Americo,


From my understanding, increasing the ISO increases how sensitive the sensor is to incoming light (the higher the ISO, the higher the sensitivity).


Increasing ISO allows for faster shutter speeds (if no other parameters change, that is).


I'm sure you will receive more technical explanations on this... []


The post of the same photo is much like the first. The DOP is very shallow. Her cheek and the few strands of hair falling across it are sharp but her lips and side of her head are not within the in-focus range. Try stopping your aperture down to f/2.0 or 2.8 and bump your ISO to 200 or 400...see what happens.