I have a Pentax Spotmatic F. I'm having a problem grasping the through the lens metering. When I frame my shot, I can see and adjust the meter through the lens. I'm assuming that I am metering based on the aperture being wide open. When I flip the TTL meter switch on the side, does that mean I'm seeing the metering at each particular F stop? If someone could explain this better, I would appreciate it.