Isogyre formation by isotropic refracting bodies. 
A simple derivation is given of a formula for the intensity pattern produced by a diffusely illuminated lens-like body held between a polarizer and an analyser.  The formula generalizes the results of Charman and of Pierscionek and Chan for a dielectric sphere between crossed polaroids.  A dark cross is universal for all lens-like bodies whose axis of symmetry is normal to the polarizer and analyser.  Intensity contours are plotted for ellipsoidal lenses.