Freezing Motion
I have been having this conversation a lot lately, so I figured it is time for my semi-annual post about freezing motion.
TL;DR: High-speed sync doesn't freeze motion.
There is a common misunderstanding that high-speed sync is good for freezing motion. It really is not in most cases. Here’s the deal.
There are two ways to freeze motion:
1. Fast shutter speed
2. Short flash duration
But you can’t mix the two, at least not well. You can’t have a fast shutter speed and get a short flash duration. If you go beyond the sync speed, your flash goes into high-speed sync, and that is NOT short flash duration. It’s the opposite. It’s pulsing, so your flash essentially acts like a continuous LED light, which doesn't freeze motion at all. Your flash also has to work harder, so you end up with a lower flash output and slower recycle times. And if you are trying to fire rapidly, you often will overheat your flash.
So, how do you get short flash durations? Use slightly lower power on a flash that uses IGBT to control the output — usually 1/8 and lower is best — and you get really short flash durations that freeze motion well. All of the Godox battery-powered flashes use IGBTs.
But that’s appropriate for a situation where the flash is the dominant light source. Great in the studio or in a gym. Or at night. But not good for the middle of the day. I look for t0.1 flash durations of 1/3000th of a second or faster to achieve excellent motion freezing. T0.1 is the term for measuring the duration of the peak of the flash output. There is a setting on most Godox flashes that will show the t0.1 time on the flash LCD.
So what’s the solution outside? Keep your shutter at the fastest speed in normal sync (1/200th), your ISO at 100, your aperture at f8-f11 depending on the ambient light, and use a powerful flash at the lowest setting you can get away with — again, trying to get down to 1/8th if possible — and use a force multiplier like a long throw reflector to really boost the efficiency of the flash. And get the flash around 6-8’ away. My MoThro long throw gives you an extra two stops of effective light output and creates a clean circle of light with a diameter equal to the distance from the subject. 8 feet away = 8-foot-wide circle. Or you can try a really fast shutter speed with HSS, but you’ll likely be disappointed, since you typically need a shutter speed of 1/3200 or faster to freeze motion. Which will chew up your flash power. And overheat your flash eventually.
For indoor or in-studio, I recommend the Godox QT600III for freezing motion. The unique QT-series strobes utilize IGBT tech as the battery-powered strobes do. The AD600PRO II, AD800PRO, and AD400PRO II also do a nice job, but cannot match the QT series for recycling speed.
For outside? As much power as you can carry. And understand that you will need a very fast shutter speed -- 1/3200 or quicker.
I dedicated a podcast episode to explaining this as well. Here’s where you can listen:
https://mondaymorningcupofmo.buzzsprout.com/1896414/10198749
I have included photos from the first test shoot I ever did with the QT600II, almost 10 years ago, and was completely floored by the performance. You can find the QT600III here.
Settings: 1/160th, f9, ISO400, QT600II at 1/32 power in SPEED mode, Sony a6300 shot at 10fps.
Freezing Motion: Part 2
Inevitably, I will get people who will still argue on the side of HSS, insisting if freezes motion. So, I took a couple of minutes to quickly show the difference between short flash duration using an IGBT-controlled strobe like the AD300PRO and other Godox battery-powered flashes, and high-speed sync (HSS) using the same flash. Our subject is the BloMo studio fan, so a good test of something that is moving fast.
The first two photos are closeups showing standard sync with short flash duration, and high-speed sync. Standard sync with short flash duration and a shutter speed of just 1/160th wins for freezing motion. I also show the straight up ambient light conditions, and I actually jacked up the ISO to add some ambient infiltration into the exposure to make it more difficult, but also so you could see the fan blades against the ambient lit background. Specs are on each photo. I had to jump up to 1/6400th in HSS and have the flash at full power in order to get decent motion freezing. (Shoot your flash at these settings all the time and you will cook it.)
