I seem to be generating a lot of noise in my shots taken above 400iso. Mainly with bird shots taken amongst foilage when lack of adequate light is an issue. I mainly use my 300mm f/4D lens, sometimes with a TC-14E II teleconverter attached. For most wildlife shots I shoot shutter priority so I can use high shutter speeds. I also change iso manually. (1). How can I increase iso & keep noise to a minimum? (2). Should I be using auto iso in rapidly changing light situations?