In the 16-minute video above, Gavin Free of the The Slow Mo Guys answers a question he often receives: “Is using a high-speed camera similar to using a normal camera?” The answer is “Yes and No”, and we end up looking into the biggest challenges in using high-speed cameras.
In photography there are two ways of controlling the amount of light that hits the sensor: shutter speed and aperture. In video, the shutter speed will be in control of how much motion blur there is. In still photography, the shutter speed is represented by a fraction like 1/125 sec, but the shutter speed in a movie or pro-video camera will be represented by an angle in degrees.
A 180° shutter speed means that the exposure time is half the duration of the frame interval, so at 25 fps, each frame exposes at 1/50 sec and that creates a very natural looking motion blur. Changing the shutter to, say, 90° at the same frame rate of 25 fps, the exposure time will now be 1/100 sec. So as the angle goes down, the exposure time is shortened, so the motion blur is reduced.
Modern cameras have an electronic shutter but back in the day it was a spinning physical disk with different angles cut into the disk, and that is where the term “shutter angle” comes from. This disk would then rotate over the film plane and expose for just that window of time.
Every time you halve the shutter angle you get half the light, so 90° is half as bright as 180°, and every time you go down and sharpen that motion blur you need a lot more light “and therein lies the problem,” Gavin says.
“On this channel the Phantom never shoots at 25 fps — what an incredible waste that would be,” says Gavin.
A Phantom camera he uses goes up to a maximum of 1000 fps in 4K — an exposure time of 1/2000 sec with a 180° shutter speed — and the image starts looking pretty dark on the screen. The main challenge he faces when shooting something in high-speed is that if he is going to reduce the motion blur he has to reduce the shutter angle and if he wants to get any depth he has to reduce the size of the aperture.
This makes him shoot most of his videos outdoors on a sunny day. And get this: in cameras which operate at 100,000fps, the exposure is only 1/200,000s.
“I am always struggling for light,” he says. And that’s one of the biggest challenges of shooting super slow motion with high-speed cameras.