- A Beginner's Guide to Aperture and Depth of Field
- Beginner Photography Tip: Advanced Controls That Will Take Your Photos to the Next Level
For beginner photographers, one of the hardest things to master is understanding aperture.
Not only does the aperture definition pose some difficulties for beginners, but how it's measured and its effects on your photos is also a lot to take in.
But in this straightforward guide, you'll learn the basic ins and outs of aperture so you can use it to your advantage to take improved photos.
Let's get started!
How Does Aperture Work?
At its most basic, the aperture of a lens is the hole through which light passes into your camera.
The larger the aperture size, the more light that's allowed in; the smaller the aperture size, the less light that's allowed in.
That part is easy to understand because it's a lot like your eyes - the larger your pupil (aperture), the more light that comes in. The smaller your pupil (aperture), the less light.
Using that analogy as a guide, you can begin to understand how to use aperture to your advantage.
For example, if you're shooting a portrait indoors and there isn't much available light, you want a larger aperture to allow as much light into the lens as possible.
Conversely, if you're shooting a landscape outdoors on a sunny day, you can close down the aperture because so much light is available.
The size of the aperture is measured in f-stops. This is where things can get a little confusing.
A large aperture opening is actually represented by a smaller f-stop.
So, an f-stop of f/2.8 is actually quite large, while an aperture of f/16 is quite small.
This inverse relationship can be hard to remember, but if you think about f-stops as fractions, things become easier.
For example, if you're shooting at f/11, think about it as a fraction - 1/11. If the image is too dark at that aperture, which way would you move it? To f/8 or f/16?
Since f/8 would be 1/8 and f/16 would be 1/16, it's easy to see which f-stop is bigger and therefore allows more light into the lens - f/8.
For a quick discussion of how aperture works, have a look at the video above by The Studio Education.
Aperture Explained: It Controls Exposure
As noted above, the primary function of aperture is as an exposure setting.
Along with shutter speed and ISO, aperture controls how dark or light an image is.
Naturally, if you shoot in manual mode and select an aperture of f/4 and take a photo, it will be brighter than a photo with all the same settings but an aperture of f/16.
Fortunately, changing the aperture doesn't require you to shoot in manual mode.
Aperture priority mode, which I discuss in detail in this guide, allows you to control the aperture while the camera controls the shutter.
Think of it as a stepping stone between shooting in full auto and shooting in full manual mode.
Aperture Also Controls the Depth of Field
The depth of field of an image refers to how much of it is in sharp focus.
A shallow depth of field, then, puts a smaller area in focus, while a larger depth of field puts more of the scene into focus.
You can see the relationship between aperture and depth of field in the chart above - as the aperture size gets smaller, the depth of field increases. As the aperture size gets larger, the depth of field decreases.
Let's say you want to create a portrait like the one shown above, and have a nice, blurry background.
All else being equal, you can do that by using a large aperture like f/4 or f/2.8.
But then let's assume you want to photograph a landscape like this one and have everything in the scene in sharp focus.
Again, all else being equal, you can get that larger depth of field by changing the aperture.
In this case, an aperture of f/11 or f/16 would be a good choice for a shot like this one.
Sharpness and Diffraction
When you're thinking about depth of field, it's only natural to assume that if you use the smallest aperture possible, like f/22, that you'll get the sharpest image possible as well.
That's not the case, though...
Aberrations often appear, even in very high-quality images.
They mostly manifest as areas that aren't quite as sharp, and most often occur in the corners of the image, as you can see in the photo above (especially in the trees in the upper-left corner).
Diffraction is also an issue, particularly as smaller aperture sizes.
That's because the aperture hole is concentrating the light into a narrow opening, causing interference between light rays. The result is a blurrier image.
Perhaps an even bigger problem is that lenses aren't as sharp at certain apertures.
When photographing a scene at a very wide or very small aperture, like f/1.4 or f/22, for example, the image will not be as sharp as if the same image is taken at f/8.
That's because every lens has a "sweet spot," or an aperture or range of apertures at which it minimizes aberrations and produces the sharpest images.
Granted, you can't always shoot in your lens's sweet spot, but doing so as often as possible will get you sharper photos with less diffraction more often.
For a detailed discussion of lens diffraction, check out the video above by Steve Perry.
As I've discussed above, aperture isn't just a one-trick pony.
Instead, when asking, "What is aperture?" you have to consider the many different ways in which it can change your photos.
Aperture influences how bright or dark your images are, the size of the depth of field, and also how sharp your images are as well.
Aperture even controls how starbursts appear and the quality of bokeh, too.
In that regard, it's a valuable camera setting to know how to use!