Take Better Photos Using Depth of Field Control
Take Better Photos Using Depth of Field Control
As photographers, one of the most valuable tools for taking better photos is the depth of field. Being able to control and use depth of field correctly is often what separates a skilled photographer from the rest.
In this tutorial you will learn:
- What depth of field is in photography.
- How you can control it in your photos.
- How to use depth of field to create better photos.
Let’s start by understanding what it is, and why it’s so important.
What is Depth of Field?
Put simply, depth of field is the area of a photograph that appears to be in focus. Let’s look at an example using a shallow depth of field.
Here you can see a photograph of flowering heather. Notice that the camera has focussed on an area of flowers near to the centre of the frame which is in sharp focus. Then as you move to other clumps of heather that are nearer to or further away from the camera, they become blurred and out of focus.
In this image there is only a small section of this photo, probably measuring a few inches, where the heather is in focus. Because this zone of focus is not very deep, it’s described as a shallow depth of field.
Now let’s compare this with a different photograph which has a deep or full depth of field.
This time everything in the image appears to be in sharp focus. Nothing appears blurred from the heather nearest to the camera to the distant hills in the background. This image is described as having a full depth of field because everything appears sharp, irrespective of how far from the camera it is.
Now that you understand what depth of field is, let’s look at how you can control it.
How do I Control Depth of Field?
There are several factors you can use to control how much depth of field a photograph has. They are:
- Point of focus.
- Lens Focal Length.
- Sensor size or film format.
Let’s look at how each of these affects the depth of field.
The aperture is the hole in the camera lens that allows light to pass through to reach the camera sensor. The aperture is created by blades in the lens which open and close to produce different aperture sizes. The larger the aperture the more light it allows through, whilst a smaller aperture reduces the light. This feature is often used to control the exposure and is part of the exposure triangle.
Another feature of the aperture size is that it controls the depth of field in the image. A wide aperture produces a shallow depth of field but as we reduce the size of the aperture the depth of field increases.
When we talk about the size of the aperture, we measure it in f-stops. The smaller the f-stop number, the larger the aperture. For example, an aperture of f/2.8 is much wider than one with a value of f/16.0. This tutorial explains more about f-stops and apertures.
To summarise, if you want to capture an image with a greater depth of field, use a smaller aperture (large f-stop). But if you want to produce a shallow depth of field use a large aperture (small f-stop).
The next factor to consider in controlling the depth of field in a photo is the lens focal length. The focal length allows us to understand the angle of view a lens can capture and if it makes the subject appear closer to the camera. But it can also affect how much apparent depth of field an image has.
Consider two lenses. One lens has a 20mm focal length whilst the other has a 200mm focal length. We then shoot two photos, one with each lens but both using an f/8 aperture. When you examine the photos, the one shot with the 200mm lens would appear to have less depth of field than the one shot using the 20mm lens.
If you want to produce a shallow depth of field effect, use a longer focal length.
A lot of portrait photographers use lenses with a focal length in the 80mm to 120mm range together with a wide aperture like f/1.2 or f/2.6. This produces a very shallow depth of field, allowing them to focus on the subject whilst throwing the background and surroundings out of focus. It’s also how I created the shallow depth of field in the heather photo above.
Point of Focus
Where you place the point of focus in a photo is also important in determining the depth of field. The nearer the focus point is to the camera, the more it reduces the depth of field. If you look back to the photo of the heather with the shallow depth of field, the heather was only a few inches from the camera. This helped to emphasise the shallow depth of field.
In the other image, the point of focus was placed on the rock in the foreground which was approximately 6 feet from the camera.
In some types of photography like macro photography, where you are photographing small objects very near to the camera, the depth of field is usually very small. Depending on the settings, you may be dealing with a depth of field that measures only a few millimetres. It can then be a problem trying to capture the entire subject in sharp focus because there isn’t enough depth of field.
Typically, macro photographers resort to techniques like focus stacking to overcome the depth of field limitation. That’s when they will shoot multiple (identical images) moving the point of focus slightly each time. They then use focus stacking software like Helicon Focus to combine the images into one with a greater depth of field.
This technique is also be used in Landscape Photography where it’s not possible to achieve a full depth of field in a single shot. It can allow you to create stunning near to far compositions.
Something else to keep in mind when choosing a focus point is that the area of acceptable focus tends to extend twice as far behind the focus point than in front of it. This is only a rough rule of thumb, but it can be helpful in selecting a focus point.
Whilst you wouldn’t change your camera sensor to depth of field, it’s worth understanding it’s effect. The smaller the sensor size, the greater the depth of field produced at any given aperture.
Think about a camera phone which has a small sensor. Most photos taken on a camera phone have a large depth of field and you can’t adjust the aperture or focal length much if at all. That’s why the phone manufacturers include a special portrait mode. This uses software to detect the face in a photo and then attempts to blur out of the background. It’s trying to create the same effect that our portrait photographer used with the 80mm lens and f/1.2 aperture.
If you look back to the example of the landscape with heather and a rock in the foreground, it was shot using a Micro Four Thirds camera using a 10mm lens. On a full frame camera that’s the same as a 20mm lens.
The crop factor of the sensor also influences the depth of field produced by the aperture. In the landscape photo, I used an aperture of f/8.0, which gives the same depth of field of f/16.0 on a full frame camera.
It’s easier to produce more depth of field using a small sensor camera, but it’s more difficult to produce a shallow depth of field effect.
Now you understand the factors affecting depth of field, let’s look at how to use depth of field in our photography.
How do I Use Depth of Field?
The secret to using depth of field in photography is to consider what the photo is about before taking it. Is there a specific subject that you want to highlight and isolate in the frame? Or do you want to the viewers eye to wander around the frame, drinking in every detail of the scene? Based on this you can decide to use either a shallow or full depth of field.
Let’s consider a few types of photography as they tend to lean towards using a certain depth of field.
Typically, a portrait photographer will want to isolate the subjects in the frame and holding the viewers’ attention. They would do this by focusing on the subjects eyes and limiting the depth of field so that the mouth and nose are also in focus. At the same time, they want to throw the background and possibly the edges of the subjects face out of focus.
You will also find wedding photographers using shallow depth of field to blur a background. This prevents objects in the background distracting attention away from the subjects in the frame.
Whilst it is possible to shoot landscapes with a shallow depth of field, most of the time we want to maximise it. This allows every part of the scene to be in sharp focus from the nearest object to the most distant as in this example.
This landscape scene was taken using a Fuji XT3 with a 10mm focal length. On a full frame camera that’s the equivalent of 15mm. The aperture was f/13.0 and the point of focus set on the heather around 3 feet from the camera. This was sufficient to achieve a full depth of field with everything in focus.
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In Sport photography, you might use a shallow depth of field to focus on a specific player or perhaps a car in a race.
Whilst this may be intentional, the shallow depth of field may also be the result of trying to achieve a very fast shutter speed to freeze the action.
This shot of the tour of Britain cycle race is a good example. I needed to use a fast shutter speed of 1/800” to freeze the riders. If the shutter speed is too slow, their movement would be blurred. I also needed to use a long focal length of 140mm to bring the action close to me. It also helped to compress the riders in the frame but produced a very shallow depth of field.
Depth of Field Summary
In this article we’ve looked at what depth of field in photography is and considered how you can control it. The secret to taking better photographs is to make a conscious decision of how you want to use depth of field and then choose the appropriate settings. Don’t leave depth of field to chance.
As a final point, don’t confuse depth of field with image sharpness. Whilst depth of field is about what’s in or out of focus, it’s different to being able to shoot sharp photographs. If you want to know more about how to capture the sharpest images possible, read my article How to Take Sharp Photos.
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