Full-field evaluation of spatially varying birefringence is realized by allowing two mutually orthogonally polarized collinearly propagating laser beams to be incident on a birefringent sample. This is achieved by use of a modified Sagnac interferometer. A half-wave plate is placed in the exit path of the interferometer to adjust the polarizations of the incident beams as required. Amplitude components of the light emerging from the birefringent object are then selected and/or combined by a polarizer, and intensities for required orientation of the half-wave plate and the analyzer are digitally recorded. It is shown that a maximum of four frames of intensity data is sufficient for complete evaluation of birefringence. The proposed technique is aimed towards birefringence measurements in microscopic biological specimens where the magnitude of retardation lies in the range of 0 − π radians. Simulated and experimental results are presented. © 2018 Optical Society of America.