One of the most important steps in learning about photography is understanding how to use aperture, because controlling your lens’ aperture settings enables you to take control over depth of field and dictate the size of the sharp area around the focus point in an image.
If you want a lot of the image to be sharp, for example, you need to select a small aperture setting such as f/22 and if you want to restrict the depth of field to isolate a subject from the background, you need a nice wide aperture setting such as f/2.8 or f/2.0.
Whatever aperture setting you use, you need to select an appropriate shutter speed to ensure that the image is correctly exposed.
If you shoot in aperture priority mode (often signified by A or AV on the mode dial), you set the aperture setting that you want while the camera takes care of the shutter speed.
Most cameras allow you to adjust aperture in 1/3-stop or EV steps. In this article we’re going to take a look at some of the common problems with using wide, middle and small aperture settings and explain how to overcome them.
Problems with wide aperture settings
SUBJECT IS SOFT
Because depth of field is very restricted at very wide apertures it’s absolutely vital that you focus at exactly the right point – especially if you are shooting a very close subject with a long lens as depth of field decreases as focal length increases and subject distance decreases.
Make sure that the active AF point is over the most important part of the subject. In some cases you may find you are better off focusing manually. If possible, magnify the live view image on your camera’s LCD screen to get a really good view of the the target area and make sure it is razor-sharp.
BACKGROUND TOO SOFT
Shooting with a very wide aperture helps separate your subject from its surroundings by blurring the background, but sometimes the surroundings can be too soft and unrecognisable.
If you want to retain a little context try closing down the aperture a little even just one stop can make a huge difference.
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IMAGE IS SOFT
Even if the focusing is spot-on, many lenses produce slightly soft results when they are fully open.
Close down a little and you’ll find the point of focus is significantly sharper.
IMAGE IS OVEREXPOSED
Opening the aperture right up means lots of light can reach the sensor so only a very short exposure is used. In very bright conditions it may not be possible to set a fast enough shutter speed and this will cause your images to be overexposed.
If you encounter this problem, the first thing to check is your camera’s sensitivity setting, you need to set the lowest value possible.
If the image is still overexposed use a neutral density (ND) filter on your lens to reduce the amount of light that enters your camera. ND filters are grey filters that cut out light and don’t produce any colourcast.
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