Early studies of ultrasound induced optical birefringence in liquids were performed in the near optical field of the ultrasonic grating. More recently, a farfield method has been developed for studying the effect. The range of experimental conditions under which the respective methods may be accurately applied vary significantly. In addition, the methods differ considerably in their abilities to provide measurements from which theories for the effect can be directly evaluated. Experimental results obtained from each method in castor oil are compared to illustrate the significant differences which occur and to clarify the advantages and limitations of each method.