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Lenses

Lenses are optical devices which transmit or refract light to either concentrate or diverge the light waves. The lens found in the human eye has an extraordinary ability exhibit this ability through through muscles attached to the outer portions of the eye stretching and contracting the lens to shape the rays of light entering the eye to form an image on the retina.

Unlike the human eye, most commercial lenses cannot be reshaped so easily. Instead, they tend to be fixed in diameters, thickness and even specialized coatings. Individually or used in groups, lens designers and engineers create a recipe of varying materials, shapes and sizes needed to deliver the light rays to the image detector.

In a camera system, as light rays enter the lens, the rays are refocused onto the image sensor by adjusting the spacing of each lens group. This adjustment is done through the zooming  or focusing features. By adjusting these features, the user can alter the focal length and whereby affecting the final image that is detected on the detector.

Lens systems can be classified as either simple or compound. A compound lens system is a collection of simple lenses of different shapes and made of materials of different refractive indices, arranged one after the other and sharing a common optical axis. They can be singles or singlets and can be glued or cemented together to form a doublet.

A simple lens can be further categorized by the curvature of its two optical surfaces. The surface can be convex, concave, and flat, and the two surfaces of one lens can be the same or different. For example, if both surfaces of a lens are convex, the lens is biconvex; if one surface is concave and the other is flat, the lens is plano-concave.  Simple lenses can also be described as positive (converging) lens or negative (diverging) lens.

In addition to altering the physical shape of the lens, lens designers can further correct the performance by applying various coatings such as Magnesium Fluoride (MgF₂) to filter unwanted light waves or reflections. MgF₂ coatings help eliminate unwanted ghosting, low contrast and other flaws due to poor transmission.

Related

• CCD
• CMOS
• Depth of Field
• Imaging System Resolution
• Lighting Techniques
• Magnification