I shoot macro occasionally with an old Sigma 90mm. I shoot handheld, almost always use only natural light, and have to manual focus and guess exposure (lens is full manual, doesn't talk to the camera). As long as you have a steady hand, keep in mind angles and how best to make the light work for you it is completely doable without external flashes and reflectors. Last time I posted macro people were amazed they were all handheld and natural light.
