LET'S BE POLARIZED (repeated)

[Note:  this is another in a series of postings that were originally hosted by Apple but went away when Apple cancelled mobileme.com.]

  There is a filter that I use frequently, whether shooting video or stills.  That filter is a polarizer.  For those of you not familiar with a polarizer filter, it can do a couple of things that can improve your images, both moving and still.

   First of all it can potentially give you a very blue sky in your sunny day images.  (Note the deep blue sky in the image above.)  I say potentially because a couple of conditions need to be met: 1) the sun must be at the proper angle to the scene you are shooting; and 2) you have to have the polarizer filter rotated to the correct angle. 

   The image at left shows how a polarizer can change the depth of color in an image.  Note the increased contrast of the clouds on the left compared to the right. ( Polarizers can also affect black and white images but that will not be discussed in this post.)  A polarizer can help reduce the dynamic range or ratio of bright to dark in the image.  The shadow areas on the left side of the image are lighter because the sky isn’t so bright and taking up so much of the camera’s dynamic range.

   Secondly, a polarizer filter can reduce reflections from objects in your camera's field of view.  These can be from highly reflective objects like cars and windows or those from water surfaces.  Similar to the sky enhancement of the previous paragraph the degree of reflection reduction depends on sun angle and filter rotation.  The image at right is an example of reducing reflections using a polarizer.

   I personally try to have a suitable size polarizer filter available on all my shoots, particularly if I know they are going to be in bright sunshine.  If the shoot is going to be outside on a bright sunny day I usually install a polarizer even if I don't need it for sky enhancement or reflection reduction.  This is because a polarizer has a about a stop of light reduction so it can act as a neutral density filter.  This can help keep your lens from having to be stopped down to f/11 or f/16 which is not usually a good thing for best image quality.

   Polarizing filters come in a variety of sizes and styles.  The ones I have range from 37 to 95mm in diameter to fit the variety of cameras I use.  I also have a 3" square filter that fits into a matte box that can be mounted on my larger video cameras.  Most of the round filters I have also have threads on their front so that another lens can be screwed onto it but a couple of them are "thin" filters that have no front threads and thus don't stick out quite so far.  This can prevent vignetting when used with wide-angle lenses.

USING POLARIZERS

   Polarizers do not work at every direction.  They work best when the sun is 90 degrees to the camera’s line of sight.  In other words the sun should be at your right or left.  If the sun is at your back the polarizer will have little effect on the sky’s color.  Also, if you are facing the sun you won’t get any sky effect.

   To maximize the polarizing effect you need to rotate the polarizer while watching the scene through through the camera’s viewfinder.  As you rotate the filter you should note the sky’s darkness changing.  TIP: This works best if you turn off auto exposure while adjusting the rotation.  With auto exposure turned on the camera will compensate for the change in light coming through and if you don’t rotate the filter fast enough you may not notice the sky changing that much.

     Also, the polarizer won’t necessarily affect the total sky area seen, particularly if you are using a wide angle lens on your camera.  That type of problem is illustrated in the image at right.  Note how there’s almost a stripe of darkening.  You can minimize this problem by either zooming in some or changing the  shooting direction.

   A polarizer can add “snap” to nearly any outdoor sunlit scene, be it a sky background or closeups of colorful flowers.  Try it.  I think you’ll see the difference.

   There are a variety of sources for polarizer filters - your local camera store or the the web.  Both Amazon and B&H Photo Video carry a large variety of sizes and brands of polarizers.  If you decided to purchase a polarizer via the links below I get a small consideration.

•   Amazon
•   B&H