projected image. Because the lenses are not
high-quality ones, the OCD is not aberration-free, which is advantageously
considered to determine acceptable cloaking conditions (i.e., the tolerance of
the device).
