The wavefront coding technique is used to enlarge the depth of field (DOF) of incoherent imaging systems.The key to wavefront coding lies in the design of suitable phase masks. To date, numerous kinds of phase masks are proposed. However, further understanding is needed regarding phase mask with its phase function being in a standard sinusoidal form. Therefore, the characteristics of such a phase mask are studied in this letter. Deriving the defocused optical transfer function (OTF) analytically proves that the standard sinusoidal phase mask is effective in extending the DOF, and actual experiments confirm the numerical results. At the same time, with the Fisher information as a criterion, the standard sinusoidal phase mask shows a higher tolerance to focus errors (especially severe focus errors) than the classical cubic phase mask.