If you are new to photography, it is likely that you have come across terms like aperture, shutter speed, f-stop, f-stop chart and so on. These terms might sound confusing, but they are part of the language of photography and describe the mechanics and technical details behind the way an image is recorded.
In the spirit of understanding the basics of photography, I present this guide to using the aperture on your camera and how it affects image making.
In this guide, I will answer the following questions:
- What is aperture in photography?
- What is f-stop?
- What is depth of field and how does the aperture affect it?
What Is Aperture In Photography?
The aperture is located in the lens of a camera and controls the amount of light that passes through to the digital sensor. The aperture consists of a ring of thin metal blades that can close down to narrow the opening, and can open up to widen it.
When you control the aperture – if you set your camera to Aperture Priority mode for instance – you are telling your camera to either narrow the aperture or open it up.
On old lenses for film cameras or manual focus lenses, the aperture can be controlled by turning a ring that sits on the outside of the lens.
Modern digital cameras control the aperture through a combination of software and mechanics. You may control the aperture setting of your camera’s lens if you set the mode dial to Aperture Priority mode or Manual mode.
There is no aperture ring on my Sony 10-18 f/4 lens. The only way to change the aperture settings is through camera controls.
What is F-stop?
In your perusal through online discussions, you may have come across another confusing term: f-stops. You might even have heard a photographer saying things like: “Stop down your lens to increase the depth of field”. So what are these f-stops?
First, let’s see where the term f-stop came from.
The term is directly related to the primary function of the aperture, which is to stop the light from passing through the lens. Without the aperture the lens is wide open, letting all available light through.
The expression “stopping down the lens” means that we are reducing the amount of light passing through the lens by introducing the obstacle in the form of aperture blades.
In the simplest terms, f-stops are the numerical values that determine the size of the aperture.
1.4 2.0 2.8 4 5.6 8 11 16 22
But, the f-stop is probably the most confusing concept in photography to understand. If we look at ISO in photography, it is easy to recognize that by increasing the value from ISO 100 to ISO 200 we increase the sensitivity by a factor of 2. Same goes for the Shutter Speed. By changing the shutter speed from 1/50 second to 1/100 second, we double the speed.
With the aperture, when we go from f/1.4 to f/2.0 the size of the aperture gets smaller, decreasing the amount of light traveling through the lens to the camera sensor. It sounds very illogical until we understand that f-number or f-stop is the ratio between the focal length of the lens (distance between the front of the lens and the camera sensor) and the diameter of the aperture.
For example, f/1.0 on 50 mm lens means that the focal length and the diameter of the aperture are equal. By changing the f-stop from f/1.0 to f/1.4 we make aperture diameter smaller and as the result, the ratio increases since the focal length stays unchanged.
We changed the diameter by a factor of 1.4 only but the area of the aperture (measured in square millimeters) was reduced by a factor of 2. In Optics the aperture area is used to calculate the amount of light entering the lens.
It can be a bit too technical for some people but you do not need to know physics to be a good photographer. All you need to remember:
When you change the aperture by one stop you are doubling or halving the amount of light passing through the lens.
The aperture of the lens moves from a wide open position to a narrow position by stepping through f-stop values that move from a low number to a high number. For example, a wide open aperture might have an f-stop value of f1.8, but at its narrowest it might have an f-stop value of f22. Thus the aperture would move from a wide open position to a narrow position through this progression of values:
1.4 2.0 2.8 4 5.6 8 11 16 22
These numbers vary depending on the lens, so you might, for example, find a lens with an open aperture of f1.4 and a narrow aperture of f32.
The Depth of Field and the Aperture
Now we understand that the size of the aperture controls the amount of light entering the camera. But, the reason the aperture considered to be one of the most important parameters of the camera because it also controls how much of the photographic subject is acceptably sharp and in focus. This acceptably sharp zone of focus is called the Depth of Field (DOF). The wider the aperture (lower f-stop numbers), the more shallow focus will be. The narrower the aperture (higher f-stop numbers), the more will be in focus and sharp.
Fast Lens vs Slow Lens
There are plenty of lenses on the market and there are quite a number of variations when it comes to their apertures. Some offer very wide maximum apertures – f1.8, f1.4 and so on – while others offer narrower maximum apertures – f4, f8 and so on. Because wider apertures allow more light to enter the camera and achieve the equal exposure in less time, they are sometimes called “fast” lenses.
This is Sigma 30mm f/1.4, the fastest lens I have in my possession.
Those lenses with narrower maximum apertures are sometimes called “slow” lenses because they let in less light to the camera and it takes a longer time to achieve the optimal exposure.
Below is Sony 55-210 f/4.5-6.3, considered to be a “slow” lens.
Fast lenses are excellent in low light conditions because they allow more light to hit the digital sensor from outside.
How to know what aperture to use?
“How to know what aperture to use?” is probably the most common question people ask when they start to learn the concept of the aperture.
There are many different ways to use aperture creatively, but I will give you two most common scenarios I face as a travel photographer.
Scenario 1: Shooting Wide Open Landscapes
When shooting landscapes, in most cases, you want everything to be in focus and sharp, starting with the foreground elements of the composition to all the way to infinity. You need to use a very narrow aperture, f/8 and up.
I used the f/11 aperture value to have the entire scene in focus.
Scenario 2: Shooting People
When photographing people you want to achieve the separation between your main subject and busy surroundings. By choosing the widest aperture and focusing on your subject you can achieve blurry, out of focus background, making a person a focal point of your photograph.
I used the widest possible aperture of f/1.4 to limit the Depth of Field (DOF) to only a few centimeters.
The relationship between the size of the aperture, the exposure, and the depth of field might seem daunting at first, but with plenty of practice, you will come to understand it intuitively. Once you develop a grasp of this dynamic, you will be well on your way to getting the most out of your camera!