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Friday, 9 March 2012

Week 10: See the light. Fill-in flash

Nearly all modern DSLR and Bridge style cameras have a built in flash, until you get to the “Pro” models, which assume you will be using a more powerful and flexible speedlight on the cameras hotshoe.
The little pop-up flash is more useful (and more powerful) than you many people think and we’re going to take a look at how to get the best out of it and in what situations it can be applied.
What is ambient light?
Before we go much further, it would be a good idea to remind ourselves of the difference between ambient light and flash light. Ambient is continuous light. It’s the light that fills the room or the outdoors; it’s normally daylight, sunlight, but it can also be room lights like tungsten or fluorescent, or even moonlight. The defining characteristic is that it’s continuous and that means that the camera can record it using an appropriate shutter speed.
Here’s some examples of ambient light:
This is a domestic scene shot under ambient tungsten household lighting. As you would expect, the camera has recorded the very warm “yellow/orange” white balance but otherwise the shot looks fine, with good detail and reasonably even lighting across the subject.
Here’s another subject, this time shot under ambient daylight. the colours and white balance are natural and the shot has good detail and lighting across the whole subject.
Why would we use flash in ambient light?
Good question. The next shot the ambient light has caused some problems. The portrait of the white flowers was shot against a window with ambient daylight. The daylight behind the subject is clearly brighter than the light on the front of the flower heads, so we get dark shadow areas, loss of details and a semi-silhouetted look.
Now, if we add some fill-flash to the scene using the little pop-up flash, we can pump a bit of light into the front and get the balance just right. In fact, adding flash does more than just light up the dark areas.
Flash adds sharpness and colour
Flash is a very rapid burst of light, it catches the subject and freezes any motion that might be there, so it helps to add sharpness to the image. It also adds colour, because it penetrates any “shine” on surfaces such as you get on waxy leaves and it saturates colours in clothing and other surfaces.
Danger! Reflection…
You do have to watch out for “flash reflection” though - if you have any reflective surface directly in front of the flash lens, the camera will record a harsh reflection of the flash, which is unsightly and distracting.
Avoid this by shooting from an angle, so the flash bounces off the reflective surface away from the camera rather than directly back into the lens. I did this with the flower subject above. The window pane would have reflected the flash, but I shot from 45 degrees so the flash bounced away from the lens.
Be creative with fill flash
Here’s another example. In this shot, I used a powerful spotlight behind the subject to create a silhouette and then “filled it”  with some pop-up flash from the camera.
Use Flash Exposure Compensation
In the shot of the carved duck above, I used the flash exposure compensation controls to dial in -1.7 stops of flash. I wanted to fill-in the shadows but blast the the thing with light! I needed to keep the ambience of the backlighting so it was important not to overwhelm the shot with flash. The flash exposure compensation (FEC) control on your camera allows you to set either more (+) or less (-) flash output.
We rarely need to set more but we use minus flash compensation all the time, to control just how much flash lighting our subject gets. It’s no different to using the power controls on the studio flash to set how much flash a portrait subject gets and the real key to daylight-balanced fill-in flash is set just the right amount of fill-flash to compliment the existing ambient light, not overwhelm it.

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