I would like to create a surface that has a spherical and/or cylindrical power. I beleive I can use a Zernike Fringe Phase surface and enter Zernike coefficients to mimic the spherical and cylindrical powers by tuning Z4 / Z5 and Z6 (spherical power + both astigmatism coefficients). However when I play around with the value of Z4 and add some spherical aberration to my surface it does not add any power to my optical system. Is this behavior expcted? Which type of surface should I use instead that would creat optical power on my system based on the Zernike coefficients?