ScrollPane Scroll Position

I have a scrollpane with the source set to ImageMovieClip. ImageMocieClip is long in length with 50 images stacked vertically. Because of the size of the scrollpane only 15 are visible at a time.

I have a button, navBtn, that I want to jump the scrollpane’s scroll position to half way down. Is it possible? What scrollpane property do I need to use?