An example of as for used as a preposition is in the following sentence: "I will take care of the dishes, as for the garbage, can you please take it out?" which means "I will take care of the dishes, regarding the garbage, can you please take it out?"
as to. With regard to, concerning. For example, As for dessert, I'd better skip it today and We are not sure as to how to pay the bill. A particularly well-known use of this idiom is in Patrick Henry's speech before the Virginia Convention in 1775: “As for me, give me liberty or give me death.” Also see as to.