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 Re: A9 III + Godox Flash | |
I did some math on this, it would appear that on the AD600 pro we are slightly advantaged compared to using a ND in terms of how much sun we can overpower at low shutter speeds, but disadvantaged at high shutter speeds.
This is the "base" setting, I define 1/200s shutter and 1/1 power on the strobe as 0 stops.
- A1: 1/200s, 1/1 strobe, T0.1=1/220s (Shutter = 0 stops, strobe = 0 stops)
Lets try to dim the background by 1 stop.
- A1: 1/200s, 1/1 strobe, T0.1=1/220s, 1 stop ND (Shutter = 0 stops, strobe = 0 stops)
- A1: 1/400s, 1/1 -0.7 strobe, T0.1=1/530s (Shutter = -1 stops, strobe = -0.6 stops)
- A9iii: 1/1000s, 1/2 -0.7 strobe, T0.1 = 1/1200s (Shutter = -2.33 stops, strobe = -1.6 stops)
- Note that using 1/400s on the A1 is better than using 1/200s and a 1 stop ND because the strobe power drops by less than 1 stop.
- Note that the A9iii has a 1/3 stop advantage over the A1 at 1/400s after accounting for the higher base iso.
- Note that the A9iii is running the strobe at lower power for the same results!
Lets try to dim the background by 4 stops.
- A1: 1/400s, 1/1 -0.7 strobe, T0.1=1/530s, 3 stop ND (Shutter = -1 stops, strobe = -3/5 stops)
- A9iii: 1/8000s, 1/128 strobe, T0.1 = 1/8260s (Shutter = -5.3 stops, strobe = -7 stops)
- A1 has a 2 stop advantage here in terms of overpowering the sun, because the A9iii loses more strobe power (7 stops) than it can dim the background (-5.3 stops) with this setting. However, the A1 is not going to recycle very fast with the strobe at 1/1 -0.7 power
I think the real advantage with global shutter is that assuming you have no problems overpowering the sun, extremely little flash power is needed. This is because punching through a 3 stop ND needs 3 stops more ws out of the flash, and HSS is even worse.
As an aside:
One thing to note here is that the ISO, ND and Strobe power affect the foreground while Shutter, ISO and ND affect the background. To get the foreground as bright as possible relative to the background, we want to maximize
- Foreground - Background
- = (ISO + ND + Strobe) - (Shutter + ISO + ND)
- = Strobe - Shutter.
Therefore what matters is the shutter, which affects the background only and the strobe power, which affects the foreground only.
The shutter also affects the strobe power due flash T0.1 values. If the T0.1 is greater than the shutter speed, then not all the light from the strobe is hitting the sensor... so in a way you my as well use lower strobe power.
I am assuming its best to keep the strobe T0.1 smaller than the shutter speed, but I am not sure if this is correct. Maybe someone with the A9iii can test this. I suspect using 1/1 power will yield a dimmer foreground.
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