Effect of wavefront errors in the microlenses on the contrast due to a certain Zernike mode. First three panels: effects on two different fibers. Due to symmetry the other four fibers behave in the same way as these two. The radial symmetry of the defocus mode causes the same effect in all fibers, therefore the curves of the two fibers overlap. Rightmost panel: effects of Zernike modes 6 to 10. Focus and astigmatism are the most dominant wavefront errors for lowering the contrast.