Alpha Photography Blog

Filters enable a wide variety of creative and functional results to be achieved. Granted, many digital cameras have white balance compensation functions, and photo editing software creates effects that manual filters are designed for. In most cases, SLR cameras will still need to use filters in order to achieve the same results.

Here are some of the more standard filters, which can be used to correct color and exposure imbalances.

Filters can be square or rectangular, mounted in a holder, or round and screwed onto the front of the lens, which is more common.

A few points to know about filters:

• Filters reduce the amount of light entering the lens, which means that you require a slower shutter speed. So, it may be necessary to use a tripod when the shutter speed goes below 1/60 second;
• Diameter of lens - make sure you buy the right diameter size filter, so it will fit onto your lens. The size is written around the end of your lens (e.g. 55mm); and
• A UV or skylight filter can be used to protect your lens - they don’t really affect the image itself, and will make sure you keep that expensive piece of equipment from being ruined.

White Balance Correction Filters

Light is a very fickle medium - changing with the slightest addition of colour. There is a standard color temperature, which for daylight, is set at 5500 Kelvin. Without being too technical, below is an outline of the main white balance correction filters to combat the most common situations:

• 80A - to correct tungsten household bulbs, which produce an orange cast. This filter will work with standard daylight film (which is the most readily available film on the market);
• 81A - this is a ‘warm up’ filter, adding a hint of red/brown to your image. This is particularly useful when using flash, as this is a harsh white light, which can wash out skin tones; and
• FL-D - corrects fluorescent light, which produces a green cast. This filter is magenta in color and corrects most types of fluorescent bulbs. The ‘D’ signifies that this filter works when using standard daylight film. There is an FL-W filter, which is to be used with tungsten film (not as readily available).

Vignetting

A problem that can be experienced when using filters is vignetting. Specifically referred to as mechanical vignetting, this occurs when a physical object obstructs the lens. Most commonly this occurs when more than one filter is placed on the lens at the same time, or the wrong lens hood is being used. The result is darkened edges of the frame.

Vignetting is sometimes a desirable quality, especially with portrait photos - this type of vignetting is evenly distributed and the subject is placed in the frame to accentuate the effect.

To avoid vignetting, only place one filter over the lens at a time, and avoid using filters with ultra-wide lenses.

Combating Glare

A fundamental piece of every photography kit should be a polarizing filter. Polarizing filters combat glare and gaze, being particularly useful when photographing on water and snow.

This type of filter works in much the same way as polarizing sunglasses. If you stare out at the ocean without polarized sunglasses the scene is too bright, but introduce the sunglasses (with polarization) and your vision becomes much improved. The same is true of any bright day. Adding a polarizing filter saturates the colors and results in a much more color intense image.

Reducing Light

Some effects require a very slow shutter speed, yet the ambient light is very bright. The filter to use in this situation is a Neutral Density (ND) filter.

For example, city scenes that you see with no person in them - this is generally the result of using a ND filter and reducing the shutter speed to the extent that the camera can’t ’see’ the people, as they are moving faster than the camera is capturing the scene.

A graduated ND filter is just as its name suggests - the density is graduated, so the level of ‘darkness’ in the filter is darker are the top and almost clear at the bottom. This comes in very handy when a scene has a dramatic contrast - for instance, a bright sky and a foreground in shadow. Position the filter on the lens so the darker area is looking at the bright sky and the clear section is looking at the shadowy foreground. Then expose the image so both are correct.

There are many other filters that create special effects, which can be achieved in post production editing. The filters mentioned above correct color and exposures. Enjoy taking fabulous photos, which are correctly exposed and produce colors that match what the eye sees.

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