Download a Better Camera App
While the stock Camera app is pretty feature-rich and works fine for most iPhone users, it lacks a lot of camera adjustment controls. Just take ISO, for example. Generally, that’s a setting that controls how sensitive a camera sensor is to light. The higher the ISO, the more sensitive. And vice versa.
Other camera apps, like Camera+ 2 and VSCO, actually let you adjust the ISO. Try to stick to lower ISOs when shooting in low-light environments. Like exposure, this may seem counterintuitive. But turning up the camera’s sensitivity to light will usually result in grainier images.