With college being closed for the mid term break and the weather being rotten today I was a bit bored so I thought I'd write a tutorial on using gradual filters.
The image below shows a landscape image with a couple of exposure problems. You could make a few photographs with different exposures and combine them in Photoshop but neutral density gradual filters are by far the quickest. You will see that the sky is well over exposed, by about two stops. The foreground is about three stops under exposed and this is because I was tilting the wide angle lens downward and there was not much light down there.
Neutral density gradual filters are made of resin and are darker at the top than the bottom. They come with different amounts of neutral density from say 1 stop to 4 stops and with a soft step or a hard step feather (see example images). A hard step grad is useful when you have a defined horizon like the horizon in a seascape, and a soft step can be used when a much more subtle effect is desired.
Hard step gradual filter
Soft step gradual filter
There are mainly two systems available one being Cokin the other Lee. They both employ a filter holder and screw in adapters to attach the holder to different sized lens filter threads. The Cokin system is by far the cheapest and their filters are about £15. The Lee system is much larger and suitable for medium and large format cameras as well as 35mm. The Lee system is much more expensive but the filters are of superior quality. Personally I use the Cokin filter holder and screw in adapters with Galen Rowell designed Singh Ray filters. Singh Ray are about the most expensive filters on the market and you can purchase them from the U.S.A in either the Lee or Cokin sizes. The Cokin neutral density filters are not branded as 'neutral density' and described as gray. This is because they are not 'true' neutral density and can give you a slight magenta colour cast. But with all filters you get what you pay for.
A word of warning though! Coloured grads are to be avoided like the plague! They produce a really unnatural effect and can be spotted a mile off.
To align the grads when composing a landscape photograph you should think about where you want the feathered edge to be and align it by sliding it up and down whilst looking through the viewfinder. Now I shoot most landscapes with a small aperture of say F22 for maximum depth of field this creates another problem. You camera sees the image though a slightly different part of the lens at F22 as opposed to a fully open aperture of say F2.8. You should align the grad whilst holding down the depth of field preview button. Don't worry if your camera does not have a D.O.F 'preview' button because you can always shoot a test shot and view this on your on camera screen.
You can also position the grad at an angle for example, the sloping side of a mountain. Or you can use a bit of Blu Tac (which I always carry in my camera bag) to have the grads positioned at different angles. You can used two together say a 1 stop and a 2 stop to create a 3 stop effect.
Below is a diagram to show there I positioned the filters to control the exposure in the example landscape photograph.
And finally the before and after images to compare.
Before
After
Linear Mode
