Hiding right in front of us is a world we cannot see. Humans evolved to see light, but only a small portion of it that is useful for our daily lives. There is more to be seen beyond this limitation, including patterns in flowers that are invisible to us. Thankfully we have the technology to break down these barriers and explore a world only seen by pollinators.
Many insects can see into the ultraviolet, and some flowers take advantage of this by creating patterns that can only be seen in these otherworldly spectra. Take these Black-eyed Susans (Rudbeckia hirta) for example. We know these flowers to have a black center and solid yellow petals, but there is a special trait that we would never have noticed without the aid of technology: almost half of every petal absorbs ultraviolet light, while the rest reflects nearly all of that spectrum. This creates a very large, UV-dark target that bees (and other observant pollinators) can see.
To be fair, it’s impossible to know how a bee might perceive such information – they see more than just UV light, and we cannot comprehend exactly how their compound eye vision interprets information in general. That said, these flowers evolved to take advantage of their pollinator’s ability to see shorter wavelengths of light – or maybe the pollinators evolved to see these patterns? It’s a “chicken and egg” scenario. I know that certain cultivars of the genus Rudbeckia have a dark ring that is visible to our own eyes, and I’ve always wondered if this was caused by selective breeding of specimens that had a genetic mutation that shifted the UV pattern into the visible spectrum. A botanist might know the answer!
To create this image, I used a camera modified for “full spectrum” photography. Camera sensors are natively sensitive to light from roughly 300nm through 1000nm, but human vision is limited to only 400nm-700nm. This means that for a camera to properly depict the world as we see it, filters are added to limit the sensitivity range to that of our own eyes. These filters can be removed by trained professionals (don’t try it yourself!), and a camera can then be outfitted with filters to limit the spectral range to something different – including infrared and ultraviolet.
The problem with photographing UV light directly has two primary components: filters and lenses. You’ll want a filter that blocks 100% of visible AND infrared light. If even 1% of the infrared light sneaks through, it’ll equal to all of the UV light that the sensor can detect and wash out your image. The best filters on the market are from maxmax.com – the XNite 330C coupled with the XNite BP1. The two filters combined are the absolute best option. You’ll also want a lens designed for the task; I used a Rayfact 105mm F/4.5 lens which is the successor to the UV-Nikkor lens of identical specifications. This lens is made of quartz optics that allow for better ultraviolet transmission. Such lenses and filters are NOT inexpensive, but there are some options for you to consider at a fraction of the cost. I’ve bought from this eBay seller before, and I can attest that this setup works quite well to start out:
www.ebay.com/itm/273863933139 - it’ll cost you more to get a camera converted to full-spectrum that it will for the lens and filters!
The camera I had converted was a Lumix S1. Fantastic camera to do this with, especially when I’ve had some documentary work requiring high-quality video in unusual wavelengths. With the high-resolution mode, I was able to shoot this image at a greater distance and crop in, negating the need for any focus stacking efforts.
If you’d like to learn more about UV reflectance photography, you can check out my new book on macro photography:
skycrystals.ca/product/pre-order-macro-photography-the-un... - a 384 page book with nearly 90,000 words of photographic instruction. While more time and attention is given to UV fluorescence photography, there is still value in exploring the capture of ultraviolet light directly.