Rabu, 30 November 2011

How a Camera Barrel Works

The lens barrel indicates focal length and maximum aperture.

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The camera’s lens barrel contains the optical equipment that helps produce a clear, focused and correctly exposed image. A well-constructed, durable lens barrel helps minimize the effects of rough handling that can damage the precision lens elements. Advanced lenses provide manual focusing and auto-focus options that work with the camera body’s shutter system.

Related Searches: Lens Assembly

The lens barrel houses and protects a group of lenses or lens elements. Lenses made from optical glass are precision ground and polished. Different lens shapes include convex lenses with an outward curve or thickness in the center. Plano-convex lenses feature one flat side plus an outward curved side. Concave lenses are curved inward or thin in the center. One lens barrel can group the lenses in various configurations, such as the Canon EF 100 mm f/2.8L with 15 elements arranged in 12 groups. Adjusting the grouping of the elements optimizes the light-bending properties for a crisply focused image.

Internal Structure

The lens barrel is made of either plastic, aluminum or brass. A chassis or internal framework supports the lens elements. The iris diaphragm, known as a stop, consists of thin metal sheets that adjust to variable light conditions. The diaphragm’s leaf-like metal pieces slide into the barrel’s interior walls to open the diaphragm and let in light. When the aperture adjusts to a higher f/stop, such as from f/4 to f/16, the metal leaves slide to the center to minimize the opening and restrict the amount of light. The ring-shaped lens mount attaches to the camera body. Advanced lenses also contain auto-focus components. An auto-focus lens communicates electronically with the camera body through the lens mount.

Exterior

The exterior of the lens barrel contains printed specifications. Notation includes the focal length, such as “ZOOM LENS 70-200mm.” This details a lens with varied focal lengths ranging from 70 mm to 200 mm for a medium telephoto effect. A distance indicator window displays values in feet and meters. Interchangeable lenses include a focusing ring on the barrel’s exterior. Rotating the focusing ring moves the internal lens, and adjusts the distance between the lens element and the camera body’s film plane or focal plane. The maximum aperture is indicated as a fraction, such as “1:3.5-4.” As the lens zooms, the maximum aperture varies.

Image Stabilization

Hand-held photography in low light conditions sometimes leads to camera shake that produces blurry images. Certain advanced camera lenses include image stabilization components in the lens barrel to counteract this motion. An acceleration motion sensor or gyroscope adjusts the internal optical elements. Images recorded at slow shutter speeds will appear sharp with this system. The exterior of the lens barrel will note if an image stabilization system is present. For example, the notation for image stabilization is “IS” on Canon lenses and “VR” on Nikon lenses. The lens barrel provides an On/Off switch to enable or disable the image stabilization feature.

ReferencesCanon: EF 100mm f/2.8L Macro IS USMHow Products are Made: Camera LensNikon: How to Read Your NIKKOR Lens BarrelKen Rockwell: Nikon 18-200mm VRResourcesNikon: HomeCanon: EF Lens LineupPhoto Credit PhotoObjects.net/PhotoObjects.net/Getty ImagesRead Next:

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