For the lead story in the July Departments pages of National Geographic magazine, photographer Adam Voorhes was tasked with a perplexing assignment: to make a photograph of a miniature wind turbine 1.8 mm tall, or rather, about half the length of a grain of rice.
“All you can see is this little line and you can see that there are three fan blades connected to it. Everything else is completely microscopic.”
Developed by a team of electrical engineers at The University of Texas, Arlington, this miniature wind turbine, whose detail (such as the holes in the fan blades) in Adam’s photograph is unseeable to the naked eye, can generate electric power from ambient wind. The idea is that one day several hundreds of them could be applied to a sleeve for your smart phone, so when your phone dies, all you have to do is put the sleeve on and wave it through the air for a couple minutes to recharge it.
Being an experienced technical photographer, Adam had an idea of what he needed to do. “We saw a picture beforehand of the turbine on a penny, so I said, ok it’s twice the size of the ‘y’ on ‘liberty’ on a penny, which is really small.” So small, in fact, it is superglued to a microscope slide cover, otherwise you would not be able to physically handle it. He would need to use a technical camera and a technique known as “focus stacking” to get the final result.
Here’s how it works: in order to get an image which is completely sharp, you need to combine multiple images taken at different focus distances which, when combined, provide a resulting image with a greater depth of field. In macro photography, such as in this case with the mini wind turbine, getting a sufficient depth of field is challenging because the depth of field is much shallower.
“The depth that we’re photographing is two tenths of a millimeter. It’s so small that your depth of field is something that we don’t even perceive; you’re looking at an image that’s almost entirely out of focus and there’s just this tiny little field of depth that’s sharp.”
Adam started by taking a photograph where one point is in focus and then systematically took over 80 frames, shifting his focus slightly in each one. He then ran all the images through a computer program that combines all the sharp points to create a final, layered image.
“It’s never perfect and there’s some clean up you have to do, but for the most part you have a wonderful sharp image that could not be created otherwise.”
Part one completed, and on to part two: showing the scale of the wind turbine through comparison.
Both Adam and his photo editor Susan Welchman agreed. An ant would be perfect, especially if it could interact with the turbine. Since this real-world interaction wasn’t an option, Adam recreated the miniature turbine in his studio by cutting two tiny pieces of plastic and gluing them together on a piece of wire that hooked onto a surface.
Having worked with ants in the past, Adam pulled up his browser history and ordered a batch of ants online.
“We put maybe half a dozen ants on the surface and we just photographed them as they wandered around. We put a little honey on the plastic to try and bait them to interact with it. We were patient, we sat there and took pictures of them for a half an hour or forty-five minutes.”
Once he captured something workable, Adam put all the pieces together to make that one final, King Kong-esque image.
“I think what really helped the most on the page was the actual size thing, just the little dot down at the bottom.”
Editor’s Note: The coin used to show the scale of the wind turbine is a quarter, not a solarcoin. This post has been updated to fix the error.