Good questions deserve answers.  My recent article on filters featured polarizing filters.  I gave a written example of how we can miss polarize a blue sky by using a wide-angle lens with a polarizer.  The area of deepened blue created with the filter cannot cover an entire wide-angle sky, resulting in varying amounts and intensities of blue.  I did not show any examples.

Ron commented in the previous (to this) post of White Sands New Mexico photos, how the vertical photo of a dead tree and sky was uneven in the intensity within its blue sky.  He asked if it was due to the misuse of a polarizer filter.  In that case it was not.  That picture shows the effect that is common when the time of year, time of day and angle of your view come together.  On many blue sky days you can scan the sky with your eyes from the horizon to straight up and see the many levels blue.  On intense blue sky days, you can also at times see a varying degree of lightening and darkening around objects like tree branches.

The photo below was made in the Holy Cross Wilderness of Colorado in 1986 with a medium format film camera.  I used a polarizer and wide-angle lens when I made this photo and it shows.  There was a “whole lotta sky” showing and you can see the miss-polarization from left to right. I have shown this photo many times because of its beauty, but it has never been of any use to me in calendars or books because of that sky.  I have (somewhere) another digital copy of this shot where I used software cloning to make that sky consistent.  If I would have had that tool back in the day, this image would have been published.  The pano format is a crop.  I do have a different view of this location that was made without a P filter, and has been published.

As an aside, when I made that trip to CO I was testing a new type of professional transparency film.  I used (misused) polarizing filters for most of my blue sky shots.   Despite living near the mountains for six years I forgot that the UV heavy sky at high elevations is also not heavily polarized.  Many of my images taken at over 10,000 feet produced black skies with the P filter and a very color saturated film.  On future trips to high mountains I did not use a P filter.

I am not an expert at anything scientific as far as visual phenomena and photography are concerned.  Just the same, it is amazing what observing light through 40 years of photography will teach.