Asphere Add-In

Use this Add-In to create the geometry for an aspherical lens. The shape of an aspherical lens is not a spherical section. This shape is difficult to manufacture since most grinding/polishing equipment operates with a spherical action. For this reason, an aspherical lens is often molded out of plastic. Mastercam uses a standard polynomial equation with user-supplied coefficients to calculate the shape of the lens, and creates the geometry using your choice of points, lines, arcs, or a spline. Mastercam creates one quadrant of the total profile.

z = c * x^2 / [1 + sqrt(1-(k+1) * c^2 * x^2)] +
a1  * x^4  + a2  *  x^6 +  a3  * x^8  + a4  * x^10 + a5  * 
x^12 + a6  * x^14 + a7  * x^16 + a8  * x^18 + a9  * x^20 + a10 * x^22 +
a11 * x^24 + a12 * x^26 + a13 * x^28 + a14 * x^30 + a15 * x^32 +
a16 * x^34 + a17 * x^36 + a18 * x^38 + a19 * x^40 + a20 * x^42

The x and z coordinates are mirrored. A positive radius, representing a convex asphere, causes the curve to slope downward. A negative radius, representing a concave asphere, causes the curve to slope upward.

The following variables are also used:

  • x start = Starting x coordinate
  • x finish = Final x coordinate
  • x step = X step size value. New points, lines or spline nodes are created at each step.

The default value for x start is zero. Use positive values for x finish and x step.

Enter a chordal deviation value when you are creating the lens with arcs. This represents the maximum distance allowed between the arcs that are generated and a spline which passes through the generated points. It does NOT represent the maximum error between the theoretical asphere curve and the arcs (total error). Total error is an indirect function of x step and chordal deviation.

Enter a the name of a .prm file in the parameter name field to have Mastercam automatically save a copy of the current parameters to that file. Click Parameter name to load the values from a previous asphere session.

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