Understanding the Camera Lens
Episode #3 of the course Introduction to photography by Robin Whalley
Yesterday, you learned about the Exposure Triangle and how to take a well-exposed image. Today, you will learn about an important piece of equipment: the camera lens.
Categories of Lens
The primary purpose of the lens is the focus light onto the camera sensor, which creates the image. But the lens also has other characteristics we can use in our photography. The lens can make objects appear nearer or farther away from the camera than we can see with the naked eye. It can also increase or narrow the field of vision. Based on these characteristics, there are three broad lens categories.
Wide Angle Lens. This has a wider field of vision than the human eye and will make objects appear farther from the camera. It also allows you to move in close to objects while still showing the surroundings, as in the photo below.
Standard Lens. This has a field of vision that’s like the human eye.
Telephoto Lens. This has a narrower field of vision than the human eye and makes objects appear closer to the camera.
Lens Focal Length
In photography, the focal length helps us understand which category a lens fits into. A wide angle lens tends to have a focal length of 35mm or less. Standard lenses will have a focal length of 40mm to 70mm, while telephoto lenses will be 80mm or more, but this isn’t exact.
When we compose a photograph, we can use the characteristics of the lens to help us. For example, in the picture of the mountains, a telephoto lens was used to make the mountains appear closer to the camera. The telephoto lens also has a narrow field of view, allowing distractions around the mountains to be excluded.
The lens attaches to the camera body with a lens mount. If your camera accepts interchangeable lenses, any lens you attach must have the correct lens mount. For example, Canon uses the “EF Mount,” while Sony uses the “A Mount” and “F Mount.” Canon lenses won’t attach to a Sony camera unless you use a special lens adapter.
Sensor Magnification
In an earlier lesson, you learned about the different sizes of sensor used in cameras. The three most popular are Micro 43, APS-C,and Full Frame. When we discuss the focal length of lenses, we relate them to Full Frame cameras because this is the same size as 35mm film.
The size of the sensor affects the focal length of the lens. For example, a Micro 43 camera will magnify the focal length of a lens by 2x. A 12mm lens on a Micro 43 camera is equivalent to a 24mm lens on a Full Frame camera.
This multiplication effect is known as the crop factor. Micro 43 cameras have a crop factor of 2x, and for APS-C cameras, it’s 1.5x.
Lens Features
A lens can also be a prime lens or a zoom lens. A prime lens has a fixed focal length—for example, 20mm—whereas a zoom lens has a variable focal length that you can change—for example, 20mm-40mm.
A useful feature you may encounter is stabilization. Some cameras have this built into the body, but it can also be in the lens. Stabilization will help steady the camera as you take the photograph. Often, you can use a much slower shutter speed than is otherwise possible.
Another feature of the lens is the type of focus it provides. Manual focus lenses require the person taking the photo to focus the lens using a focus ring on the lens. Autofocus lenses are focused by the camera as the shutter button is pressed. We’ll talk more about controlling the focus to ensure your images appear sharp and clear tomorrow.
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