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POIARIZING FILTERS

For more detailed information on this subject,
Also See: Kodak's Great Polarizing Page

A polarizing filter is usually mounted in a two-ring holder. The threaded inner ring attaches to the lens while the outer ring holds the filter and can be fully rotated. Explaining and un derstanding how a polarizing filter works is a greal deal more difficult than using one. So first let's see what it can do and how to use it, and then we'll see how it works. A polarizing filter does three im portant things:

1. 
   1. Darkens blue skies.
   
   2. Removes or reduces reflections from nonmetallic surfaces such as water and glass.
   
   3. Increases the color saturation (intensity) of color pictures.

This comparison shows the effects of using
a polarizing screen. With a polarizing screen
on the right, the sky is a deeper blue.

Just because blue sky appears in the viewfinder doesn't mean you have to make it darker. This is especially true when a dark-colored subject, such as a deep red barn, is seen against blue sky. By darkening the sky, you reduce the contrast between the barn and sky, an effect you normally don't want. However, such darkening would increase the contrast between the sky and a white steeple or white clouds, effects often desired. Look through the viewfinder and decide if the sky looks better with or without the full polarizing effect or with the filter adjusted mid-way. Another benefit of a polarizing fil ter is its ability to cut through haze. It is often more effective than a haze fil er for color film because it can reduce more of the scattered blue light.

Pictures that include glass surfaces often
show distracting reflections or glare. You
may be able to remove or reduce the
reflection or glare by using a polarizing screen.

DARKENING A BIUE SKY

The polarizing filter does for color pictures what a red filter does for your black-and-white pictures-it makes those fluffy white clouds pop out from the sky. It does so by darkening the blue sky. The darkening is even adjustable. You can make the sky dark blue medium dark blue, medium blue, and so on. To get maximum darkening of the sky take pictures at right angles to the sun (shoulder pointing at sun) when the sun is fairly low in the sky. The

To find the part of the sky that can be most darkened with a polarizingfilter, pointyour shoulder at the sun. The sky directly infront and behind you can be most darkened. If the sun is near the horizon, the sky overhead can also be darkened.

Darkening diminishes and disappears as you turn to face the sun or turn your back to the sun. When the sun is overhead, only a small arc of sky near the horizon can be darkened. With a single-lens reflex (SLR) camera, you can see the darkening provided. Simply look through the viewfinder as you rotate the filter. Stop when you see the effect you want. Some polarizing filters have a small handle that you point at the sun to position the filter for the maximum effect.

Linear and Circular Polorizers
Until recently, only linear polarizing filters were commonly used in photography, and they did the job well. But for cameras with a semi-silvered mirror (which so far includes all auto focus SLR cameras) the linear polarizing filter causes underexposed and possibly out of focus (for autofocus SLR cameras) pictures. If you are uncertain if you need a circular polarizer, check your camera manual or with your camera dealer. A circular polarizer will work with all cameras and will give results virtually identical to those from a linear polarizing filter. The only reason for not automatically buying one is that it costs two to three times as much as a linear polarizer. If necessary you can use a linear polarizing filter on a cam era with a semi-silvered mirror if you:

1. Determine exposure without the filter, and then manually set it for ll/2 stops more (the filter factor) before attaching the filter.
2. Manually focus an autofocus camera when the camera cannot set the correct focus.

CONTROLLING REFIECTIONS

You can also use a polarizing filter to reduce or eliminate reflections from water, glass, and other shiny surfaces such as table~tops. You can't eliminate reflections from bare metal surfaces because the reflected light is not polarized (see the explanation of how polarizing filters work). Again, the viewing angle determines the maximum effect. At an angle of approximately 35 degrees from the surface, you obtain the maximum reduction in reflections when the polarizer is rotated to the correct position. As you vary from this angle, the reflections return. Don't automatically reach for a polarizer to remove reflections. First consider whether the reflections help or hinder the picture. Then make your decision.

Polarizer Filters

B&W Filters: Daylight	Filters for B&W Films: Factors	Light Balancing Filters	Conversion Filters	Polarizing Filters
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