Hey all im renting the 600 EXRT for some group family shots this weekend so tested it out on my dog. this is all just on camera trying to bounce it different ways. Any tips would be great i really dont have much idea what i am doing. i have the 5d Mark iii. Also why would there not be a built in transmitter in the mark iii to the 600 ex? technology is definitely there to have the flash off the camera and release it without having to buy a $150 transmitter.