We propose the use of a smooth spherical lens in the Christiansen filter cell. The realization of common filtering functions with such a filter configuration is discussed. A systematic design technique based on inverse Fourier cosine transform or inverse Laplace transform is established, with which a desired, prescribed response can be tailored by properly configuring the lens of the filter. Four Christiansen filters centered at 545 nm with a full width at half-maximum of 2 nm are analyzed in detail.