Scaling of slider images

Hi, Great theme by the way. My site has four slider images at around 1400 x 800. Viewed on a large screen, OK. Viewed on a small tablet or phone, the images are cropped and valuable portions of the images are lost. Interestingly, the slider text scales OK. My site needs to have the complete images viewable on all platforms otherwise the site is a nonsense. Have I missed a setting somewhere?