Aperture-How does it work?
ByAlthough automatic and program settings on today’s cameras are quite remarkable, there are many images that cannot be photographed well using strictly automatic. If you want to be able to capture an image the way you visualize it, you will need to master the manual settings of your camera.
Exposure is controlled by coordinating the shutter speed, aperture, and ISO settings. You will make decisions on each of these three options for every image to control the desired outcome for your photograph. These three settings used correctly together create a properly exposed file that produces a proper photographic print.
The aperture, or f-stop, is an expanding and contracting mechanism that changes the size of the opening that allows light to reach your film or digital image sensor through the lens. I think of the aperture as being similar to the iris of your eye. It gets larger and smaller like the iris of your eye does as you move from darker to lighter and lighter to darker conditions.
It is kind of hard to take a picture of an aperture in a lens so I made this graphic, to the left, to give you an idea what an aperture looks like. The six sections move to make the opening larger and smaller.
The human eye can distinguish about 16 stops of light. A digital camera can record only four or five stops really well. This is why we are so often under whelmed with the results we get. This is why it is so difficult to photograph a landscape scene that has a good exposure of the sky and good exposure of other parts of a scene, like dark green grass and trees, at the same time.
This is why a professional learns to control light. A smaller aperture with a high f-number like f16 lets less light in the lens as the rays of light are directed through a smaller opening. A greater depth of field is also created. A larger aperture with a smaller f-number like f4 lets in more light through a larger opening but the image will have less depth of field.
The common numbers used on film camera lenses are full stops. They are f1.4, f2, f2.8, f4, f5.6, f8, f11, f16, f22, f32, f64. Each step is double (or half) the amount of light with f1.4 letting in the most light and f64 letting in the least amount of light. For example f16 lets in twice as much light as f22. Similarly, f4 is half the amount of light as f2.8.
Now we are working with 1/3 stops in digital cameras. They are f3.5, f4, f4.5, f5, f5.6, f6.3, f7.1, f8, f9, f10, f11, f13, f14, f16, f18, f20, f22 and so on. Each step is one third the amount of light entering the lens. It is still a full stop or double the amount of light from f11 to f8 but there are now two more options at 1/3 increments in between to work with.
It will take some practice and time to understand this, so don’t give up. At some point it will be second nature to you if you keep working with it!
