You don’t have to be a professional photographer to understand that manual mode ultimately gives you the most control over your images. But let’s face it, not everyone has the great luxury of being able to pay attention to a camera’s settings. The light changes, subjects move, scenes vary—or maybe you’d rather just enjoy a day out with your kids than have to worry about fiddling too much with your camera. That’s why the manufacturers of DSLR cameras and even many modern point-and-shoots have kindly included a few basic ways to have some control over your photographs without really having to pay too much attention to the details. But how do you decide which mode to choose, and is any one better than the others?
Besides manual mode, the two primary settings on most DSLR cameras are shutter priority and aperture priority. When shooting in shutter priority, you select the shutter speed and the camera selects the aperture.
When shooting in aperture priority the opposite is true: you select the aperture and the camera chooses the corresponding shutter speed. Both modes have advantages, but aperture priority ultimately gives you more control over the overall quality and visual focus of your images.
Use shutter priority to freeze images or capture motion blur
Shutter priority is useful for situations when you know you need to use a fast shutter speed to freeze action (when photographing hyperactive children, for example) or when you have a tripod and are trying to capture motion (such as moving water, traffic, or maybe even those hyperactive children). Aperture priority is better for almost everything else.
Use aperture priority for everything else
The primary advantage of aperture priority is that it gives you control over depth of field. This means, of course, that with aperture priority you are in charge of how much and what parts of your image are in focus. This is one of the most important things you can do as a photographer to turn your ho-hum pictures into something extraordinary.
Use a large aperture to create a blurred background
Have you ever shot a photo at a carnival, a concert or some other event where the background is full of advertising, crowds of people and other distracting elements—and then had trouble telling what, exactly, was supposed to be the subject of the image? Depth of field can help you bring focus - literally - to an otherwise confusing and busy scene. A wide-open aperture (with a smaller f-number, such as F1.4 to F5.6) will allow you to isolate one part of the image while the rest of it will fall out of focus. When shooting in this range, those oppressive advertising banners and crowds of people you don’t know or who aren’t particularly interesting will fade into a palette of fuzzy color, and the viewer’s eye will naturally fall on the photo’s intended subject.
A wide aperture will also improve your macro-photography. You can use smaller f-numbers to isolate a single bee on a bush full of flowers, one cookie on a tray or a drop of water on a blade of grass. Your ability to bring out the fine detail in a single object while de-emphasizing everything in the background can make the difference between a stunning photo and an unremarkable one.
A final advantage of using a smaller f-number is that you can take better photos in low light, thus avoiding the dreaded built-in flash. In low light a flash creates ugly shadows and gives your subjects a somewhat un-dead complexion, which is fine for teenage vampire fans but doesn’t usually appeal to those of us who want to look like we’re among the living. Using a wider aperture (small F number) in low light obviously works best when shooting portraits, since the background will lose a lot of detail in these situations. It is less useful when shooting poorly-lit scenes where you want more of the image to be in focus.
Use a smaller aperture for landscape
When photographing landscapes you also need to control depth of field, but for the opposite reason; in these cases you want as much depth of field as your camera is able to capture. It is not always possible (or preferable) to step completely away from the foreground, which means you need to make sure that both your foreground and background are equally in focus. Foreground details such as tree branches, fencing and rock formations can help create a balanced image, and can also prevent an otherwise sweeping scene from looking two-dimensional. If you don’t use larger f-numbers when photographing this type of scenery (such as F11 to F22), you may find yourself with an image that has a blurry foreground or background when what you want is sharpness across the entire image.
For everything else, use F8 or F10
What about those in between numbers? F8 and F10 are often referred to as the “sweet spots”, because they are good for all those pictures where depth of field doesn’t matter. “Flat scenes”—those that don’t have a lot of depth (such as the front of a building, a graffitied wall or a person shot against a flat backdrop) are best shot in this range because F8 and F10 will typically give you the sharpest possible image. Depending on your lens, pictures shot at higher and lower apertures may lose sharpness in the corners (this is an optical problem that can have a number of causes but is usually built-in to the lens itself).
Aperture priority has some drawbacks
Every automatic or semi-automatic mode on your camera comes with a price, the most obvious of which is that your camera’s light meter doesn’t necessarily know what kind of shooting conditions you’re working in. Using aperture priority may contribute to over or underexposed photographs, especially in situations where the light is uneven or where the highlights are particularly bright. For example, when shooting a snowy scene on a sunny day your meter may be fooled into believing the scene is brighter than it actually is, thus creating an underexposed image. And it’s also possible to set your aperture to a point where the shutter speed can’t actually go high enough to give you the correct exposure in that particular situation. When shooting at small apertures, failing light may also cause your shutter speed to drop to the point where camera shake creates blur in the finished photographs (although sometimes that's what you want). For these reasons, aperture priority is best suited to situations where the light is relatively diffuse, such as cloudy days.
Modern photographers are lucky to have cameras that are essentially computers with lenses - this gives us a lot of options for capturing better photographs, even when shooting in automatic modes. While it is always preferable to use the manual mode, aperture priority is a good compromise if you are still learning about your camera’s features or if you’re just out enjoying a day with family or friends and don’t want to have to trouble yourself too much with your camera’s settings. And besides greatly improved images, mastering aperture and depth of field will have the added benefit of making that ominous manual setting seem a lot less intimidating.
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