Open Camera from Lock Screen on Galaxy Grands and some other Samsung Galaxy devices, by motion unlock. If you want to rotate the phone to launch camera app do as follows:
1. Go "Lock Screen" from "Settings" app
2. If the screen lock is Swipe, then tap "Lock Screen options"
3. Scroll down and enable "Camera Quick Access"
4. From now on, you just need to hold the phone straight and then tap and hold your finger on screen while rotating the phone to open Camera app.