When shooting portraiture in the daytime against backlight, most of the time the face of your subject will be captured dark. To avoid this from occurring, one effective flash technique is daytime sync, also referred to as fill-in flash photography. It is possible to use daytime sync with a built-in flash. However, by utilizing another flash technique called high-speed sync, which is one of the features on an external flash, you can capture portraits with a nicely defocused background (‘background bokeh”). This can really make your subject stand out in your images, especially if you use a bright lens. (Reported by: Teppei Kohno)

EOS 760D/ EF50mm f/1.8 STM/ FL: 50mm (80mm equivalent)/ Aperture-priority AE (f/1.8, 1/500 sec)/ ISO 100/ WB: Flash/ External flash (High-speed sync)

 

With high-speed sync, you can shoot with wide-open aperture

Shooting procedure
A: Use a bright lens
B: Set the external flash to high-speed sync mode
C: Select Aperture-priority AE and set the widest aperture
D: Focus on the subject and shoot

 

What is high-speed sync?
Most cameras have what is called a ‘maximum sync speed’. This means you are unable to use shutter speeds over the listed maximum sync speed when shooting with a flash. For most cameras, the maximum sync speed is 1/200 second, although it varies with the camera used. High-speed sync is a feature of an external flash that allows the user to “overcome” this maximum sync speed, and shoot with a flash at high shutter speeds regardless of the situation.

 

How does it affect background bokeh?
When using a built-in flash to shoot the bright outdoors, aperture will need to be narrowed down in order to avoid overexposure, making it impossible to largely defocus the background. If you are shooting portraiture in the daytime and want to use your maximum aperture to create a well-defocused background bokeh, you will need to use an external flash.

 

How do I use high-speed sync?
To capture portraits such as the top image using high-speed sync, first you will need a bright lens with a large maximum aperture (small f-number). Then, after affixing the external flash and turning the power on, set the flash to high-speed sync mode. Set your exposure mode to Aperture-priority AE mode and select a small f-number, such as f/1.8. By attaining focus on the subject and releasing the shutter, the external flash will automatically fire and you will be able to capture daytime sync images, but with a defocused background.

 

How to set high-speed sync on an external flash

To set high-speed sync, press the button indicated with "1" on the external flash once. When the feature is enabled, an icon near "2" will appear. To return the setting to normal, press the same button "1" twice, and the icon will disappear, deactivating high-speed sync (in the case of Speedlite 430EX III-RT).

 

TIP: With high-speed sync, you can defocus the background without it being blown out

When shooting portraiture under backlit conditions, the face of your subject will be captured quite dark, like the negative example #1 below. To avoid this, you can try to use either exposure compensation or the built-in flash, but both have drawbacks, further explained with negative examples #2 and #3 below. In order to obtain an image where you not only have optimum exposure with no blowout, but also a significant background bokeh, you will need to use high-speed sync.

 

Negative example #1: No flash

EOS 760D/ EF50mm f/1.8 STM/ FL: 50mm (80mm equivalent)/ Aperture-priority AE (f/1.8, 1/1,000 sec)/ ISO 100/ WB: Auto
Shooting under backlit conditions without a flash will result in your subject being depicted dark. It is possible to defocus the background, but we want to capture the subject brightly.

 

Negative example #2: With exposure compensation

EOS 760D/ EF50mm f/1.8 STM/ FL: 50mm (80mm equivalent)/ Aperture-priority AE (f/1.8, 1/500 sec, EV+1)/ ISO 100/ WB: Auto
Using exposure compensation enables you to depict the subject brighter while still having a defocused background. However, as the background becomes brighter as well, the image looks overexposed.

 

Negative example #3: With a built-in flash using daytime sync

EOS 760D/ EF50mm f/1.8 STM/ FL: 50mm (80mm equivalent)/ Aperture-priority AE (f/4, 1/200 sec)/ ISO 100/ WB: Flash/ Built-in Flash
Using the built-in flash, set to daytime sync, will capture the subject bright and defocus the background somewhat, but as you are unable to set a shutter speed faster than 1/200 sec, the aperture could only be opened until f/4. That is why the bokeh effect in the background is not as defocused, as apparent from the size of the bokeh circles. One more thing we still need to do something about.

 

Good example: Taken with high-speed sync

EOS 760D/ EF50mm f/1.8 STM/ FL: 50mm (80mm equivalent)/ Aperture-priority AE (f/1.8, 1/1,250 sec)/ ISO 100/ WB: Flash/ External Flash (High-speed sync)
By setting the flash to high-speed sync, there will be no more limits to the maximum sync speed, allowing you to shoot at high shutter speeds at wide-open apertures, even at daytime outdoors. For the example above, the aperture was set wide-open at f/1.8 and it was possible depict the subject brightly with creamy, largely defocused background bokeh.

 

Here is our recommended external flash!

 

Speedlite: 430EX III-RT
An external flash unit with plenty of reach, incorporating a number of options in a compact, lightweight and portable package. Capable of radio-transmitted wireless flash, the unit can serve as a slave unit at a distance from the camera. The flash head can tilt 90° up, pan 150° to left and 180° to right, enabling the unit to emit light in the direction required.

 

For more tips on how to use external flash, check out:
In Focus: The Basics of External Flash Photography

 

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