paco_rosso

Think this. The illuminance (lux) is: E = k * 2^EV Where k is a 270 / S and S is the ASA sensitivity (the firs number in the ISO sensitivity, the ISO value cameras adjust). 270 is for international units, and only god knows what it can be in those medieval units used in the US. So you are adding an illuminance E1 to another illuminance E2. Let's go: First, lets call n to difference beetween E1 and E2. So E2 = E1 * 2^n. Now add both illuminance: Etotal = E1 + E2 Et = E1 + E1 * 2^n. Et = E1 (1+2^n). In the case you say, both E are the same, so n = 0. Then Et = E1 * 2. Et is 1 stop greater than E1. As E1 was the illuminance with EV1 = 8 then EVtotal = 9. We can build a sum table if we think in the difference in stops beetween both EV. This is: dEV EVt 0,0 1,0 0,3 1,2 0,5 1,3 0,7 1,4 1,0 1,6 1,3 1,8 1,5 1,9 1,7 2,1 2,0 2,3 2,3 2,6 2,5 2,7 2,7 2,9 3,0 3,2 3,3 3,5 3,5 3,6 3,7 3,8 4,0 4,1

9 EV. Think this. The illuminance (lux) is: E = k * 2^EV Where k is a 270 / S and S is the ASA sensitivity (the firs number in the ISO sensitivity, the ISO value cameras adjust). 270 is for international units, and only god knows what it can be in those medieval units used in the US. So you are adding a illumination E1 to another illumination E2. Let's go: First, lets call n to difference beetween E1 and E2. So E2 = E1 * 2^n. Now add both illumination: Etotal = E1 + E2 Et = E1 + E1 * 2^n. Et = E1 (1+2^n). In the case you say, both E are the same, so n = 0. Then Et = E1 * 2. Et is 1 stop greater than E1. As E1 was the illuminance with EV1 = 8 then EVtotal = 9.

When mixing ambient light with flash we get two exposures. So you need to guess what is the exposure the ambiente gives when shooting at 1/250. If ambient light is f:11 at 1/250 and your flash gives about the same f... then what "stops" the movement is the ambient light no the flash. It is: blurry image. ¿How hight should be the flash exposure over the ambiente one to "stop" the move? ¿3, 4, 5 stops? So: no, with sunlight flash do not stop the motion.

¿Why?

Some flashes says in its screen the f number once you have focused the lenses ¿Does it not help?