why lenses are round?

Answer 1

If you are talking about the shape of the whole lens, not all lenses are round -- look around at all the different shapes of glasses people wear.

If you are talking about the curvature of the surface, lenses have a curved surface(s) to bend the light.

If it bends out (convex lens) the light bends inward and comes to a point (the focal point) when it comes out the other side.

If it bends in (concave lens) the light bends away from the center of the lens (spreads out) when it comes out the other side.

Answer 2

Well, which kind of lens are you refering to?

The SLR's extention lens's glass, the SLR's overall body, normal camera's len's glass or normal camera's len's body?

The human's contact lens? or perhaps the specticles's lens?

Lenses are classified by the curvature of the two optical surfaces. A lens is biconvex (also called double convex, or just convex) if both surfaces are convex, likewise, a lens with two concave surfaces is biconcave (or just concave). If one of the surfaces is flat, the lens is plano-convex or plano-concave depending on the curvature of the other surface. A lens with one convex and one concave side is convex-concave, and in this case if both curvatures are equal it is a meniscus lens.
If the lens is biconvex or plano-convex, a collimated or parallel beam of light travelling parallel to the lens axis and passing through the lens will be converged (or focused) to a spot on the axis, at a certain distance behind the lens (known as the focal length). In this case, the lens is called a positive or converging lens.
If the lens is biconcave or plano-concave, a collimated beam of light passing through the lens is diverged (spread); the lens is thus called a negative or diverging lens. The beam after passing through the lens appears to be emanating from a particular point on the axis in front of the lens; the distance from this point to the lens is also known as the focal length, although it is negative with respect to the focal length of a converging lens.
If the lens is convex-concave, whether it is converging or diverging depends on the relative curvatures of the two surfaces. If the curvatures are equal (a meniscus lens), then the beam is neither converged nor diverged.

Most lenses are spherical lenses: lenses whose surfaces have spherical curvature, that is, the front and back surfaces of the lens can each be imagined to be part of the surface of a sphere. Each surface can be convex (bulging outwards from the lens), concave (depressed into the lens), or planar (flat). The line joining the centres of the spheres making up the lens surfaces is called the axis of the lens; in almost all cases the lens axis passes through the physical centre of the lens.

I hope this helps, but please make your question a little more specific next time like, Why are camera's lens round or why are contact lens round.. or something like that.

Answer 3

lenses are around for cameras so we could take good pictures of people

Answer 4

For easily zooming in and out! Why all wheels are round?

Answer 5

you've never noticed the bevel outward? if they were square then god would kill kittens and babies. are you TRYING to murder our kittens and babies?