Does a polarize simply filter photons or does it change the polarization of photons (as well)? let's consider only one photon being sent, at a time, via the polarizer I think the answer might be that: for photons polarized at say 45 degree to the horizontal (or vertical) plane of the polarizer the polarizer is a convertor, i.e. it changes the polarization of the photons into vertical or horizontal (randomly). for photons polarized at say 0 or 90 degree to the horizontal (or vertical) plane of the polarizer the polarizer acts as a filter because it is unable to convert the spin of such photons, the angle is too much/great. maybe I did not understand polarization well second question: does a photon have a "definite" polarization prior to measurement/filtering?