Filters are an important part of many photographers toolkits. Even today, with the software tools available to the Digital Photographer - optical filters are essential.
It is much easier to get the image as close to what you are trying to achieve at the camera and use software for fine tuning. No matter how much you try with software if you have an image that is not good quality to start with you can't fix it! With software you can make good quality pictures great.
Graduated ND (Neutral Density) Filters have the effect of reducing the exposure over part of the image. A portion of the filter is clear and another portion is grey and blocks some amount of light. This helps to stop the washed out highlights particularly evident in the sky.
Rectangular type filters (such as the Cokin range) are far more useful than screw-in types. As you can move them up or down and thus position the horizon where you want it in your composition. With a screw-in filter, you have to compose with the horizon in the centre of the frame.
Graduated ND Filters generally come in 3 different grades:
- Graduated ND2 - light
- Graduated ND4 - medium
- Graduated ND8 - dark
Graduated filters can have either a soft or hard transformation between the dark and clear part of the filter.
The below sample images give an indication of what can be achieved. In the first image the sky looks OK but the foreground is very dark. After the introduction of the filter things are much improved.
Image taken midday on a bright sunny day without ND Filter.
Image taken a about a minute later with a soft transition Graduated ND4 Filter in place.
Note:- Both images above also have a circular polarizer to enhance the blue in the sky!