The authors propose a method of interpreting amplitude only V(z) curves, derivable from ray theory without arbitrary assumptions. The method has been applied to V(z) curves measured with both cylindrical and spherical lenses, achieving an absolute accuracy of Rayleigh velocity of better than one part in one thousand in each case. This level of accuracy matches that previously available only from cylindrical lenses. It is shown how optimal filtering of the V(z) curve may be performed to eliminate high-frequency coherent ripple due to internal lens reverberations and to minimize noise with minimum degradation of the actual curve. In numerical simulations the method has been shown to have a high degree of immunity from noise and to be effective for short ranges of defocuses. The processing algorithm has no arbitrary steps and should be easily capable of hands-off automation.
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