The Exposure Triangle – Aperture

This is the first in a three-part series on the exposure triangle.

Understanding Aperture

Aperture is one of the three pillars of creative photography. In very simple terms, an aperture is a hole within the lens of camera. It can be opened or closed to vary the amount of light reaching the camera’s sensor. It operates in a similar way to the pupil in the human eye. You only need a basic understanding of how an aperture works to be able to apply this to photography, but it can make a huge difference to your pictures if you understand how changing apertures impacts the results.

One of the effects amateur photographers want to learn is that of capturing a pin-sharp subject against a blurred background. This technique is perfect for portrait photography. Landscape photographers often want to produce the effect of having a scene in focus from the foreground right through to the background. Changing aperture is the easiest way to control the depth of field in a picture, and once you’ve mastered the technique your pictures will take on a far more professional look.*

Modern digital cameras can produce great results in automatic mode, but you lose the creative control if you don’t make choices about the aperture and shutter speed settings. If you’re serious about photography, you should learn how to operate your camera in manual mode. By making decisions about ISO settings, shutter speed and aperture you develop an understanding of the technical aspects of cameras that influence how your pictures appear. This is not to say that you should always shoot in manual mode. It is simply to say that you should have enough knowledge to choose the best mode to capture the vision that you have in mind for any given scene or situation.

Aperture is measured using the f-stop scale. The lower the f-number, the wider the aperture. Many consumer level zoom lenses typically have a narrower range of f-stops, with the widest around f/3.5 to f/4. Specialist prime lenses offer f-stops as low as f/1.2, and these are perfect for portrait photography.

Lenses with wider apertures are great for shooting indoors and in lower light conditions. They allow the photographer to use faster shutter speeds, and are also popular in sports photography where freezing action is necessary (although depth of field is greatly reduced, so they may not capture all the action in sharp focus, when used wide open. Auto-focus mechanisms can struggle to operate in low light, and lenses with wide apertures mean you can maintain accuracy.

It’s important to understand that the level of sharpness a lens can produce varies as the aperture changes. If you need to capture very fine detail, it helps if you know a lens’ so called ‘sweet spot.’ This is usually at an aperture of between f/8 and f/11, but sometimes about 2 stops down from the widest aperture available. You can do your own testing to find the sweet spot for a particular lens. Mount your camera on a tripod and take a series of shots of a sheet of newspaper with different aperture settings. By zooming into each image on a computer monitor you can often identify which aperture produces the sharpest results.

*Perhaps the most important thing to understand about aperture settings is how they impact depth of field. This is essentially how much of a picture is in focus in front of and behind the main subject. Isolating a subject against a blurred background can produce an almost three dimensional image. Using this technique allows the photographer to pick out a subject and make it very clear what he wants you to see in a picture. Portrait, wildlife and sports photographers generally shoot at wider apertures to isolate their subjects.

Landscape photographers often shoot at apertures of f/5.6, f/8, f/11 or higher. As well as working close to their lens’ sweet spots for sharper images, these narrower apertures produce a wider depth of field. One of the key elements of a great landscape photograph is to include some foreground interest, and shooting at narrow apertures means you can keep the whole scene in focus. For example, a picture of a flower or tree in the foreground set against a sweeping view makes a stunning landscape photograph.

The narrow depth of field effect produced by shooting at wide apertures can also be achieved in photo-editing software. So called ‘blur tools’ can be used to soften the background of a picture and make the foreground stand out. However, it’s worth mastering the techniques of controlling depth of field using by aperture selection, and this saves time in the digital darkroom.

Most cameras offer an aperture priority mode, and this is a great alternative to full auto. The photographer can select the appropriate aperture for a picture and the camera adjusts other settings to achieve the correct exposure.

I mentioned that aperture is one of the three pillars of creative photography. Next week, we will discuss the second leg of the exposure triangle: Shutter speed. Following that, we will talk about the third leg: Sensitivity (ISO).

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Very concise article, thank you.