I am a beginner, and am having trouble with operating the camera. Here are my questions: I have an 80 CFE, and an A12 back. I know I have to set the ISO manually, but, after it is set, can I go to the A or AB mode? Does the lens have to be set in the F mode (ring closest to the end of the camera-farthest away from the camera)in A or AB mode? Does the camera automatically set the aperature and shutter speed after I meter before I take a picture, or do I use the meter readings and adjust the camera?