Based on the circle of the least confusion related to spherical aberration and the optimum semi-angle of the electron beam in EMs, the spatial resolution can be estimated by,
d0 = 0.6 Cs1/4 λ3/4 -------------------------------- 
Cs -- Spherical aberration coefficients
λ -- Electron wavelength
We can see that Equation 4242 is related to spherical aberration (Cs) of the objective lens.
Example of estimated resolution limits are shown in Figure 4242. At high accelerating voltages (e.g. 200 kV) the spherical aberration is dominant, while at low accelerating voltages (e.g. 1 kV) the chromatic aberration is dominant.
Figure 4242. The estimated resolution limits at 1 kV and 200 kV as function of Cs and Ccassuming only one of them is present in each case. The energy width of the beam was assumed to be 0.7 eV.