Vivitar 6000AF TTL Auto Focus Macro Ring Flash for Canon Cameras Uses AF camera's TTL circuit for exposure control Guide Number - 59 (ISO 100 in feet) Auto Flash Range - 0.5 inches to 10 feet Calculator Chart - Printed on reverse Flash Duration - 1/1000 second in manual mode; 1/1000 to 1/40,000 second on auto TTL mode