Invisible Attraction

This image is a fun example of “ultraviolet reflectance”, which is different than the “ultraviolet fluorescence” images I’ve been posting lately. At first glance it might not be as transformative as the fluorescing images but take a look at what this looks like in ordinary light: donkom.ca/bts/DKP_9421-VIS.jpg

This is the sort of vision that insects might see. To further that, it was shot in natural sunlight to mimic the right amount of ultraviolet light. Insect vision is far more complex than this, but we’re peeking being the curtain here in some interesting ways. Some flowers, like this dandelion and these forget-me-nots, change their reflectivity characteristic in UV in a substantial way from what we would normally see. Patterns arise that are normally invisible to us, but what if we could see them? That dandelion has a bulls-eye target in the center!

The Forget-me-nots are equally interesting, as some flowers are brightly reflecting UV light while the neighbouring flowers absorb all of it. This almost checkered pattern could be an insect attractant as well, and whole I’ve never studied insect behaviour I believe these patterns exist to bring pollinators to the table.

I’m sure many of you are asking an important question: how can the camera capture this? It starts with modifying the camera to “full spectrum”. This removes filters in front of the sensor that block infrared and ultraviolet light and limits the camera to the range of light that human eyes can see. Once the full range is opened up, we need to limit things down to just the spectrum we want, in this case UV. There are two filters that I use here to be completely certain that all visible and infrared light is blocked, but that UV light passes through: The XNite 330C and the XNite BP1 available from maxmax.com ( www.maxmax.com/shopper/category/9187-filters ). It’s important that you have full blockage of the infrared spectrum, as even 1% of IR light can equal that of the UV light that reaches the camera and that would seriously contaminate your results.

The next thing to consider is lens choice. I found that my Canon 50mm F/1.4 lens is a great choice because it has fewer lens elements and a simpler optical formula. The glass and coatings will block or reflect UV light, so simpler lenses tend to be better choices for this kind of photography. If you are able to find a lens dedicated to UV work it’ll likely have quartz elements instead of glass, but expect to pay upwards of $6000 for the gear. I went the less expensive route. There are also some vendors that sell lenses known for their UV transmission and are sold for VERY cheap on eBay: www.ebay.com/itm/Kyoei-Kuribayashi-T-Mount-Variant-35mm-F… – worth the purchase if you’re considering this kind of work, it’s the cheapest part of the equation!

I’ll be honest – most flowers are uninteresting in UV reflectance. Some flowers have exceptional patterns, but it’s a bit of a guessing game. The process of finding the right flowers can be enjoyable though, and getting a good combination of unusual UV characteristics can make for an interesting image – like this one.

Bonus round: here’s what the same scene looks like in infrared: donkom.ca/bts/DKP_9421-IR.jpg

click image for larger version