Imagine if you will…a rectangular glass or resin filter, having only half of the glass coated with a dark coating that doesn’t add a color cast to your image. Where a Circular filter allows you to darken the entire visible area of the photograph, Graduated Neutral Density Filters allow you to even out exposure in a photograph.
As you know, when shooting a landscape the sky portion of the frame is typically one to three (and occasionally more) stops brighter than the foreground elements of the frame. By holding the graduated filter to the front of your lens with the dark line at or just below the horizon, you can even out the exposure so that your foreground and sky elements are closer together in their exposure value. Depending on your choices, you will find these filters with two edge definitions: Hard (for a defined horizon) and Soft (for when you prefer a softer blended edge between the light and dark portions of your frame).
Graduated Neutral Density come in “stops” – that is, how much light is kept from reaching the sensor. 1, 2 and 3 stop ND filters (and often 4 stops and more) are available in different sizes. Check out the Resources provided below to start your research on Filters; you’ll find info on circular polarizers and other camera filters there as well. You can also read Jay Goodrich’s blog posts on Filtration and Filtration Revisitation to get a better handle on all the offerings out there.
Before you say it – yes … we know that in Lightroom there is a Neutral Density filter tool, but at Teton Photo Workshops we recommend getting as close as you can in camera before optimizing your RAW image in LR (or your photo editing software of choice).
Lee Filters ~ http://www.leefilters.com/index.php/camera/ndgrads
Cokin Filters ~ http://www.cokin-filters.com/creative/filters/
Tiffen Filters ~ http://www.tiffen.com/filters.htm
Breakthrough ~ http://breakthrough.photography
REMEMBER: If you purchase a Singh-Ray filter, use code ‘GOODRICH10′ to receive 10% off your total order!