by Harry Flashman
photographers who used polarizing filters in the days of film (remember
waiting for the one hour D&P shop for your prints) have strangely seemed to
avoid this filter for their digital cameras, especially DSLR’s.
Whilst there are no polarizer advantages unique to digital cameras, digital
cameras with limited dynamic range can benefit greatly from the selective
suppression of excess contrast. Due to the limited UV sensitivity found in
most digital cameras, polarizers also work well for haze control, especially
with the haze we have in Thailand, thank you Malaysian forests!
Quality polarizing filters are different from most others in the fact that
they are made up of two distinct elements. There is an outer ring that
rotates the outer “glass” relative to the inner element. This increases or
reduces the degree of polarization to allow the photographer an endless
range of polarized effects from one filter.
The principal behind these filters is to remove reflections, and funnily
enough it is reflections that take the color out of color photography. Look
at the surface of a swimming pool, for example - a shiny white,
non-transparent surface. Now look through a polarizing filter and you can
see right down to the tiles on the bottom of the pool. And the people
frolicking in the pool!
What you have to understand now is that these filters remove reflections
from any surface, not just water. The reason you cannot see through some
normally transparent windows is because of reflected images on the surface
of the glass. The reason some tree leaves appear to lose their color is
through reflected light from the sky above.
One of the traps for young photographers is that because you know the grass
is green, you see it as green when you look through the camera viewfinder -
even though it is not truly well saturated green. Look again at the scene in
the viewfinder. The green grass is really a mixture of green and silvery
reflections, dark shadows and pale green shoots. Put the polarizing filter
on the lens and slowly rotate the outer ring. Suddenly the silvery
reflections disappear and become a deep, solid green color. The grass is now
made up of green, dark green and pale green. This green will really leap out
at you and smack you fair between the eyes!
Your next beach scene when taken with a polarizer will really amaze you.
Again, slowly rotate the outer ring on the polarizer. Look critically
through the viewfinder and you will see the sky take on a much deeper color
to highlight the white clouds. Keep turning that outer ring and the sea will
change to a deep blue to green luminescent hue. The end result is at your
command. Try taking the same shot this weekend, but with varying degrees of
polarization and see the differences in the final shots.
So, if the polarizer is such a wonderful bit of gear, why do we not make it
a standard piece of equipment on all cameras? Well, like everything, there
is a downside as well as the upside. In the case of the polarizer it does
its bit of brilliance at the expense of the amount of light that gets
through to the lens. With most polarizing filters you will lose about one
and a half stops of light. What this means is that the shutter speed will be
at least twice as long to record the same scene, or that the aperture will
have to be twice the size. This means that you are more likely to get camera
shake effects and suffer from lack of depth of field when using the
polarizer. However, with shots in the bright sun, a polarizer will bring a
new dimension to your shots.
By the way, when using any filter on your camera, I suggest you use a
stepping ring to increase the diameter of the filter, so there are no
unwanted vignetting effects, especially with wide angle settings. My regular
camera has a 55 mm diameter lens, which I have then stepped up to 62 mm so
takes all my old filters. This is really a good idea and cuts down the
number of lens adapters you will need. Including the polarizer.
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