Since the camera was invented, we have tried to copy one of the greatest wonders of our body; the human eye. Unfortunately, despite being over 100 years since the first time that we captured light, we are still far from overcoming Mother Nature.
Why? Because in the visible spectrum your eye sees much better than your camera.
The parameter that describes this behavior is called Dynamic Range. This basically defines the difference between the minimum and maximum value of brightness that a device (like your eye or the sensor of your camera) is able to record. In the real world, Dynamic Range defines the ability of your camera to see details in very dark areas and very clear (bright) areas of the scene.
If you’re wondering how much more your eye sees, the answer is staggering. Your eyes have about twice as much range that they can see and capture.
That’s why when you look at a marvelous sunset with your eyes you’re able to see all the details in the scene (in both the sky and the land). But as soon as you try to capture it with your camera, you’ll get an overexposed sky or a underexposed foreground. The Dynamic Range of your camera is only able to capture detail in one of those areas so you have to choose.
But if even the best cameras have a Dynamic Range which is only half that of the human eye. So how can we hope to shoot a beautiful sunset or a wonderful sunrise and capture all the marvelous details?
There are different methods to overcome this problem, but my favorite is the use of Graduated Neutral Density filters (GND).
What is a Graduated Neutral Density Filter?
A Graduated Neutral Density Filter is one made of two distinct parts; a completely transparent area, and a darker section. By setting the darkest part of the filter to correspond with the brightest portion of the scene, you can reduce the exposure difference (dynamic range) in the frame.
To reduce the exposure difference is to reduce the dynamic range of the scene, and thus allow your camera to simultaneously capture detail in both bright and dark areas of the scene. Basically, to make an analogy, GND filters are like a kind of sunglasses for your camera.
Types of GND filters
Graduated Neutral Density Filters are typically distinguished by the type of transition that exists between the transparent and dark areas of the filter. For this reason, we can identify three families of GNDs:
- Hard-edge filters, which are characterized by a clear boundary (it’s obvious where one begins and the other ends) between the transparent and dark areas. They are therefore used when the separation between the bright and dark areas of your scene is very defined, such as the horizon at sea.
- Soft-edge filters are characterized by a soft transition (they change from light to dark more gradually) and are therefore used when the transition between light and dark areas is not so clear. A classic example is a shot in a mountainous area.
- Reverse filters, which are nothing more than hard-edge GNDs with the dark area that fades away the more you move from the line of separation to the upper border of the filter (meaning it’s darker in the middle than on the edge). Basically, they were invented to better manage sunrises and sunsets, where the light is more intense on the horizon line (middle). If you love seascapes like me, this filter will be one of your best friends forever!
Which to buy?
Another distinction is between filters is the construction material. Higher quality filters are made of optical glass. Putting an inexpensive resin filter in front of a lens worth hundreds (or thousands) of dollars is not a great idea.
Finally, GND filters are distinguished by graduation, or their ability to block light through the darkest area. Essentially how dark they are at the extreme. Normally in landscape photography, this difference is between one and four stops during sunset and sunrise, depending on weather conditions. This is the reason why you will find these gradations almost exclusively on the market.
Shop for Graduated Neutral Density filters on Amazon.com or on B&H Photo Video’s site (they ship worldwide).
How to use a GND filter in the field
The use of GND filters in the field is very simple; try to take exposure readings in the darkest and in the brightest areas of the scene (usually the sky). The exposure difference will indicate the intensity of the filter to be used. Let’s assume that the light meter reading for the sky is 1/250th, and the one for the rocks in the foreground is 1/30th. The difference between those readings is three stops (250th > 125th > 60th > 30th), so to balance the exposure you must use a 0.9 (3-stop) GND.
At this point, just mount the filter with its dark side over the brightest part of the scene. This is why a GND screw-in filter does not make sense. You would not have the possibility to align the dark area in accordance with the scene as well as a drop-in style filter.
To avoid having to hold the filter with your hands (that could be a problem if you are going to use them together with other filters) you can buy a holder, that once mounted in front of your lens will do the job for you. There are many valid solutions on the market, but the best one (in my opinion) is the V5 Pro Holder by NiSi filters. This is the only one that lets you simultaneously install three different filters and a polarizer without any vignetting issues (as wide as 16mm on full frame cameras).
At this point, the limited Dynamic Range of your image will be just a bad memory!