Filters 101 (Part 2)

Written by: Jeff

You can read the first part of this article here.

•DENSITY FILTERS

Density filters are like sunglasses that you would wear on a sunny day. They effectively darken the scene and are available in different strengths. The most commonly used type of density filter is the neutral density (ND) filter since it does not add any color cast. Density filters are necessary if you plan to capture motion blur on a bright day. Without it, the extended exposure necessary for capturing motion blur will cause you to blow out your highlights.

CC Photo by MmMmMmMatt
Landscape photographers use a specialized type of density filter called the graduated neutral density (GND) filter. A GND filter is shaded at the top part of the filter and slowly fades until the bottom of the filter is clear. This filter was designed to darken the sky in a photo without affecting the foreground. The two most popular GND filter variants are soft-step and hard-step filters. In soft-step filters, the transition between the shaded part to the clear part is very gradual and subtle which is good for horizons that are not completely flat. Hard-step filters have a more defined boundary between the shaded area to the clear area.

CC Photo by ccdoh1
GND filters are also available as both the threaded and the square filter version. It is better to get the square filter GND so that you can adjust exactly where the transition of the shaded to the clear area will be.

There are a lot of techniques in Photoshop that emulates the effect of a graduated neutral density filter like the one found in our previous article. Photoshop will only help accentuate what detail you managed to retain in the sky and not save a blown photo.

•POLARIZERS

Polarizers come in two variants: linear and circular. These variants do not refer to the physical shape of the filter but how it directs the light coming into your lens. Linear polarizers direct light waves into a linear fashion while circular polarizers direct light into a spiral or circular motion.

The only important thing to remember when buying a polarizer is that linear polarizers do not work with DSLRs or cameras that have the ability to auto-focus and auto-expose. This means that you have to focus and fix the exposure before you attach a linear polarizer to the lens. Circular polarizers, on the other hand, can be attached to the lens during metering and auto-focusing.

Polarizers darken the sky, the greens in the foliage and cut reflections in your photo. In my opinion, this is the filter that does the most for DSLRs. Polarizers attach to the front of the lens much like any other filter with the addition of another rotating element at the front of the lens. The rotating element at the front is what controls the amount of polarization. You can look through the viewfinder and see the amount of polarization while you rotate the filter.

CC Photo by OliverAlex
The effect polarization is also dependent on where your camera is pointed. The effect is at its maximum when the camera is aimed perpendicular from the rays of the sun. If you’re out taking photos at noon then the amount of maximum polarization would be at the horizon. Polarizers will exhibit no effect if it is aimed at the sun.

You should also use caution when using polarizers with wide angle lenses since the amount of polarization is different across the sky. Some parts of the sky will appear bluer than the rest if the angle of view of your lens is too wide. The photo below was taken with a lens set at 10mm. You can see that the sky is bluer at the center of the photo where maximum polarization is present.

CC Photo by J.Rosario

SOME NOTES ON FILTERS

1. Filters, not just density filters, will lessen the light entering your lens since it adds another element for the light to pass through. Be sure to check the specs of your filters to see how much it affects your exposure.
2. Filters will not affect how sharp your photos are unless your filter is dirty.
3. You can stack filters on top of each other to mix their effects. The rule of thumb is that you can use three filters at the same time before the quality of your photo is affected. Be sure to double check your lens’ manual if this holds true for you.

RELATED READING:
Filters 101
How to Fix Washed Out Skies

Related posts:

1. Filters
2. Filters 101
3. How to Clean Your Lenses Properly
4. Macro Photography 101, Part 2
5. Starlight Effect: Creative Use of Aperture

Previous Post: Filters 101