Introduction

The aperture – the opening that permits light to pass into the camera – is controlled by an adjustable diaphragm. Obviously, a larger opening will allow more light into the camera than a smaller one.

Aperture sizes are expressed as f-numbers, as illustrated in the table.

F-numbers are expressed as fractions and not as whole number.

This causes some confusion for many people. The smaller F-number like F/2.8 has larger aperture opening than larger F-number such as F/11. In summary:

When you use your camera’s Aperture Priority Mode, you fix the size of the opening. Your camera selects the appropriate shutter speed that will, in combination with the size of the aperture, yield a proper exposure.

In early morning, the available light is soft and low. Using a large aperture allows the maximum amount of light to enter the camera. In this case, setting the aperture at f/2.8 necessitated a shutter speed of 1/60^th of a second.

Had the Auto Exposure Mode been chosen, the camera might have selected a small aperture and a slower shutter speed. That would likely have resulted in unwanted blurring because of the motion of the cubs.

 

Smaller  F-number =

Larger Aperture Opening

Lion Cubs (Kenya)

There are occasions when indoor lighting is very dim. In this temple the main source of natural light was the window. The selected aperture of f/8 gave a reasonable depth of field. The resulting shutter speed of 1/15^th of a second was the minimum speed needed to render the monk sharply. A tripod and cable release were used to eliminate camera movement or vibration.

 

Smaller  F-number =

Larger Aperture Opening

Monk Praying (Burma)

Small apertures such as f/11 and f/16 allow less light to reach the camera’s sensor. As a result, the camera automatically decreases the shutter speed in order to obtain the correct exposure.

Setting the Aperture Priority Mode at f/16 for this picture meant the camera chose a shutter speed of 1/30^th of a second. The slower shutter speed resulted in a slight blurring of the carousel lights and captured the sense of movement the photographer sought.

 

Bigger  F-Number =

Smaller Aperture Opening

Carousel

In this photograph of a waterfall, we set the camera’s Aperture Priority Mode to its smallest aperture f/16. In this case, the shutter speed automatically defaulted to 1/15^th of a second.

Water Falls (Sichuan, China)

Conclusion

Once you become accustomed to the principle that a larger aperture will result in a fast shutter speed and that a smaller aperture will force the camera to select a slower shutter speed, you can create a variety of interesting photographic effects using the Aperture Priority Mode.