Understanding Aperture

In my last blog on moving away from Auto Mode we touched upon the Exposure Triangle and how three fundamental elements will significantly impact your images. They were:

  • Aperture
  • Shutter Speed
  • ISO

In this blog we are going to look at Aperture in more detail.

What is Aperture?

Aperture refers to the opening of the lens where light passes. It is measured numbers referred to as f/stops (F.1.4, 2.8, 4, 5.6, and so on).

A useful diagram demonstrating apertures can be found here.

A large aperture (low f/stop number such as f2.8) allows lots of light in through to the sensor which will impact your image exposure. A small aperture (larger f/stop number such as f16) will give you less exposure because it allows less light through to the sensor.

Aperture and Depth of Field

Depth of field relates to the amount of sharpness around the subject in which you are photographing. It is a incredibly powerful tool in the creativity of your images, and always is a consideration for any subject I am photographing.

Depth of field allows you to blur a background, or to bring both a background and foreground into focus.

A wide aperture creates a shallow depth of field (DOF) which has the ability to separate the subject from its background, and direct the viewer to what is important in the image. It can help you take a great image in a less than ideal environment by blurring distracting or cluttered backgrounds.


The picture above was taken at f/2.8, allowing the flowers in the background to be out of focus and the viewers eye to be drawn to the intended focus point of the image.


The same image again but this time taken at f/11.

As you will see a narrow aperture as in the picture above means much more of the scene is in focus. A narrow aperture does not suit this particular image, but you may use a narrow aperture for landscape photography or a situation where you need the full content of the image in focus.

Aperture and your Camera

Aperture Priority is usually found as a menu option on your camera an ‘A’ (Nikon and other camera makes, ‘AV’ Canon)


In aperture priority you control the aperture and the camera will select the correct shutter speed to produce a correctly exposed image (given an ISO sensitivity). It is a very popular mode of shooting for both professionals and non professional photographers, and offers a level of creativity that will dramatically change your images.

If you have a zoom lens for your camera it will have constraints as to the minimum and maximum apertures it can achieve for each end of its zoom range. Higher end zoom lenses may only show one aperture because it can maintain the largest aperture throughout its entire zoom range.


It is worth noting that your choice of aperture (f/stop) will ultimately also effect your shutter speed.

A shallow depth of field will allow lots of light to enter the lens, your shutter speed will therefore be faster as it will not need to stay open long in order to achieve a correct image exposure.

Equally if you want more of an image to be in focus you may use a deeper depth of field and as a result your camera may chose a slower shutter speed in order to obtain the necessary light through to the sensor to correctly expose the image. A slower shutter speed can present you with some tricky issues and you may require a tripod to get a steady image, but that is for another blog.

Now you hopefully have more understanding as to how powerful aperture priority is as a shooting mode. The next time you take a picture consider depth of field and see for yourselves the incredible impact it can have to your image.

In a future blog on Programme Mode we will cover how you can start to control the aperture in your images whist still allowing the camera’s technical ability to support you.

If you would like to learn more about how to work your camera on a 1-2-1 basis, I offer training workshops for anyone new to photography, or for individuals who want to learn a specific skill either for their business or simply for taking better family photos.

If you would like more information about learning to make the most of your camera with me please get in touch

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