I read a useful article about using a polarizer to make skies richer in colour so I bought a circular-polarizing filter for my most frequently used lens. But I rarely seem to be able to get the filter to produce a rich blue sky. Can you explain the technique for using a polarizer?
The article was correct, Donna, since a polarizer can indeed deepen the colour of a blue sky. However, it’s worth emphasizing that the filter will have little effect if the sky is white or grey as on a hazy or overcast day. In other words, it cannot add colour. This filter also has an even more significant benefit: wiping glare from reflective surfaces (except unpainted metal) such as wet foliage, buildings with windows, the surface of a pond, and so on. By removing glare, it allows the true colours to show through. As well, a polarizer can help reduce the effects of atmospheric haze so the subject will appear more sharply defined on a day when there’s a lot of haze in a scene.
You did not mention the technique you’re using, Donna, so here’s a brief summary of my recommendation. While viewing the scene through the camera’s viewfinder, or on the LCD screen in Live View, rotate the polarizer in its mount. When you achieve the desired effect—either full or partial darkening of a blue sky, for example—you’re ready to compose and take the photo. If the polarizer does not seem to have much effect, you must change your shooting position. Remember this: a polarizer provides the greatest benefit when the sun is at a 90-degree angle to the subject.
In other words, find a shooting position so the sun is to your side. You will get very little, if any, polarizing effect if shooting into the sun or when the sun is directly behind your back. (In strong side lighting, be sure to install the lens hood after rotating the filter, to minimize the risk of flare from stray light striking the front of the polarizer.)
Hint: For additional insights about polarizing filters, you might also want to review two previous Q&A items: “Are filters necessary for digital photography?” and “What do I need to do to get a good exposure when using a polarizer?”