With all due respect, this says more about you than him. If you're doing something you like, you should try to be the best you can at that. The fact that you feel down that you don't have your father's approval, while a disappointing, shouldn't hold you down and pay him little mind. He is the one that should at least be respectful towards your honest, hard work you put.
If you want to change his mind, you need to prove it is useful and has substance.