Strobe light and shutter speed

Albert Pedrosa
Photo mania

INSIDE the comforts of a big aircon bus, I suddenly found myself in a majestic six-lane highway with pine trees on the sides. The typical smell of an aircon bus was replaced with a fresh scent of air coming from the pines. I swear I thought I was in another country. Could this be Tagum City, my final stop in my “lighting and retouching” workshop?

This continued for a couple of miles before we could finally enter the city--the city of gold. They say that Tagum is one of the major producers of gold in the country.

Their city hall has the size and looks of Ayala Center Mall and just recently, they opened their international standard rubberized oval and other sports facilities.

Tagum was my last stop after Surigao, General Santos and Davao. Although these cities have their own unique way of surprising you, there was one common thing they had. They were all enthusiastic about learning the techniques of strobing. Most of them unfortunately, didn’t also know that strobes cannot be controlled by shutter speed.

In fairness, they know that you cannot shoot more than the flash sync. This leads me to write about this topic, fearing that some Cebuano photographers might find this idea helpful at some point. This is not advanced mathematics and physics, just a look at the plain, old characteristics of light.

In typical ambient lighting, the exposure triangle, which is composed of the aperture, shutter and ISO, controls the exposure or light. In strobing, since this is not a typical light source, only the aperture and ISO applies. The shutter has no use but must be below the flash sync speed.

An ambient light or a continuous light illuminates a scene by pouring in photons continuously. By controlling the exposure time, the shutter can control the amount of light entering the focal plane. The more light entering, the brighter it becomes. In the case of a strobe where it only fires once at breakneck speed, the shutter cannot control it.

A strobe travels about 4000th of a second and only fires once. If the shutter can control the light by means of time, then the strobe by no means cannot be controlled because it is too fast. Therefore, whether you shoot it at 1/250 or 1sec, as longs as there’s no ambient light, the illumination should be the same.

Flash sync speed is also limited to only 1/250 and below. If you shoot more than the prescribed speed, you’ll see partial darkening in the sides. This is actually the shutter curtain. Below the flash sync speed, the shutter curtain opens in full before it starts closing. In higher speeds, the curtains start closing before it even fully opens.
Therefore, the only way to control strobe is through the aperture and ISO. Of course you can also control it using your strobe power. My advice is for you to test it and experiment on it. Know that the slower you set your shutter, the more ambient light would come in mixing with your strobe. Try controlling both strobe and continuous light at the same time.

I would like to personally thank Don Pagunsan and Ronald Rivera of GenSan Camera Club and Dr. Harvey Leonardia of Camera Club of Tagum for their warm hospitality.

Keep on shooting, everyone.

(photography@grp.ph / www.grp.ph)