The ML-3 is a close-up flash for use with the EF 50mm f/2.5 Macro Lenses. Guide number is 11/36 (ISO 100 m/ft). The ML-3 contains two flash tubes which can be switched on or off independently for creative control, as well as 2 built-in miniature lamps as a focusing aid. (Recommended for EOS cameras with Aperture-priority AE and manual exposure control.)