Friday, 1 May 2009

Use your flash on a sunny day...

When I originally decided to start a blog, I set out to tackle two distinct themes, technology and photography. With that in mind I decided today to write a piece attending to the latter. This may turn into a series of the simple tips and tricks I've picked up over the years from my own trial and error and from some great photographers.

There have been so many innovations in photography over the last few years it's hard to keep up. Reading the specs of even the cheapest compact pocket digital camera, one would think all you needed was the ability to stand vertically, point the camera in vaguely the right direction and pow! magic happens. The reality is of course very different. What ever additions or automations appear, what ever surprising applications of digital processing arise, photography remains an art. There are, however a few basic principles and a couple of simple techniques that can turn a dull snap into a decent picture and these techniques apply what ever equipment is at hand.

Photography is about composition and exposure. Both contribute to a photo's ultimate artistic merit but exposure is also driven by technique and a tiny bit of science. On modern digital cameras, exposure control is normally a mystery, hidden by "Auto mode" and left to the supposedly superior intellect of the camera's on-board processor. In reality, that processor, or at least the exposure program it runs, isn't particularly smart.

So what is exposure? Exposure is a term that describes the level of reflected light captured by a camera in order to record an image. In most cases, "correct" exposure means an accurate representation of the scene has been captured where detail is visible in both the highlights (brightest areas) and shadows (darkest areas). In modern digital cameras exposure is controlled by the aperture setting, the shutter speed, the digital sensor sensitivity (ISO value) and, in some circumstances, the flash. At the risk of adding to much complexity, most digital cameras can actually control two different exposure values simultaneously for any given image. The second exposure is controlled by the flash.

All automatic cameras use pretty much the same exposure calculation paradigm. They all attempt to assess a scene and then set the camera's exposure control to achieve an even exposure. In this context, the rather vague and inexact term "even" actually has a numeric translation - 18% grey. An 18% grey card is a tool used by photographers down the years to check exposure. A card that is prepared 18% grey actually reflects light pretty much in the middle of the range between white and black. In other words, your camera's exposure meter aims to make your image look as close to grey as possible! In reality, an image contains a vast range of lights and darks. Your camera tries to find an exposure value that will enable all these different tones to average out at - you've guessed it - grey! So what does this mean in prac
tice? The easiest way to explain this is an experiment. Take your camera, set it to auto and take a shot of a white piece of paper. Look at the result and you will see, instead of a fresh white sheet of paper, you'll have something that looks like it was washed with a pair of dark socks! it will be a washed out grey colour. Ok, now find something jet black, take a shot on auto've guessed it, the black item appears grey and lacking in contrast. In both cases, the camera has set a combination of shutter speed and aperture that achieves a scene that averages to 18% grey. This behaviour has many implications and is the key reason why so many auto-mode snaps end up either looking uninspiring and washed out, or as if they were taken in a cave!

OK, here's the first tip - Use your Flash...
The message here is simple, use your flash when ever you can. Even during the day, in fact especially during the day. Why? You'll have heard it said many times, "never take a shot into the sun" or "always have the sun behind you". While this does provide even illumination of your subject, it also means they are probably squinting. Also, your subjects will look flat and uninteresting, all the contours and definition of their features erased by a solar blast. Finally, you can't always guarantee to have the Sun and your subject where you want them.

Now most people will have taken shots before where the subject is strongly backlit. what typically happens is you end up with a well exposed background and a subject with a featureless face shrouded in total shadow. The reason for this is pretty straightforward, the background light source is dominant, much brighter than your subject's face. The camera attempts to set an exposure that balances the brightness levels in the overall image. It sets a combination of aperture and shutter speed that reduces the amou
nt of light recorded by the sensor to a level defined by the large bright source in the background. Unfortunately, in this situation, the relatively tiny amount of light reflected by the subject cannot compete and the subject is thrown into a dark gloomy shadow.

Now remember earlier I suggested your camera can manage two different exposures simultaneously? The flash unit (built in or external) can come to your rescue. While the camera's main exposure program sets the exposure value for the dominant background, turn on the flash and magic happens. With the flash on, press the trigger and a blindingly fast set of events take place. The camera will launch a pre-flash before the shutter is opened. The intention of the pre-flash is to test the amount of light required to correctly expose the foreground subject. The amount of light is controlled by the duration of the flash burst. Once the amount is computed, the shutter opens for the time required to correctly expose the background and, at the same time, the flash fires for the amount of time required to correctly expose the foreground subject. The end result is an image with a well exposed background and a properly exposed subject, all this happens in the blink of an eye. You see? two different exposure controls applied to a single daytime photo. There are some other desirable outcomes from using daytime flash. The flash helps the skin tones of human subjects to look warm, rich and healthy. Those unsightly shadows under the eyes and chin so typical in sunny day shots will be filled in giving a pleasing, detailed and flattering result. Finally the eyes will benefit from a catchlight, a tiny reflection of the flash pulse in each pupil. The catchlights make the subject look alive and somehow three dimensional.

Both of the images I've included in this post were taken using this technique. Each shot has a low key ambiance yet both were taken in the middle of a field on a bright sunny afternoon. In this case I have used off camera flash and a SLR but similar results could be achieved with a compact. The secret is in managing the two exposures, ambient and flash. In this case, I have reduced the dominance of the natural light by under exposing the ambient light by 1.5 to 2 f-stops. The flash is set to expose the foreground optimally (in this case I used a manual flash power setting, but you could leave the flash on its normal automatic setting and allow it to set its own optimum exposure)

As I said at the top,
nearly all cameras have the ability to do this, if you're using a simple point and shoot compact camera, find the control that sets the flash to "always-on" when you're taking your next set of sunny day shots. You'll be surprised by the results and you'll wonder no longer why those frantic press photographers always use flash during the day for those "must-get" publication shots they earn their living from.

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