Question about how lenses are made

Discussion in 'Optometry Archives' started by Vile, Aug 1, 2004.

  1. Vile

    Vile Guest

    I would like to ask what and how minus lenses are made? As well as
    how plus lenses are made. This will help my research better on vision
    improvement. I believe I came across that minus lenses are concave in
    the center somehow. I would also like to know if binoculars and
    telescope lenses are similar or not.
     
    Vile, Aug 1, 2004
    #1
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  2. Vile

    Mark A Guest

    You are basically correct that near-sighted lenses (minus powers) are
    concave, and far-sight lenses (plus power) are convex. However there are
    some complicating factors such as the use of aspheric and atoric lens
    surfaces. Unlike some lens in binoculars, telescopes, and camera, eye
    glasses are usually not symmetrical (double concave or double convex).

    Binoculars and telescopes are more complex because the provide variable
    magnification and are typically made from multiple lenses elements that are
    glued together (in addition to those lens elements which move in relation to
    each other in order to vary the magnification and/or the focal point). Some
    designs are symmetrical, while others are not. But basically they are convex
    lenses. I suggest you do a google search to get more information.
     
    Mark A, Aug 1, 2004
    #2
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  3. Vile

    Dr Judy Guest

    A simplified explanation: Any lens has two surfaces front and back. If the
    curves are such that it is thicker in the middle than on the edges -- (| or
    () then it is convex and the power is plus, if the curves are such that it
    is thicker on the edges than in the middle it is concave -- )| or )( then
    the power is minus. A convex lens causes light to converge, a concave lens
    causes light to diverge.

    For better cosmesis, spectacle lenses are usually done with both curves
    rounded in the same direction --- ( ( . Each surface has a power and by
    adding them together you get the total power of the lens. So a -3 lens
    would have a front surface power of say + 6 and back surface of -9 while a
    +3 lens would have front surface of say +6 and back surface of -3.

    Telescopes and binocular have lenses made the same way. Their lenses are
    more likely to be biconcave or biconvex. A spectacle lens is a single lens,
    a binocular or telescope uses two lenses (ocular and objective) usually one
    with minus power and one with plus power and a space between them. If the
    binocular is focusable, the space between the lenses is variable. Finally
    the two lenses may each actually be a multi lens system. The use of two
    lenses means that the retinal image is larger with a smaller field (ie
    appears closer) than the retinal image with only the eye or an eye and
    spectacles.

    The binocular or telescope, as a system, will affect the vergence of the
    light. Unlike a spectacle lens which always has the same vergence effect,
    by focusing the binocular or telescope you can alter the vergence of the
    light exiting the system. If you use the binocular or telescope without
    your glasses and adjust focus until the image is clear, then the vergence of
    the exiting light will have the same vergence properties as light exiting
    your spectacle lens.

    For more detail see:

    http://science.howstuffworks.com/lens.htm

    http://science.howstuffworks.com/telescope.htm

    Dr Judy
     
    Dr Judy, Aug 1, 2004
    #3
  4. Vile

    Vile Guest

    Thanks that is helpful.

     
    Vile, Aug 2, 2004
    #4
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