Last week I talked about how aperture can be used to control the amount of light entering into the camera. This week, I'm going to go through the basics of depth of field or focal length.
As we learnt last week large apertures of f/1.4 - f/3.5 are wide and allow a lot of light into the camera. They also create very shallow depth of field. This allows you to focus in on one aspect of your photograph and blur the rest of the foreground and background. Lenses with large apertures tend to be used for still-life and portrait photography where it is useful to be able to blur unwanted distractions.
In contrast, small apertures of f/16, f/22 are very narrow. They have very large focal ranges and tend to be used when you want everything in the photo to be in focus. Landscape photography uses narrow apertures to allow both the foreground and the background to be equally focused so the viewer gets a panoramic view of the scene.
The diagram below helps to explain the relationship between aperture, distance and focal range. It's from Christopher Russo (I googled aperture and came up with this).
Figure 1 has a wide aperture eg. f/2.8 and the camera is close to the main subject. You can see from the areas shaded in green that the focal distance is small. Only the yellow person will be in focus and the foreground and background people will be blurred.
Figure 2 also has a wide aperture (f/2.8) but this time the camera is further away from the subject. The focal distance has been increased and more area is in focus, although the grey people are still a little bit blurred.
Figure 3 has a narrow aperture (eg. f/16) and the camera is close to the main subject. All the subjects are in focus. The narrow aperture has increased the depth of field.
If you're anything like me, reading these diagrams and the explainations will make your head hurt with little improvement in understanding. It wasn't until I actually understood aperture that I understood the diagrams - but I put them there incase they help someone. The best way to get a grasp of aperture and depth of field is to play around with it and see what you can do. To give you a head start I'll show you the photos from last week again.
Instead of concentrating on the shutter speed and light aspects of the photos, look at how the background changes from semi-focused to almost completely blurred as the aperture is widened. This is the depth of field becoming smaller as the aperture is widened.
If you have a P&S, you can partially control the aperture by adjusting the settings. When you select 'landscape' your camera will choose a narrower aperture to maintain focus throughout the photograph. If you select portrait it will use a wider aperture and attempt to blur out some of the background.
Next Week : Black and White
Next Week : Black and White