Ultraviolet Flower Photography Guide | FUJIFILM Exposure Center – USA

11 minute read

Ultraviolet Flower Photography Guide

Equipped with FUJIFILM GFX100 IR, Nate Rochefort explores the ultraviolet spectrum to create enchanting floral displays

FUJIFILM GFX100 IR is an excellent infrared (IR) camera, and has few or no issues documenting IR wavelengths. Ultraviolet (UV) photography, however, creates additional technical hurdles. Still, with the right equipment and knowledge, it is possible to create high-quality UV images. Flowers are common subjects for UV photography, because just below the naked eye’s visible range, some flowers display a dark, UV-absorbing area.

I’ll discuss the tools and techniques more deeply in this article.

This specialist version of GFX100 is ordinarily unavailable to the general public – its capabilities reserved only for professional forensic, scientific, or conservation uses. However, for the purposes of this infrared photography series, Nate has been granted exclusive access to GFX100 IR with the intention of using its otherwise practical infrared and UV functionality for artistic pursuits.

Photographing Flowers in UV

Digital UV photography has historically been more challenging to perform over infrared (IR) due to many impediments, such as adequate illumination sources, limited camera sensitivity to UV wavelengths, and UV transmission through camera optics. Other challenges are due to UV’s short wavelength. As discussed in part two of this series, the short wavelengths restrict UV’s ability to pass through various camera system components. The main aspects that determine UV transmission are lens elements, the internal filter that replaced the camera’s hot mirror, and the dyes that sit atop the color filter array (CFA). Together, these roadblocks mean that a UV photograph requires long exposure times and a strong source of UV illumination.

Lens element issues can be solved by using a prime lens. However, little can be done regarding the replacement filter and the CFA, short of redesigning or disassembling a camera.

These technical hurdles can lead to hesitation or avoidance and has limited UV photography to being performed primarily in a controlled environment.

With these limitations in mind, I explored the possibility of using GFX100 IR in the field, using flowers as a subject. There are a few tools needed for UV photography:

  • A camera capable of recording UV images
  • A UV filter
  • An adequate illumination source

Since the GFX100 IR is a full-spectrum camera, I only had to resolve the other two items. For the filter, I chose a 365nm UV bandpass filter. I opted for this because of its slightly higher wavelength transmission region of 365nm. For illumination, I had three sources available – a 365nm UV LED, a modified flash, and the sun.

Movement is the primary concern when performing UV floral photography outside a controlled environment. Nearly all images must balance the demands of finding accurate focus, achieving correct exposure time, and limiting high ISO noise that could degrade quality.

I ended up leaning on GFX100 IR’s outstanding high ISO performance, powerful dynamic range, and mirrorless design to compensate for those limitations – and it performed exceptionally. While a tripod was required for all images, the camera itself helped resolve many issues.

The ISO performance meant that I had greater latitude with my exposure times. The dynamic range allowed for underexposing in the camera, knowing that the image information would be recoverable in editing software. And, perhaps most impressive, focusing was not an issue.

Typically, focusing would be a little bit of a guessing game. There is a significant difference in focusing distance between visible and UV light. Still, GFX100 IR was able to accurately and consistently achieve focus, even when I looked at what appeared to be a nearly black viewfinder. The camera could also get reasonably close to an accurate exposure metering – however, the viewfinder provided the most reliable way to dial in the appropriate exposure.

UV White Balance

We have no concept of color in the UV region, so it is common to present UV images in black and white. However, while much more involved than IR, it is possible to color correct UV images. The easiest way of doing this is by photographing a target that appears neutral in the UV spectrum.

A professional tool for this is a Spectralon, which has known reflectance characteristics through the UV spectrum. It is costly, but a more affordable option is thread tape or plumbers’ tape in white or gray. To white-balance an image, set your composition and make a photo with the white balance target in the scene first. Then create the photo you intended. You will use the image with the target to set your white balance when editing.

Hidden Patterns in Flowers

The woolly sunflowers below are shown in both visible light and UV light. In the UV image, a dark bullseye pattern is visible. Why do some flowers display this dark pattern? To answer that question, we need to look at the visual system of some of their most frequent visitors: pollinators. Or, specifically, bees.

Humans have trichromatic vision, meaning that our vision and all the hues we see are composed of three colors. While vision is a complex process, in simple terms, humans have four types of photoreceptor cells called rods and cones. Cones are the cells responsible for our color vision. There are three types of cone cells, each corresponding to the colors red, green, and blue.

Like humans, bees have photoreceptors sensitive to three different wavelengths. However, their photoreceptor cells are not sensitive to the same wavelengths as humans. Instead, they are sensitive to green and blue light, with a third type of photoreceptor cell that’s sensitive to UV wavelengths.

Floral UV Pattern

The UV pattern observable in certain flowers results from a collection of UV-absorbing pigments, like flavonoids, which appear yellow in the visual spectrum. Below is a macro image of the woolly sunflower petals. In the visible light image, it is possible to see the darker yellow pigment that extends out from the center of the flower before transitioning to a lighter shade of yellow at the end of the petal. In the UV image, the cause of the darker yellow pigmentation is shown to be the result of the accumulation of UV-absorbing pigment.

Not all yellow flowers produce UV-absorbing pigment along their petals. The blanket flower is one of these. While the blanket flower still showcases a dramatic bullseye UV pattern, its pattern results from the UV-reflective petals and strong UV-absorbing center.

The presence of yellow in the flower does not immediately indicate a UV pattern. Likewise, the absence of yellow does not mean the flower will reflect UV. Below are images of the subalpine daisy. It has white petals and shows strong UV absorption across the entirety of the flower head.

Red clover, pictured below, is another non-yellow flower that shows significant UV absorption. With pink tube-shaped petals, the red clover does not resemble the typical flower associated with significant UV appearance. However, the red clover relies on pollinators like bees for reproduction – this gives us a hint as to why it has such a dramatic appearance in UV.

The occurrence of UV patterns in flowers still has much room for additional research. Currently, the agreed-upon theory of UV occurrence is that the patterns are a tool for the flower to attract pollinators and act as nectar guides. Patterns signal to pollinators that the plant contains nectar and pollen, then further guide the insect toward the center of the flower. A recent study from the University of British Columbia suggests that the UV pattern may help the flower adapt to weather extremes, like high temperatures and droughts.

How to Create False Color UV Flower Photography

What if humans had similar photoreceptors to bees? So-called ‘bee vision’ has been a popular method of attempting to represent UV photographs of flowers as a bee may see them.

This process would take two pictures: one in visible light and one in UV, by reassigning the visual light image’s red and green color channels, then substituting its blue channel with the UV image.

In the past few years, more research into the visual system of bees has cast doubt that these types of false color UV photographs show how a bee sees the world. They do, however, show how we may see the world if our vision had a different spectral range – and are quite visually striking.

To create this type of image, you need two photographs that are as identical as possible; one visible and one UV. The steps involved are similar to the IR channel-swapping method discussed in part three of this series.

Create a new channel mixer layer in the visible light and UV image.

In the visible light image:

  • Red channel: red to 0%, green to 100%, blue no change
  • Green channel: red to 100%, green to 0%, blue no change
  • Blue channel: red no change, green no change, blue to 0%

In the UV image:

  • Red channel: red to 0%, green to 0%, blue to 0%
  • Green channel: red to 0%, green to 0%, blue to 0%
  • Blue channel: red to 40%, green to 40%, blue to 20%

You can now take the channel-adjusted UV image and flatten all the layers. Copy the flattened image and duplicate it into a layer above the channel-swapped visible light image, then set the opacity of the UV layer to 60%. Merge the two layers. If the photos were aligned correctly, you should begin to see your false color image take shape, albeit with very muted tones. To correct this, Photoshop’s Auto Tone and Auto Contrast options do a pretty good job of adjusting the image’s appearance.

Edited ultraviolet image of woolly sunflower with red petals and vibrant purple tips

Photo 2023 © Nate Rochefort | False color UV image, made by combining the green and red channels of a visible light photograph with a UV photograph | FUJIFILM GFX100 IR and FUJINON GF120mmF4 R LM OIS WR Macro, 1/80 sec at F7.1, ISO 8000

To end, here is a selection of false color and UV photographed flowers, created using the techniques outlined here.

GFX100 IR is a specialist camera designed for forensic, scientific, and cultural preservation applications, and is not available for general sale.

To learn more about GFX100 IR and its conditions for use, visit the dedicated page here. Alternatively, explore the rest of the GFX System and experience the power of ultra-high resolution photography.


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