Basic Photo Tips

Basic Photo Tips

There are certain photographic truths that apply to all cameras, regardless of whether they’re DSLRs or compact point-and-shoots. Depth of field is one of those truths. It’s a photographic term used to describe the area of an image—from near to far (or, in front of and behind your subject)—that looks sharp.

Let’s say you’re taking a picture of a friend standing outside surrounded by trees and shrubbery. Naturally, you’re going to focus your lens on your friend. Everything that’s on the same plane (also known as the plane of critical focus), i.e., objects that are the same distance from the lens as your friend, will also be in focus. If you increase the depth of field, some of the trees and bushes behind and in front of your friend will also look sharp.

Before we go into details about how and when to change your depth of field, let’s talk a little about sharpness and the human eye. Notice that earlier we didn’t say that the objects falling within the depth of field range were in focus, but rather that they looked sharp. There’s a difference.

To put it simply, a lens can only focus on one distance at a time since the sensor (like a strip of film) is a flat surface. So, if your subject is eight feet from the lens, other objects that are also eight feet from your lens (along the plane of critical focus) will be in focus. The objects in front of and behind the subject will not be as sharply focused as those that are perfectly parallel to the sensor at the same distance. And, in fact, the sharpness of objects will get softer the farther away they are from the in-focus subject.

However, depending on the image and its depth of field, our eyes may not be able to discern the differences in sharpness. The apparent sharpness of an image, in part, depends on image size and the viewing distance from the image. If you stand close to a large print, for example, you will notice the softer focus areas more readily than if you were standing farther way from the print or if the print were smaller.

It Starts with the F-Stop

When it comes to depth of field, the most important tool you have is the f-stop, or aperture setting. The size of the aperture controls how much light enters the camera. In turn, the aperture affects how much of the image appears sharp. A higher number, like f/8 or f/16, means the camera will use a smaller aperture opening and, therefore, deliver a broader depth of field, with more of the image appearing in focus. A lower number, like f/2, gives you a larger aperture opening and a shallower depth of field, softening the background (which creates an often-desired effect called bokeh).

In order to manually adjust f-stops to affect depth of field, your digital camera needs to have an aperture priority or manual exposure mode. In aperture priority mode, you choose the aperture and the camera chooses the shutter speed (in manual mode, you choose both). Keep in mind that, unlike DSLRs with a full range of aperture settings, some compact cameras have a limited range of f-stops, often topping out at f/8 or, at the higher end, f/16. No worries, both are sufficient to give you increased depth of field.

Assuming you want an increased depth of field, with more of the image appearing sharp, set your camera on aperture priority and stop down the aperture (set the aperture to a higher number). At the same time, be sure to check the shutter speed the camera has chosen. If it’s too slow to hand hold, either use a tripod to steady the camera or open up the aperture until the shutter speed is faster.

Choosing Between Broad and Shallow Depths of Field

So, when should you use a broader depth of field? Any time you want all or most of the components of your photograph to appear sharp. Landscapes, a field of flowers, the interior of a room, and a group of people are all good candidates for increased depth of field.

That’s a broad range of subjects and one might think that all photographs will benefit from an increased depth of field. Not true.

Decreasing depth of field can result in a more powerful image, depending on the subject matter and the feeling or message you want to convey. Portraits are the perfect example of when to use a shallow depth of field. By allowing the background to soften or blur while your subject is sharply focused, it puts the emphasis on the person rather than on his or her surroundings. A field of flowers may look wonderful when the entire flora fall within the camera’s depth of field. But perhaps you particularly like a small group of those flowers or even an individual blossom. If you have a shallow depth of field, the eye will be drawn to those few choice plants or single flower.

The Long and Short of It

Most digital cameras have zoom lenses, allowing you to shoot at different focal lengths. These different focal lengths also impact how much depth of field you get in a picture.

The rule of thumb is that the shorter the focal length, the broader the depth of field. Conversely, the longer the focal length, the shallower the apparent depth of field.

Check it out for yourself. Standing in place, set your lens to its widest focal length and take a photograph. Then take the same picture, from the same distance, zooming in to the lens’ longest focal length. More of your picture will appear sharp when you shoot in wide angle.

Along the same lines, the distance from camera to subject affects depth of field. Using a “normal” focal length (try somewhere in the middle between wide angle and telephoto), take a photograph while standing a few feet from your subject. Then, keeping the zoom at the same “normal” setting, step back about 8-10 feet and take the same photograph. The depth of field should be greater in the picture when there was more distance between your lens and the subject, so more of the image will appear in focus.

Think about how you take pictures. When you shoot a landscape, chances are you shoot at wide angle. Not only does a wide angle give you a broader angle of view, but it allows you to capture a larger area with more of the image in focus.

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