header slideshow image not resizing on small screen

Hi how can I get the image to scale to fit on smaller than say 580px width, it cuts off the sides of the picture not showing the full image.

Is there a way to make it resize properly, I have tried both fullwith and not fullwidth and the normal is better than the fullwidth but still stops when going to smaller screen.
I know it uses the backstretch.js but is there a way to change it.