Find f(n) when n = 2^k, where f satisfies the recurrence relation f(n) = f(n/2) + 1 with f(1)=1.

I'm very confused by this theory any help would be appreciated. I was using f(n)= C1*n^(logb(a)) +C2

where C1 = f(1) + c/(a-1) and C2 = -c/(a-1)

but a =1 im very confused