Frost Kaleidoscope2 ~ More ice crystals imaged by Jesper Grønne (Art of Nature site) on a window in Denmark.
©Jesper Grønne, shown with permission.
Jesper used a 85mm f/1,2 lens and a reversed 50mm outside it to give an enlarged macro image. The image covers just a few millimetres.
The secret of the magical colours is that he imaged the frost between two crossed polarising filters.
Ice is birefringent or double refracting. Placing a polarising filter each side of the crystals reveals colours from interference between the two differently polarised rays resulting from the birefringence.
Colours are also produced by thin film interference. Distinguish between them by rotating the camera polariser. Birefringent colours then change while those from thin films hardly do so.
Jesper's earlier ice images 1,2,3,4