Shooting Through: Use Depth of Field to Eliminate Foreground Obstructions

Depth of field techniques can create some magical effects, from making soft, pleasing backgrounds in portraits to having everything from a foot to infinity appear sharp throughout the frame in landscape work. One of the tricks that can be played with aperture settings is to eliminate distracting foreground elements by focusing “through” them while using a wide open aperture setting to create a shallow depth of field. This can be used to “eliminate” bars at a zoo, a chain link fence at a baseball game or, in this illustration, a rope that surrounded a merry-go-round in Madrid, Spain.

The ride was closed for the winter, and the owners had surrounded it with a rope fence to keep kids from hopping on and playing inside (though knowing kids you can be sure they found a way through!) To illustrate this technique, two equivalent exposures were made with the same lens from the same point of view. The lens is set on manual focus and focused on the closest horse. (Autofocus might have “snagged” on the rope.) A fast lens with a maximum aperture of f/1.4 was used. The first exposure was f/11 at 1/60 second (above) An equivalent exposure was made at f/1.4 at 1/4000 second (below). Note the very soft background. In essence, the very wide aperture setting put the rope so out of focus that it “disappeared.”

Settings: 50mm f/1.4 lens. Both images focused on the foreground horse. Right: f/1.4 at 1/4000 second. Above: f/11 at 1/60 second.

Hyperfocal Distance & Zone Focusing

This entry is aimed at those who want critical focusing control in their work. The techniques apply to working with a fixed focal length lens and working in manual focus.

Image: To make sure that focus was sharp from the foreground of this old truck to the facing truck in the background I worked in manual focus mode with a 24mm lens and used the hyperfocal distance technique described in the text. Copyright: George Schaub

Focus on an object very far away and take a moment to look at the distance scale on the lens; you might see that the distance setting is beyond the last numerical value on the distance scale (usually that's 30 feet on a 50mm lens) and is marked with an infinity sign. Now check the parameters of the f/16 notation on the depth of field scale-this shows that your zone of focus stretches from about 15 feet (the distance on the border of the f/16 mark on the left side of the depth of field scale) to well beyond any marking on the distance scale. As there is no distance beyond this infinity, this setting tells you that you are in focus from 15 feet to, well, the moon and beyond.
But what about the fact that you have the right side of the f/16 depth of field hash mark well beyond any footage indicator-does this mean you are "wasting" depth of field potential? In a word, yes; but there's an easy way to get it back. (Note, in some lenses the footage markers within the depth of field scale work in reverse to how we're describing it here. If your camera works in this fashion, just reverse left and right as you read on, Actually, the direction in which the distances move is much less important than the idea of manipulating distance settings on your lens to maximize depth of field.)
If you're shooting from the rim of the Grand Canyon out into the distance, your depth of field setting is unimportant, as long as the infinity setting is enclosed within the hash marks of the aperture in use. But if you have subjects in the scene that sit closer than 15 feet, you can set the lens so that you still have focus at infinity and include a focused item in the foreground as well.
The technique you use to do this is called using hyperfocal distance. The first step here is to turn off autofocus. Then you align the infinity marker with the right-side hash mark on the depth of field scale with the aperture number in use, then take note at what distance the left side aperture number falls. The left side number is the minimum distance at which you will have focus, when your furthest point of focus is at infinity.
For example, if we set hyperfocal distance on a 50mm lens at f/16, we find that our zone of sharpness is about eight feet to infinity. This is a pickup of seven feet from our previous setting; we don't lose anything by setting hyperfocal distance, we just gain a bit more foreground sharpness.
You can also manipulate the zone of focus when the farthest shooting distance is less than infinity. Called zone focusing, it's based on the same idea as hyperfocal distance; you manipulate the depth of field scale so that aperture settings enclose certain distances-these distance settings become your zone of sharpness.
For example, let's say that our farthest subject is ten feet away; by setting the number 10 next to the f/16 hashmark on right side of the depth of field scale, we see that we know have a zone of sharpness from about 4&1/2 to 10 feet. Likewise, setting at the 30 foot mark shows a near-focus of seven feet. Keep in mind that these settings are estimates of the actual depth of field; however, the settings certainly will be close enough for most of your shooting needs.
Pre-setting zone of focus can be a real help when you're doing spontaneous candids, or when you just don't have time to focus each shot. By pre-setting your zone of focus so that you can shoot without worrying about focus from, say, four to fifteen feet, you can photograph without bringing the camera to your eye, and still get almost every shot you take in focus. Of course, your composition may be a bit off, but "shooting from the hip" is an old tradition with candid street photographers.
Of course, there are times when you can be more deliberate about what you want to bring into focus. By using the depth of field scale you can make fairly precise settings to get the most out of the available zone of sharpness. For example, let's say you're shooting a statue in front of a building and want to include both the statue and building in focus. Without using or being aware or depth of field manipulations you might not get the effect you wanted; with them you can play some amazing visual tricks. It's safe to say that depth of field manipulations are underused by most photographers, especially those with autofocusing cameras; get a handle on them so you don't lose out on their amazing potential to make the most out of every shot.
The depth of field preview button is an important player in this game as it stops the lens down to its taking aperture, thus allows you to see the effect the lens setting has on focus. At some apertures, such as f/16, the viewing screen becomes quite dark; so dark, in fact, that you may have trouble seeing what's going on. If this happens, open up another stop so you can see focus on the viewfinder better, then stop down to your selected aperture when you take the shot. This won't give you an exact idea of the depth of field at your taking aperture, but it will certainly give you a better idea of final picture focus than will looking through the lens at maximum aperture. If your camera does not have a preview button, get another camera and in the meantime use the depth of field scale on the lens.

Depth of Field

The aperture setting determines the “thickness of the pipe” through which light flows, thus the volume of light and exposure. But as, if not more importantly it influences depth of field, thus plays a major part in creative focusing decisions.

You can think of depth of field as a grid of distance markers from the front to the back of your photo, sort of like a football field. When you make different aperture settings you are influencing how sharp objects at the ten, twenty, thirty yard lines, etc, will be. You are also influencing how sharp they will be in relation to the point or distance you actually have focus set.

Some settings will make the difference of sharpness between, say, the ten and thirty yard lines quite dramatic, and others will make it less so, and others will eliminate any sharpness difference between those distant points.

How can we control the fact that this image shows sharp foreground trees as well as the massive falls miles away? That’s the kind of control depth of field gives you. With a 24mm lens, exposure at ISO 250 was f/9 at 1/125 second.

Creative Focus: Part 1

At first glance it would seem that focusing is a simple matter. You look through the lens, press the shutter release button to activate the autofocus mechanism and make the photograph. Or, when using a manual focus lens, merely turn the focusing collar on the lens until the image seems sharp in the viewfinder, and then press the shutter release. This would work fine if we lived in a two-dimensional world. Yet subjects in most scenes sit different distances from one another. Some may be close together while others could be miles apart. Working with focusing techniques you can either make subjects at great distances appear sharp within the picture or have a background that is as close as a foot to your subject appear unsharp.

Focusing is one of the most important creative options. The technique for creative focusing play is called selective focus or depth of field, and it is based on the idea of “circles of confusion”, or what our eyes perceive as sharp and unsharp in an image.

Think of a magnifying lens slanted toward the sun and a piece of paper receiving the rays of light through the lens. As you move the lens back and forth the rays from the sun form a circle or a point on the paper. When a lens is mounted on a camera it directs light toward the film or sensor. Those rays that converge on the film or sensor at a point, or at a near point, are what we perceive as sharp in the image. Those that form a circle beyond a certain diameter are perceived as unsharp in the image.

Our eyes tolerate a certain diameter of circle, or “blob” as being sharp. We do this at a certain distance and with a certain degree of magnification of the image. Change the viewing distance and/or the magnification and what appeared as sharp might later seem unsharp. That’s why when we enlarge prints that looked good in a snapshot size print (4 x 6 inches) to 11 x 14 inches the print may look slightly unsharp. Close inspection of image before enlargement can help prevent this problem.

Next: Viewfinders and Live View

Photo and Text copyright George Schaub 2010. Depth of field controls set up what is sharp and unsharp in the photograph. A deep depth of field, as shown here, means the eye perceives everything from front to back as in focus, or sharp.

Basics: Lens Aperture

Exposure is controlled by the aperture and the shutter speed settings. The aperture setting also influences depth of field, thus plays a major part in creative focusing decisions. Aperture settings are called f-numbers, and are expressed by "f/" followed by the number of the aperture set.

Aperture settings are indicated on a lens by a series of numbers; with some cameras and lenses there is no aperture scale on the lens barrel and the settings appear in the camera's viewfinder and/or LCD panel. A typical aperture scale might read: 1.4, 2, 2.8, 4, 5.6, 8, 11, 16. Each number indicates the ratio of the actual diaphragm opening to the focal length of the lens in use, thus any same aperture on any lens always allows in the same amount of light. As these are actually fractional numbers the smaller numbers signify larger openings. Thus, f/2 (or 1/2) represents a wider opening (or greater value) than f/16 (or 1/16).

As mentioned, f-numbers represent the same light value regardless of the lens or format in use. Thus, f/2 on a 50mm lens for a 35mm camera delivers the same amount of light through the lens as f/2 on a 200mm lens for a medium-format camera, even though the diameter of the openings themselves are different. If this wasn't the case the entire light control system in photography simply wouldn't work.

Each subsequent number in an aperture scale represents a halving or doubling of the amount of light that the aperture allows through the lens. (You can calculate the next higher number in any one-stop-step scale by multiplying the previous number by 1.4). Each step in the scale (say, from f/2 to f/2.8) is called a stop. Thus, every time you open up or close down the lens by one stop (opening means going to the next lower number, or wider opening; closing down means going to the next higher number, or narrower opening) you are changing the amount of light entering by the power of 2. A one stop change (say, f/8 to f/5.6) is a 2X difference; a two-stop change (sat f/8 to f/4) is a 4X difference; and so forth.

The best way to see how aperture settings effect light transmission is to take the lens off the camera, hold it up to the light and click through the aperture settings. (Note: Some lenses do not allow for aperture changes on the lens itself, but rely on the camera to change apertures,) You'll see that the maximum aperture, say f/2, is the widest opening. As you click through the scale, you'll see the diaphragm in the lens getting smaller. Think of water as it flows through a pipe. Given that the water will always fill the pipe, a larger diameter pipe will allow more water through. This can be applied to light flow and the aperture diameter.

Most lenses and cameras today allow for partial stops, like older lenses with click stops, or detents, between the aperture settings. On older lenses these are half-stops, and though not marked indicate a halfway point between the two aperture numbers on the ring. On newer lenses you can have 1/3, 1/4 or other fractional spreads. These step-less aperture settings means any value can be set, such as f/9.7 or f/11.3. These values are indicated in the camera viewfinder and/or the LCD panel on the camera.

Aperture rings are usually inscribed with all the available full stop settings on the lens, from the maximum, or widest, to minimum, or narrowest lens opening. The range of the aperture scale may differ depending upon the construction of the lens and its focal length. One scale may read f/2, 2.8, 4, 5.6, 8, 11, 16, while another may read f/4, 5.6,8, 11, 16, 22, 32 (the latter is more typical of zoom or telephoto lenses.) The lowest number in the scale (thus the widest opening) is called the maximum aperture; the highest number on the scale (thus the narrowest opening) is called the minimum aperture.

Photo and text copyright George Schaub 2010. Aperture settings allow you to control the depth of field, what appears sharp and unsharp in your photo. To get focus from foreground to background here an f/16 setting was used.