Parameters
ns0: refraction index of the first medium corresponding to the smallest wavelength
nl0: refraction index of the first medium corresponding to the largest wavelength
R1: radius of curvature of the first surface
e: center thickness of the lens
ns1: refraction index of the lens corresponding to the smallest wavelength
nl1: refraction index of the lens corresponding to the largest wavelength
R2: radius of curvature of the second surface
ns2: refraction index of the last medium corresponding to the smallest wavelength
nl2: refraction index of the last medium corresponding to the largest wavelength
y: height of the object
xir: distance from the vertex of the second surface to the image for the largest wavelength
xib: distance from the vertex of the second surface to the image for the smallest wavelength
dxi: axial chromatism
yir: height of the image for the largest wavelength
yib: height of the image for the smallest wavelength
dyi: height chromatism
CrT: ratio dyi/ yi with yi = (yir + yib)/2
