A Graduated Neutral Density Filter are not like the Neutral Density filters I have talked about in the past. Those cut the light into the entire lens opening. A graduated ND filter, is dark on one side and gradually goes to clear about half way down the filter. They come in two sizes. Circular sizes screw right on to a lens like any other filter. Square ones are larger and cover more than the lens opening allowing one to move the graduated part around. While you can get holders for the square filters, most photographers prefer to hold the filter in front of the lens.
It is not as straight forward as you might think. The trick I finally learned was to use the Depth of Field Preview Button on my camera (see your manual for where this button is located on your camera and how to use it). Once pressed, I could see the effects of the filter. If I did not press the DoF Preview button, I could not see it (or just barely). The camera keeps the aperture of a lens wide open for focusing purposes only stopping down the lens when you press the shutter. The DoF Preview button stops down the lens to the aperture set so you can see the effects of a filter or tell what is in focus based on the aperture used.
I know many people would rather just do the work in their favorite photo editor. That takes time. In my case, it took me 10 minutes to get the photo on the left you see above to look like the one on the right. The right side one only took a couple of minutes to do a little sharpening and pull back highlights and shadows. That time adds up if you have a dozen or more photos to process.
For more expert advice on how to use a Graduated Neutral Density (GND) filter, click here to visit Landscape Photographer extraordinaire Jeff Lynch’s blog.