Photo Technique: On-Camera Flash Diffusion

Flash is a necessary evil in insect photography. This necessity is due to two unfortunate traits shared by most insects: small size and stubborn unwillingness to sit still for the camera. These traits confound each other in a way that renders insect photography uniquely challenging. Small subjects need to be close to the lens, placing them squarely in the zone where depth of field becomes razor-thin. Depth of field can be increased by using a small aperture, but that restricts the amount of light reaching the sensor. With so little light entering the camera, a proper exposure requires the shutter to be kept open for a long time. As most insects are busy creatures with better things to do than wait about for the shutter to close, getting a clean shot under natural lighting requires a fair bit of luck.

The easiest solution is to augment the ambient light with flash, allowing for faster shutter speeds. This is what most insect photographers do, although flash comes at considerable aesthetic cost. Pure, unadulterated camera flash is as unflattering on insects as it is on people (remember all those vampire-looking people in the party photos?). With light shining from a single point source, any given part of the subject will either be in complete darkness or in full exposure. Photos taken with a direct flash have glare, overblown highlights, and distracting shadows. The image rarely looks natural.

The key to creating a natural-looking image using artificial light is to mimic the direction and character of natural lighting. This means replacing the point source with a diffuse light. Photographers have invented a great many ways to do this, including bouncing the flash off those large umbrellas used in portrait studios, placing various sorts of translucent veils between the flash and the subject, and devising any number of other odd contraptions.

I use several techniques, including some effective but cumbersome ones primarily suited for studio work, but in the field I find one method in particular both aesthetically pleasing and reasonably portable. I designed a simple paper tent to diffuse Canon’s twin macro flash. Here is what the device looks like on the camera:

The whole contraption is made of translucent tracing paper, cardboard, tape, and paper clips. Unlike most macro photo gear, the homemade diffuser costs only pennies. The tracing paper is arranged into a two-layered tent, with the layers separated by a centimeter or two, and is fastened with paper clips to a broad collar mounted at the base of the flash heads. The diffuser sits between the heads and the subject, turning the harsh raw lighting into a even white glow that mimics a cloudy sky. In use, the setup looks like this:

How effective is the diffuser? Compare the two harvester ant images below, both taken with a Canon dSLR, MP-E 65mm macro lens, and MT-24EX twin flash. The top photo is with the diffuser and the bottom photo without:

Notice how the fine details of the head sculpture emerge in the diffused light photo compared to the undiffused photo. Below is a sample of several additional images created using this flash diffuser:

The on-camera diffuser does have disadvantages. It hangs several inches out in front of the lens, spooking sensitive subjects and getting in the way when chasing insects through the undergrowth. I have experimented with other materials for the diffuser, including translucent plastics, but in the end I find that paper’s tendency to crumple and bend is actually an advantage. Paper gives way in the face of tight spaces while still diffusing the flash, whereas hard plastic serves as a solid barrier to camera movement. The paper can always be smoothed back out with a little massaging, and every few weeks I replace the wrinkled and dirty sheets with clean new ones. In humid situations like rain forests, the diffuser can be laminated with clear packing tape to keep moisture from compromising the paper.

A couple caveats. First, this diffuser does not work with long macro lenses (100mm and higher), as the working distance for those lenses is too great to hang a tent off the front of the lens. I use this diffuser exclusively with Canon’s MP-E 65mm macro lens. For longer lenses I have to find a different solution. Second, the diffuser reflects a fair amount of flash off the top of the paper and away from the subject. The power of the flash has to be bumped up a stop or two to compensate, and batteries burn out more rapidly with this setup. Finally, the on-camera diffuser is only one way of many to improve lighting for macro photography. It is one that I’ve found to be particularly useful for work in the field, however, and much of my macro portfolio was generated under the soft glow of the diffused twin flash.