The 'secret' to taking good photographs of fluorescent minerals is that there is no secret. Basic rules of photography apply here as anywhere—focus, composition, exposure, and the old adage of ‘practice-makes-perfect’.
One nuance is that these subjects emit their own light; light with wildly varying intensities. The imbalance in intensities may not be apparent, because an observer automatically compensates for it.
But such compensation won’t happen on film or digital CCD.
The typical result then, when photographing a specimen with several fluorescing minerals, is a photo overexposed for one mineral and underexposed for another.
Another related aspect is extreme color distortion: both film and CCD respond non-linearly to color by intensity—as intensity increases violet may shift to blue, red to yellow, green to white, etc.
The solution? Experiment to find the best balance for your setup and the specimen being photographed, while carefully controlling UV illumination to bring exposures within your recording media limits. In short, "bracket, bracket, bracket". In time, the best settings for your particular type of specimens and photo gear will become familiar.
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With good UV illumination and displayably bright specimens, exposures may run from ~1/30th to 2 seconds at ASA 100 for most aperture settings. Tripods (or other fixed mounting arrangements) should always be used when photographing fluorescent minerals.
Digital photography offers key advantages: (1) it allows wide-ranging experimentation with no incremental film cost, and (2) simplifies digital editing. If shooting digital, select the largest image/lowest compression format. You can always reduce size to suit later, but not the reverse. Be wary of JPEG artifacts, especially with red subjects.
Another point worth noting is the oft-mentioned ‘blue haze’. This may occur if your film or CCD is sensitive to reflected UV. Another problem arises if your camera lens itself fluoresces. Check before shooting. A simple solution to both is a non-fluorescing UV filter for your camera.
Note much of what is termed ‘blue haze’ is actually the previously mentioned non-linear response to color by intensity; on longer exposures blue tends to be exaggerated, especially with digital camera CCDs.
For example, a violet fluorescing rock that glows only dimly, if photographed with a camera set for auto-exposure, can result in a stunning blue photograph, but looks nothing like the rock. The camera waits until 'enough' light reaches the CCD, which is clearly too much, and during exposure the greater sensitivity to blue results in major imbalance.
It may look "pretty"—maybe even better than the rock—but it is wrong.
In such cases exposure must be adjusted manually. Shorter exposures/larger apertures—or more UV/brighter specimens will improve the result. If shooting digitally, in addition to exposure and f-stop control, you may also adjust white-balance settings to help compensate for unfaithful color balance.
Remember to wear UV-blocking glasses to protect your eyes when working with ultraviolet, especially at close range when photographing.
STRIVE FOR ACCURACY
Some distortion can be faithfully restored using a good digital photo editing tool, such as Adobe’s Photoshop®. There is a great deal of difference between it and less expensive offerings. I recommend Photoshop®.
When editing, always have the fluorescent specimen at hand to compare actual fluorescence to the image on your screen (or print). Also, note that a truly bad photo cannot be recovered via such methods; they are only useful over a small range. Color calibrating your monitor is also recommended.
The number one rule in ultraviolet photography: Always compare your final result to the actual specimen fluorescing. Make it real = make it good.
WHAT DO I USE?
Ultraviolet photography can be an enjoyable pursuit. To accurately capture the subtle glows of a fluorescent specimen is a rewarding challenge. And take it from me, you can safely ignore most of the techno-blather posted on the subject: anyone can do it. So, grab your camera, lights and rocks and give it a try!