Wednesday, April 14, 2010

Characteristics of Camera Lens

-Focal length: Light rays which are parallel to the axis of the lens, after passing through a convex lens meet at a point on the other side of the lens. This point is called as a focus of the lens. The distance between focus and the optical centre (or node) of the lens is called as focal length of that lens. Focal length of a camera lens may also be defined as the minimum practicable distance between film/image sensor and (the optical centre of) the lens. Focal length of a camera lens is usually marked in mm on the front of the lens. Focal length remains fixed for a given lens (other than zoom lens). SLR camera may take lenses having different focal lengths.

-Angle of View: The angle through which a scene is recorded on the film/sensor. The angle of coverage of a photograph. Angle of view varies with focal length. Smaller the focal length, wider the angle of view and vice versa. Angle of view is measured diagonally.

-Lens Elements: A camera lens is generally a combination of a number of glass pieces called as lens elements. Such lens is called as a compound lens and its final effect is similar to a single convex lens. Camera lenses are designed and manufactured with utmost care using superior optical glass. One should choose lens with least lens elements

-Lens Coating: Every lens element is coated with a very thin layer of some chemical to avoid internal reflections and scattering of light resulting from various surfaces of the lens elements. These internal reflections reduce image contrast and the resulting image looks dull. Lens coating minimizes this effect and improves the image quality. Lens coating are very delicate and have to be preserved with proper care.Cleaning/wiping of lens damages these coatings to some extent.

-Speed of Lens: Highest transmitting power of the lens. It is usually denoted in terms of the f-number of the widest practical aperture of the lens. Fast lenses make photography possible in poor light conditions and are also helpful in getting a bright viewfinder image in SLR camera.

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