The Canon ML 3 Ring Light/Macro Flash is a close-up flash for use with the EF 50mm f/2.5 Macro Lenses. Its guide number is 11/36 (ISO 100 m/ft.). This ML 3 macro flash contains two flash tubes which can be switched on or off independently for creative control, as well as two built-in miniature lamps as a focusing aid. It is recommended for EOS cameras with Aperture-priority AE and manual exposure control.