Kase Armour 100 Magnetic Square R- GND 0.9

R-GND (Reverse Graduated Neutral Density) Reverse gray gradient filter
R-GND gray gradient filters have a gradient that varies in strength and density across the surface of the glass filter. Half of the filters are clear and the other half is a GND gray gradient filter, which becomes lighter at the top. When photographing with long shutter speeds, it is important to be able to control the light. Depending on what you want to block the light from, you can place the gray gradient filter in the correct position. In a landscape scene the sky is normally brighter than the foreground and at sunrise/sunset a fairly narrow beam of light around the sun is much brighter, so an R-GND filter is placed in front of the lens and moved to a position where the brighter part of the scene is covered by the R-GND filter and the margin between sky and sun, along with the margin between the sun and foreground, are blurred using the transition zones of the R-GND filter. The scene is normally metered for the highlight area and shadow area and the difference in stops dictates the strength of the filter used. Using an R-GND filter avoids the heavy darkening sky normally associated with using stronger GND filters in sunrise/sunset scenes, the transition zones are normally soft.