Pretty much anybody who gets into photography has probably wondered how to photograph action shots and freeze motion as if it is stuck in time.
An example would be in splash photography where you can capture the splash in detail and freeze the motion of it within the image.
Most people may assume that the only way to do this is to use a really high shutter speed, but in this tutorial we show you how to freeze motion using the flash duration.
Why Use Flash Instead Of Shutter Speed To Freeze Motion?
When you are setting up an exposure you will be considering your f-stop to determine your desired depth of field and your shutter speed to determine the amount of motion blur in the image.
If you are shooting something which moves extremely fast then you will need quite a high shutter speed to freeze any motion.
We know that if you increase your shutter speed then the overall exposure will be darker unless you open up the aperture (increase the f-stop number) or increase ISO.
These two actions of changing the aperture and ISO can work but only to a certain extent.
First of all you wouldn’t want to open up your aperture too much that it affects the depth of field that you desire in your final composition.
Of course if you are using a wide open aperture then this could be fine.
When it comes to ISO, if you increase it too much then you will be introducing more and more noise to the photo.
So, you can see how simply increasing the shutter speed can be an issue.
However another way to counteract the shutter speed is by simply introducing more light into the image.
This can be in the form of artificial light such as flashes or continuous light.
One issue here is that you simply might not have enough light to make up for it.
Let’s look at an example:
You have your composition set up and your f-stop is at the widest (lowest f-stop number) that you are fine with.
You also can’t increase the ISO any further without introducing too much noise into the picture.
However you need to increase your shutter speed from 1/200th to about 1/800th to make sure you can freeze the motion of your subject.
A shutter speed of 1/200th is 4 times slower than a shutter speed of 1/800th so it lets in 4 times as much light (with everything else being equal).
So you need to introduce 4 times as much light intensity through the use of artificial light into the image.
There are two problems here:
- You may need too many lights that you either don’t have or can’t afford.
- If you are using flashes instead of continuous light the maximum sync speed of the camera can become a bottle neck.
What Is The Maximum Sync Speed Of A Camera?
The maximum sync speed of a camera is the maximum shutter speed that it can operate at while syncing to a flash effectively.
If you use a shutter speed higher than the maximum sync speed while using a flash, then you will end up with the issue of black bars being introduced to the photo.
So if you have been using flash and asked the question “why is the bottom half of my picture black?”, then you know now that it is because you are going above the maximum sync speed of your camera.
What Is The Maximum Sync Speed For Most Cameras?
Most cameras will have a maximum sync speed of around 1/200 or 1/250, but always check your manual as some cameras are able to operate faster at around 1/320 while others may be slower at around 1/180.
As you can see, most cameras cannot operate at a fast enough shutter speed while using flash to freeze very fast motion in an image.
This is where you use the flash duration to freeze motion instead.
How Does Flash Duration Freeze Motion?
A flash can be used to freeze motion by using a short flash duration, but you also have to take an extra step to make this work correctly.
For a flash to freeze motion you first need to kill off any ambient light in a scene. This is a crucial step as you want the flash to be the only key light that lights up the scene.
Why Do You Need To Eliminate Ambient Light?
By eliminating ambient light, the only light in the scene will be from the flash. So even if the camera shutter speed is longer than the flash duration the camera will only see the scene lit up for the flash duration.
Since the flash duration will be set up so that it is very fast, this is what will freeze the motion in the shot.
How Do You Eliminate Ambient Light?
Ambient light is just the light that is present in the scene at normal settings. By killing off ambient light you basically want your exposure to look black if you were not using flash.
You do this by setting your ISO to a low level, set your f-stop accordingly for the scene and set a fairly fast shutter speed.
If you are doing an action scene you can try something around f11 to start off. For example, if you were doing splash photography you may want a large depth of field to capture all of the splash in focus.
For the shutter speed, set it to about 1/200 or 1/250. Again don’t worry about the shutter speed being fast enough to freeze action as the flash will do this. Just keep it equal to or slower than the maximum sync speed.
If you are indoors this should be enough to kill off the ambient light and show a very dark image if you are not activating the flash.
If you are finding that you still have ambient light in the exposure then try to block off light whether that be from drawing a curtain or using black card or flags.
How To Set Up The Flash Duration To Be Fast?
With speedlight flashes, the flash duration is dependent on the flash power.
So for a very fast flash duration to freeze any action you want to start off using the lowest flash power settings.
Depending on the speedlight that you use you will have different flash durations for different levels of power.
If we use an entry level speedlight like the Yongnuo 560IV, even at this price point the fastest flash duration is 1/20000th of a second. Definitely enough to freeze some motion.
Sometimes you may find that using the absolutely lowest flash power settings will make the exposure turn out a little dark.
If this happens try to increase the flash power (lowers the flash duration slightly) in increments until the flash power is adequate.
By doing this in small increments you should get to a stage where there is enough light with a short enough flash duration to freeze any motion in the image.
Visual Examples of Freezing Action With Flash
The following two videos are great examples to show you how you can freeze motion using speedlights so give them a watch if you want a visual example of how it’s done.
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