The depth of field is simply how large the focused area in a photo actually is. Let’s see how this technique can be used to help create emphasis in your photos.
Everyone has seen photographs in which everything in the picture is crystal clear, from the foreground flower to the distant mountains. You’ve also seen pictures where only the main subject is sharply rendered, and everything else is blurry.
These are two examples of the effect which the depth of field can have. The image where the main subject is sharply rendered but the foreground and the background are blurry in varying degrees are examples of a shallow depth of field.
In more accurate technical terms, depth of field can be defined as being the range of object distance within which objects are imaged acceptable sharpness. Thankfully, particularly if you are using a compact digital camera, you don’t need to know about the complexities behind the depth of field calculations, just how to maximize it to your advantage.For Simplicity, here are the key practical points about depth of field:
1 – A wide aperture gives you a shallow depth of field
2 – A small aperture gives deep depth of field
3 – A telephoto lens, or long zoom, at the zoomed setting appears to give a shallow depth of field
4 – a Wide angle lens appears to give a deep depth of field
In points 3 and 4 as shown above the wording ‘appears to’ is used because the perception in the shot is usually as described, it is not always technically speaking, accurate. It depends on this subject magnification and scene perspective or viewpoint that makes a direct comparison of focal length and depth of field it difficult. However, although this may sound complex, you can now start to play with the depth of field effects in your images.
When to Use shallow depth of field
The most common use for a shallow depth of field is in portraiture, where you want to emphasize the subject. By using either a long focal length on your lens and or a wide aperture, such as F2.8 (which will give you a larger aperture), you can get the effect of a sharp subject and blurry background.
This will allow the light to reach the sensor in a different way when compared to using a smaller aperture. We will look at some comparisons in the next few sections of this post. Use this technique on any shot where you want to separate it from the background. A shortcut is to use the portrait mode on your camera if it has one.
When to use deep depth of field
This is slightly more flexible, but a good example of when to use a deep depth of field is when taking landscape photographs. Typically you will use a wide-angle zoom lens, and a small aperture of F8. This will help to ensure that the sharply rendered area in the shot stretches from near to the camera out to the far distance. A shortcut here is to use your camera as landscape mode if it has one.
Close-up and depth of field
It is worth pointing out that in close-up shooting, particularly if your camera has a good close-up or macro mode, the depth of field will be very shallow indeed; a mere millimeter or two at the most. Use a smaller aperture such as f8 to help deepen, or increase, the depth of field if you want more of the small object to be sharply focused.
Throwing the background out of focus
By selecting a suitable aperture, it is possible to throw the background out of focus by changing the depth of field. The example shown below of the same scene was taken with different f-stops to illustrate how this influences the depth of field in a visual manner.
First, the smallest aperture, f22, was used, which gave the sharpest image out them all. As we move from f22 to f16 you can see that less of the background is sharp. Even more obvious as you move to f5.6 where the trees and the grass are heavily blurred. This technique is used to draw the viewers attention to a specific area in the photo. When you compare the effect from f22 to f1.8 it is easier to see that the attention goes to the small cluster of leaves and flowers at the end of the branch.
By using a smaller aperture (f22), you will need a longer shutter speed to achieve the required exposure. This allows the light that is in the further areas of distance, the background, to reach the sensor and imprint a clearer image. Where the aperture is larger (f1.8), you will need a much shorter shutter speed to achieve the required exposure, and therefore, the light that is in the distance does not have enough time to clearly imprint the scene on the sensor, and as a result, it will be blurred.
The physics behind the effect that aperture size has on f-numbers, or f-stops, have on photos is quite complex. But, here are some simplified ways to think of them which may help make sense of this.
The first thing to remember is that a low f-stop of f2.8 gives a larger aperture, while a higher f-stop, such as f8, gives a smaller aperture. Big number = little hole, and little number = big hole, to put it simply. The bigger the hole, the more light that can pass through, and on the flip side, the smaller the hole, the less light can pass through.
You can use bigger apertures to let more light in if it is dark and you don’t want to use a flash, this can also help to get faster shutter speeds. When you start to practice working with the depth of field, you begin to see how you can adjust a combination of aperture, shutter speed, and even ISO to achieve different results.