Starting from a peculiar image observed below a bubble floating at a water-air interface, the article analyzes several optical properties of these special types of refracting objects (coined \textit{bubble axicons}). Using mainly geometrical optics, their relation to common axicons, the shadow sausage effect and elementary optical catastrophes (caustics) are discussed.
Comments: 16 pages, 16 Figures
Subjects: Optics (physics.optics); Popular Physics (physics.pop-ph)