To validate the new method, we conducted a second experiment comparing our sensor to the standard method of a rotating polarization filter (i.e., n analyzer) in front of a CCD camera with the same pixel pitch as the polarization CCD camera. (Newport, Irvine, California, 20LP-VIS-B mounted on a Thorlabs (Newton, New Jersey) NR360 stage, imaged with an Imperx (Boca Raton, Florida) IGV-B1920W image sensor). Starting with a bovine flexor tendon sample subjected to a nominal preload, a step strain of 2.5% was applied and held for the duration of the measurements, where the displacement magnitude was computed relative to the gauge length of the sample (measured via digital calipers). We first imaged the tendon using the rotating polarizer in 15-deg increments and computed the DoLP and AoP (top row, Fig. 4). While applying the same strain, we then repeated the measurement using our DoFP polarization sensor (bottom row, Fig. 4). Both image sensors have the same pixel size (7.4 by 7.4 μm), and we used the same lens. The results are very similar, except for the DoLP, which is lower for the rotating polarizer. This is due to the error in using a rotating element to measure a nonstatic scene. Because of significant stress-relaxation of tendon under step-strains, the force is never constant, even over small time periods. Figure 5 shows an example, where the measured force (shown in black) is not constant in the tissue over time. Using the DoFP sensor, complete measurements of the first three Stokes parameters take place at each green time point, whereas the rotating polarizer only samples an individual angle at each red time point. At a minimum, this requires three separate rotation angles; however, significant changes in the force take place during the time of polarizer rotation. The constant downward drift results in differences which are contributed by changes in force and not by the optical properties of the tissue. Our sensor, with its fixed optics and simultaneous capture of four polarization orientations, does not suffer from this error. This also gives our sensor the ability to sample the dynamics of sudden changes in tissue strain, as in the rapid ramping of the force at the start of the test.