A hard edge is used when there is an abrupt change in brightness. For example a field with a horizon to a bright sky. A soft edge is a wider smoother change from light to dark. This is used when the light and dark portions are not distinctly separated.
As a general rule, a hard grad would be used for images containing a horizon, or any hard transition between the sky and the foreground - even with jagged or mountainous horizons, the exposure can be controlled far easier with a hard grad.
Neutral density filters do not affect the coloration of the image and the 0.9 density provides a 3 stop reduction in light from entering the lens.
The Nisi100 x 150mm 0.9 Soft-Edge Graduated Neutral Density Filter helps to darken specific areas of an image, such as bright skies, while allowing for a normal, unaffected exposure in the other regions of the image.
Graduated neutral density Filter Size 3.9 x 5.9" / 100 x 150 mm Density 0.9 (3 stop)
|What's in the box||
100x150 Graduated ND9 filter