Il Mistero del forellino negativo. (traduzione da The Physics Teacher, novembre 1991, a cura di Silvano Sgrignoli)

“Negative pinholes” – black spots which are an optical reverse-counterpart for small holes – are a nice idea indeed and a good benchmark for the effectiveness of ray-tracing techniques. The article shows how an intriguing paradox raised by negative-pin-hole images can be turned into an interesting classroom activity.