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Graduated neutral density filters are one of the neatest innovations to have come around in photography and photographic accessories. What types of types of graduated ND filters exist? Is it easy to learn how to use a graduated ND filter? What are the benefits of a graduated ND filter for your photography?
Physical filters that fit on lenses have been in use since near the beginning of photography itself. Neutral density (ND) filters are often used in situations where exposure needs to be adjusted and using lens aperture, shutter speed, and film or sensor sensitivity does not give enough control.
Why Neutral Density Filters Are Used
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The world of photography quickly figured out that you could apply neutral density to only part of an image. A scene in front of your camera that has a large bright area and a large dark area causes a problem with metering to determine exposure.
Do you measure for the bright area to be properly exposed? If you do this, the darker areas end up underexposed, perhaps severely underexposed, with little detail showing.
The same thing happens in reverse if you set exposure based on metering the shadow. There will be good detail in the darker areas but no detail in the highlights. Exposure is outside the dynamic range of your recording medium.
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If you average the exposure value for shadow and highlight, you get a workable exposure, but detail and maybe color will suffer on both sides. Now, if you could block some of the brightness from the highlight side, then you could get a balanced exposure within the dynamic range of your digital camera or film.
A graduated neutral density (GND) filter lets you do just that.
A well made ND or GND filter should not affect color or image sharpness. That’s part of what the “neutral” in graduated neutral density or neutral density means.
Types of Graduated ND Filters
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Graduated neutral density filters are dark on one side, clear on the other, and the transition is gradual. A plain split ND filter has no transition area, it goes from full to clear.
Graduated filters can have a hard or soft transition, but they don’t go from 0% to 100% on a line. Rather, the changeover is progressive. It is very similar in concept to progessive lenses for eyeglasses. The old style of bifocals had a hard line, progressives don’t.
There are, however, variations in how much area is used for the change. A hard edge GND changes over in a very short area of the filter whereas soft edge GNDs have a larger 0-100% area.
A reverse GND is clear on one side and the other side has a density that is darkest at the center, a little less at the edge.
Benefits of a Graduated ND Filter
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We mentioned balancing exposure values to create a manageable dynamic range, but what does that mean? What situations would benefit from doing that? Certain scenes in nature are difficult to properly expose for the entire range of bright to dark within the frame of what will be imaged.
A sunset or a sunrise come to mind right away. In order to catch the beautiful colors in the sky while keeping detail and interest in foreground areas, you need to hold back on brightness while allowing enough exposure for shadow areas.
Architectural subjects may sometimes have similar challenges, perhaps because of different materials used for adjoining areas. Any scene that has a large expanse of dark and another of light is a good scene to apply GND filtration.
Soft Edge GND Filters
A soft edge GND filter, like this Haida 100 x 150mm NanoPro MC Soft Edge Graduated 0.9 Neutral Density Filter, has about 3 stops of density on one side, fading to completely clear on the other, with the center having a soft edge. Other strengths of density are available.
Square filters in a holder give you exacting control over where to place the edge and what direction the dark to light fade goes.
You can spin the filter holder around on the adapter and slide it up and down or side to side within the holder. That way, you put it in precisely the position it needs to be. This holds true for any type of GND filter and other filters as well.
Hard Edge GND Filters
The hard edge filters have a stark divide in the center. It’s still a gradual transition, but the change over occurs within a very short distance. An example of this type of filter is the Haida 100 x 150mm NanoPro MC Hard Edge Graduated 0.9 Neutral Density Filter.
While it may seem that a soft edge GND filter is more usable, there are many uses for hard edge GND filters. Lake and ocean vistas with a clear view of the horizon would benefit from a hard edge GND filter. Experiment with the dark part over the sky and over the land and see how it changes the final result. Some of the architectural scenarios we may run into would benefit from this as well.
Reverse GND Filters
Reverse GND filters, like the Haida 100 x 150mm NanoPro MC Reverse Graduated 0.9 ND Optical Glass Filter, also have a gradual fade from light to dark, but the darkest part of the fade is near the center of the filter. So it is like a soft edge GND with a hard edge transition in the center.
These are specially designed for the specific exposure range conditions in a typical sunset or sunrise view. Once you try one of these, you will likely want to use it for every sunset and sunrise you shoot.
GND FIlters Are Extremely Useful Photographic Tools
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In order to create and capture usable images in conditions where the scene has a wide dynamic range, there are only a few ways to handle the challenge well. One way is HDR, another way is Photoshop.
But graduated Neutral Density Filters are my first choice. Ease of use and versatility are what give them the edge in my gear bag...pun intended!