Fotasy FX580 Flash Multiplier for Use with Telephoto Lenses, Fits Canon 580EX/ 580EX II (Clear) This Flash Multiplier is for use with telephoto lenses of 300mm or longer, excellent for photography on wildlife, birding, wedding, evening party, portraits and more Increases the flash output by about 2 to 3 f/stops Allows you to shoot at greater distances and shoot with smaller apertures Lens is lightweight and durable, focusing and concentrating the flash output into a narrow beam. Easy attachment and removal, and folds flat for compact storage in supplied case, lightweight for easily carrying.