External Flash Techniques
Many people will wonder: my camera has a flash on it, so why would I want another one? The answer is simple: the built-in flash on most cameras is far from worthy compared to even a low-end external flash. You can get much better results with a decent external unit, easily justifying the cost and extra effort of carrying it around.
There are many ways an external flash can be superior. First, versatility: many external units allow you to direct the flash in some direction besides head-on, e.g. you can bounce the light off a ceiling. With an extension cable you don't even need the flash attached directly to the camera, providing options such as side lighting. Second, flash power: an external unit can almost always provide more light than your camera's flash. This can be extremely useful if you need to illuminate a large area or an object at a distance. Third, cycle time: the built-in flash on most cameras takes an absurdly long time to recharge, usually 5-10 seconds. A good dedicated speedlight will often cycle in less than a second in typical conditions. Fourth, fancy features: my Nikon SB-28 has a zoom head which allows me to "zoom" the flash to match varying focal lengths. Many high-end flashes have spiffy features like this.
Once you start using a nice speedlight, you won't want to use the camera's built-in flash ever again. The rest of this document covers the "how" and "why" of a few techniques, and offers a few equipment tips.
Using bounce flash
[A] reason so many newspaper pictures are so monotonously similar is that they are all taken with flash at the camera.... Seen with a front flash, the whole world tends to look alike. With it, control of the medium and any semblance of style, a fragile thing at best, are sacrificed completely.
-Wilson Hicks, Words and Pictures
Most people use their camera's flash in dark environments where the flash-to-ambient light ratio is high. This causes the camera flash to become the primary source of light for the photo, often a very hard light that blasts away all texture and mood. Furthermore, the flash is offset from the lens but still very near it, thereby casting visible shadows from foreground objects onto the background. For example, examine the two photos below which I took for Geek Radio:
Which one has better lighting? Do you need to think about it? The first shot, taken for the Mountain Dew Bread article, has heinous shadows to the right of the subject. Overall tone is also flat and lifeless -- the flash blasts away most texture. For the final, published image I airbrushed out the shadow, but it still doesn't look right when examined closely.
The second image, taken for the Lego Watch review (but not used), has far, far better lighting. No harsh, artificial-looking shadows are visible, and the diffuse light bounced from the ceiling brings out far more texture in the subjects. Compare, for example, the hair of my fearless Geek Radio partner Mark Harlan: in the direct flash photo it looks dull and of uniform brightness, whereas in the bounce flash photo it comes to life and covers a broad dynamic range. The latter photo also demonstrates a technique commonly used by auto and truck magazines, whereby the presence of an attractive woman in the picture dramatically increases its value to certain segments of the viewing audience.
If the words of Wilson Hicks aren't enough, looking at indoor photos taken with direct flash versus bounce flash should be enough to prove the latter often achieves much better results. This is an extremely valuable trick to have in your bag.
Variations on the theme
The general technique of bounce flash isn't limited to bouncing the flash off a white ceiling. You can also use a white card -- or colored card if you desire -- to achieve a similar effect, especially for close-up photography. In this situation the card also gives you more precise control over the light, as you can bounce it from several directions and distances.
This series of photos illustrates different effects created with an external flash and white card. The first shot was taken with the Coolpix 950 and its built-in flash. The shadow to the right, as in the photo of Mark above, is very distinct with the hard, direct light. The second photo was taken with my Nikon SB-28 external flash bounced from the ceiling, a considerable distance away compared to the camera-to-subject distance. This has hardly any shadow, but also a yellow cast which I'll discuss later. The third shot was taken with the SB-28 raised above, turned left, and bounced off a white card onto the subject. This produces nice, even lighting with a soft shadow behind the subject. The last photo has the SB-28 turned right and bounced off the white card, casting a shadow to the left of the subject.
Which shot is best? I'd say number one is ruled out due to the harsh shadow. Even after serious computer editing it's still going to look bad. Shot two with color correction to remove the yellow cast looks good, assuming you don't want any shadow. Shot three is probably the best off-the-camera shot before correction, and the soft shadow adds some depth to the photo. Shot four has better highlights on the subject's right side, but the shadow to the left is somewhat ugly. If I were planning to brush out the background, however, shot four would be an ideal starting point.
Warning: color temperatures
So why does shot two above have a yellow cast to it? Answer: color temperature. My digital camera set its white balance for the flash, but the flash-to-ambient light ratio is considerably lower than the camera expected since the light had so far to travel. (The light got there in plenty of time, but it was so diffuse that it covered an extremely broad area rather than just the subject's area.) The ambient light was very warm (yellow/amberish) compared to the flash's light.
Any photography book which discusses color will discuss color temperatures, so I'm not going to rehash that here. I want to bring up the point, however, that a speedlight will not necessarily illuminate everything in a picture, and ambient light may also play a role. In many cases your flash will illuminate a foreground subject but not the background, so the background will have a distinctly different color cast. Ever take a picture of someone under fluorescent light, to see the person with fairly normal color but the surrounding area a sickly greenish yellow? This is difficult to avoid with direct flash unless the background is very close, or you play some tricks with filters. Bounce flash will typically illuminate a much broader area, which can help but may not eliminate the effect.
If necessary, I fix these problems in Photoshop. I duplicate the image on two layers, color-correct the top layer for the foreground subject, and correct the bottom for the background. Then I mask off the top (foreground) layer and airbrush on the mask to bring back just the foreground subject.
Flash mounting and brackets
Pictured here is my odd contraption holding my camera and flash. This is a Stroboframe Quickflip 350 flash bracket, which positions the flash significantly above the camera lens. Most cameras have "hot shoe" mounts so you can stick the flash directly on the camera, but this isn't always the best place to mount the flash.
For fill flash -- using the flash outdoors in the sun to lighten shadows -- or bounce flash techniques, mounting the flash on the camera is fine. For direct flash, however, the Stroboframe or a similar bracket provides a distinct advantage: by raising the flash well above the camera lens, shadows are cast directly back and down from foreground subjects. When shooting people indoors, for example, the shadow is cast where the camera lens doesn't see, effectively eliminating it.
Keeping the flash significantly away from the lens also eliminates "red-eye" problems. Red-eye is caused by light reflecting off a person's retinas, and when the flash is right by the lens, the retinal reflection goes right back at the lens. If the flash is significantly off-axis, however, the lens won't see this effect.
A note specific to the Nikon Coolpix 900/950 cameras: The SK-E900 flash bracket which Nikon sells for these cameras is extremely lame. It positions the flash immediately beside the camera lens, so you have even more horrid shadows than with the built-in flash, and you also have horrible red-eye problems. Perhaps it's better than using the built-in flash, but you'll almost certainly be better off with a Stroboframe or similar bracket. Note that the Coolpix 950 does not mount quite right on a Quickflip 350; I needed to cut a notch in mine to allow the camera to seat properly.
By now the merits of using an external flash unit are hopefully evident. I love my SB-28, and use it whenever I can. It should be noted that a big flash and bracket turn a tiny camera into a huge contraption, however, so I don't carry this around often. I'll use it when I plan to take photos of something and I don't care if the subject knows I'm doing it, but I don't get many candids this way. Regardless, it's an extremely useful tool, one I consider well worth the investment.