Before we understand Reverse Graduated Neutral Density Filter, lets first understand what is a Graduated ND Filter.
A Graduated ND Filter is a Glass Filter with dark portion on top gradually getting lighter towards the center of filter and finally becoming a clear glass. They are used in lighting scenarios where there is a difference in light stops in sky and the other half of the landscape image. They help you darken lighter areas while keeping the dark areas unaffected.
Though Graduated ND filters work in most situations, there are some typical situations where they start creating problems e.g. Sunrise and Sunset. Both during Sunrise and Sunset, Sun is closer to horizon making the light very tricky with it being maximum near horizon and gradually dimming both towards foreground and sky.
For shooting Sunrise and Sunset scenes with Sun being just around horizon, Reverse Graduated ND Filter comes in handy.
Can’t I simply use the normal Graduated ND Filter upside down?
The answer is a straightforward NO. A graduated ND filter has dark area on top and light area at bottom with graduating darkness in the middle of the filter. Even if we just flip it, it will still get progressively darker towards the darker side of filter and lighter towards lighter side of filter. We are talking about tackling a situation where we need darker area of filter right in the middle to counter more light where Sun is positioned.
So what are Reverse Graduated ND Filters?
A Reverse Graduated ND filter is darkest in the center; gradually fades to lighter in one direction and abruptly to clear glass on the other. Since its rectangular in shape, one can easily adjust the position of center dark area to position right where the bright Sun is helping you manage exposure and create balanced exposures.
How to use it?
Though there is no rocket science to use this filter, it is important to be little careful while positioning this filter. The darkest part in center must be right where the Sun is positioned. I usually turn the Live View on to see its effect real time and slide it up or down to position it correctly.
Which one to buy?
Though there are some brands who are into making Reverse GND Filters, I prefer NiSi Reverse GND Filter for its top notch built quality and neutrality. You will never falter in your landscape photography with NiSi Filters in your bag.
If you are a landscape photographer at any stage of your photography skills, then this piece of glass is highly recommended to you. Buy it and start enjoying Sunset and Sunrise photography even more.
Here are a couple of images shot using NiSi Reverse GND: