I've always thought of Feminism as an extremely broad and loose collection of different beliefs and ideologies, sharing a common goal of establishing equal rights and opportunities for women. Not necessarily sharing a common view on how to achieve that though.
A feminist could also be a masculinist, and vice versa, no?
True. Being a feminist is being an equalitarian first and foremost, and there are many different ways to achieve that.
Contemporary gender studies, on the other hand, are not, in my opinion, necessarily feminist, and they are more often that not a very sterile and dogmatic branch of social science.