Depth Of Field Refresher — Why Is DOF So Crucial To Your Photography?

Down the years, it has often come to me as a surprise that even the experienced photographers have only a vague idea of what the depth of field is? and of the role it plays in creating fine photographs.

But on reflection, I feel most of these people could be broadly classified as either landscape photographers or those who specialize in covering events such as weddings. The significance of this will be revealed as we work our way through this tutorial. For now let’s start with the concept.

What Exactly Is Depth Of Field?

The depth of field (DOF) is the distance behind, as well as the distance in front of your subject, that is acceptably sharp at a given aperture.

In other words, it is the zone of sharpness. This zone is usually about 1/3rd of the way in front of the subject and 2/3rd the distance behind it.

The basic rule is — the smaller the aperture (e.g., f/11, not f/4), the deeper the zone of sharpness, i.e., the area that is acceptably sharp, both in front of and behind the subject. I will expand on this point a bit later on.

Professional photographers, who shoot scenic pictures or college graduation group photographs, know this well. They normally use a wide angle lens and set the aperture in the range of f/11 or f/16.

In most of the pictures shot with a simple pocket digital camera, you may have noticed the cars in the parking lot behind and the distant skyscrapers… all are in focus: a very deep depth of field indeed! This is because compact cameras have very small sensors which entail enormous depth of field  and this is thus one of the reasons why you need to upgrade to a DSLR.

But unlike landscape photography, there could be times when such a universal depth of field (DOF) is not at all desirable. Too many things in focus can confuse the eye! But if you only want a nice picture-postcard shot of Nainital Lake, then go ahead and look for good DOF by using a smallish aperture. However, small apertures come at the cost of slower shutter speeds. So take care of using a tripod or firm support if the shutter speed needed is lower than 1/60th of a second.

On the other hand, if you want to capture a well-composed picture of a  flower in sharp detail with the rest of the scene out of focus, you will need a shallow DOF.

This will ensure that the viewer’s eye is drawn to the main subject (the flower) while other distracting elements are thrown out-of-focus. In fact, the shallow DOF will make your subject pop or stand out against the background, making it a terrific flower photograph. You can preview this effect with a DOF preview button. (You can learn how to make the most of this creative camera control here.)

Talking of a group photograph, an experienced photographer would likely take a group shot using a wide aperture, perhaps f/2.8 or even f/2 and most probably set the shutter-speed to about 1/2000th of a second, or even 1/4000th of a second with ISO 100 in daylight. Voilà! A super-sharp photograph of your gang: the rest is an inconsequential mish-mash.

However, if your group just wants a nostalgic record of your visit to the Eiffel Tower, he’ll probably use f/8 or f/11, so as to get the famous landmark to loom up sharply in the background… because that’s exactly why you all are posing in front of it — a memento of your trip to Paris! While we are at it, you can check out some handy tips for taking great group photographs here.

And when you want to be included in the group picture, use the self-timer (fight off the urge to rest the camera on the bonnet of the car with its engine running).

What Do You Need For Playing With The DOF?

Besides the aperture, there are two other factors that affect depth of field:

1. The focal length of the lens in use, and
2. The distance of the subject from the sensor or film plane.

To increase DOF, then, you can go for one of the following three options:

a) Use a wide-angle lens, say, one of 28mm or 24 mm focal length.
b) Use the smallest possible aperture.
c) Get as far from the subject as possible (but don’t let it disappear from view altogether!).

And to decrease DOF, you can use either of the settings:

a) Long Lens: Use a lens with as long a focal length as is consistent with your aims.
b) Wide Aperture: Use as wide an aperture as possible.
c) Get Closer To Subject: Get as close to the subject as possible.

Somewhere within these tips lies the solution which will help you capture the image effect that you want. Here is the graphical representation of the factors stated above.

The Lens And The DOF

Wide angle lenses, as the name implies, are, by their very nature (as enjoined by the laws of optics) possess a wider angle of view. The deviation from the normal view (as seen by the human eye) is determined by the focal length. In other words, a 24mm or 28mm lens would have a wider angle of view than a 35mm lens. Along with a wider angle, they also have a great depth of field, making them ideally suited for shooting interiors, landscapes, etc., where you need to stretch the distance.

Telephoto lenses, on the other hand, have a narrower angle of view than a normal lens. This goes with a shallower DOF than a normal lens. Along with this property you also get the benefit of compressing the distance. That is why tele-lenses are ideal for portraiture. But too long a focal length means that the faces get compressed too.

And here goes a quick tip about portraits: I have found that 75mm to 150mm is the best focal length for portraits, with 150mm end being the best for tight head shots (on cameras with APS-C size sensors, like the Nikon D5100 or Canon 550D).

Creative Uses Of Depth Of Field

Other uses of DOF can be found in commercial photography say interiors, architecture, food, packaging, wildlife photography, close-up photography and macro photography. Let us examine some of these areas with the help of a few examples.

Product Photography : Depth of field play an extremely important role in photographs shot for advertising and other media. The commercial photographers judiciously use the depth of field to distinguish the product from the clutter and yet present it in totality. Product photographs have made it easier than ever to buy (and visually feel) the products through imagery.

Along with product photographs, packaging also plays a crucial role. In fact, packaging is such an important part of retail marketing operations that large corporates spend millions on it. Then they need to advertise those innovations to the public.

Nature Photography: The two pictures below show scarlet Simul blossoms alongside a stalk of unopened buds.

Example 1: Settings — shutter speed: 1/2000 sec and aperture: f/6.3

Example 2: Settings — shutter speed: 1/640 sec and aperture: f/11

Example 1 has been shot at 1/2000th second, f/6.3, while Example 2 has been shot at 1/640th second, f/11 – both at ISO 200. Notice how the slight shift in focus has, in Example 1, thrown the buds out of focus, whereas in Example 2, it is just the reverse – the flowers are out of focus. Both have been shot at a focal length of 270mm (405mm on a Nikon D3100, due to the 1.5 crop factor).

The Macro Shots: True macro photography means capturing the subject life size (1 : 1 ratio) on film or sensor. That means, if the bug you are shooting is 5mm in length, its image on the sensor has to be 5mm long, if it is to qualify as a true macro shot. This type of photography usually needs special macro lenses.

Nevertheless, some of the newer bridge and superzoom cameras are able to focus as close as 1 centimeter from the front element. However, you have to be a bit careful while taking macro shots because extreme magnification results in extremely shallow DOF.

There is no dearth of examples of how depth of field (DOF) can be and is used by discerning photographers. It is always a good idea to study the DOF requirements before taking a shot. This will help you answer the oft heard question: Which lens should I use? Depth of field is such a vital part of the creative photographer’s toolkit that none of us can afford to ignore it.

So, to recapitulate, the four elements of depth of field are aperture, focal length, distance from camera to subject and the size of the sensor.

Taken together and applied judiciously, these four elements can greatly improve your photography.