A deep blue sky can be an essential component of a picture.
WHY AREN’T SKIES BLUE IN MY PICTURES?
You may have noticed that blue skies do not often turn out as blue in your landscape pictures, but usually turn out bleached white, as if it had been a cloudy and gray day. You probably wonder if you are doing something wrong. Well, you probably aren’t doing anything wrong; you’re just not doing it right.
Ever wonder why blue sky turns out so pale in your pictures?
THE SKY & THE GROUND REQUIRE DIFFERENT EXPOSURES
In a landscape, both the sun and the sky illuminate the ground. (The sky itself is a source of light.) If you aim your camera down to exclude any sky from the viewfinder so its light meter reads only the ground, and then point it up so it reads only the sky, you will have two different exposure readings, because the sky is brighter than the ground. If you take a picture of the sky only, it will be correctly exposed and the picture will show a nice blue sky on a clear day. But using the same exposure settings to shoot the ground will make the ground look quite dark.
Your camera’s meter averages the exposure when you have both sky and ground in equal amounts in the viewframe so that the ground is a little bit darker than it would be if you exposed for it only, and the sky is rendered a little paler. If you are shooting slide film or a digital camera (where the image has not been manipulated, but show a scene exactly as it was photographed), this is probably how your landscapes look - sky too pale and ground too dark.
With negative film, the real impact on the sky occurs when your prints are made in the lab. The person doing the printing looks at your image, recognizes that the ground is too dark and adjusts the image’s density to make the ground brighter. The problem, however, is that the whole image, not just the ground, is affected by the adjustment, and your sky is rendered much paler, losing much of its blue cast. The print could just as easily have been adjusted to make the sky darker, which would then look nicely blue, but the ground would look too deeply shaded. It’s a trade-off, and most photo printers assume you want the ground to look properly-exposed.
How do you get around it?
If you are shooting with a digital camera, you can sometimes adjust the balance between sky and ground yourself afterwards, using image-editing software. However, there must be detail in the sky in the first place in order for you to emphasize it. The better answer, one that’s very effective, is to use a gradated neutral density filter on your lens when taking the picture.
A gradated ND (neutral density) filter will turn your skies blue again.
THE GRADATED NEUTRAL DENSITY FILTER
A filter that is clear in one half while the other half gradually changes to a neutral density filter is called a gradated or graduated neutral density filter (also called a split neutral density filter or a gradated gray filter). Light passes unchanged through the clear portion of the filter, but is partially blocked by the denser part, making it a very handy filter to have, especially for landscapes that include the sky.
When you shoot a landscape that has sky in it, attach the filter to your lens so the denser (darker) part is on top, and ensure that the dividing line between the filter’s dense half and its clear half (the "transition line") is level with the horizon. The dark upper part of the filter reduces the amount of light from the sky that reaches the film or a digital camera's sensor. The lower part, which is clear, allows for normal exposure of the land. The resulting print will then have a darker (and therefore bluer) sky and properly-exposed ground.
Since the dense portion of the filter is neutral - simply transmitting less light with no color changes - this filter works for both color and black and white film, and with a digital camera.
This filter is available as a circular filter that can be turned in its mount or as an unmounted 3" by 3" square or 4" by 5" rectangular filter that is part of an interchangeable filter holder system. (See Filter quality to learn about filter systems.)
The dense portion does not have to be placed so that it affects the upper part of your image. It can also be used at the bottom of the image or rotated so it affects only one side of the image, or even used in a diagonal position. A gradated ND filter placed to block a bright foreground can balance the amount of light between it and the background. For example, you might position the dense portion at the bottom when using flash so that your foreground will not be overexposed, or when there is, for example, a bright ski hill in the foreground with darker trees in the background.
When the sky occupies only a small portion of the viewframe, a square or rectangular gradated ND filter can be correctly positioned to filter the sky - something you can't do with a round filter.
OPTIONS FOR GRADATED NEUTRAL DENSITY FILTERS
Ability to reposition the filter's transition line
It's important when using the gradated ND filter to place the transition line where it looks natural in the image, such as on a horizon line. If the transition line is visible - as it can be if placed over an area of continuous tone or if it bisects a uniformly-lit vertical object such as a column - it tends to disrupt the image's harmony. Viewers know they are looking at something unnatural, a line that doesn't belong.
The square and rectangular types of gradated ND filters can usually be adjusted up or down to affect more or less of the image, giving them a major advantage over circular filters. This flexibility provides more opportunities for creative photography because the transition line does not have to be in the middle of the frame, as it is with the circular filter. Some gradated ND filters are available with either a soft or a hard edge where the denser portion begins. The soft or feathered edge allows a more gradual-looking transition.
Different densities of filter
Further, there are different degrees of density available in gradated neutral density filters, permitting more or less light to be transmitted to the film through the dense portion. The density choices are commonly one, two and even three stops, with the two-stop variety being the most popular.
Two ratios for the filter's areas that are clear and denser
Some manufacturers make a gradated ND filter that is divided 60/40 instead of 50/50. 60% of the filter is clear and 40% is gradated. The reason for providing photographers with this choice is that a great number of landscapes are photographed with more land and less sky, hence the need for a larger transparent area.
Soft and hard transition lines or No transition line at all
See "Minimize the appearance of the transition line" below.
Quality
As with any filter, there are differing levels of quality available from different manufacturers. Some inexpensive plastic or resin filters may be advertised as being neutral gray, but may have a slight color cast to them. This doesn't mean that all resin filters, however, are inferior. Some are of excellent quality. Manufacturer's reputation and higher price are generally good indicators of a good filter. (See Filter quality.)
Placement of the filter's transition line on the horizon makes the transition look natural.
MINIMIZE THE APPEARANCE OF THE TRANSITION LINE
The effect of a gradated ND filter is quite pronounced when using a very wide-angle lens at a small aperture setting. The transition is distinct, whereas a picture taken with a telephoto lens at a wide aperture through a gradated ND filter is more subtle and the effect is more subdued. The smaller the aperture, the more distinct and sharper is the boundary between the dense section and the clear section. Use the camera's through-the-lens viewfinder and stop down the lens to check the effect before deciding on your aperture setting. Pressing your camera's Depth of field preview button allows you to see the effect.
Keeping the filter as close as possible to the lens will maximize the transition's softness. A filter with a "soft" or feathered transition line blends nicely into most scenes, even when using a wide-angle lens which tends to show the transition line more than longer lenses. A "hard" transition line filter provides gradation that might be useful with a telephoto in shooting a fairly-flat horizon when the transition line is placed on the horizon line.
Another type of ND filter changes density gradually across the entire filter so there is no distinct transition line at all.
EXPOSURE
Determining exposure when using a gradated ND filter is no different than determining normal exposure without it. A camera's built-in exposure meter will give a reading that should prove to be correct without the need for adjustment. If you are using a hand-held light meter, take your reading from the area of the scene that will be photographed through the clear portion of the filter. This is usually the darker part of the scene. You can also measure the highlight area of the scene and adjust your shutter and aperture settings based on the filter factor of the dense area of the filter. (See Filter factor). Don't forget to bracket exposures if the image is an important one that you want to get just right.
A blue gradated ND filter is one of many available choices in colored gradated ND filters.
BLUE SKIES IN YOUR IMAGES WHEN THE SKY IS NOT BLUE
If the day is overcast with a pale sky, and your picture would benefit by having a blue sky, all is not lost.
You may be able to get that lovely blue sky in your picture by using a gradated blue filter in place of a gradated neutral density filter. See Gradated filters that are colored.
A polarizing filter will also deepen the blue of the sky. However, unlike the graduated ND filter, the density of blue can vary from one side of an image to the other under certain circumstances.
TRY THE POLARIZER, TOO, FOR BLUE SKIES
Another very effective filter to use in controlling the depth of color in a blue sky is the polarizer or polarizing filter. Certain conditions must be met in order for the polarizer to be most effective. You will learn all about them here.
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