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Tips & Tutorials >> All Tips & Tutorials In Focus: The Basics of External Flash Photography- Part

Beyond Shutter Speed: Using Flash Duration to Freeze Motion

Did you know that flash output of a Speedlite affects the duration of the flash? If you take advantage of this, you can freeze movement that occurs extremely quickly even without using high-speed sync. In this article, we explore more about the concepts behind this technique and find how it can be applied to water splash photography.

moving water in glass

1) The theory: 2 important concepts to remember
2) Application: How to freeze water splashes


Before we start: 2 important concepts to remember

Concept 1: In a completely dark room, the light from the flash is what enables the subject to be captured

Photography is about capturing light. Subjects are visible because the camera's image sensor captures the light reflecting off them. If there was no light present, a shot will appear completely black.

Unlike the sun or other stationary light sources, the flash from a Speedlite/in-camera flash is momentary. Hence, when you are shooting in a dark room where there is no other light source, even if you leave the camera shutter open for one hour, the subject will not be exposed to light except for the fleeting instance where the flash is fired.

In other words, in a completely dark room with no other light source, the flash duration determines the exposure time.

Concept 2:  The flash output affects the flash duration

On a Canon Speedlite, the flash intensity (flash output) is generally controlled by the flash duration.

A stronger flash (higher flash output) means that the flash fires for a longer duration (up to around 1/500 second, depending on the Speedlite model). The subject is exposed to light for a longer time, resulting in a higher chance of visible motion blur if the subject is in motion.

Meanwhile, a weaker flash intensity (lower flash output) means that the flash is fired for a shorter duration—as short as several hundred microseconds. The subject is exposed for a shorter time, reducing motion blur.

Smaller flash output

A: Flash duration (exposure time)

Higher flash output

B: Flash duration (exposure time)

What this means: We can freeze action by reducing flash output

Flash duration can be extremely short, exposing the shot for a shorter time than even the fastest possible shutter speed. The key to controlling this is the flash output. When harnessed, it is possible to capture fleeting moments not visible to the naked eye, as our example below shows.


Application: How to use flash duration to freeze moving liquids

water splash in glass

FL:72mm/ Manual exposure (1/200 sec, f/14)/ ISO 400/ WB: Auto
Flash: Speedlite 430EX II (Manual mode, 1/64)

The setup

Positions of the subject, camera and Speedlite

A: Off-camera shoe cord
B: Approx. 0.6m
C: Approx. 0.4m

I used an off-camera flash setup, where the Speedlite was positioned directly above the subject to provide direct lighting. The camera was on a tripod, and the Speedlite connected to it via an off-camera shoe cord. I turned off all the lights, leaving the door open slightly: just enough for the subject to be vaguely visible.

Know this:
For scenes like this, the electronic viewfinder gain on a mirrorless camera such as those in the EOS R system could help you to see subjects even in the dark.


Step-by-step procedure

Step 1: Attach your backdrop to the wall

Attach a piece of plain coloured cloth or paper in the background. The material should not reflect the light from the flash. Here, I chose black because it provides the best contrast against the subject.

Step 2: Pre-focus

You need the focus to be very precise. For best results, use manual focusing to fix the focus position.

Step 3: Set up your flash

(The steps and button layouts may differ depending on your Speedlite/camera model. When in doubt, refer to the user manual.)

i) Change your flash mode to Manual mode.
You can do so either by operating the dials and buttons on the Speedlite, or on the camera via the menu settings.

On the flash

Press the MODE button and select [M].

On the camera

Look for ‘Flash control’ or ‘External Speedlite control’ in the Shoot menu, and then navigate to ‘External flash func. setting’ or ‘Flash func. setting’ item.

ii) Select the flash output.
Set a low flash output level to get a shorter flash duration. You may want to try different output levels to see which has the best effect. Control exposure using the ISO speed (see Step 4 for more details).

On the flash

Press the “+/-“ button to display the flash output level screen. Use the dial or cross keys to select the desired output level.

On the camera

You can also change the flash output level by selecting the item on the ‘External flash func. setting” screen.

Also see: Start Flash Photography in 9 Steps!

Fun fact: The flash duration can be as fast as several hundred microseconds—in other words, faster than the 1/8000 second maximum shutter speed on many professional camera models!

Step 4: Exposure settings

This will depend on your subject and intended results. However, in general:

Use a narrow aperture
You need a large depth of field to ensure that the subject is captured clearly and in-focus.

Use your ISO speed to control the exposure
The narrow aperture, combined with the low flash output you will be using to shorten the flash duration, might result in insufficient light. Increase the ISO speed if you need a brighter shot.

Set the shutter speed at the flash sync speed

For a successful shot, you need to reduce the effects of ambient light as much as possible. In reality, shooting in pitch darkness is difficult and you might need just a bit of light to identify your subject. The flash sync speed (or X-sync speed) is the fastest shutter speed possible for the Speedlite to fire when the shutter is fully open. It is usually 1/200 sec to 1/300 sec depending on the camera model, and using it ensures the least interference from ambient light.

Step 5: Release the shutter at the right timing

Release the shutter according to the subject's timing. This takes careful observation and perhaps some practice, but in return, you get an amazing shot!

Know this: Thinking of continuous shooting? Be aware of the flash recycle time

After each flash, your Speedlite will need time to recharge before it can fire another flash. This is called the flash recycle time, and depending on your Speedlite model and output, it can take up to a few seconds. In other words, even if you do a high-speed burst, there will probably be frames that are black because your flash was still recycling. A faster flash recycle time (like that on the Speedlite EL-1) increases your chances of success, but you get the highest chances of success when that is combined with good timing.

Also see: Can I take continuous shots during flash photography?

For more Speedlite techniques and tutorials, check out:
[Flash Technique] How to Achieve Dramatic Colours in Backlight
How to Capture Raindrops to Create Surreal-looking Portraits
Taking Stunning Car Photos, Magazine-style


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