Map Tree Frog Hypsiboas geographicus
Amazon Rainforest, Ecuador
Canon 5DM3 | Canon 100mm f/2.8 | 2 sec | f/2.8 | ISO 1000 | Canon Speedlite
On a clear February evening, deep in the Ecuadorian Amazon, the full moon hung low on the horizon. As twilight set in, many birds and animals retired to their roosts - at the same time, a new assortment of amazing nocturnal creatures were just waking up.
Whenever I get the chance, after the sun sets in the rainforest, I grab my headlamp and camera gear and set off down the trail to see what I can find. On this particular night, I didn't have to look far to find something of interest. Before long, I spotted a Map Tree Frog (Hypsiboas geographicus). Having seen countless photographs of tree frogs, and having taken a few myself, I knew they make excellent subjects! After making my discovery, then came the time to figure out a way to photograph it in an interesting way...
Immediately, I knew I wanted to include the moon in my photograph. At first, I thought of photographing the scene using a wide-angle lens, in order to include the night sky. That however, would've rendered the moon very small in the frame. Instead I chose to use a macro lens - the Canon 100mm f/2.8 - to better balance the two subjects.
Tree frogs have massive, bulging eyes protruding out from their heads - giving them an almost cartoonish appearance. I hoped that by positioning the moon behind the frog's eyes, it would seem as though it was balancing it atop its head. This was a tricky prospect as I found out the moon moves surprisingly quickly when looking through a 100mm lens!
Though the end result of this photograph is rather simple by design, there is a lot to think about in order to achieve this image. Here I will break down each component...
Shooting at 100mm, with one subject about 30 centimetres from my lens, the other about 382,500 kilometers away, give or take a few, understandably it just wasn't possible to get everything in focus!
Depending on where I set my focus, one of the two elements would be rendered as a blur. Of course in this case, I wanted the main attention to be on the frog, therefore that's where I chose to set my focus. I did this by turning on my camera's live view function, dimly illuminating the frog with a headlamp, zooming in to 10x on the LCD and manually focusing on the eyes.
Once I had the shot lined up and my focus set properly, I experimented with different apertures. If I used a small aperture, I would have a deeper plane of focus, allowing me to render much of the frog sharply. However, the smaller the aperture, the smaller the moon would appear in my image. Using the camera's depth of field preview button allowed me to see how large the moon would be at any given aperture setting. As I shifted from smaller to larger apertures, reacting to the bokeh of the lens, the moon softened and grew in the frame. I ended up choosing my lenses largest aperture (f/2.8) as I preferred the moon to appear quite big.
Exposure and Lighting
Lighting this image was fundamentally the same as using fill flash for wildlife or portrait photography. I simply set my camera to expose for the ambient light (the moon) and provided fill light to my main subject (the frog) - just as I would when photographing a shadowed bird against a bright background for example. Of course this scenario is much more pronounced, given there was basically zero ambient light being cast on the frog.
First I needed to set my camera to properly expose the moon. Though the moon was full, due to its position just above the horizon, it was quite orange and rather dim. At f/2.8 | ISO 1000, I required a shutter speed of 2 seconds. One might ask, why not use a lower ISO to afford yourself a better quality image? If I used something like ISO 250, my shutter speed would then be 8 seconds. When using a 100mm lens, the movement of the moon would easily be detected with a shutter speed of that length - causing the outline of the moon to lose definition and become oblong as the moon tracked across the frame.
My second task was to figure out the best way to light the frog. Given that this was taken at night, I would need to use an artificial light source of some kind.
Using a headlamp to fill in the shadowed frog might work but would require the frog to sit perfectly still for the entire 2 second exposure. Instead, I decided to use a flash so I could dial in exactly how much light to output and not risk subject movement affecting the image.
Another reason for choosing to use a large aperture and a higher ISO, making the camera very sensitive to light, was to eliminate the need for a high flash output. Tree Frogs are nocturnal, therefore they too are highly sensitive to light. By using these camera settings, I was able to use just a minimal amount of flash to illuminate the frog.
When using flash to illuminate any given subject, there is no real formula or right or wrong. Experimenting with angle, intensity and number of flashes is the key to better understand lighting. In this situation, I placed my flash off axis in order to avoid both the flat look of direct lighting and eye-shine... (unlike this image of a Spectacled Caiman where by placing my light source directly over the lens, I accentuated the eye-shine caused by a layer of subretinal tissue called the tapetum lucidum.)
An important factor to remember is not to stress your subject and try to limit your impact by withholding the use of excessive intensity and frequency of flash.
A lot of people get confused as to how you can take a long exposure like this and have the animal be sharp. The answer to that is: when zero ambient light affects the animal and what illuminates them is only the light of your flash, the shutter speed is no longer a factor as to the sharpness. The shutter speed is 2 seconds - definitely not fast enough to stop motion, especially when an animal is on the move. However, if your flash is firing at 1/16th power - that equates to a pulse of light lasting 1/10,900 of a second. This is what freezes the motion of your subject.