Everything you need to know about exposure compensation when using a polarizing filter.
Words and Photography by Urth HQ
Polarizing filters (both linear and circular polarizing filters) stop linearly polarized light from entering a camera lens. By filtering out this light, polarizing lens filters help eliminate reflections and haze from your photos. They also increase the contrast and color saturation of certain objects such as blue skies, foliage, or a smooth water surface.
The density of light that enters a camera is measured in f-stops, with each stop number representing a doubling or halving of light. A large aperture such as f/2.0 will let more light into the camera, compared to a smaller aperture, like f/11.0, which blocks out more light.
If you want to understand more about how f-stops, we’ve written a quick guide to f-stops.
How Much Light Do Polarizing Filters Cut?
Polarizing filters cut out the equivalent of around 1.3 f-stops of light, which means if you’ve got a polarizing filter on you’d need to compensate for 1.3 f-stops of light by adjusting your shutter speed, aperture setting, or ISO to get the same exposure.
An easy way to see the difference is by going into aperture priority mode on digital cameras and checking out the shutter speed reading before and after you put the polarizing filter on. This should give you an indication of the difference in light exposure. Sometimes having the auto focus on can affect the reading, so it’s best to keep your lens on manual focus for this test, especially if you’re not using a tripod.
Although 1.3 f-stops is the average amount of light a polarizing filter blocks, this can vary according to the scene and your position relative to the light waves coming from your light source. The average is slightly different between linear polarizers and circular polarizers. You can learn more about the difference between linear polarizers and circular polarizers here.
How to Adjust the Amount of Light Cut
When you rotate linear polarizing filters, you also adjust how much of the light reflected you can block out. The maximum polarization effect is achieved when the lens is pointed at 90 degrees to the sun or light source, and can sometimes be affected by your depth of field.
To achieve this, make an L shape with your first finger and thumb, pointing the thumb at the sun or light source. Where your pointer finger rests will indicate where the polarizer has the optimum impact. Of course, this doesn’t always work for every scenario, especially if you use a wide-angle lens, so take it (literally) as a general rule of thumb!
If you’ve been thinking about picking up your first polarizing filter, have a look at Urth’s line of polarizing filters, all made with premium optical glass and guaranteed to help take your photography to the next level.