Design Concept

I decided to try some macro photography and purchased a set of extension tubes. Wanting to leverage my existing 580ex flashes I devised a DIY diffuser for use with macro. The design differs from conventional wisdom for macro lighting which utilizes ring flash and crossed lighting, and is based instead on my observations and experience lighting larger objects with single and dual flash. The flash is bounced off the flat panel on the top, back into into the box chamber, then out the front similar to the way a bare flash bounces around inside a studio softbox.

Front view

Rear view (note position of off camera flash)

In creating the diffuser my first goal was to create an even source of light from the camera axis. But something else I've learn about lighting is the effect its direction has on the perception of what looks "normal" and "natural". In person we rely on stereo vision, shifting narrow focus, and parallax (how the foreground / background relationship changes as we move our heads) to get clues about depth and object shape. In a photo we rely entirely on different forms of contrast to create the same illusion: contrasting tone, color, sharpness, shape, etc. When looking at a photo we see the pattern of tonal contrast and the brain matches it to memories of seeing similar objects in the same light.

Most outdoor and indoor light comes from overhead most of the time. Outdoors there is one light source - the sun - but two light directions: the direct rays of the sun, and the "fill" light reflected from the sky. Both create a downward modeling pattern on faces and other objects. When a photo is illuminated with light from that same direction - above the subject - it will wind up seeming more naturally modeled in a photo. So I designed the on-camera diffuse so the light would be even and from the direction of the camera axis, but with a natural downward direction. Here are a few of my first test shots taken with just the single flash on the camera:

When shooting larger objects I use two flashes most of the time: one on a camera bracket as fill and another on a stand as key light to create the highlight pattern. Conventional wisdom for lighting human faces is to put the key light in front of the face to get light into the eyes for good "eye contact" and to model the shape of the nose sticking out between them. But in general a much stronger impression of 3D shape in a photo is created with back-side lighting. So my basic two-light macro strategy is similar to that used for a backlit full-face portrait: use the frontal flash to create the frontal lighting with a natural downward angle as seen in the shots above, then enhance the illusion of 3D shape with back rim light from the second flash. Here is an example comparing single and dual flash: Single Flash (top) / Dual flash (bottom)

The modeling on the Santa figure is nearly identical to the modeling on a real human face when a single flash is raised over head on a bracket. So I was quite pleased with the results because they look "natural". When the second flash is added for back-rim light the natural angle of the frontal lighting is retained much in the same way as outdoors in natural light when the subject's back is placed to the sun.

Here's a test shot of some berries comparing single flash (top) / dual flash (bottom)

Here is another dual flash shot where the rim lighting enhances the illusion of 3D.

These are just my preliminary test shots. As mentioned I'm just getting started in macro and will replace these with more interesting subjects when I get around to shooting some.