Purpose To establish a screen film system sensitometric method of X ray scale exposure by changing the distance between focus and film.
目的建立以焦点胶片距离的改变，取得X线阶段曝光的屏片体系感光测定方法。
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Conclusion: Considering the absorbed dose of the patients and avoiding the image distortion, it is suggested that the selection of focus-filmdistance should be matched with the tube and grid.