DIY

IMAGING

INVISIBLE STROBE FLASH

Near-infrared photography captures bats and other night movers. By Jerry Reed

A few years ago, I began documenting the bats flying around my backyard bat house, using inexpensive, monochrome security cameras and a DVD recorder. The little mammals streaked impressively through the frame, but I was disappointed when I started single-framing through to see what they looked like. In each frame showing a bat, it was a mere blur.

Photography by Gerald S. Reed

I decided to use a xenon strobe to freeze the bats in the images. It wouldn’t be synched to the video frame rate, but the combination would be statistically likely to capture at least a few usable stills.

The problem was, some bat experts I consulted thought the strobe would delay their activity and might even drive them away. So I needed to make a subtle strobe, which sounds like an oxymoron.

I knew that xenon tubes produce a wide spectrum, and many tinted plastics block visible light but pass near-infrared (NIR) wavelengths that monochrome

MATERIALS

Xenon flash lamp Party and Halloween stores carry 120V AC versions, and auto stores have smaller 12V DC strobes. You can also assemble a kit from Electronic Goldmine ( goldmine-elec.com).

12V DC power source if you use an automotive strobe “Limo Black” window tint film from an auto store

Monochrome security camera Color CCDs are less sensitive to light, and many color video cameras have built-in IR filters that block the illumination we’re working so hard to create.

Lens with a C or CS mount to fit the camera Cheap security camera lenses will work, but good-quality used lenses made for 8mm and 16mm movie cameras are better. The CS mount fits new monochrome cameras, but you can use older C mounts with an inexpensive adapter. Avoid electronic zoom/focus and auto-iris; manual focus and aperture (f-stop) adjustment are best. For nighttime videography, everything is wide open anyway.

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