You’ve seen those wonderful photos where a pop of flash is used to balance lighting of a subject in daylight, so called fill-in flash. Some photographers struggle to make it work for them so let me explain…
Mixing flash & daylight
I had great question from a photographer at the Photography Show in Birmingham last week. He wanted to know how to avoid overexposed shots when using flash. He’d taken some pictures in aperture priority without flash and felt they lacked something. He thought that a touch of flash would give them a suitable lift. However as soon as he turned on the flash the result was way overexposed photos. So deterred by his results he turned the flash off and carried on without using flash.
I’ve gone out and shot some photos to show exactly what the photographer described, and how you get over this issue with fill-in flash in daylight.
The issue is that when you use flash, your camera is normally limited in the range of shutter speeds it can use. Your maximum shutter speed with flash is likely to be in the range 1/125s to 1/250s depending on the camera you have, and that is the problem.
In my example above the left-hand picture (#1) was taken in aperture priority with the aperture set to f/2.2. The camera opted for a 1/3200s shutter speed to give a correct ambient light exposure.
The right hand picture (#2) was taken with the addition of flash. It is way overexposed as the shutter speed is limited to the 1/200s sync speed on my EOS 5D Mark IV when using flash.
The secret is to set the flash to high speed sync. This allows the camera to keep the shutter speed high enough to correctly expose for the ambient light and then add a touch of flash, like I did with picture #3 on the right here. The daylight was slightly different so the camera selected 1/2500s as the shutter speed.
High speed sync limitations
Unfortunately the “rules of photography” give with one hand, and take away with the other. When you use high speed sync, your flash power reduces by a stop for each 1-stop increase in shutter speed. You can easily run out of flash power.
I often use a pair of Speedlites in my softbox when working outside. Doing so gives me at least one more stop of power for high speed sync in addition to helping with E-TTL flash.
Did you disable high-speed sync?
Canon cameras set to aperture priority will aim for fill-in flash all the time, when it gets dark the shutter speed will slow so much that you can’t handhold and your subject will get motion blur. My questioning photographer had found a custom function on the EOS 7D Mark II that he though would avoid that… it limits the shutter speed to 1/60s to 1/250s when using flash with aperture priority. However it takes no heed of high-speed sync and the limit is really a limit, you simply can’t get above the sync speed whenever you use aperture priority with flash.
So if you are using flash with aperture priority and high speed sync won’t work – check your custom functions or settings in the camera’s flash menu…
Many thanks to