Eastern tent caterpillars, Malacosoma americanum, photographed at Raven Run Nature Sanctuary, Kentucky (Click to view large)

What is the secret to the evenly balanced exposure across both the foreground and background in this fisheye photograph?

It is not a clever processing job in photoshop. Rather, I used a handheld flash set to sufficient power to bring the foreground caterpillars up to the same light levels as the sky. Fill flash is an effective technique. In the absence of a flash I could either expose for the sky, leaving the caterpillars in the dark:

Or, I could expose for the caterpillars, leaving the sky blown out:

Careful use of flash allows the best of both worlds, with a minimum of digital correction.

photo details:

Sigma 10mm f/2.8 EX DC HSM Fisheye Lens on a Canon EOS 6D

Lighting: Canon 430 EXII Speedlite with a Lastolite Ezybox diffuser