In The Bag: I went with two Nikon D70 bodies and my three must have lenses: A wide angel 12-24 F4.0 Tokina (slower, heavier, but sharper than my 10-24 Tamron), a 28-70 F2.8 Tamron, and my 70-300 Nikkor. I carried only one flash, a non-automatic Yong Nuo 560. I chose it over my usual SB-800 because it has one special feature: Its simplified triggering electronics allow it to synchronize at all shutter speeds, and it will work on Canon bodies too. When set to 1/4 power, it will discharge completely at1/1000 of a second when used with a Nikon D70. This is pretty much the practical performance ceiling because a shorter shutter speed or a more powerful flash setting will result in clipping (the loss of flash power at the back end of the discharge curve. Trust me). I decided to not carry a monopod for extended off-camera lighting. Instead, I attached the Yong Nuo to the camera with a Nikon SC-17 partially disabled for full synchronization (see this earlier post) and would hand hold the flash.
Photographing In The Shadows: One can get some dramatic images by placing your subject completely in shadow and allowing the background to be fully lit by direct sunlight. Here, your flash provides the only effective key light on your foreground subject. If no fill is added, the shadows will be dark and dramatic. The edge on the shadow will be fairly sharp, but this really can't be helped, considering the limitations of the equipment and the amount of flash energy available for the shot.
With a subject like this Aztec headdress (Photo #2), the vivid colors alone could carry the image. Again, had I the luxury of better lighting, this image could have really hummed, but for a shot made on the fly with no preparation time, the results are pleasing, and potentially publishable.
Backlit Subjects:"Backlit Photographs" are those where the main light source is coming from behind the subject. Assuming that your a photographing outdoors, the light will "halo" your subject, usually resulting in some overexposed highlights. When photographing without supplementary lighting (flash or reflector), the subject and the background receive the exact same amount of light, usually from the blue sky above, which tends to run on the cool side. If you need to maintain detail in the highlights, you'll need to adjust your exposure downward, underexposing both your subject and the background. The addition of a flash will only effect your foreground subject, leaving the background "in the dark" (Photo #3).
One important caveat: If you try to lighten the background to increasing your exposure time, you will also lighten your subject by the same amount. The additional light provided by your flash will potentially overexpose your image.
Compositional elements aside, I rather like the photo, primarily for the abundance of yellow and green. I find the children in the foreground a little distracting, but you have to laugh at the juxtaposition of the inflatable bananas and the Carmen Miranda headpiece. Those bananas, by the way, were used by the "Banana Drill Team", another concept you have to laugh at. But humor is a big part of Carnaval, and you have to chuckle when you find it hidden in plain sight.
This shot was made from a low camera angle, with the flash held as high above as my arms would allow. If you compare the nose shadows in the left and right samples in Photo #5, you can see that there are fewer highlights (bright spots) on the left sample than on the right. This is because I was able to get my flash slightly above the nose on the left shot, but not on the right. This is an important difference, and worth remembering when you use you flash outdoors. I'm sure that if my flash was mounted on-camera, the results would have been much worse.
If possible, consider how much you want the side lighting to contribute to the shot, and how much fill you'll want to add. Full-on flash fill works for the two on the right, but adds a bit too much light to the dances on the left. This is not to say that you can always predict exactly how such images will finally turn out, but anticipating the possible consequences is one half of the battle.
Now for the record I default to exposure settings that tend to underexpose my images, simply because I usually try to include some portion of the sky as a background and I want it rendered somewhat darker than normal. My go-to lens is usually a wide angle, which allows me to photograph at shorter distances, allowing the output from my underpowered flash to have a greater impact on the shadow exposure.
I have said in earlier posts that Carnaval offers photographers a chance to experiment with composition, lighting, and a variety of other people photography skills. Just remember to smile a lot, and enjoy both the joy and humor that are all around if you just keep your eyes, and ears, wide open.