While most DSLRs offers a host of controls and settings, there are really only three you need to worry about – aperture, shutter speed and ISO. Over the coming weeks, we'll look at each of these variables and show how you can use them to create better pictures. In this first part, James Ostinga and Andrew Fildes put the spotlight on aperture.
Aperture is one of the most important controls at your disposal and you'll get more control over your image making if you understand how it works. Aperture refers to an adjustable opening inside a lens which can be made larger and smaller to control how much light reaches the sensor when the shutter opens.
Depth of Field: Aperture also has an important secondary role. It controls depth-of-field, or how much of a scene is in focus either side of the point you actually focused on. A narrower aperture setting increases depth-of-field, while a wider aperture setting reduces it.
A narrow depth of field can help you direct viewer's attention to the
most interesting parts of an image. In a portrait that's usually the
eyes. In this shot the aperture is wide open at f/2. (Camera: Sony
Alpha A380. Exposure: 1/2000s @ f/2. ISO: 100. Focal length:
With a wide aperture it’s possible to put a person’s face in sharp focus, while everything in the background and foreground falls away into a soft blur. This is really useful for isolating an element so it appears to “pop” out of the photo.
Conversely, with a narrow aperture it’s possible to create an image where every part of the scene – from foreground to background – is rendered in sharp detail.
F-stops: Aperture is measured in terms of f-stops. Common f-stop settings are: f/2.8, f/4, f/5.6, f/8, f/11, f/16, f/22 and f/32. A little confusingly, it’s a case of the smaller the f-stop number, the wider the aperture. So, an aperture of f/2 is wider and lets in more light than an aperture of f/22.
Aperture Priority: All digital SLRs and some compacts offer an exposure mode called Aperture Priority. You select it with the exposure mode dial on top of your camera where it’s abbreviated to Av (on Canon and Pentax bodies), or A (Nikon, Sony, Olympus and Panasonic models).
With the camera set to Aperture Priority, you choose the aperture while the camera selects a shutter speed to balance the exposure. If you’re main concern is depth-of-field, aperture priority is a great choice.
When you’re using Aperture Priority, keep an eye on the info display to make sure the camera is choosing a suitable shutter speed. If the shutter speed flashes or blinks the camera is telling you that it cannot balance the exposure with the aperture setting you have selected. Choose a new aperture or change the ISO. Also be aware that if the camera chooses a particularly slow shutter speed, you may need to use a tripod (or choose a faster ISO, and/or a wider aperture).
ABOVE: With Aperture Priority selected, you choose the
aperture while the camera automatically sets shutter
Sharpest Aperture: There’s another thing you need to know about aperture. Most lenses produce their sharpest results in the middle aperture settings, usually around f/8 or f/11. It’s not a depth-of-field issue. Rather, the physics of optics makes it difficult to build affordable lenses that are pin-sharp over the entire aperture range. Stopped down to f/22 or f/32 or wide open at f/2.8 or f/4 many lenses are slightly soft.
Shooting Portraits: By using a large aperture setting such as f/2.8, you can create an image with a very narrow depth-of-field. This can be useful for portraits, where you can make the subject “pop” by focussing on the eyes and allowing the background to blur. This technique is commonly used by photographers to focus viewers’ attention on a particular part of an image.
1. Set your camera’s exposure mode to Aperture Priority (A or Av)
2. Set a wide aperture such as f/2, f/2.8, f/4 or f/5.6
3. Zoom in. The longer the focal length, the easier it is to throw the background out of focus.
4. You can amplify the effect by increasing the distance between the subject and the background.
A narrow depth of field can help you hide a distracting background. In this case the aperture is wide open at f/2
throwing the background into soft focus but leaving the subject's eyes sharp. (Photo by Bill Frakes. Camera:
Nikon D3S. Exposure: 1/1600s @ f/2.8. ISO: 6400. Focal length: 400mm. Image courtesy Nikon.)
This article is based on a story first published in Digital Photography + Design, Feb-Mar 2010.