TECHNIQUE | Ant Acacia , balancing natural light and flash
SHOOTING ACACIA ANTS IN SANTA ROSA NATIONAL PARK
Recently I was working in Costa Rica's Santa Rosa National Park for my upcoming coffee table book project. My publisher wanted some shots of the ant acacia, perhaps the most famous example of coevolution. Acacia ants (Psuedomyrmex sp.) and acacia trees (Acacia/Vacheyllia sp.) depend on each other for survival in the tropical dry forests of Costa Rica (and other areas of Central America). The ants inhabit hollow thorns and feed on lipid and amino acid-rich Beltian bodies on the trees' leaflet tips and sugary extra-floral nectary glands at the base of the leaf petioles. In exchange for food and shelter, the ants protect the acacia tree from herbivores (e.g., deer, caterpillars), vines, and even from wildfires by clearing brush around the base of the tree. Famed tropical ecologist Daniel Janzen showed in his doctoral dissertation that without each other, the ants and trees die, making the association a textbook case of coevolutionary mutualism.
Because the conditions throughout the week I was in the area were windy, dry, and sunny, I had extra challenges beyond getting in there and taking pictures without getting stung by the ants, which swarm en masse when something touches the the acacia they live on. I decided I did not want a black background but rather something greenish/brownish or even blue to hint at the tropical dry forest habitat. I also decided I would need f/16 to get reasonable depth of field.
Both of these choices meant very slow shutter speeds, a tough sell with moving ants and a breeze that was blowing consistently at a minimum of about 25 kph. Plus my acacia tree was in the shade. Even if I had located a tree in the sun, I would have faced two problems. First, I would have been dealing with harsh tropical sunlight which generally is not pleasing for photography. Second, even in that light, I was looking at an exposure of around 1/125th second at f/16 and ISO 400. A shutter speed of 1/125th was not going to cut it for a moving subject at high magnification on a windy day.
I quickly determined that I needed to use flash. If I used just one flash, as I did and as indicated below in the cool lighting diagram drawn by my son Chris Basco, the light from my flash would have fallen off long before it reached the background shrubs and trees. So, what were my options for avoiding a black background? Well, there were five, and I chose the last one.
First, I could simply haveslaved a second flash to light up the background. This was problematic for two reasons. First, the background was quite far away, and at high magnification with a 150 mm macro lens, I'm only seeing a tiny patch of background. Second, I was moving around to different areas of the acacia tree, meaning the background spot I need to light up would be changing. Keeping a background flash aligned exactly where I wanted it as I changed framing and moved around would have been a nightmare.
Second, I could have held a large leaf behind the acacia tree, say something like a Heliconia or a banana leaf. This actually is not a bad option, and I use it at times. In this case, however, this solution posed three problems. First, my son Chris was holding the flash so that he could position it where I needed it shot to shot. He couldn't hold the leaf at the same time. Second, though I could have dug out light stands and clamps to hold the leaf, the wind would have made this problematic as the leaf would still be blowing and folding in the wind. And third, keeping the leaf exactly in position as I moved the camera around would have been an additional headache.
Third, I could have used a print background. Indeed, I have some little 8x10" matte print backgrounds for macro that I'll use on occasion. These are prints of out of focus vegetation, a mini-version of what I and most people who do multiple-flash hummingbird photography use. As you might guess, however, this solution posed the same three problems as the second option above.
Fourth, I could have tried to position my flash so that it lit up some of the other leaves of the acacia tree to give a hint of color in the background. This can work quite well in many macro situations but here it was problematic for three differentreasons. First, since I was shooting f/16, closer background elements such as the leaves of the same tree that subject is on would be in focus enough to be distracting. Second, with the wind, those leaves would have been moving around a lot anyway, making for an inconsistent background. And third, the ant acacia trees have very slender stems and thin compound leaves composed of tiny leaflets. The architecture of the tree simply didn't offer the elements for a pleasing background.
Fifth, I could choose to work with my subject in the shade and properly expose a sunlit part of the background. To do so, I set my camera in manual mode. Since the intensity of the sun on the background was consistent, my exposure for it stayed the same. Had I used aperture priority, my background exposures would have been inconsistent. I chose f/16 , 1/160th, and ISO 400 to render the background a dark yellowish-green. Here's what my picture looked like with no flash:
Not bad, eh? The subject is just a big underexposed :-) but the background looks OK. There's a hint of color there. Actually the fact that the subject is woefully underexposed is exactly what I wanted. Now I can let the flash take care of the light on the subject. Since the flash is doing nearly all of the work on the subject, ghosting from subject movement during the longer ambient exposure will be minimal to non-existent. (I did try to shoot between strong gusts but even then there was movement, making ambient ghosting a big concern.) And by using manual flash mode, I could set my flash such that I knew the effective shutter speed for the light hitting my subject.
I used a Phottix radio transmitter in the camera's hot shoe and an off-camera flash with a Phottix radio receiver. The flash had a softbox fitted to it to give diffused light. I set the flash in manual mode at 1/8th power, meaning the flash duration would be somewhere between 1/5000th and 1/7500th of a second. That's a fast shutter speed, certainly fast enough to freeze an ant, even with a stiff breeze. Note that I used a clamp to secure the branch but I had to clamp it low down and with great care not to disturb the ants. So, the clamp helped but it certainly didn't eliminate movement from the wind. Here's the ant from the image above but taken just a second later and now with the flash added to the exposure (and a touch more sunlight hitting the background). The look for the flash is very natural to my eye, and the softbox has given a nice large catchlight (similar to an overcast sky catchlight) in the eye of the ant.
I used the exact same technique with a wider framing to include more of the plant here. You can see that with the wider framing, the background becomes less uniform but I still very much like it.
And for a different look, I exposed properly for a patch of blue sky peeking through the trees for another shot of one of the Psuedomyrmex ants sipping sugary water from an extra-floral nectary gland.
In the end, the basic technique here is quite simple. I'm balancing ambient light and flash in much the same manner as one would when shooting birds out in the forest. The twist is that the flash is effectively the main light on the subject, which means that getting the flash off-camera and diffusing it were the keys to pleasing lighting. But, there were a number of extra challenges in this situation. I don't pretend that these are prizewinning photos, but I consider them successful on their own and especially considering that I had the deck stacked against me in terms of the conditions nature was offering :-)
Knowing one's camera and having multiple solutions to potential problems is what allows a photographer to get the shot no matter the conditions. Hopefully this little article will give you some ideas for the next time that you're out in the field. If you have questions or comments, please leave them below, and I'll respond as soon as I can.