Using Aperture to Blur the Background

January 27, 2016

Last week I learnt about how the camera sees the world. It is a pretty grey world if you are a camera, it is programmed take every photo as an 18% grey tone. This is fine when you are taking a colourful photograph but when you are taking photos of white on white or black and black the photograph can not look the way you expect. The overall tone of the picture is called exposure. When the camera is on auto it is in control of the exposure. If you are clever you can override it, set the camera to manual and learn to set the exposure yourself. To do this you need to understand how to set three different things in your camera:

When set on auto the camera will chose the best settings for each of these to make that 18% grey image.

What is Aperture?

When you take a photo light enters the camera and hits the sensor. The amount of light hitting the sensor will change the way the photo looks. To get into the camera the light has to pass though a hole in the lens. This hole can be made bigger or smaller to change the amount of light coming in. The size of the hole is called aperture.


As well as controlling the amount of light entering the camera the aperture also controls how much of the image is in focus.  This is also called depth of field. In the first photograph all the image is in focus and the depth of field is from the front of the photograph to the back. In the bottom photograph only the flower is in focus. The background has become blurred and the depth of field is just to the flower.


So how do you blur the background?

The first thing you need to do is to find out how to put your camera into Aperture Priority Mode. You may need to read your camera manual. I have three different cameras, a compact, a bridge and a DSRL. On each of these the setting was the same. I turned the dial to section with P, M, S and A and chose A.

Next you need to work out how to change the aperture. Each of my cameras had a different way to do this. There will be lots of different aperture settings, each prefixed with an F. Work out which is the smallest and which is the largest.  Confusingly the small aperture numbers mean that the lens has a large hole which lets in a lot of light and vice versa. F1.4 means a lot of light is entering the camera and the hole in the lens is large. F32 means a small hole in the lens and not much light getting in. The actual range of numbers will depend on the lens.

Choose a subject in a well lit place. Make sure you have a background that is not too close to the subject and take a photo with the aperture on the biggest setting.




Now change the aperture to the smallest setting and take the photo again. This time the background should blur.


It takes a bit of practice and the camera needs to be focused on the subject, but once you have done it a few times it is much easier and makes for a great shot. Why not give it a try?


8 responses to “Using Aperture to Blur the Background”

  1. Yay this makes me so happy that you’re learning this stuff, it’ll make a huge difference to your photography 🙂

  2. Galina V says:

    I love the blurred background in photos, especially of close-up flowers. I managed to do it a few times without actually knowing what I’m doing, lol

  3. I am learning more about photography too. Only recently I bought my first DSLR and I am learning now how to use it. It takes lots of time and practice I must say but it is really interesting. Love your tips!

  4. Wow Alison, that was really interesting. I always struggle understanding this sort of thing but your post has certainly helped to clarify it for me a lot me. I shall have a play around with that when we have a sunny day!!!
    Angela x

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