By putting it in aperture priority mode, you can let the camera choose the optimum shutter speed while guaranteeing that the aperture stays at what you set (pre

By putting it in aperture priority mode, you can let the camera choose the optimum shutter speed while guaranteeing that the aperture stays at what you set (presumably the highest - f/1.8) In order to make sure the shutter speed the camera selects for you isn't too slow and causes blurriness, boost up your ISO to as high a value as acceptable (acceptable is subjective here).