The optical resolution limit δD according to Lord Rayleigh is given by δD = 0.61 λ/α0 where an is the aperture of the objective lens and λ the wavelength. Assuming identical conditions in an electron microscope, one would obtain (depending on the accelerating voltage) a resolution of several 0.001 nm. However, the actual resolution limit is found to be worse by a factor of a hundred. This is due to the aberrations of the objective lens. Generally, the image wave if>(x,y) is given by the convolution of the object wave ψx,y) with the Fourier transform of the wave transfer function exp(ix) (assuming isoplanacy),