Zoom Not Working

I want to zoom out the image since it is so large you can only see a small portion of it. I found this code to use.

    <script type="text/javascript">
        function OnClientLoad(sender) {
            //sender.zoomImage(50);
            sender.zoomBestFit();
        }
    </script>

Neither 'zooms' work. They both skew the image to the wrong proportions. How do you do exactly what the zoom out toolbar button does? That works fine.