slight career problem...erm...HELP! please =]?

[h0p3]

hi, well my dad has his own company and his line of buisiness is lyk building, engineering, architecture stuff=] and im in secondary school and my brother is in university doing architecture. and im deciding what i want to be when im older and deep down i want to be a photographer but ages ago me and my friend randomly said that we were going to be civil engineers which i know i would not enjoy at all, and when i told my dad he was really happy cos this meant it was lyk me and my brother are both going to be doing careers like his when were adults. and ive realised i really want to be a photographer but i dont know how my dad will react cos ive suddenly changed my mind to what in his eyes seems to be form a amazing engineering job to becoming a photographer, i would be alot happier becomnig a photographer and my dad has always said to me he doesnt care what i do as long as im happy,,,(which basically means i dont care what you do as long as im happy) so how do i tell him that ?