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I often give presentations at many of the camera clubs in my area. During a recent one, a photographer asked how I control the contrast range in my images. The images he referenced led me to answer with Graduated Neutral Density filters. The next question I fielded was, "If you shoot digitally, why do you bother using filters?" This brings me to an offshoot of this article. Why is there a mindset that if you're a digital shooter, you don't need filters? I'm of the mindset that I want to capture the RAW information with as much perfection as possible. I don't want Photoshop to become a "rescuer." I want it to be an "optimizer." Additionally, I want to be a photographer, not a mouse wrangler. Less time in front of the computer provides more time in the field.
I know there are multiple approaches to mimic the effect of a graduated neutral density filter using Photoshop, but all take time. The bottom line is it takes a lot more time than the 10 seconds it takes me to slide a graduated neutral density filter in front of my lens. Also, I'm firmly of the belief that if the image is worthy of flash card space, it should be captured properly from the get-go.
Much of the instructional work I do deals with teaching scenics. With this in mind, there are two essential filters I place on my list of required items for a class: graduated neutral density and a polarizer. I recommend grad filters to tame the contrast when shooting reflections and also to tame contrast at sunrise and sunset. Place the dark part of the filter over the light part of the image area and the contrast range is tamed. A more evenly lit photograph is the result. Each situation calls for a different strength. I carry one-, two-, and three-stop densities. Additionally, there are soft and hard edge options. If the transition point between the light and dark area is abrupt, it calls for the hard-edge variety. Conversely, if there's a smooth gradation, the soft edge is more beneficial. To optimize their use, the result should look natural. A pet peeve of mine is when I see a graduated filter improperly used on a reflection. If the end result is a reflection that comes out lighter than the section of the image being reflected, the photographer used a filter that was too dark and results in something that isn't natural.
To use a graduated ND filter properly, there are a few keys to keep in mind. An important fact to remember is to use the DOF preview button to accurately position the dark part of the filter over the light area of the image. If you fail to do this, unless you shoot the scene with the aperture wide open, the aperture at which you shoot will impact the point of the dark-to-light transition. This is especially critical if you're using the hard edge variety. Another factor to consider is exposure. Be sure to use the meter reading after the filter is dropped in place, not the one before it's positioned. The meter reading will change as the filter is lowered into place and compensate accordingly.
Realize that the use of a graduated neutral density filter is not restricted to just sunrise and sunset. Additionally, it's not limited to placement on the top portion of the frame. I want to emphasize this and offer a thought. You may encounter a situation where the foreground is brighter than the rest of the image. Situations may include fast moving rapids or layers of white limestone. In both instances, it may be essential to tone down the brightness of the foreground. Simply place the dark part of the graduated filter on the bottom to accomplish this. As always, be cognizant of where the line of transition falls and meter the scene once the filter is in place.