When it comes to flash photography, most people would agree that it is essential when shooting indoors primarily, where available light is not enough to illuminate the subjects, thus the additional flash can be utilized to provide the source of light or simply just to enhance the lighting conditions. Creative use of flash lighting can create very desirable results, but this is not limited to only indoors. I have seen many fellow peer photographers happily tugging away the external flash unit when venturing outdoors, with the thought in mind that the available natural light is sufficient in most cases, and use of flash could deteriorate the image quality. This statement is true to a certain extent, but I choose to believe that flash can be very helpful too while shooting outdoors under the bright sun.
Here are the situations when I do come across the necessity of engaging the external flash unit while I was baked by the burning sun shooting.
1) To counter back-lit situation
Flash as fill-in
Sometimes the subject is positioned in a way that the background creates a very strong back-lit, casting the subject into shadows, and losing the details in the background to overexposed highlights. Flash can be used to illuminate the shadow areas of the subject, while maintaining the exposure balance in the extreme background situations.
2) To reduce motion blur, and boost the shutter speed.
There are situations when constant movement of the subject becomes the major concern, especially under shady areas where the shutter speed may not be enough to keep up with the motions. I engaged the flash to just push the shutter speed up a notch or two, and manage to freeze some actions, like the one shown in the above picture as the elephant trunk grabbed the banana from the giver's hand. Originally shot at ISO200 shutter speed 1/200 seconds, and it was blurred due to motion. I then used the external flash on TTL, camera set to ISO200, shutter speed 1/500 seconds, and that did the trick in obtaining blur-free tack sharp picture.
3) To create the 'catch-light glow' effect on subject's eyes.
The magical thing about any eyes, human or animals, is the ability to reflect light. When flash is fired with small intensity, the eyes will sparkle and glow and this effect is called the catchlight, which is very desirable when it comes to portrait or any people-related photography, with the emphasis usually placed on the eyes.
4) To darken the background.
In situation where it is not exactly a strong back-lit, but the background is bright and distracting, the flash can be deployed to darken the background, by providing direct illumination to the main subject while adopting high shutter speed. Throwing the background into a darker tone can pop out the subject more effectively.
5) To provide light to places the natural light cannot reach.
In outdoor macro photography, when it comes to insects, lighting is the main problem as they tend to hide under leaves or shrubs. Even shooting under high ISO could not get a nicely exposed subject, hence flash can be used to provide the light source to the place the natural light cannot reach. Do take note that the image may come out not natural by using this method, but hey, at least the subject is well lit and it beats the crap out of a severely underexposed dark image !!
6) To squeeze out the creativity juice.
Having some basic knowledge of using the flash, a few things can be achieved even shooting outdoors, such as low key (perfectly black background) photography as demonstrated on the insect above. The background was not really black, but with very narrow aperture I managed to blackened the background, and the insect was lit with flash being fired at very close range, wirelessly off from the camera. This sort of effect could not be achieved without the aid of the flash.
So there you go, I have listed my reasons why I still keep that external flash unit and the fully charged batteries in my camera bag even when I know my full photography session is out under the harsh sun. The flash can be a powerful weapon, and it adds drama to photographs is used correctly. Of course, there is still so much I need to learn and improve on my flash techniques, but even with such limited knowledge I possess i can see how much the flash has impacted my pictures already.
Oh, and if you are asking me why I do not have human subjects as my photography experiments? To be honest, I am running low on voluntarily human subjects these days, and if you do wish to contribute to the world of photography, do drop me a message. I know, like that is going to happen, ever !!