Understanding Aperture

sigma 150-600mm

Aperture is one of the three elements of Exposure Triangle that are responsible for correctly exposing the photos. Aperture decides whether to create shallow or deep depth of field (more or less bokeh). In this blog post, I am going to shed some light on what exactly the aperture is and how you can control it to click photos with desired depth of field.

In case you want to learn more about shutter speed, read: Understanding Shutter Speed

What is aperture?

Aperture is the opening of the lens’s diaphragm made up of multiple blades which allow the light to enter the camera. The amount of light that enters through the lens depends upon the opening of the aperture (diaphragm). The wider the aperture opening, the more will be the amount of light that enter the camera. Similarly, the narrower the aperture, the less would be the amount of light that enters the camera.

aperture

Let’s take an example, assume the opening of the aperture as the opening of a water bottle. It is raining outside and you have to fill two bottles with rain-water, the diameter of the bottle ‘A’ is 1 inch and that of the bottle ‘B’ is 2 inches. Any guesses which bottle will you be able to fill first? Bingo, bottle ‘B’ will be filled faster because of the bigger opening of the bottle and as the opening of the bottle ‘A’ was smaller, it took more time to fill the same quantity of water.

How is aperture measured?

Aperture is measured using the f-stop scale and the value of aperture is denoted by ‘f/’ followed by the f-stop number.

The f-stop number signifies the opening of the aperture. As we move from one f-stop to other on the f-stop table, the amount of light entering through the aperture increases by double or decreases by half. Let’s have a look at the f-stop table:

aperture stops

So you see a pattern here? Take the first f-stop f/1 and second f-stop f/1.4 in the table. Now double the first f-stop and you will get third f-stop, similarly double the second f-stop and you will get the fourth f-stop. keep on repeating this and you will be familiar with the f-stop table in no time.

The f-stop is inversely proportionate to the opening of the aperture.

  • The smaller the f-stop number = the bigger will be the aperture opening = more light will enter the camera
  • The higher the f-stop number = the smaller will be the aperture opening = less light will enter the camera

aperture

How aperture affects depth of field?

Before we proceed with this discussion, let’s understand what depth of field means.

The range of distance that is acceptable sharp in a photo is known as depth of field. In simple words, when you click a photo, there is some area in front and behind the point where you focus which appears in focus and is acceptably sharp. This range of this area is known as depth of field.

The depth of field is affected by three factors: Focal length, Aperture f-stop and camera to subject distance. The f-stop being one of the factors affecting the depth of field, let us now understand how this happens.

  • The smaller the f-stop number = the bigger will be the aperture opening = the shallower the depth of field (more blur effect)
  • The higher the f-stop number = the smaller will be the aperture opening = the deeper the depth of field (less blur effect)

This summarises that the smaller the f-stop, the shallower will be the depth of field which is good if you need to create blur effect in portraits and macro photography. Similarly, the higher the f-stop, the deeper would be the depth of field which can be used for landscape and cityscape photography to get the maximum area in focus.

aperture

How aperture affects shutter speed?

Shutter Speed is the length of time for which the shutter is open to expose the image sensor/film. The shutter speed is denoted in seconds or fractions of a second, e.g. 2 sec, 10 sec, 1/50 sec, 1/250 sec, etc.

The aperture f-stop and shutter speed are inversely proportionate. This means that if you increase the f-stop, the shutter speed will decrease. Similarly, if you decrease the f-stop, the shutter speed will increase (assuming the ISO is constant). Suppose you are shooting at f/4 and 1/100 second, as you increase the f-stop from f/4 to f/5.6 the aperture becomes smaller and the light gets cut by half. To compensate, the shutter speed will decrease from 1/100 second to 1/50 second to correctly expose the photo.

Similarly, if you decrease the f-stop from f/4 to f/2.8 the aperture gets wider and the light entering the camera gets doubled. To compensate, the shutter speed needs to be increased from 1/100 second to 1/200 second to get the correct exposure.

How and when to use smaller f-stop?

As we discussed above, smaller f-stop (f/1.8, f/2.8, etc.) means faster shutter speed (keeping the ISO constant). So one thing you need to consider while shooting at smaller f-stop is that you will have to choose a faster shutter speed. Also, the smaller f-stop produces shallow depth of field, which means more of bokeh effect.

So a smaller f-stop would be ideal for clicking photos where you want to freeze the movement of the subject such as a moving car or a flying bird. You can also use smaller f-stop to click portraits and macro photos with shallower depth of field (more blur effect).

aperture

How and when to use higher f-stop?

Higher f-stop (f/8, f/11, etc.) means slower shutter speed (keeping the ISO constant). This means that while shooting at higher f-stop, you will have to choose a slow shutter speed to correctly expose the photo. Also, the higher f-stop will produce deep depth of field, which means less bokeh effect.

Using the higher f-stop you can click photos where you want to capture motion, such as light trails, star trails and light painting. You can also use higher f-stop to click monuments, building and landscapes to achieve deep depth of field (less blur effect and more are in focus).

aperture

Controlling aperture using the Aperture Priority mode

Aperture Priority mode lets you control the size of the aperture as per your requirement, at the same time, the shutter speed will automatically be defined the camera. Your camera will also define the required ISO sensitivity, if you have turned off the auto ISO option. My advice would be to set the ISO at 100 (or the minimum number in you camera) to avoid grains in your images.

Here’s an example explaining how you can use the aperture priority mode to get good results:

Suppose you want to click a portrait with shallow depth of field (more bokeh/blur effect), all you have to do is set low f-stop (aperture number) on your camera and the camera will on its own choose an appropriate shutter speed as per the available light.

On the other hand, if you wish to click a portrait with deep depth of field (less bokeh/blur effect), simply set high f-stop (aperture number) and let the camera decide the apt shutter speed.

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About Author

Kunal Malhotra
Kunal Malhotra, a photography enthusiast whose passion for photography started 6 years back during his college days. Kunal is also a photography blogger, based out of Delhi. He loves sharing his knowledge about photography with fellow aspiring photographers by writing regular posts on his blog: The Photography Blogger. Some of his favourite genres of photography are Product, Street, Fitness and Architecture.