Yongnuo yn560-iv speedlite is a long range manual flash unit capable of triggering other flashes from up to 328' away as well as being triggered with the rf-603 and rf-602 wireless transmitters. the yn560-iv is powerful with a guide number of 190' at iso 100 and 105mm. the unit is also quite versatile with a zoom range of 24-105mm, which is able to be expanded to 18mm with the built-in wide-angle diffuser. additionally, this output can be adjusted from 1/1 to 1/128 power in 1/3 and 1/2 ev steps.