Keeping Dry using Max Flash Sync Speed

Kirsten-6

Working with Kirsten-Ria on a recent water based photo shoot relied on quite a few things coming together to get the images we wanted…the tide, a nice sun lit backdrop and, not least, it involved Kirsten being game for wading into the water!

I’d scouted a nice spot up near Southsea Marina, which would provide some relatively still water and a lovely dipping sun to provide some interesting catchlights on the water.

Even approaching sun set time, the sky was clear meaning the power of the sun was still quite strong up until it dropped. I wanted to retain most of the bright shimmering sun light on the water which was my starting exposure for the main image above. Camera equipment and water tend not to mix too well so key for me was being able to light Kirsten from the comfort of the shore line.

This was my starting point….
Kirsten No Flash-1

Settigs: 1/250, ISO 200, f/10. At an aperture of f/10 I’d retained the bright lights of sun reflecting off the water as I wanted. All I needed to do now was light Kirsten.

My key light source was my flash gun, mounted in my Lastolite 24×24″ Ezybox. Whenever I am working in bright light with flash I use a 1/250 shutter speed. Why? Because this is my flashes max sync speed. At this speed the shutters of my camera are juuuust slow enough to expose the entire camera sensor during the firing of my flash. Anything above this speed will mean the camera sensor is never fully exposed as the flash fires, and will result in a visible black band of the shutter moving across the frame. Still, I could use a slower speed than 1/250 (e.g 1/100) BUT with a loss of range of my flash gun.

Below the max sync speed of your flash, shutter speed has no effect on the output of your flash. What does impact the range of your flash are Aperture and ISO. Put simply, the wider your aperture and the higher your ISO, the more you are likely to achieve correct exposure at a greater distance to subject. By using a higher shutter speed I will be forcing the widest aperture and highest ISO I can to achieve the desired ambient exposure (i.e how I wanted the backdrop to look in the image above with no flash).

To achieve the same ambient exposure as shown above I could have also used the following range of settings which would have looked the same….

1/160, f/13, ISO 200
1/125, f/14, ISO 200
1/100, f/16, ISO 200

As my shutter speed lowers I have to increase the aperture to compensate. Meaning….I lose less range out my flash and increasing my chances of having to join Kirsten in the water.

At 1/250, f/10, ISO 200 I have better chance if standing further away from Kirsten and keeping dry!

In reality using a single flash gun, at this aperture and ISO, I was close to being at full flash output to get correct exposure even standing just a meter or so from the water. But a meter or so was enough for me, or rather Miriam King who provided make up and also assisted with the holding of the light! I didn’t bother using my flash meter to establish what power setting I needed my flash at (using manual mode). I knew from experience that my flash would need to be fired at pretty much full power, especially with the baffle of the softbox in place, so with a couple of quick test shots I was able to get the right exposure for Kirsten.

All in all, a very successful shoot….

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