Choosing an External Flash (2): What Else Can A Flash Do?
There is more than one way you can use an external flash. In addition to flash power, how your flash performs in techniques such as bounce flash photography, continuous shooting, slow shutter speed (slow sync) photography, high shutter speed (high-speed sync) photography and close-up photography matters a lot too. We explain more. (Reported by: Masakatsu Nagayama)
FAQ #1: What is bounce flash?
A1: Bounce flash is a technique that involves bouncing the flash off a ceiling or wall surface to illuminate the subject indirectly.
This technique disperses the light from the flash and makes it softer. Compared to directly shining the light on the subject, you get softer shadows and more natural lighting.
Bounce flash is often employed during indoor portrait photography.
How bounce flash works
B: Soft light
D: Light from flash unit
Direct light from flash
This sample shot was taken using normal flash light that was fired directly at the subject. Although the colours appear vivid, the subject looks flat and unnatural, and the light texture also feels harsh.
Firing the flash at the ceiling creates bounce flash that is soft. Shadows are also less noticeable, and the resulting image looks more natural with enhanced dimensionality.
What kind of external flash unit is good for bounce flash?
The ideal type of external flash unit for bounce flash photography has a flash head that can be tilted and rotated.
When you use bounce flash, you will “lose” more light compared to when you shine the flash directly onto your subject. If the flash power is too low, you may end up with insufficient lighting. Choose a flash with more flash power if you plan on using this technique.
Application tip: Colour cast may occur if light is bounced off a coloured ceiling or wall, so it is best to use a surface that is as white as possible.
The Speedlite 470EX-AI (above) is optimised for bounce flash photography. It has a relatively high guide number of 47, and features Auto Intelligent Bounce (AI. Bounce), which can automatically calculate and set the optimal bounce angle.
Bounce flash is often used for indoor portrait photography. Notice how the flash head is angled towards the ceiling.
FAQ #2: Can I take continuous shots during flash photography?
A2: You can if your flash unit has high flash power (high guide number). However, the number of continuous shots possible depends on various factors.
When flash is fired at full power, some time is needed for recharge before it can be fired again. However, if you are not using the flash unit at full power, it is possible to fire the flash continuously until the charge runs out.
Having a strong flash power helps
The continuous shooting speed and number of continuous shots possible vary depending on the flash unit in use, but one with a stronger flash power or higher guide number will offer greater versatility.
1. You can increase the number of times the flash can fire continuously by reducing the amount of light that is emitted per flash. One way is by opening up the lens aperture.
2. The flash unit or battery may deteriorate in performance due to overheating if you fire the flash continuously too frequently. Follow the instructions in your product manual on the number of times flash can be fired. After each set of continuous firing, allow some time for the flash unit to cool down.
FAQ #3: What is flash sync speed?
A3: It is the fastest shutter speed at which flash photography is possible.
Sync speed refers to the fastest shutter speed at which flash can be used for photographing. It depends on your camera, and is indicated by the X-sync speed. For Canon cameras, the X-sync speed is 1/250 second for high-end models and 1/180 or 1/200 second for those in the other classes.
The “focal-plane shutter” structure and its effect on sync speed
When photographing with flash enabled, the camera automatically sets the shutter speed to a value lower than the sync speed as shutter speeds faster than the sync speed is not selectable.
Such a restriction on the shutter speed exists because of the “focal-plane shutter” structure in DSLR cameras.
A focal-plane shutter comprises two light-shielding curtains. Upon pressing the shutter button, the first curtain opens, after which the second curtain closes immediately. Exposure takes place during this interval.
If the shutter speed is faster than the sync speed, the second curtain would start to close before the first curtain is completely open. This prevents the shutter curtains from opening up fully, which will block the exposure and cause black bands to appear in the image.
In the manual exposure and Shutter-priority AE modes, even if you have selected a shutter speed that is faster than the sync speed, it would switch automatically to the sync speed once the power of the flash is turned on.
FAQ #4: Can an external flash be used for close-up photography?
A4: You are recommended to use flash units designed exclusively for close-up photography, such as a ring-type flash.
Conventional flash units are not suitable for close-up photography and macro photography. This is because the effective flash range is predetermined for each flash model. Photographing any subject that is closer than this distance to the camera may either create shadows in the image or result in overexposure.
Instead, use an external flash that is designed for macro photography. These can be largely divided into two categories:
Ring-type flashes such as the Macro Ring Lite MR-14 EX II have a round-shaped flash head and can illuminate an area evenly in all four directions. It allows you to take close-up shots with almost no shadow.
Some ring-type flash units allow you to fire light from only a half of the ring to create shadows intentionally in a specific direction.
Twin flash units such as the Macro Twin Lite MT-26EX-RT feature two flash heads, one each on the left and right sides. The light cast from both sides makes shadows less noticeable. You can adjust the distance between the two flash heads, their orientation, as well as the flash output to suit your needs.
Macro Ring Lite MR-14EX II
This ring-type flash has a shortest firing distance of approximately 20mm from the front of the flash head.
Macro Twin Lite MT-26EX-RT
This twin-type flash supports wireless firing through radio transmission and allows fine control over flash output.
Click here to read the previous article on flash power:
Choosing an External Flash (1): Flash Power
For more details about Canon’s Speedlites, check out:
Which Canon Speedlite Flash to Choose? (Compares the 3 older Speedlites)
Buyer's Quick Guide: Speedlite 270EX II
Buyer's Quick Guide: Speedlite 430EX III-RT
Buyer's Quick Guide: Speedlite 600EX II-RT
Canon Unveils the Speedlite 470EX-AI: World's First Speedlite with AI Bounce Technology
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Digital Camera Magazine
A monthly magazine that believes that enjoyment of photography will increase the more one learns about camera functions. It delivers news on the latest cameras and features and regularly introduces various photography techniques.
Published by Impress Corporation
Runs an advertising studio, and started being a freelance photographer in 1998, where he has been active mainly in the advertising scene, shooting for magazines and online media. His speciality lies in snapshots of city life.