This series of articles is excerpted from Rocky Nook’s Enthusiast’s Guide to Exposure by John Greengo covers the controls — shutter, aperture and ISO. The week, John covers depth of field.
Depth of field
With large apertures(low numbers, e.g., f/1.4, f/2, f/2.8) you can expect a shallow depth of field. This shallow depth of field will result in a photo that has one area in focus, and regions in front of and behind it that are out of focus with an increasing level of blur the farther they are from the point of focus. At the opposite end of the spectrum, small aperture openings, like f/11, f/16, and f/22, will create images with large depth of field, showing much of the scene in focus.
Depth of field is relative
Depth of field can be a bit tricky to estimate because it’s controlled not only by your aperture setting but also by the focal length of the lens and the focusing distance. Focal Length Controls Depth of Field The focal length of a lens will affect the amount of depth of field exhibited at a given aperture. Wide lenses tend to have a great depth of field. Telephoto lenses tend to have a shallow depth of field. Using an aperture of f/5.6 will result in a great depth of field with a wide lens, whereas it will be quite shallow when used with a telephoto lens.
Depth of field depends on a number of factors. The easiest of these factors to control is the size of the aperture. This series of images shows how results change by adjusting the aperture setting.
Focusing distance controls depth of field
The distance that your lens is focused at will also impact the depth of field. Focusing on a subject far away will result in an image with lots of depth of field. Focus at a close distance and your image will result in very shallow depth of field. This can readily be seen with a macro lens or any lens that can focus on subjects at very close range. Try it out: Set your lens to focus on an object two feet away (0.6 meters) and you’ll likely notice that your scene has very shallow depth of field. Use that same lens to focus on something far away, and you will see greater depth of field.
Great depth of field
In some photographs, you may want everything to be in focus so that the viewer can discover and enjoy all the details that the image has to offer. Landscape and scenic images are frequently captured using this technique. The entire scene is important, so why not keep it in focus so that it can be enjoyed in the same way you might experience it in the real world. These great depth-of-field images are often captured with wide-angle lenses that are stopped down to f/11, f/16, and f/22. This combination of wide-angle lens and stopped-down aperture is quite common to the landscape photographer. You might even call it a recipe: find a great landscape, use a wide-angle lens, and set the aperture to f/16—it works all the time.
To shoot these great depth-of-field images, you’ll likely need a tripod. When setting the aperture to such a small opening, like f/11, f/16, or f/22, you’ll need to compensate for the small amount of light passing through the aperture by using a much longer shutter speed. In all but the brightest situations, you’ll end up with shutter speeds well below the limitations of handheld shots. You could increase the ISO, but that adds noise and reduces the quality of the image. The ISO should only be increased in cases where you need a faster shutter speed. In a case where you need greater depth of field and faster shutters, raising the ISO would likely be a necessary step. If you don’t need a faster shutter speed in your great depth-of-field image, you should use a tripod to support your camera.
Shallow depth of field
Portrait photographers often want to draw attention to the face or eyes of their subject. One way to direct attention to those areas is to have a narrow area of focus on a subject’s face or eyes. With the rest of the scene rendered into a soft blur, your eyes can’t help but be drawn to the area of sharp focus. This technique works for not only portrait photographers, but anyone that wants to direct attention to a particular area of a photo. It gives the photographer directorial control over the content of the image. It allows you to include elements important to the narrative of the photograph while also emphasizing the most important aspect of the photo. Shallow depth of field is a great technique for directing attention to where you want it to be.
In order to harness this technique, you’ll want to be very familiar with your camera’s focusing system. The main techniques for doing this are Focus Lock and selecting an individual focus point.
When you have your camera in the standard focusing mode (AF-Single, One Shot) the camera will focus with a halfway press of the shutter release. When the camera achieves focus, you may hear a beep-beep or see an in-focus confirmation light. This means your camera has determined proper focus and the lens in now locked in at this position. The focus will stay locked in as long as your finger maintains the halfway press of the shutter release. With the focus locked in, you are free to recompose the image. When you’ve settled on the composition that looks good to you, press the shutter release all the way down to take the photo. This focus-lock technique allows you to independently control both the focus and the composition.
A different way to focus on a point away from the center of the frame is to select a specific focus point. Most cameras have a large number of focusing points to choose from. By default, most cameras come from the factory with all focus points simultaneously activated. In this case, the default point is on the subject closest to the camera. If you want to be precise about where your point of focus will be, you’ll need to take control of the focusing system. You can select any individual point within the area you want in sharp focus. The technique for adjusting the focus points is different from camera to camera, so you may need to consult your manual for specific information. When you select a focus point, you can simply press the shutter release halfway to focus and the rest of the way when you are ready to take the photo.