Depth of Field
Depth of field is an important tool in photography and is controlled by the aperture settings of the camera. How we portray visual scenes influences the message, which our viewers establish in the narrative of a story. As photographers, one of the most powerful and creative tools we have at our disposal is how we represent depth in an image.
First off let’s establish the correct language:
- Depth of field (DOF) can also be described as the focus range.
- DOF is the distance between the nearest and farthest objects that appear acceptably sharp.
Shallow Depth of Field
Refers to isolated focus at a specific depth in an image. This leaves the foreground and background out of focus with only the subject crisp and sharp. This is ideal for drawing your viewer’s attention to where you want them to look.
Large Depth of Field
Also referred to as a deep DOF. In this case there is focus throughout the image with both the foreground and background in focus. A lens is only able to focus precisely at one distance in each frame. However, the decrease in sharpness is gradual on either side of the focus point and is influenced by the aperture value. With a large DOF the decrease in focus can be imperceptible.
So how do we make this happen?
The DOF is controlled by the aperture represented by the f-stop value on the camera. A cameras aperture is the hole or opening that controls the amount of light, which passes through the lens. Consider the pupil of a human eye, the aperture of a camera works in the same way.
The size of the aperture influences DOF in the following ways:
If the hole (aperture) is the size of a pinhead i.e small, there will be a large depth of field and both the foreground and background of the image will be in focus. This is achieved by having a high f-stop value or aperture. Eg. F – 9
If the hole (aperture) is the size of a coin i.e. large, there will be a shallow depth of field and the foreground and background will appear out of focus with only the subject sharp. A large aperture is achieved with a low f-stop value or aperture. Eg. F – 2.8
Now you know how to do it… let’s consider when to do it:
Shallow DOF – The world is a noisy place and we need to tune into the specific sounds that have the most relevant and positive impact on our lives. The same is true for photographs; they can be noisy and lose their impact if there is too much distraction within a frame. As photographers we must tune our viewers into the elements that are relevant to the story we are telling.
This is where a shallow depth of field is important. Draw your viewer to the elements within a frame that have the most impact. For example, in wildlife photography, sharp focus on the eyes of a subject is paramount to conveying the emotion of the story. As the saying goes, the eyes are the windows to the soul and in the animal world, eyes are one of the most fundamental forms of communication. The same is true for humans. If you can successfully capture this emotion, your images will be powerful beyond what you thought was possible. Having the focus crisply placed on the eyes and blurring out background elements will allow the viewer to be undistracted from the emotion of the story. The soft focused elements in the frame will still be relevant to the image and influence the story, but you will be subtly highlighting to the viewer how they are affecting your subject through the emotion the eyes are portraying.
Large DOF – On the other hand, some scenes are perfect and conveying the over all beauty of every element in the frame is the intention of the story. This is often the case in landscape shots, depending on the scene. With landscape images there can be several elements in the frame at different depths which all have equal influence on the story and scene. In this case you want the viewer to be drawn into the magical land you are representing and get lost within their journey through this space. I want them to be able to walk (in their minds) from the tree in the front of the photograph to the mountain on the horizon. The viewer will not be able to do this if they can’t really make out what the tree looks like because it is out of focus.
Tip: A cameras aperture has many creative functions beyond just depth of field. For example when there is a focused light source in the frame that you are shooting, such as a ray of sunlight bursting through the leaves of a tree, a fantastic effect is creating a starburst. You can do this by pushing your aperture value very high (f18 <).
Aperture Priority Camera Mode – AV :
This is considered a creative mode on the camera and gives you full control of the aperture settings while allowing the camera to take care of the shutter speed. AV is a favourite mode amongst many pro photographers and is a great way to get a handle on aperture. The camera will automatically set the shutter speed correct for a neutral exposure in conjunction with the aperture you have chosen. You have the option to either choose your ISO setting or set it to Auto and allow the camera to choose the correct ISO for a neutral exposure. All the user then has to consider of the exposure triangle is the aperture which is essentially controlling the depth of focus in the image and how isolated the subject will be. This is a great way to get an understanding of aperture by taking the other factors off of your hands. You can test the different effects of aperture on the depth of field and decide when certain aperture values are appropriate for the different effects you wish to create in your images.
Tip – For action and energetic scenes, I do not recommend aperture priority. Having no control over the shutter speed may result in blurred images if the camera selects a shutter speed, which will achieve a neutral exposure but be too slow to capture the motion and subjects crisply. For action scenes you should be focusing on the shutter speed to achieve the desired effect… but this is for another post.
Until next time, happy shooting!