As outdoor photographers, there's a lot we can't control. Some days the weather's nice and the air is clear. Other times, the air is hazy and nothing really looks quite right. What's a photographer to do?
I'm not talking about fog here. That's an even worse problem. When you can't even see the trail in front of you there's little chance of photographing the mountain that trail leads to. No, I'm talking strictly about haze today. With haze, you can still see what you want to photograph, but you can't see it clearly. On a hazy afternoon, contrast is lowered and detail can get lost.
If you've never been to a location when the air is clear, you might even think that what you see thought the haze is what things are supposed to look like. But once you know how things could look, haze can be a real disappointment. That mountain vista is tantalizingly there, but it just doesn't look right.
When the air is hazy, dust and other particles reflect and scatter light. The effect is most pronounced with shorter wavelengths such as blue and ultraviolet. As such, this can impact not only detail and contrast, but also color rendition. Images shot under hazy conditions tend to have a bluish color cast. The effect increases based on the distance to your subject since more air mass means more dust particles to scatter the light. Foreground objects may look completely normal while background objects in the distance appear bluish and, well... hazy.
Some old-school photographers still slap a UV filter over their lens to absorb some of that extraneous ultraviolet light. But while most film emulsions were sensitive to ultraviolet, modern digital camera sensors generally aren't. UV filters have minimal effect on digital capture. Filter makers do also make specialized "Haze" filters that are essentially UV filters with a slight warm tint added. When you think about what these filters actually do though, their use really doesn't make sense. Your camera will filter out most of the UV light already, and adding the slight warm tint of a haze filter may appear to decrease the bluish cast caused by the haze, but there are better ways. Any filter you attach to the front of your lens affects the entire image indiscriminately yet the haze problem varies based on distance.
When you get home, there are a few things you can do in Lightroom and Photoshop to help remedy your hazy images. In either program, you can tweak the color balance to compensate for the bluish cast at least as well as that haze filter in front of your lens could. Better yet though, you're in complete control as to the amount of correction you apply in the digital darkroom. You can also selectively apply the correction, targeting it to just those areas of the image where it's needed, and to the degree it's needed. You can dispense with the adjustment completely in foreground areas that don't need fixing.
Adjustments such as Levels and Curves can also be used in Lightroom and Photoshop to help restore some of the lost contrast. But arguably the control to go to first is the Clarity slider. Clarity is basically the same thing as sharpening, which also works by increasing contrast along image edges, but in Clarity increases contrast over wider areas.
When photographing through haze though, there's no true way to restore detail that was never captured. That dust not only scatters light rays, it also partially blocks your view of what you're trying to photograph. You can digitally restore the appearance of what you've lost, but this is basically no more than an illusion. Clarity and other techniques work by exaggerating the detail that remains so you don't notice what you've lost. It can't truly return the detail that was never recorded in-camera.
Sometimes, the best way to deal with haze is simply to avoid it. If you photograph the same scene at another time, you may find no haze to contend with. And in this light, it's worth examining what makes haze bad sometimes and not other times.
Sometimes haze can be caused by air pollution. While this may be a major problem when shooting in cities and industrialized areas, it's generally less so when shooting in national parks and other areas far from major urban centers. The haze could also be tied to nearby forest fires, something that can unfortunately happen even in the remotest of areas. Often there's no obvious connection to any single cause. Hazy conditions can sometimes simply be a fact of living in a modern world. You can't completely avoid man's influence on the environment anywhere on earth. And even if you could, natural causes can result in haze too. Fires can be caused by lightning strikes. Even a volcano half a world away can spread dust particles over a wide area that eventually reaches you.
Regardless of the cause, haze generally gets worse as the day progresses. Often, the dawn skies will be crystal clear but the air at sunset is plagued by haze. Water vapor evaporating from lakes, streams and even vegetation traps dust particles and holds them suspended. Dust that might have dissipated early in the day builds up later in the afternoon resulting in visible haze.
You can chock this little tidbit up as another good reason to get up in time for sunrise. Don't just assume that sunset is the same thing as sunrise except in reverse.