We obtain the regular refraction interval for a conic F with respect to its focus. In all cases this interval is
, where e is the eccentricity of the conic. Also we obtain the regular refraction interval for an arc of
sinusoid
with respect to the midpoint of the line segment [AB]. Finally we determine the starlike arcs Γ for which the regular refraction interval with respect to the origin is the same for every arc Γ' ⊆ Γ. Such curves are arcs of the ellipses with the origin of axis in a focus and a class of starlike arcs of logarithmic spirals.