Aperture and depth of field are essentials every serious camera owner should know like the back of their hand.
Merely understanding these settings, however, is not enough. For effective photography, it’s imperative that you also understand the impact these settings have on viewers.
That, my friends, is the goal of this lesson.
Brace yourself for an in-depth photo lesson that shows you not only how to use aperture and depth of field, but how to use these settings to capture expressive, captivating photography.
Depth of Field 101
If you’ve ever taken a photo, you have utilized depth of field. By becoming savvy as to the effects depth of field has on your images, you will more effectively be able to harness its visual power.
To truly understand depth of field, you must understand a lens, a camera and how it works.
In simple terms, depth of field is the measure of sharpness within a photo. The “depth” refers to the area of the photo on the Z axis that is in focus.
To get a better idea, let’s take a look at a typical photo and break it up into its various dimensions.
As you can see, the horizontal orientation from left to right is labeled X, up and down is labeled Y, and the 3-dimensional dimension into the picture is labeled Z.
Z is the implied axis based on a central perspective that all cameras adhere to. In reality, there is no real depth to a photograph. It is 2-dimensional. You can’t reach into the photo.
Through the use of a single viewpoint (the lens of your camera), however, scientists and engineers have created the “photograph”. The perception of depth, of course, is all an illusion.
More on that in another lesson….
Because photography is created from a camera with a single viewpoint (one eye or lens), a limitation develops. Simply put…
One EYE (Lens) = One Point of Focus
Simple enough, right? One lens can only have one point of focus at a time.
This point of focus, called the focal point, is where your photo will be the sharpest (100% in focus). When you use the focus ring on your camera to focus the image, your camera is essentially moving around the lens to one specific point to focus.
Now, the area immediately in front of and behind this point of focus create an transition from fully in focus (100%) to not in focus at all (0%).
This range of area that is mostly in focus is called the depth of field.
Everything outside of this area is out of focus.
Take a look at the photo below for reference. An arrow points to the focal point and the circle roughly defines the depth of field area where the image is in focus.
Depth of field, of course, depends on a number of things (lens selection, what objects are in the depth of field, etc etc). We’ll get to all this jazz shortly.
First, we must understand how depth of field is controlled with your camera’s eye, or aperture.
Aperture – the Remote Control to Depth of Field
For those of you that aren’t too familiar with camera technology, let’s do a quick recap. To take a picture, light must be exposed upon a light-sensitive medium within your camera (film, digital sensor, etc).
The hole that allows light in is called the aperture.
Because not all situations have equal light, varying levels of light are needed to take pictures in different places.
To compensate for these changes in light, apertures are made in varying sizes. These different openings work similar to the pupils in our eyes, getting larger to allow more light in and shrinking when there is an abundance of light available.
Here’s where things are quite interesting. Think of the aperture as your typical garden hose. You’re outside watering your grass and notice that the flow of water is pretty smooth and slow. You want to make the water more intense – stronger.
Solution? Simply use your thumb to constrict the hose opening and make the water come out in a thinner projection, but with a much stronger intensity.
The same phenomenon occurs when the aperture opening is constricted.
With a larger aperture, more light is allowed in but in a less “intense” manner.
As a result, you end up with a much less focused image. This is what is called shallow depth of field.
Referring back to the Z-axis diagram from earlier, when you use a large aperture (measured as a smaller f-stop number such as f2.8), the depth of field around the focal point is not very big. This means that most everything outside of this Z range is blurry and out of focus.
So what happens when you constrict the light hole and use a much smaller aperture size (measured as a larger f-stop number such as f/16)?
The light takes a much longer time getting into the camera but, as a result, creates a much more detailed image.
Take a look at an example of a photo with expansive depth of field below:
Now that we’ve got the basicmechanics of depth of field covered, let’s dive into each different type…
Expansive Depth of Field (Small Aperture Size)
Because of the smaller aperture size (a larger f-stop number such as f/11, f/16, or f/22), the result is a photo with expansive depth of field.
With expansive depth of field, the resulting image tends to have everything in focus, from foreground cactus to far background mountains.
When using this size of an aperture, composition is easy.Basically what you place in the frame of your camera is what you will get.
There is no worry about your photo coming out different from what it appears like on the camera. The smaller aperture size ensures that the image will come out looking very much how you see it in person.
Technically from a focusing point of view, you also don’t have much to worry. Because the depth of field is so large, you can relax on focusing on just the right focal point.
You can be a little off on your focusing and still end up with an image that is super sharp.
There is, however, one hic-up that small apertures do bring to photographers…
Because the aperture size is so small and allows such a small amount of light, it takes much longer to expose an image than if it had a larger aperture. The result is that you will have to use longer shutter speeds.
To prevent camera blur during exposures, it’s a good idea to bring a tripod if you know you’re going to use a small aperture in lower light situations (sunset, sunrise, or an overcast day).
Common uses for Small Apertures:
Landscape photographers love small apertures (large f-stops) as they capture expansive vistas from foreground cactus to background rolling mountains.
Large aperture causes bright lights to create stars when the light from these objects enters the aperture.
Shallow Depth of Field (Large Aperture Size)
Large aperture sizes (a smaller f-stop number such as f/2.0 or f/2.8) reduce depth of field depth on the Z axis around the point of focus. The result is a shallow depth of field that is significantly blurry outside of the area in focus.
This amount of blurriness is determined by the distance of objects on the Z-axis when photographing.
If, for example, you use a large aperture to photograph a model standing one foot in front of a wall, because they are so close to the wall, the wall will still be in the depth of field area and remain in focus as the picture below shows.
The solution is simply to move the model farther away from the wall, creating more Z-depth between subject and background.
Case in point: sports photography.
Take a look at any sport photo where photographers use extremely long telephoto lens to capture athletes. Because of such long lenses, the athlete will be compressed with the background stadium, 100’s of yards away. With the combination of large aperture and far-away background, the result is an image with extreme shallow depth of field.
The same situation applies to wildlife photography and most telephoto shooting.
To create shallow depth of field, you need to ensure three parameters are in place:
- Zoom – The more distant you are from your subject, the more depth you will create on the Z axis
- Subject and Background Distance – the farther your subject is from the background, the more blur that will occur
- Large Aperture – the larger the aperture, the more blurry the background.
As with expansive depth of field, large aperture photography has its problems…
Focus Point Errors
Unlike small apertures where focusing is not as much of a burden, large apertures require extreme precision. If your focus is off even slightly, it could end up causing your photo to be focused in the wrong area.
A great example is in sports photography. If you focus incorrectly you could end up with a photo of a blurry athlete and a 100% focused patch of grass.
This is a common mistake for photographers that use telephoto lenses. It requires precision focusing abilities which one develops solely from practice practice practice! Fortunately, the more you focus, the better -and quicker-you’ll get.
The Composition Challenge
Unlike with expansive depth of field, when you use a large aperture what you see isn’t always what you get.
Because so much blur occurs, often you are required to use your imagination to picture what a subject would appear like with a blurred background.
The solution is to imagine what your subject would look like when the overall background colors, patterns, and light are simplified.
When composing for shallow depth of field, make note of the light and color differences from the background/foreground and your subject.
You can use these differences to accentuate colors in your subject. For example, if your subject is wearing a bright red shirt, placing them in front of a darker background with dark colors could really make them “pop” in the photo. Conversely, placing them in front of a background with similar colors could create a different visual effect.
The world provides a playground of colors and light contrasts for shallow depth of field. The key is to experiment with different angles and positions that alter the background.
Medium Range Depth of Field
Not every photo will require (nor be best suited) for expansive or shallow depth of field. Often times, the middle-range depth of fields work best.
With middle-range apertures, you won’t have to worry about long shutter speeds or overly shallow depth of field that leaves parts of your subject out of focus.
The ideal sweet spot for most cameras is around f/8 to f/11. This should provide you with an ample amount of sharpness around your focal point.