We introduce a new approach for teaching interference and diffraction, which expresses the Huyghens-Fresnel diffraction formula in terms of the observation plane. This makes it easier to obtain the expressions for Fraunhofer diffraction and for Youn's fringes, which appear as special cases, as well as the far-field condition. This allows interference and diffraction to be covered in a fraction of the classroom time usually required. Once the approximation is made, all waves are expressed in terms of their angular distance from the optical axis. The method may be applied to more complex cases like Newton's rings and diffraction by multiple slits.