Using these media

Figure 10, taken from Witt & Mao (1994), showing finite source effects on microlensing lightcurves. The plots on the left show the lens-centered geometry (star) with the relative source motion (open circle) and image configuration. The right-hand graphs compare the PSPL lightcurve (thin line) with the finite-source one for the same system (thick line). In their notation, μ is the total amplification and b is the impact parameter.

Witt & Mao (1994)
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Finite source effects on lightcurves