The feasibility of MTFA (modulation transfer function area) for assessing imaging quality of visual telescopic systems is described. A method for simplifying the MTFA has been discussed briefly. The way for characteristics frequency selection by using linear regression analysis is presented. Through the MTF measurements of several 8 ? 30 telescopic systems the regression statistics have been obtained from the measured curves. We found that the characteristics spatial frequency may be chosen in a wider range. The optimum frequency is close to the half limit frequency. A simplifying scheme for the parameters used in MTF measnremeiit, i.e. wavelength, field angle, azimuth and dioptric, is also presented.