Polarizers
There are two types of polarizing filters, polarizers for short: linear and circular. Most SLR cameras use circular polarizers due to the use of a reflection mirror. Digital cameras in general do not have reflection mirrors, and, as a result, can use both (i.e., linear or circular) polarizers. The left image below shows a typical polarizer. A polarizer has two glass surfaces. The bottom ring screws on to the front thread of a lens, and the top ring is rotatable. As the top ring rotates, one can see the effect through the LCD monitor. Polarizers can greatly enhance outdoor images by increasing contrast and color saturation, eliminating reflections from glass and other non-metallic surfaces, and darkening the blue sky. Unfortunately, using a polarizer may be a little difficult with a 2500 because 2500's lens does not have a thread to which a polarizer can be screwed on (below right).
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How do we use a polarizer? Simple. Just hand hold it in front of the camera lens as shown in the first image below. Because the polarizer is hand-held, it would be more convenient if the size is larger than necessary. For example, although a 37mm or even 28mm polarizer would work fine with the 2500, I personally found out a 46mm or even 49mm polarizer work better because a larger filter will not cause vignetting even though it is a little off center. The effect of using a polarizer obtained by rotating one of the two rings. (Since we do not screw a polarizer on to the lens, we have more flexibility.) First of all, point the filter to the direction you wish to take a shot (the second image below). Then, rotate one of the two rings. As the ring is being rotated, you will see the difference. You can stop rotating when the desired effect is achieved. The third image shows the maximum impact. Finally, move the camera right behind the polarizer as close as possible and take a shot.
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One of the major uses of a polarizer is to reduce or even eliminate reflection from glass and other non-metalic surfaces. For maximum polarization, the incoming light must have an incident angle of 30 degree, and the camera is aimed at the subject at an angle of 30 degree from the other side (see image below).
The following images show this effect. The left one was taken without a polarizer and the right one was taken with a polarizer in its maximum effect. As you can see, annoying reflection is minimized.
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| Without a polarizer | With a polarizer and max. effect |
| Click on the image to see a larger one | |
The following is another example showing the reduction of reflection from the cover of a book:
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| Without a polarizer | With a polarizer and max. effect |
| Click on the image to see a larger one | |
The following shows a more dramatic example. The left image was taken without the use of a polarizer and the right one was taken with a polarizer. As you can see from these results, reflection off the water washes out all colors, making the image foggy.
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| Without a polarizer | With a polarizer and max. effect |
| Click on the image to see a larger one | |
One of the best-known use of polarizers is darkening the blue sky. However, not all part of the sky can be darkened. A simple rule goes as follows (see the image below). Point your index finger at the sun and extend your thumb at a 90 angle to your index finger. Pointing your lens in the direction of your thumb will achieve the maximum effect.
After determining the position of the maximum effect, point your polarizer in that direction and rotate one of the two rings until the desired effect appears. Then, put your 2500 behind the polarizer and take a shot.
The left image below is taken without a polarizer, while the right one shows the same scene but with the maximum effect. It is clear that part of the sky (i.e., the upper part) in the right image is considerably darken, making the cloud stands out vividly.
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| Without a polarizer | With a polarizer and max. effect |
| Click on the image to see a larger image | |
Note that since images taken with a polarizer eliminates reflection from objects to some degree, images may look darker.
Polarizers can also increase the contrast and color saturation of an image because they can remove reflection. The left image below was taken without a polarizer. The cloud in the sky is fuzzy, and the green color of the trees and leaves is not what I see. The right image below was taken with a polarizer and maximum effect. The difference is clear. Now, the sky is darker, the cloud stands out, the green layers are more accurate, and the reflection from water is removed making it more vivid.
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| Without a polarizer | With a polarizer and max. effect |
| Click on the image to see a larger image | |