My cameras all have filters.  That includes the (almost permanent) UV filter, which is always the first thing I buy after getting a camera.  Besides that, one of the most understated filters is the polarizer.  I know lots of guys with expensive gear, but no polarizer.  And is hampered when shooting the cityscape and sunset from his 37th story office.

I remember the old Polaroid sunglasses commercial showing a guy beside the pool looking at the girls swimming around.  The sunglasses clear the glare from the water, and sees crystal clear to the swimmers.  That is the basic principle of a polarizer.  This is a very subtle advantage when taking pictures of landscapes and skycapes.  It is particularly evident when taking pictures of the water or the beach.  To explain further, this all relates to that wonderful organ called the eye.  The human eye adjusts what it sees and translates accordingly.  This happens unconsciously and is an important hidden function of the human body.  It works, and that’s all there is to it.

On the beach we see the clear water, and what else is underwater.  With some automatic pre-processing it is a lot clearer compared to taking a picture of the objects under water.  The light which reflects from the underwater object gets diffused before escaping to the surface.  And there’s a lot light reflecting as it hits the surface of the water.  All of this makes for a murky image.

The polarizer is like a fine filter which only allows light coming in from a certain angle.  This resolves the glare and murky image.  The sky looks a lot more blue, a darker shade of blue, in fact.  Taking a picture of someone beside the glass window would lessen the reflection and show what’s out the window.  However, because it filters out ambient light, the resulting images are darker.  It’s usually not a good idea to use flash to solve this situation.  In which case, the only solution would be a tripod for long exposure times.  In my experience, I can live with it.

Yup, after the UV filter, the third thing I bought was the tripod.