The creation of a strong focal point and making sure the most important pieces of your images are in focus is crucial to producing a great photograph. This is done most effectively through a thorough understanding of the focal plane of an image and its depth of field and understanding how to manipulate these to produce the effect you are going for.
What is The Focal Plane?
The Focal Plane is the area in which the subject of your image is in sharp focus. The focal plane spans horizontally across your frame, all the way from the left to the right. Picture it as a line of tape across your shot. No matter how many subjects you have in your shot, as long as they are standing along that line, they will be in focus. If they move in front of or behind that line, then they will suddenly be out of focus because they have stepped out of the focal plane.
While the focal plane is the sharpest plane of focus in an image, it is not the only part of an image that actually appears to be in focus. There will be points that are adjacent to the focal plane that are not in perfect focus but the brain will register them as being in focus if they lie within a certain range.
Your focal plane will get wider or narrower depending on your f-stop (aperture; the part of the camera that controls light entry) and the depth of field.
What is Depth of Field?
Another important element of your photo that is crucial to understanding focal plane is depth of field. Depth of field is the area around the plane of focus that still appears to be in focus. You can adjust the depth of field to be deeper (so that more of your image appears in focus) or shallower (so that less of your image appears in focus) by adjusting your f-stop.
Understanding depth of field allows you to distinguish the foreground from the background and create a strong focal point in your photo. If you know how to control your depth of field, you will then have the opportunity to decide how much of your image is in focus and which parts are brought into focus in the first place.
Aperture & Distance: The Two Biggest Factors in Focal Plane and Depth of Field
If you are shooting in anything other than a totally controlled environment, you will have to know how to adjust your camera for the changing light. Adjusting your aperture is the way to do this. Aperture is the part of the lens that controls the amount of light that passes through to the camera’s sensor. When you increase aperture, the diameter of the opening that lets light into the camera widens to let more light in. When you decrease aperture, the diameter narrows, letting less light in. Aperture corresponds to the f-stop numbers on your camera, with lower f-stop numbers meaning a higher aperture.
To achieve a shallow depth of field, set your f-stop to a low number (like f/2.8) to widen your aperture and allow a lot of light into the lens. You will have to adjust your shutter speed to be faster in order to compensate for all the light coming into the lens. When you are shooting with a low f-stop you do need to be careful to make sure you are still getting all of your subjects in focus! You will need to remain directly in front of them or else parts that should be in focus will be shifted out of the shallow focal plane.
To achieve a deep depth of field, set your f-stop to a high number (like f/11). This will narrow your aperture and significantly decrease the amount of light coming into the lens. You will need to shoot with a slower shutter speed, but these settings will then result in a deep depth of field.
Below is a quick guide to how you can make the depth of field deeper or shallower:
Deep depth of field = large f-stop (small aperture) + slow shutter speed
Shallow depth of field = small f-stop (large aperture) + fast shutter speed
Distance Between the Subject and the Camera
You can make your depth of field shallower by moving the camera closer to the focal plane and make it deeper by taking the camera further away. Moving closer to a subject is a great technique to take photos with soft backgrounds while using a limited lens.
Distance Between the Subject and the Background
Give the effect of a shallow depth of field by moving the subject further away from the background. This creates an image with a hyper-focused subject standing in front of a blurred background. To bring more background into focus, move the subject closer to the background.
Why does the Focal Plane Matter?
Just like your eyes focus and refocus on points of interest, the focal plane directs the attention of the viewer to the parts of the image that are most important by focusing on the subjects of the image and blurring out any distractions that may be in the background or foreground. If you don’t understand the focal plane and its importance, your photos will be chaotic and busy. Understanding the focal plane and depth of field will elevate your photography skills and help you effectively highlight the most important parts of your images.
Once you understand exactly what the focal plane and depth of field are, you can begin to apply these principles to your photos! As you get more comfortable, you can manipulate the different settings that go into creating different depths of field and focal planes to create unique, professional photos!