I was under the assumption that a circular polarizing filter would filter circularly polarized light. I now understand that what is commonly called a circular polarizing filter only filters based on linear polarization - and then makes the linearly polarized light circularly polarized.
Surely it must also be possible to build a filter that removes light polarized with a certain spin direction. Does such a thing exist for photographic use (or other use) and what would be the effect of using one?
As the photographic circular polarization filter is a polarization filter combined with a λ/4-plate, which converts the linearly polarized light to circularly polarized light, you can simply turn the filter around and you'll get a filter that filters for one direction of circularly polarized light and makes the result linearly polarized.
However, as the light that is reflected from an appropriate surface (like glass or water) is linearly polarized, there wouldn't be much use for such a filter, except maybe to take pictures of a 3D movie in a cinema (which uses circular polarization), of which the cinema guys probably wouldn't approve.
In addition, you'd have to put another filter (in the "normal" direction) behind it to convert it back to cirularly polarized light because the linearly polarized light confuses the autofocus sensors of some cameras.
