Causes of loss of the image-converter tube's resolution, intended for the high speed processes research, is one of the fields of considerable interest. Thus it was established, for instance, that one of possible causes of information loss are photocathode current overloads. However, it can not be considered, that the mechanism of this phenomenon has been finally ascertained. The actuality of the problem is determined by that increase of the time resolution allows to hold fundamental scientific researches more successfully. Its known, that in image converter tube, destined for high speed processes researches, semitransparent photocathode is drifted on glass substrate (input window), on which preliminarily the metallic annular film electrode has been created. It's done for the good photocathode electrical contact creation and leveling potential along the circumference of photocathode as well. At this photocathode's outlying region is located on the film electrode and the internal region-directly on the glass. In this scientific paper was researched the influence of processes proceeding on the boundary of division of photocathode-film electrode, on time resolution of image converter tube and the influence on photocathode degradation also it's offered the mechanism of current overloads and photocathode degradation, stipulated by mentioned processes.