Techniques: Introduction to Flash

When I first started out in photography, I used to hate flash. Like many people I thought it made the lighting look terrible, gave that horrible harsh lighting on people faces and was just downright unpleasant. However, what I have learned is, I was just using flash incorrectly and once I learned how to use it properly I realised that flashes are the most useful tools for creating amazing photography which is why I happen to own five of them and am always using them for most things. So for those of you who think flash is awful, I challenge that you just haven't been shown how to use it properly.

So why would we use flash? Well it's a good question, most of the time it's because we just don't have enough light to get the exposure that we want so we need to add some light in there just to help us out. Flash can also be used to achieve certain effects, like freezing motion, light painting and strobe photography. I'll write about these a little later.

To get started, you'll want to get yourself a nice external flash, something like a Canon 430EXII or even a cheap Yongnuo will do okay. What you should keep in mind though is that flash metering can be done using ETTL (Electronic Through The Lens), which automatically adjusts power and zoom, or you can do it manually where you choose the power and zoom of the flash. Some cheap flashes do not support ETTL metering so in these cases, keep in mind you'll have to be choosing the flash power and zoom manually which can be tedious if you're in a fast paced environment so I wouldn't recommend it.

What is useful to know is what kind of light each setting controls. The following shows what each setting does to light when using flash:

  • Shutter Speed: this controls the ambient light. Longer shutter speed let in more ambient light. Subjects illuminated with flash tend to look the same even with changes in shutter speed. However, areas with only ambient lighting will dramatically differ. Understanding this is key to doing certain kinds of shots, especially night portraits.

  • Aperture: this controls the overall lighting sure, but it mostly changes the flash power. Smaller apertures will result in the flash lit subjects appearing darker.

  • ISO: This is a global thing and changing it will tend to change your overall exposure

For flashes, we generally have three modes we can use. These modes relate to when the flash fires during our exposure. The options include:

  • Front Curtain Sync: This is where the flash fires at the beginning of the exposure

  • Rear Curtain Sync: This is where the flash fires at the end of the exposure

  • High Speed Sync: For when you want flash with high shutter speeds e.g. something higher than 1/250s. You will only get this one on an external flash, at least as far as I'm aware and not on your inbuilt flash

You see how the motion is in front of the people? That's cos this is a long exposure combined with front curtain sync, the scene is frozen at the beginning and the motion is in front.

You see how the motion here is behind her? That's cos of Rear Curtain sync, it freezes the image at the end of the exposure.

So you may have noticed your inbuilt flash doesn't seem to work for a shutter faster than 1 /250s. Now why is that? Well, it has to do with how the camera take an image. When you press the button on a DSLR, the mirror flips up and reveal the sensor. There are two little curtains that cover the sensor, one is the front curtain which goes first and opens the shutter to light, and then the rear curtain which goes second and covers it up By the way, this is why it's called front and rear curtain sync.

For long shutter speeds, the front curtain opens and reveals the entire sensor and then the second curtain comes to cover it. However, for faster shutter speeds, such as 112000s, the curtains move close together to only reveal a tiny portion of the sensor at a time, i.e. the entire sensor is never exposed at the same time so we can't use a flash because the flash wouldn't light the entire sensor. High Speed Sync actually gives pulses of light to ensure the entire image is covered. To get a better understanding of what I'm talking about, I recommend the following video from the Slo-Mo guys which actually shows you physically what's going on and helps you understand what these terms mean and the limitation of shutter speed on flash.

Bouncing The Light:

So generally you want to using either off-camera flash or bouncing your light around. Now why would you do that? Well because you want to create a soft light. Now the softness of light is related to two things, how large/bright the light source is and how far away it is from your subject. A speedlight is really small so firing straight onto your subject creates some harsh lighting. To create softer lighting, you should aim it at a ceiling or a wall and bounce it off there. This is why it's useful to have an external flash which can turn side to side and up and down.

The next question is, well what do I do if there's nothing to bounce off? Well, either use it straight on with a diffuser (I actually find myself doing this a lot, especially outside) or take it off camera to create some drama. What you might find if you shoot straight on is that your background is really dark, well what you can do is drag your shutter, something slightly longer like 1/30s, this will let in more ambient light and hopefully brighten up the background. In these cases I prefer using rear sync. This is also useful for night portraits although you might need to use a longer shutter, e.g. 1 /4s or 1 s.

For this photo, there was terrible ambient light, so I tried to bounce of part of the wall behind me and dragging the shutter to 1/30s to try and capture some ambient light behind them.

I bounced the speed light off a low ceiling to try and create some softer light in this photo

For this photo, I used two off camera flashes which I triggered using a wireless trigger. The first was the white light set up at a 45 degree angle to him using a shoot through umbrella and flash stand. Then to give some separation between him and the background, I decided to place a second flash behind him with a purple gel to give him an outline.

So moral of the story is learn how to use flash properly and suit it to your situation. Don't just dismiss the usefulness of flash, it can do amazing things. More of which I will show you later when I talk more about light painting, night portraits, ghosting and strobe photography.