I've been learning to use filters, and flying with the camera in manual mode, and am confused about how and when you can adjust the EV value. In digital SLR land, I can do this in manual mode and even some aperture or shutter priority modes. On the P3A, I can't figure out when you can change it and when you cant, and, more confusing, it seems to do it itself, like when I put a ND filter on. Guidance appreciated.