The field distribution and electron-optical properties of electrostatically-focused image converter with plane cathode are precisely determined by means of resistance network analogue and numerical computation. The axial potential distribution is found to be expressible by the empirical formula φ = A sinh kz. Graphs are given, showing the dependence of coefficients A, k, the position of Gauss-image-plane, and linear magnification on inter-electrode spacing. An approximate formula for calculating distortion-coefficient is derived, which agrees fairly well with experimental result. Design factors are discussed.