In our last post , we talked about neutral density filters.
That got me thinking about other filters that are especially helpful to have and the polarizing filter came right to mind. In fact, a polarizing filter is the one filter that every photographer should have in his or her camera bag.
What a polarizing filter does is really pretty simple. It limits the light that is able to enter your camera's lens based on the angle of that light, only allowing illumination that is moving in a particular direction to pass through the filter.
But what does that do for you?
Well, most light is unpolarized, meaning that it is moving in lots of different directions. So a portion of this unpolarized light will always pass through a polarizing filter unaffected.
But light that is reflected off a nonmetallic surface is polarized, so it is all moving in a single direction. Because this reflected light is all moving in one direction, you can use a polarizer to filter it out by positioning the filter in such a way that it blocks that particular angle of light. And since reflected light is often the source of glare, haze and unwanted reflections in your images, blocking it cleans out that haze and gives your photos better contrast and color saturation.
So a polarizing filter can help you capture images with richer, more vibrant colors, fewer unwanted reflections and less haze. And these are effects that can't be replicated with photo-editing software.
A polarizing filter can make for better photos:
The first thing you'll notice about a polarizing filter is that it is comprised of two rings. The back ring screws onto and attaches to the front of your lens. The front ring rotates. By turning this ring, you can change the angle of light that is allowed to pass into your camera lens.
To use a polarizing filter, first screw it onto the front of your lens. Then rotate the front ring while looking through the viewfinder or using live view. As you turn the ring, you'll see the polarizing effect gradually increase and then, as you continue to rotate the filter, decrease. If you continue turning the front element, you'll see this pattern repeat.
To set up your shot, turn the polarizer to the position that looks best to you and take your photo. Then I recommend dialing the polarizer down a bit and taking another shot. I have found that what looks good through the viewfinder is often too much polarization when you pull the image up on your computer screen. Dialing the amount of polarization down a bit often gets me to a better photo.
The effect of a polarizing filter is strongest when the camera is shooting at a 90-degree angle from the sun. In other words, a polarizer will have the most impact when the sun is shining from the side rather than directly in front or behind your subject. In fact, you won't see any effect at all if you are shooting into the sun or with it at your back. So you don't want to use a polarizer when you are photographing a sunset.
The polarizer reduces the amount of light coming into your camera by about 1½ to 2 stops. Your camera's automatic exposure system will compensate for this. But that may mean reduced shutter speeds and that, in turn, could mean that you are flirting with camera shake problems. So be sure to keep an eye out for this and if you get into the danger zone, open the aperture or adjust the ISO to increase shutter speed, or use a tripod to keep your camera steady.
By the way, a rough rule of thumb for handholding your camera is that you can go without a tripod if you keep the shutter speed faster than 1/(focal length). So if you were shooting at a focal length of 100mm, you would need a shutter speed of at least 1/100th of a second to avoid camera shake..
You can use a polarizing filter on a cloudy day. Contrary to what you may have read, polarizing filters work in cloudy conditions and, in fact, can be really useful in weeding out haze and reflections and increasing color saturation on bright overcast days.
But the effect won't be as strong as on sunny days. And, since the polarizer cuts back on light, you may run into exposure and autofocus problems if you're shooting with a polarizer on a dark, overcast day. In that case, you may find that there's too little light to work with and you would be better off shooting without the polarizer.
Polarizing filters tend to be thicker than other filters due to the addition of the rotating ring on the front. This can cause vignetting problems—where the edges of the filter show as dark corners along the border of your image—especially if you are shooting with an extra wide-angle lens. Keep an eye out for this. You can easily crop out the offending areas later using photo editing software or, if you will be shooting frequently with ultra wide-angle lenses, you may want to consider purchasing one of the low-profile polarizer on the market.
Using a polarizer with an ultra wide-angle lens can cause problems in addition to vignetting. Since this kind of lens can cover such a wide area, the angle of light can change significantly over that range so that the effects of the polarizer can vary dramatically from one end of the scene to the other. For that reason, some people recommend that you avoid using a polarizer on an extreme wide-angle lens. My take on this is that you should just be aware of the issue and keep an eye out for weird lighting effects.
There are two types of polarizing filter: circular and linear. If your camera has an autofocus feature (and most newer cameras do), be sure to get a circular polarizer because the linear type can confuse your camera's autofocus and metering systems.
As much as I love using my polarizer, there are lots of times when it's not the way to go. A polarizer can make a scene too dark or can cut out reflections that could add detail and interest to an image.
And even when a polarizer works with a scene, be careful about overdoing it. There is definitely such a thing as too much polarization. This is where the result is an image that is odd looking, off-putting or just a bit creepy and unrealistic. Often, you'll find that you can get a better image by backing off a bit on the polarizer.
Finally, don’t forget to remove the filter from your lens after you've finished using it. It's easy to forget it's there. But remember that a polarizer reduces the light into your camera. So don't leave your polarizer on your lens unless you're planning to use it.
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f you are just getting started in photography, exposure is one of the first things you need learn.
But even beyond that, getting a good handle on exposure and how the different components of exposure work together is essential if you want to take control of your photography and the images that you are creating.