Tools of the Trade: Gradual Neutral Density Filters
As a landscape photographer, I am in a constant struggle trying to even out my exposure between a dark foreground and a bright background. What most people don’t know is that there is usually a huge difference in the exposure times between the sky and ground. If my sky meters for1/30th at f/16, my ground will meter a 1/2nd. Inevitably, if I were to shoot at 1/2nd or 1/30th, I would lose the detail in either the sky or ground. A common failing of point and shoot cameras, and even some DSLR camera’s that is that it can only really detect a few stops of light range. So if your landscape is dynamic and there are dramatic differences in light, its likely those cameras will not be able to properly expose the image.
The tool I reach for to fix this problem is a Gradual Neutral Density filter. GND’s come in all shapes and sizes, each with a different application depending on the circumstances. The main purpose of a GND is to darken certain portions of the picture so as to allow for an even exposure between foreground and background. The majority of the day, the sky is at least a few stops lighter than the foreground and during dusk and dawn, that gap is much bigger. Often if you expose for the foreground, you blowout you sky, and if you expose for the sky, good-bye detail in your foreground.
That’s where GND’s come in. They are clear sheets of glass or plastic that goes in front of the lens, darkening half of it to allow for an even exposure. So say that your sky is 6 stops different than your foreground. If you throw a couple GNDs on the sky, you will have a nice even exposure. Of course with conditions constantly changing, these filters come in various stops to allow the right fit. The most common ones are .3, .6, and .9, which translate to 1-stop, 2-stops, and 3-stops respectively. These can be combined together to make up for a large difference between your sky and ground. Often while shooting sunset or sunrise, I am using at least 5-stops worth of GND’s. These filters also come in varies levels of transitions too, for more specific
The most common type of these filters is soft transition, meaning that from the middle to the top of the filter, the change from lighter to darker is slower. The other common type are hard transition, which have an only a slight gradual from middle to top. On top of the two major kinds, there are more specific types like reverse and strip GND’s. A reverse is similar to a normal GND, but instead of the normal light to dark going from middle to the top of the filter, it starts dark in the middle and gets gradually lighter at the top. These are especially great at sunrise or sunset in that typically the brightest part of the sky is around the horizon and not at the top of the image. A strip GND is very specific in that only a small strip on the filter is dark. This is useful in only a few situations like if the sun is below the clouds giving great under light, but that little sliver of light where the sun sits is completely blown out.
I imagine this sounds pretty complicated to those that haven’t used them before, but the concept is simple enough. It darkens your bights so that everything in the image is evenly exposed. I can honestly tell you that if properly used, these can transform your images from bland to spectacular. There are various levels of these filters that make it easy for beginners to spend little to start to try it. A basic set of them with a holder will be less than $100, which is a cheap way to make better images in my humble opinion.
Until next time, happy shooting.