concave lens

(noun)

A lens having at least one concave surface, such that light rays passing through it bend away from its optical axis.

Related Terms

Examples of concave lens in the following topics:

  • Refraction Through Lenses

    • Such a lens is called a converging (or convex) lens for the corresponding effect it has on light rays.
    • shows the effect of a concave lens on rays of light entering it parallel to its axis (the path taken by ray 2 in the figure is the axis of the lens).
    • The concave lens is a diverging lens, because it causes the light rays to bend away (diverge) from its axis.
    • The more powerful the lens, the closer to the lens the rays will cross.
    • Compare the effect of a convex lens and a concave lens on the light rays

  • Thin Lenses and Ray Tracing

    • An ideal thin lens has two refracting surfaces but the lens is thin enough toassume that light rays bend only once.
    • Another way of saying this is that the lens thickness is much much smaller than the focal length of the lens.
    • A thin symmetrical lens has two focal points, one on either side and both at the same distance from the lens.
    • The treatment of a lens as a thin lens is known as the "thin lens approximation. "
    • Shows how to draw the ray diagrams for locating the image produced by a concave lens and a convex mirror.

  • Combinations of Lenses

    • A compound lens is an array of simple lenses with a common axis.
    • In contrast to a simple lens, which consists of only one optical element, a compound lens is an array of simple lenses (elements) with a common axis.
    • A convex plus a concave lens (f1 > 0 >f2) produces a positive magnification and the image is upright.
    • An achromatic lens or achromat is a lens that is designed to limit the effects of chromatic and spherical aberration.
    • In the most common type (shown in ), the positive power of the crown lens element is not quite equaled by the negative power of the flint lens element.

  • The Lensmaker's Equation

    • A lens whose thickness is not negligible is called a thick lens.
    • If the lens is biconcave, a beam of light passing through the lens is diverged (spread); the lens is thus called a negative or diverging lens.
    • The signs of the lens' radii of curvature indicate whether the corresponding surfaces are convex or concave.
    • The sign convention used to represent this varies, but for our treatment if R1 is positive the first surface is convex, and if R1 is negative the surface is concave.
    • The signs are reversed for the back surface of the lens: if R2 is positive the surface is concave, and if R2 is negative the surface is convex.

  • Refraction and Magnification

    • A device that produces converging or diverging light rays due to refraction is known as a lens.
    • In general, two types of lenses exist: convex lenses, which cause parallel light rays to converge, and concave lenses, which cause parallel light rays to diverge.
    • In essence, a convex lens allows magnification.
    • A magnifying glass is one convex lens, and this by itself allows the magnification of objects.
    • It is actually the water acting much like a lens in a microscope that gives it the appearance of bending.

  • The Compound Microscope

    • It is made of two convex lenses: the first, the ocular lens, is close to the eye; the second is the objective lens.
    • The first lens is called the objective lens and is closest to the object being observed.
    • The objective lens creates an enlarged image of the object, which then acts as the object for the second lens.
    • The distance between the objective lens and the ocular lens is slightly shorter than the focal length of the ocular lens, fe.
    • where m is total magnification, mo is objective lens magnification, me is ocular lens magnification.

  • The Thin Lens Equation and Magnification

    • How does a lens form an image of an object?
    • A ray entering a converging lens parallel to its axis passes through the focal point F of the lens on the other side.
    • The third ray passes through the nearer focal point on its way into the lens and leaves the lens parallel to its axis (rule 4).
    • The thin lens equation is:
    • Ray tracing is used to locate the image formed by a lens.

  • Concavity and the Second Derivative Test

    • A related but distinct use of second derivatives is to determine whether a function is concave up or concave down at a point.
    • Specifically, a twice-differentiable function $f$ is concave-up if $f''(x)$ is positive and concave-down if $f''(x)$ is negative.
    • If it is concave-up at the point, it is a minimum; if concave-down, it is a maximum.

  • Image Formation by Spherical Mirrors: Reflection and Sign Conventions

    • Spherical mirrors can be either concave or convex.
    • A summary of the properties of concave mirrors is shown below:
    • The focal point is the same distance from the mirror as in a concave mirror.
    • This figure shows the difference between a concave and convex mirror.
    • This is a ray diagram of a concave mirror.

  • Aberrations

    • An aberration is the failure of rays to converge at one focus because of limitations or defects in a lens or mirror.
    • This aberration happens when the lens fails to focus all the colors on the same convergence point .
    • Since violet rays have a higher refractive index than red, they are bent more and focused closed to the lens. shows a two-lens system using a diverging lens to partially correct for this, but it is nearly impossible to do so completely.
    • Spherical aberrations are a form of aberration where rays converging from the outer edges of a lens converge to a focus closer to the lens, and rays closer to the axis focus further.
    • The apparent effect is that of an image which has been mapped around a sphere, like in a fisheye lens.