Using a 5DM3 and a EF 24-70mm 1:2.8 L I'm taking photos of a toddler holding a newborn on her lap. The toddler's head is just above the newborn's. I'm using natural nearby window light (not much) so I am shooting wide open at 2.8 and have my ISO somewhere around 500-600.
The issue is that I use the focus point to focus on the toddler's face, though the newborn's face becomes soft and out of focus. Is my only option to increase the light and just close my aperture?
If so, what do you do if you still want to add some blur to the background but need to close the aperture?