How To Blur The Background With Your Phone Camera


I was in the park messing around with my phone camera and I started thinking, how do photographers manage to get that blur background look in their pictures and can I do the same with my phone camera.

One of the coolest techniques in photography is when you see pictures that have a sharp foreground with a blurred background, so I did some research to see if it was possible to do this same technique with a smartphone, this is what I found.

In the world of photography, this is called ‘depth of field’ or Bokeh and it is most often achieved by changing the aperture of the lens. Using a wide aperture will result in a narrow depth of field which means the focus area of the lens is quite small resulting in a blurred background. A small aperture will result in a longer depth of field which means the focus area of the lens is wide resulting in a larger area being in focus.

I have also discovered that most smartphones these days have a fixed aperture which makes it a lot more restrictive in achieving the blurred background look using the aperture technique. However, this is not going to stop us, there are some other techniques we can use to achieve the effect we are seeking in out pictures. Let’s dive into this subject and see what we need to do to achieve those cool, out-of-focus backgrounds with our smartphone.

What is Depth of Field?

The term ‘depth of field’ is very widely used in photography circles and is the technique used to control the focus (focal) area of the camera lens. The focus area can be manipulated to allow a photograph to be sharp from the foreground right through to the background, or it can be used to isolate a subject in the photograph and blur the background or foreground to give more emphasis on the main subject.

The background blur is controlled by using the aperture of the lens, a wider aperture will provide a very narrow area of focus which means that a subject can be in sharp focus while the rest of the image is blurred. A small aperture can result in the whole image being in sharp focus. There are a lot of variations between a fully wide aperture and a very small aperture and this variety can give a lot of control over how our photographs look.

The aperture of the lens is often referred to as an f-stop or aperture stop, each f-stop of the lens controls how much light is let into the lens and it also affects the depth-of-field. Smartphones tend to have a fixed f-stop and so we will have to work around this if we want to get ‘depth of field’ in our photographs.

f-stop indicators on a camera lens
traditional camera lens f-stop numbers (green)

‘Depth of Field’ is also affected by the size of the camera sensor, this is the chip behind the lens that collects the light and turns it into a picture electronically. The rule is, the larger the sensor, the more easily it is to achieve blurred backgrounds in your pictures. Unfortunately, the vast majority of smartphones have quite small sensors so it may be more difficult to create pictures with blurred backgrounds without some additional assistance.

Why is Depth of Field Important?

Using depth of field can enable us to take more professional looking photographs and can also help to highlight areas in our photographs that we want to stand out and hide areas of the photograph that we want to take out of focus. ‘Depth of Field’ is one of the fundamental techniques used in photography and can be seen in many different photographs. Google Images is a good place to see this in action with a lot of different images utilizing ‘depth of field’. Incorporating ‘depth of field’ encourages us to slow down and think about our photography in greater detail which will help us to produce more beautiful photographs.

Another important factor to consider is the widest aperture of the lens in relation to the sensor size. A lens with a maximum aperture (f-stop) of 1.8 on a small sensor will only let in a fraction of the light of a large sensor with a lens with a maximum f-stop of 1.8. This not only affects the exposure time of the picture but also the ‘depth of field’. As smartphones tend to have small sensors, we need to look into this further to understand the implications for our pictures. On traditional cameras, the smallest f-stop is often displayed on the lens, but smartphones don’t usually do this, so it is necessary to look at our smartphone documentation to determine the maximum aperture. A note on aperture; the wider the aperture the smaller the f-stop number, and the smaller the aperture the bigger the f-stop number, this can be quite confusing at first.

What is Sensor Size?

When photography first became popular, cameras used cellulose film that was coated with a light-sensitive emulsion. Cameras would use a mechanical shutter to expose the film to light. The film would then be sent off for processing by a photographic processing lab and you would get your pictures (prints) back a few days later. Camera manufacturers like Canon and Nikon started making cameras with 35mm film and these quickly became popular with professional photographers and enthusiasts.

Today we use digital cameras that have image sensors rather than cellulose film but the digital sensors are based on that old 35mm film sizes. A digital camera with a sensor size equivalent to 35mm is now called a full-frame camera and other manufacturers have different sized image sensors that are relatively sized to 35mm, some larger and some smaller. Smartphone sensors are just a fraction of the size of a full-frame sensor due to all the other technology that manufacturers need to fit into the smartphone and because of this, the smartphone camera has limitations compared to larger digital sensors. Smartphone manufacturers are continually improving their cameras and it’s really only a matter of time before they start taking on the larger sensor camera manufacturers. Smartphone cameras already dominate the compact camera market and have taken a huge chunk of market share from traditional compact camera manufacturers.

What is Bokeh?

Bokeh is just another name for background blur used by camera enthusiasts and professionals. Bokeh is typically broken down into two categories; good-bokeh and bad-bokeh. Good-bokeh describes a picture that not only has a blurred background but the blurred area has a beauty of its own, so it can make the whole picture pop and look amazing. With top quality lenses, you will often see blurred backgrounds with small balls of colored light, this would definitely be classed as good-bokeh. Bad-bokeh, on the other hand, is a blurred background that detracts from the subject and can confuse the picture to the point that the picture is unpleasing to look at, this is often the result of cheaper lenses and low-quality cameras.

Bokeh comes from the Japanese word boke (暈け or ボケ), which means “blur” or “haze”, or boke-aji (ボケ味), the “blur quality”. The Japanese term boke is also used in the sense of a mental haze or senility.[7] The term bokashi (暈かし) is related, meaning intentional blurring or graduation. Bokeh is pronounced BOK-UH, thank’s Wikipedia!

There is quite a lot of technical information relating to the subject of background blur or bokeh but I am not good to include it in this article, if you wish to know more about the technical aspects I would recommend having a read of the Wikipedia article about ‘depth of field’ as a starting point, it will explain all of the math and physics relating to the subject.

When Should You Use Depth of Field?

‘Depth of Field’ can be applied in many different scenarios and can make our pictures stand out from the average snapshot. It shows that we have a wider grasp of photographic knowledge.

Sometimes when taking pictures, we may want to emphasize a subject, it may be the beauty of a butterfly or a busy bee collecting nectar from a flower. If we have a wide ‘depth of field’ the bee might blend into the background of the image and so we don’t get the impact we were looking for. On the other hand, we may have a scene that we want everything in focus to get the full scale, a landscape for example. These are just a couple of scenarios when we may want to use ‘depth of field’ in our images.

How Might We Achieve Depth of Field With A Smartphone?

Smartphones are usually designed with a fixed focal length this means that we need to find another way to influence the background blur in our photographs. One technique we can use is the distance from the subject, the closer to the subject the lens is the narrower the ‘depth of field’ becomes giving a blurred background and consequently the further the subject is away from the lens the wider the ‘depth of field’ resulting in the whole image being in focus. Using distance, we can achieve similar results as changing aperture settings on a traditional camera.

There are several smartphone apps available that can help you achieve a blurred background in your pictures, here is a list of the top apps you can try for free:

Android

  • After Focus
  • Photo Editor by Aviary
  • PicsArt
  • Cymera

IOS

  • FaceTune 2 – Blurring the background in pictures of people.
  • FabFocus
  • AfterFocus
  • Tadaa SLR
plumb blossom with smartphone
My first attempt at a smartphone pic with a blurred background (Samsung Galaxy S8 Plus)

Summary

It is also possible to purchase external lens extensions that clip over the smartphone lens, these not only provide zoom or wide angle features, not only do these affect background blur directly, but some also allow aperture manipulation so we can get more flexible ‘depth of field’ results from our smartphones. I am planning to investigate these in more detail in the future. I will post my findings and let you know what kind of results you can expect.

So, after doing some research and putting into practice what I have learned I have concluded that it is possible to get background blur in your smartphone pictures but there are some limitations around how we can achieve it. Smartphones have fixed focal lengths so it is not easy to change the focal length to manipulate the depth of field of the lens using the settings on the smartphone.

I have also identified that it is possible to get a blurred background using distance rather than aperture to achieve the desired effect. Moving the lens closer to the subject with a result of a narrower ‘depth of field’ while having the subject a long distance from the lens will result in a wider range of focus.

I have identified the limitations of smartphones in photography by identifying that they usually have small image sensors that restrict their ability to produce ‘depth of field’ using aperture settings and that the widest lens aperture not only affects how much light enters the lens but that it also has a big impact on ‘depth of field’ results.

I have also discovered that there are a variety of apps available for both Android and IOS devices that can help us achieve the blurred effect we are looking for in different situations.

In addition to apps, there are lens extensions that not only allow us to extend the features of the smartphone camera with telephoto zoom and wide angle features but may also help us achieve better ‘depth of field’ results, but, I need to do more research into these and will be producing an article about these in the future.

I hope this article has been of some help in explaining how you can add background blur in your smartphone pics, keep an eye open for the next article and in the meantime enjoy your smartphone photography.

Jeff Muir

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