Prisms  | How a prism bends light
Obtained from www.howstuffworks.com |
Thesimplest kind of lens is actually a prism. A prism is a piece of glassshaped like a triangle and bends light towards its thickest part (thebottom of the “triangle”), which is called the base. The thinnest partof a lens is called the apex. Notall lenses are prisms, but any lens can be thought as two roundedprisms joined together. The same rules would apply, so all lenses bendlight towards their base.
Convex Lenses  | | The kinds of convex lenses* |
Convexlenses are known as many names, being also called positive lenses, pluslenses, converging lenses, and condensers. Convex lenses are fat in themiddle and skinny on the edges. There are three main types of convexlenses: plano-convex lenses, double-convex lenses, and concavo-convexlenses. Concavo-convex lenses have another name—positive meniscus.  | How a convex lens bends light
Obtained from www.howstuffworks.com |
Thethree kinds of lenses aren’t there merely to confuse you. They are alldifferent. The plano-convex lenses are flat on one side and curvedoutward on the other and get used in projectors. Double-convex lenseshave two outward-curving edges and are basically magnifying glasses,and a number of them are used together in microscopes. Theconcavo-convex lenses are curved in on one side and have a more outwardcurve on the other. They correct hyperopia (farsightedness) andpresbyopia. Convexlenses 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 thecenter 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.
Concave Lenses  | | The kinds of concave lenses* |
Oppositeto convex lenses, a concave lens is skinny in the middle and wide onthe outside. Concave lenses also have many names. They include negativelenses, minus lenses, and diverging lenses. There are also three typesof 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 inwardcurving edges and are used as reducing glasses to shrink the appearanceof objects. Convexo-concave lenses (or negative meniscus) have oneoutward curving edge with one greater inward curving edge.  | How a concave lens bends light
Obtained from www.howstuffworks.com |
Almosteverything 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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