Nearly all digital cameras, including all DSLRs and nearly every mirrorless ever made, show a view recorded through the lens. By definition, DSLRs use an optical viewfinder which makes it the easiest to see subtle changes in the view when using filters such as a polarizer.
A Circular Polarizer, further referred to simply as Polarizer, is a special filter which filters out light with a certain polarization. It is used to diminish the effect for haze and reflection which results in increased saturation when taking photos of nature. When shooting through glass, a polarizer helps see more clearly by reducing surface reflections. Here is an unpolarized shot of the Cotopaxi:
First is to know when to put it on and when not too:
- It is not advisable to keep a polarizer on constantly, although some people who do that, because usually reduces light by 2 stops. The only exception to this are Hoya HD filters which reduce light by just one stop. This forces the camera to either use a slower shutter-speed, which makes things that move blurry, or higher ISO which makes images more grainy.
- Polarizers are not useful in dull or diffuse light. They only have an effect when the polarization of light differs sufficiently.
- They are useful in bright directional light and you should see the effect right away when it is. Even in bright light, their effect is strongest at 90-degrees from the sun. If you are shooting into the sun or directly away, there will be very little difference.
- Polarizers are not recommended for ultra-wide-angle lenses, due to the previous point. Specifically, if the scene being photographed includes light that is parallel and perpendicular relative to the sun, the polarizer will only affect part of the light and results will look very strange.
Here is the same scene of the Cotopaxi taken with a Hoya HD Circular Polarizer mounted:
Note how details are more visible on the side of the volcano. There are also more details in the snow-covered area which are highly reflective. The biggest difference in this scene though is a change in color. The sky blue is actually caused by light bouncing in the air between water and dust particules. When the polarizer is in effect, a notable proportion of the blue goes away, making vegetation look greener and more saturated.
Second is how to use a polarizer:
- Looking through the viewfinder, frame your shot, zooming if necessary, then rotate the outer ring of the polarizer. Make sure the filter has been screwed sufficiently tight. Otherwise, you’ll unscrew the whole thing and it can fall to its death.
- Rotate the ring until you see the most pleasing image. Generally the sky gets darker to a point and then start brightening up. At the darkest point, the effect is maximal but you may not want to go that far if it makes the scene look unnatural, such as the sky being much darker than the foreground.
- Polarizers also remove reflections. If that is the goal, rotate the ring until you see the least reflection where you want it to go away. It is rare that it disappears entirely unless the surface is completely flat.
Here is the final shot of the Cotopaxi with the Circular Polarizer rotated to maximize its effect:
One can see here that there are more details throughout the image and that colors appear more natural. Another thing to note is that all images are about the same brightness despite the polarizer cutting down light significantly. In all these cases, the camera has set to Aperture Priority mode with the aperture set to F/6.7. Since these were captured using a 250mm lens, the shutter-speed stayed at 1/250s for all shots. Auto ISO was on though, so the camera took the three shots at ISO 200, 400 and 800, respectively. Without Auto ISO the camera would have changed the shutter-speed, potentially causing some blurring. For those shooting in Manual mode, one must change a parameter manually to compensate for the loss of light.
Finally, it is completely worth investing in a quality polarizer. The effect cannot be replicated by software and a poor polarizer can introduce flare. The Hoya HD series not only transmits more light then competitors, it is also made of hardened glass which protects it from impact. They are also coated with a water and grease repellent layer to make cleaning easier. Currently, the Hoya HD3 is the cream-of-the-crop of polarizers. Just make sure to get the right size!