Anytime I talk about fighting glare on glasses—be they the prescription kind or the sun-fighting kind—someone always asks whether they should just use a circular polarizing filter to eliminate the reflection. This might sound like a good idea but the problem is that, more often than not, it doesn’t work very well. Worse still, when you use a polarizer on people, you can sometimes eliminate too much of the natural shine on skin and in eyes that makes them look alive. If you polarize a portrait, you might remove some glare on glasses on some occasions, but you may also make your subject look dead. And that’s typically not high on the list of how you want to make your subject look.
The real problem with polarizing glasses is that, as often as not, it doesn’t work very well. You may minimize a bit of the reflection on the glasses, but chances are, you probably won’t eliminate it. Instead, the only reliable way to remove glare from glasses is to change the angle between the light and the glasses. When the sun or ambient light is creating the glare, you’ll want your subject to turn their head away from the light in order to change the angle of reflection. A chin down, for an overhead light, can work wonders. And, for a light on the right, turning the head left will help significantly, too.
Working in the studio with lights you’ve set up, you may simply take the key light and raise it up a foot or two and then a foot or two more toward the side of the subject. It’s light close to the lens axis that typically reflects terribly in glasses. Move the light farther from the lens axis and watch that reflection disappear. Even if you’re tempted to, don’t polarize the lens because it will likely have an unappealing impact elsewhere in the image.