This post contains some of my assignments for the ‘Basics’ module (chapter 3) of the Matador U travel photography course.
In my previous post I talked about the shutter speed and its impact on photos. Today I’m going to discuss another important variable in the exposure triangle: the aperture. As I said in my previous post, the aperture controls the exposure, that is the light that hits the sensor, but it also affects the depth of field or DOF (=the size of the portion of a picture that appears in acceptable focus).
What is aperture?
The term aperture defines the size of the opening of the diaphragm inside the lens (a kind of hole into the lens - the hole through which the light makes its way to the sensor). The size of the opening of the lens diaphragm (the hole) becomes wider or tighter as you rotate the aperture dial on your camera body.
How aperture works
The aperture is measured in f/numbers, and higher f/numbers correspond to tighter apertures (this is a bit counter-intuitive, isn’t it?) So, if you take your camera now and set it the lowest aperture number available you are actually opening up the lens diaphragm. Now, rotate the dial in the opposite direction until you reach the highest f/number (for many lenses this is f/22 or f/29) - you’ve just stopped-down the lens.
The relation between aperture and shutter speed
The wider the aperture the higher the amount of light you’ll let in. Conversely, as you stop down the diaphragm you will progressively decrease the exposure. Therefore when you stop down the lens, you need to slow down the shutter too. This shouldn’t be difficult to understand: with a tight diaphragm you’ll need more time to let enough light in to hit the sensor and achieve good exposure. Vice versa, when you shoot with wide aperture values you’ll be able to use higher shutter speeds. If this concept is still not clear, you may want to read the shutter speed post if you haven’t read it already, or look at the images below. Keep in mind that I’m not talking about ISO right now because I’ll do it in the next post.
This is what happens when you change the aperture keeping the shutter speed at the same value:
The exposure of the image is fairly good at f/4 with a shutter speed of 1/50.
This time I used an aperture of f/9 keeping the shutter speed at 1/50 - the picture is now underexposed.
I stopped-down the lens (f/22) still keeping the shutter speed at 1/50: the image now is severely underexposed.
How aperture affects focus
As I said above, the aperture affects the DOF of a photo, that is the size of the portion of a picture that appears in acceptable focus. More precisely, the wider the aperture (=the lower the f/ number), the smaller the area of focus – a tiny area of focus is referred to as shallow DOF. As you stop down the lens diaphragm, the area of focus – and the depth of field – increase. A large DOF is also referred to as deep focus.
A photo taken at f/4: the foreground and the orange in the background are out of focus - for this picture I used a shutter speed of 1/40.
For this image I used an aperture of f/9. The foreground and the orange in the background are now less soft than they were in the previous picture. Note that I had to slow down the shutter speed (i used 1/8) to achieve a good exposure.
Aperture f/22 - shutter speed 1/6 - the foreground and the background are now in acceptable focus.
It’s important to keep in mind, however, that the DOF is also influenced by various other factors, including:
- the distance between the camera the subjects – moving close to a subject tends to restrict the DOF.
- the focal length of the lens – longer focal lengths tend to restrict the DOF too
Aperture in action
There’s no right or wrong aperture settings, only aperture settings that are appropriate for the type of image you’re shooting.
Examples of situations where large apertures are appropriate include:
- low light conditions or action shots – opening up the aperture maximises the shutter speed and helps avoiding motion blur or camera shake
- portraits or still life photography, when you want your subject to stand out - using a large aperture in this case helps to throw uninteresting or distracting elements out of focus.
On the contrary, tight apertures become necessary when it is important to maximise the DOF - in landscape and architecture photography, for instance. This is the reason why most professional landscape and architecture photographers use a tripod: the aperture range they move in requires inevitably slower shutter speeds.
Another thing to keep in mind is that very few photographer go beyond f/16 because most lenses become overall less sharp between f/16 and f/22 due to lens diffraction, as explained in this article.
For this picture I had to use an aperture of f/16 which resulted in a good DOF but required an exposure of 5 seconds. It goes without saying that I also had to use a tripod for such a long exposure.
Here I used an aperture of f/7.1 - had I used a tighter aperture I would have obtained a slower shutter speed, which wouldn't be appropriate given that I was shooting from a moving boat.
The aperture value for this picture is f/2.8 - my aim was to direct the eye of the viewer on the fruits first, therefore I needed to throw the rest out of focus. The men in the background are still important visual elements but they're secondary elements.
In this picture I wanted the fish to stand out so I used an aperture of 2.8, throwing the fishmonger out of focus. I also got close to the fish itself so to restrict the DOF.
Comments and feedback are welcome as usual – Thanks for reading!
2 Comments
One of the better explanations of aperture I have read, thanks for posting!
Thank you!
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[...] I’ve covered two of the three variables that influence exposure: The shutter speed and the aperture. In this post I’m going to discuss the third variable – the ISO, that is the [...]