Polarized ivy

Queen's likes to think of itself as the Ivy League of the north. We certainly have enough ivy.


More fall architecture photos are on the way. First, though, we have a technical post. Let's play spot-the-difference:

When light reflects off a smooth non-conductive surface, the s-polarized waves (those with an electric field perpendicular to the plane of reflection) are more likely to be reflected, while the p-polarized waves (whose electric field is oriented in the plane of reflection) tend to be absorbed or refracted. The difference between the two is maximized when the angle of reflection is the Brewster angle, typically in the range of 50° to 60° for common materials like water and glass.

We can therefore use a polarizing filter set at two different orientations to the plane of reflection to create two very different effects. We may choose only the p-polarized light from the ivy for our photograph (first image), or we may choose only the s-polarized light (second image). In the first case, we effectively eliminate the specular reflection of the sun on the shiny surface of the leaves. In the second case, the glare and reflections are enhanced relative to the rest of the subject.





Linear vs. circular

Matthew's picture

A word of caution if you're buying a polarizing filter: There are two varieties, linear and circular.

The linear polarizer transmits light of one polarity, and blocks the orthogonal polarity.

The circular polarizer is actually two stacked filters. The first is a linear polarizer; the second takes the linearly polarized light and makes it circularly polarized- essentially, making the light wave rotate around its axis as it travels.

Autofocus sensors can be confused by linearly polarized light; if your camera has AF, you need a circular polarizer. If you shoot film and use a ground-glass screen to focus, you can use the cheaper linear polarizer.

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