  Simple formulas for optimization of VUV and X-ray SASE FELs are presented.
The FEL gain length and the optimal beta-function are explicitly expressed in
terms of the electron beam and undulator parameters. The FEL saturation length
is estimated taking into account quantum diffusion in the undulator. Examples
of the FEL optimization are given. Parameters of a SASE FEL, operating at the
Compton wavelength, are suggested.
