The Canon Speedlite 600EX-RT is a professional-grade shoe-mounted flash designed for advanced DSLR photography. Featuring a powerful guide number of 197 feet at ISO 100 and 200mm, this flash delivers exceptional lighting control across a zoom range of 20-200mm (extending to 14mm with the wide panel). The built-in 2.4 GHz wireless radio transmission system allows reliable wireless flash triggering with up to 15 individual Speedlites across 5 groups, with a range extending to 98.4 feet - all without requiring direct line-of-sight. Built for durability, the 600EX-RT features improved hot shoe contacts, enhanced flash head durability, and comprehensive dust and water sealing throughout. The dot-matrix LCD display, backlit controls, internal sound generator, and 18 custom functions provide intuitive operation and customisation. Powered by four AA batteries with recycle times from 0.1 to 5.5 seconds, this secondhand unit is ideal for photographers seeking professional wireless flash capabilities at a more accessible price point.