Ev stands for exposure value. A change of one Ev adjusts the exposure calculated by the camera by a factor of two.
+2.0 Ev
4X as much light
+1.0 Ev
2X as much light
0.0 Ev
Calculated exposure
–1.0 Ev
1/2 as much light
–2.0 Ev
1/4 as much light
105
105 