I have tried to take photo in my house at night. The light in my house is using yellow bulb but it is not dark. I used my camera (300D) to take photo by trying the combination of ISO 200-800, white balance - yellow light option, F2.8-5.6, built-in flash... it is hard to focus the object. The object is sharp and blur on and off. I don't know why. Can anyone teach me how to do?