Q: I have finally decided to buy a circular polarizing filter for my Nikon AF-S 70-300mm ED VR zoom lens and wonder what are the differences between a $79 filter and a $250 filter? Also, what effect, if any, will a polarizing filter have on White Balance and exposure compensation?
Answer: As you might expect, the better polarizers employ superior glass that helps maintain the fine image quality that your high-grade lens can provide. They also benefit from superior multi-layer coatings for greater transmission of light and less flare. Some brands (like Heliopan and B+W) use brass rings to hold the glass and that also increases the cost. Unless you are a professional photographer, I don't think you need a $250 filter. Expect to spend about $160 for a high grade circular polarizer in 67mm size, such as the Hoya Pro 1D, HD or Super-HMC series.
Digital SLR cameras require the so-called circular (not linear) type of polarizer to ensure accurate autofocus and light metering. Buy a medium-priced filter of a known brand that employs high-grade glass and numerous layers of chemical coatings for the best results. Photo: (c) Peter K. Burian
A polarizer employs grey glass and that does reduce the amount of light that will be transmitted to the camera. You have probably read about the so-called "filter factor"; the grey glass causes a loss of light of approximately 1.3 EV or stops. Since your camera employs a through-the-lens light meter, it measures the exact amount of light that will reach the sensor; hence, it automatically compensates for the filter factor. There is no need to adjust the exposure simply because you are using the polarizer. (The filter factor is important only if you are using an external light-metering device.)
A polarizer is useful for wiping glare from reflective surfaces - including dust or moisture particles in the air - allowing the rich colours to show through. If the filter produces a slight colour cast, you can fix that in software. Photo: (c) Peter K. Burian
Although a polarizer uses a totally neutral glass - at least in theory - I have found that some can add a slight colour cast, usually magenta. That may not be a problem if you use Auto WB since the system may be able to compensate for it, providing accurate overall colour balance. But if you use a WB preset, such as Sunny WB or Cloudy WB, images made using the polarizer may exhibit a slight colour cast. Some DSLRs provide a White Balance Fine-tuning feature that you can use to prevent this problem, but frankly, it's easy to fix in image editing software.
NOTE: Peter Burian teaches two excellent online photography workshops - Mastering the Digital Camera and Photography and Mastering the Canon EOS Digital Rebels - at BetterPhoto's online digital photography school. Also see Peter's Pro BetterPholio website: www.peterkburian.com.