Lenses and Vision

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How a prism bends light Obtained from www.howstuffworks.com

    The simplest kind of lens is actually a prism. A prism is a piece of glass shaped like a triangle and bends light towards its thickest part (the bottom of the “triangle”), which is called the base.  The thinnest part of a lens is called the apex. 

    Not all lenses are prisms, but any lens can be thought as two rounded prisms joined together. The same rules would apply, so all lenses bend light towards their base.

The kinds of convex lenses*

    Convex lenses are known as many names, being also called positive lenses, plus lenses, converging lenses, and condensers. Convex lenses are fat in the middle and skinny on the edges. There are three main types of convex lenses: plano-convex lenses, double-convex lenses, and concavo-convex lenses. Concavo-convex lenses have another name—positive meniscus.

How a convex lens bends light Obtained from www.howstuffworks.com

    The three kinds of lenses aren’t there merely to confuse you. They are all different. The plano-convex lenses are flat on one side and curved outward on the other and get used in projectors. Double-convex lenses have two outward-curving edges and are basically magnifying glasses, and a number of them are used together in microscopes. The concavo-convex lenses are curved in on one side and have a more outward curve on the other. They correct hyperopia (farsightedness) and presbyopia.

    Convex lenses can be thought as two rounded prisms joined at their bottoms. Light will get refracted to the base of a convex lens, which is in the center of the lens, so the light will eventually focus on one spot. This spot is called the focal point.

*  This figure is drawn by myself.

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The kinds of concave lenses*

    Opposite to convex lenses, a concave lens is skinny in the middle and wide on the outside. Concave lenses also have many names. They include negative lenses, minus lenses, and diverging lenses. There are also three types of concave lenses that resemble their convex counterparts. Plano-concave lenses have a flat surface and one inward curving side. They are one of the many lenses found in cameras. Double-concave lenses have two inward curving edges and are used as reducing glasses to shrink the appearance of objects. Convexo-concave lenses (or negative meniscus) have one outward curving edge with one greater inward curving edge.

How a concave lens bends light Obtained from www.howstuffworks.com

    Almost everything about concave lenses is the opposite of convex lenses. Therefore, since the base of the concave lens is on the edges, the light gets refracted there. This will spread out the light, and it will grow wider and wider and wider....  

*  This figure is drawn by myself.     

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