The Thick Lens Ray Trace
The radius of curvature on the left side of the lens (R1), the
radius of curvature of the right of the lens (R2), the refractive
index of glass (n) can be changed in the scroll bar which is on
Additional comments by J. Varriano:
The value of the refractive index of glass is displayed in the
upper part of the scroll bar.
Note that the rays that strike the outer portion of the lens focus to a point that is before the focal point of the rays that hit the central portion of the lens. This can cause a blurry image and is referred to as spherical aberration since the spherical shapes of the lens' surfaces combined with the way that light bends (Snell's Law) cause this problem. Its severity increases as the radii of curvature of the surfaces decrease (the lens gets "more round") and/or the refractive index of the glass increases. (Try it and see!)
A standard way to eliminate spherical aberration is to simply place a circular aperture before the lens so that the aperture blocks the rays that would otherwise hit the outer portions of the lens. This does cause the image to sharpen at the expense of reducing the image brightness. An alternative is to use a lens with aspherical surfaces, but this is quite expensive since it is very difficult to manufacture such a lens.
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Copyright(c) 1997 S.Kamikawa last update