Recently, geometrical magnification using small focus has been noticed in coronary arteriography to obtain more improved resolving power. For this study, we made a device called "I.I. Zoom" with 20 changeable switch which could make up to two fold image enlargement, and investigated the size of the projectional image in "I・I Zoom"and the geometrical manification using MTF and ROC. Using this "I・I Zoom", we have been able to get more improved resolving power even in the case of large focal spot angiography and could select the fine visual size.