Change the Aperture to
Adjust Depth of Field
Adjusting the aperture opening controls the amount of light that enters through the camera lens and affects the depth of field, which is the range of what is in focus.
When you increase the opening of the aperture (a smaller F-number like f/5.6 - f/9), more light is let in and fewer objects will be in focus. Use a wider aperture when you desire to blur the background and have only your main subject in focus. This can be a good setting for helping butterflies or flowers stand out from a busy background filled with leaves and other blooms. But be careful that you don't open the aperture too wide if you want all of the wings or petals to be sharp. Experiment with which setting is ideal for the effect you are trying to create.
I think wildlife photos are usually enhanced by scenery that is also in focus, but if you want the texture of fur and markings to stand out, a wider aperture is needed to extract unnecessary distractions, such as the grass around this antelope.
When photographing fast moving objects such as nearby birds in flight, a high speed will require the aperture opening to be wide in order to let in enough light. So in that case the range of what is in focus will be very narrow. The in-focus range will also be affected by the length of your lens. The longer the lens, the more likely the background will be blurred, especially if you have a close subject.
I used a 300mm zoom for the photo below, making the background very blurry. You can see that the birds holding fairly still in the foreground are blurry and the flying bird is sharp. There is a large variance in focus even though the flying bird is only about 9 inches behind the birds in front.
When you want both the foreground and background in focus, the aperture opening has to be smaller (a larger F-number like f/16 or higher), allowing less light to pass through the lens. But as you decrease the amount of light going through the lens, you need to slow the speed to keep the photo from turning out too dark. When attempting to get foreground objects plus distant landscape in focus, the speed may have to be as slow as 1/30 second or slower to get brighter and richer colors. In these cases it really helps to use a tripod or rest your arm against a tree or rock. In the photo of Pikes Peak below the aperture was set at about f/20 and the speed at 1/30 second, so I rested my elbow against the rocks to keep it sharp.
A smaller aperture opening can make an entire sharply angled coastline or pathway of flowers be focused. Full sun helped these photos to remain bright even with an f/16 setting. No tripod was necessary because the speed could remain over 1/30 second.
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