Smooth and Mushy Backgrounds – Aperture Size and Bokeh

Understanding the basics of photography is essential for any photographer looking to capture stunning images. One of the most critical aspects of photography is the concept of aperture size, which directly affects the amount of light that enters your camera and ultimately the quality of your images. While the concept of aperture size may seem daunting at first, mastering it can lead to a vast improvement in the quality of your photos.

Think about those beautiful images where the bird is beautifully sharp but the area behind it blurs into a gentle colour. This isn’t Photoshop magic, it can be done with your camera and a few settings.

In this post, we’ll take a closer look at aperture size, exploring what it is, how it works, and why it’s so essential for capturing great photos. From understanding the basics of aperture size to exploring different camera settings and techniques, this post is the ultimate guide to mastering one of the most fundamental aspects of photography.

Aperture size – f-Stops

The aperture is part of the camera that lets light in and makes the picture.  The bigger the hole (aperture) the more light that gets in, the smaller the hole the lower the amount of light let into the camera.  

The aperture is known as the f-stop or f-number. f-stop comes from what it is describing! The size of the hole or aperture is a fraction of the focal length of the lens.

Confused? Don’t be!  

Just remember the larger the hole letting light in (aperture), the smaller the number.  They appear to be odd numbers, this is just because of the maths involved with working out the fractions!

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The f-stop will control the depth of field – how much of the image is in focus.  In some situations, you will want the whole image in focus, such as a landscape and in others, you want just a single object in focus.  

Larger aperture Smaller aperture
More light coming in Less light coming in
Shallow depth of field Bigger depth of field
More out of focus More in focus and sharp
Soft blurry background Sharp background

A landscape at f/2.8 will look very different from the same scene taken at f/16.

The lavender fields at Snowshill in the Cotswolds provide the perfect example of how an aperture setting can alter the appearance of the landscape.

At f/2.8 a narrow area of lavender is in focus. At f/16 the lavender field as well as the house and the fields beyond are in focus.

Lenses, background distance and setting aperture priority mode

Different lenses will have different minimum and maximum f-stop and this will determine how much you can play.  The maximum aperture size will usually be found on the lens itself.

To make things easier your camera will have aperture priority mode. AV on Canon cameras and A on Nikon. This will be selected from a round dial on the top of the camera body. This means you can adjust the aperture size but leave the other parts of the exposure to the camera to figure out.

This works well while you get to grips with what the aperture does. You just need to be aware that as the aperture decreases the amount of light reaching the sensor decreases so you will need a longer shutter speed to compensate.

You don’t need to do anything other than realise that your shutter may stay open longer as you decrease the aperture size (increase the F-stop number) and you may need to use a tripod or support to stop shaking affecting the picture.

The effect can look even more defined if a longer lens is used, over 100mm it becomes really obvious, under 35mm and the effect is harder to make as you need to be close to the object or have a large distance between the object and the background.

Camera, object and background distances

The further away from the background an object is placed, the more blurry the background will appear. This can be seen in the two photographs of the grouse. In the first, it is standing next to a piece of heather and this is all in focus. In the second, the F-stop is the same at f/6.3, but the bird has moved away from the heather and these are now just blobs in the background.

Grouse is close to the background
The background is a distance from the grouse

Having your camera and the object close together can also change how things appear. The closer the camera is to the object and the smaller the f-stop, the shallower the depth of field.

This can make things difficult if you are trying to photograph something very small, very close to the lens. In these situations you need to decide on what is your primary focal point and make sure that is pin sharp, accepting that everything else may be blurred.

Aperture size and other settings

Aperture size and shutter speed are linked through the exposure triangle.

To get a picture that looks the same, if you make the aperture smaller you will need to adjust the shutter speed or ISO to allow more light in.

This can be a bit complicated to start with, which is why I always suggest starting with aperture adjustments only and when you understand that start playing with the shutter speed at the same time.

What is bokeh in photography?

Bokeh refers to the aesthetic quality of the out-of-focus areas in a photograph, often characterized by soft, blurred circles of light. It can be used creatively to isolate a subject or add depth and dimensionality to an image.

The mush at f/2.8 has shapes and these are indicative of the shape of the aperture and is known as bokeh.  This can be used to make amazing images with lots of sparkles.  

The images below show how the most boring subject can become interesting with a small f-stop (f/2.8)and lots of light and reflective surfaces behind it.

In the first image the hexagonal shape of the aperture is really obvious, something that can be used to give even more effect.

Smaller cameras, phone cameras and aperture settings

Smaller compact cameras don’t always let you adjust the aperture size as you may want to.

If you want a blurry background, make sure to set the f-stop as low as it will go. This may be f/5.6 or f/6.3. Remember what I have said about getting a distance between your object and the background, if you do this, then you can instantly start to blur the background even with a higher f-stop.

If you can’t set the aperture on your camera then setting portrait mode will allow some blurring to happen. In some of the newer camera phones taking the photograph in portrait mode will tell the camera that you want the background to be blurred and you can select the amount of blurring afterwards in the editing mode of your phone.

Getting started with aperture

Aperture is one of the three settings in the exposure triangle, along with shutter speed and ISO. The aperture controls the amount of light that enters the camera, and it also affects the depth of field and bokeh.

Depth of field is the range of distances in a photo that is in focus. A wide aperture will create a shallow depth of field, with only the foreground and background in focus. A narrow aperture will create a deep depth of field, with everything in the photo in focus.

Bokeh is the quality of the blur in the out-of-focus areas of a photo. A wide aperture will create smooth, creamy bokeh. A narrow aperture will create harsh, angular bokeh.

The best way to learn how to use aperture is to experiment with different settings and see how they affect your photos. Start with aperture adjustments only, and then play with shutter speed at the same time. With a little practice, you’ll be able to use aperture to create the effects you want in your photos.

Want to learn more about photography? Read all my Photography Guides

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