|Red Field, Green Field - Tehachapi, California|
Specifically I was talking about banding. For whatever reason, when I tried to use a circular polarizing filter with my DP2 Merrill I found banding problems in those photographs. Red Field, Green Field above is an example of that. If you look carefully at the sky you can see it, although it is quite subtle in that particular image. I had to delete some other photographs because it was more pronounced. After that I stopped using the filter.
I have heard that if you use the Sigma brand circular polarizing filter that the banding problems do not appear. I don't know if that is true, it is just what I've heard. I've also heard that people have had success with Hoya's multi-coated filter.
There is one more reason that you may want to avoid using a circular polarizing filter with the DP2 Merrill camera: it reduces the light entering the camera. The reason that I mention this is that the camera is a low-ISO-only camera, and that (because of how it handles highlights and shadows) it is best to overexpose an image anywhere from 1/3 of a stop to a full stop and adjust in post-processing. As you can imagine, overexposing, using a low ISO and using a circular polarizing filter will in many circumstances put the camera in position where you have to sacrifice depth-of-field in order to keep the shutter speed where you need it.