for my entire (amateur) photographic life, I have used my index finger to press the shutter button, but there's a drawback. if I want to change the aperture value after obtaining the focus, I have to let go of the shutter button, roll the Main Dial to set my aperture value and then press the shutter button again.
I have begun experimenting, using my middle finger instead to press the shutter button leaving my index finger free to roll the Main Dial whenever necessary. for the time being, it's working although my middle finger doesn't respond as quickly as my index finger (yet), and my two smaller fingers get tired quickly holding the Mark III in place.
out of curiosity, does anyone else here use their middle finger to press the shutter button when hand-holding their DSLR?
regards,
Gregory
(edit: clarified finger nomenclature using DarkPenguin's thumb-index-middle-ring-pinky)