I’ve seen plenty of pictures where automatic flash, E-TTL, gets it wrong. Ever since I completely switched to radio flash I have been able to use Speedlites and E-TTL in bright light more than ever before. I’ve also worked out why you need two, or more flashes in bright light.
E-TTL clever tech for automatic flash exposure
E-TTL is really clever, it’s designed to locate the part of the frame that is lit with flash and concentrate on getting the exposure for those parts correct. It does this by using a pre-flash that is 1/32 power. The problem in bright light is that the pre-flash might not be bright enough to see where the flash subject is and how much more or less light needs to be used to light the subject.
Two Speedlites – double the powerWith off-camera flash, each flash is assigned to a group, up to five of them with radio, and just three with optical wireless. Adding another Speedlite in the group is largely invisible to the camera that’s doing the clever flash exposure metering. So if there’s two flashes in the same group, then you get two flashes firing a pre-flash at the same time doubling up the effective power on the subject from 1/32nd to 1/16th. The camera sees this much more clearly and is better able to gauge the correct exposure required for the picture.
I use a couple of Lastolite brackets to put two (Lastolite Ezybox II Speedlight Bracket) or four (Lastolite Ezybox Quad Bracket) Speedlites in the same place or modifier.
If you are not sure whether another flash will help, try taking a picture with a single flash in manual at 1/32nd power, if you can see a difference compared to no-flash on the camera LCD, then it’s likely the camera can too. If not, then double up the flashes.
More Speedlites = more consistent E-TTL flash exposures in bright light
The old disused canal provides an endless range of locations, bridges provide shaded options for pictures.
Moving out from the bridge, and in to the bright early morning sun I continued to use the flash to add light to the model who would otherwise be in shadow.
Of course other brands make multi-flash brackets that can be used with a wide range of softboxes, umbrellas and other light modifiers, the key is to group the Speedlites together to increase the power of the pre-flash.
Huge thanks to Emma for modelling for me, make sure to check out her modelling page.
Gear used for these photos
- EOS 5D Mark III
- EF 17-40mm f/4L USM and EF 135mm f/2L USM
- Speedlite 600EX-RT x 2
- Speedlite Transmitter ST-E3-RT
- Lastolite Ezybox II Medium Softbox
- Lastolite Ezybox II Speedlite Bracket
Thank you Brian, that’s a really good tip and something I had taken for granted and just assumed the lack of power in one flash for the misreading of the exposure. I will try this on my next shoot on Friday. Best James
In effect you were right it’s lack of pre-flash power. Also it gets worse the bigger the modifier or the more layers of diffusion you are using.
Brian / p4pictures
You can also set the preflash to full power in the custom functions.
Sounds interesting, but I believe there’s no way to increase the power of the pre-flash by changing the flash custom functions.
C.Fn 07 set to 1 will change the power of the TEST flash between the default 1/32 power and full power. I tested with my Speedlite 600EX-RT and there’s a noticeable increase in the brightness of the test flash (triggered by pressing the red TEST button on the flash).
However if you press the flash exposure lock button on the camera to send out the normal pre-flash, then the value of C.Fn 07 has no effect on the brightness of the pre-flash. Also if the pre-flash was going to be full power, then the flash would not be able to recycle quickly enough for the actual exposure. Quite important given that in normal E-TTL there is only a few milliseconds between the pre-flash and the main flash.
If you have some other way then I’m really keen to hear about it.
Brian / p4pictures