Photography & Display

Fluorescent Mineral Photography

A collection of techniques and tips from Mark Cole

Fluorescent mineral photography is a challenge. People (and cameras) usually take pictures of well-lit scenes and rarely have to worry about overexposing an image.

When photographing fluorescent minerals the game is changed dramatically. The camera now has to capture vividly glowing, saturated colors in a dark room.

Cameras just aren’t designed to do this. Some handle it better than others, but most must be tweaked to produce an acceptable image.

Shooting in the dark usually requires long time-exposures of a widely variable subject. Many specimens have multiple minerals fluorescing different colors – some much brighter than others.

For example, one of the hardest pieces to photograph is the classic combination of calcite, willemite, hardystonite, and esperite.

The esperite ( a bright yellow fluorescing mineral) often appears green, the willemite appears white (a bright green in reality), while the calcite might be captured as its normal orange, and the dark blue/purple fluorescing hardystonite might not even be visible.  But with careful attention to camera settings, a few tricks (and lots of hair pulling) an acceptable shot can be taken.

Listed below are some of the most important considerations for successful fluorescent mineral photography, as well as many of the problems people face when first shooting “glow rocks”.  This document assumes that the reader has a basic understanding of digital photography and terms, and is not written to be a guide to using a camera for the first time.

Let your eyes “dark adapt”

You should be comparing the image that you see in the camera (or preferably on your computer monitor) to the real thing. If your eyes are not used to the dark it will be difficult to gauge the proper exposure.

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Focus and focal length – many cameras, especially point-and-click, have difficulties focusing in low light situations. This can usually be solved by “locking in” the focus in white light, then turning off the lights while maintaining the focus (every camera does this a little different – consult your manual).

An additional problem with focus is the distance from the lens to the subject. It may be tempting to fill the viewfinder/view screen with the image but remember that many cameras/lenses have a minimum focal length of around 12” or more (assuming you’re not using a macro lens).

If you move the rock too close to the lens no amount of focus will work and your pics will be blurry. Take the shot at a distance and crop the photo using image editing software.

You can determine the focal length of your camera by using Google to search for the specifications.

For example, search for “Canon Sure Shot minimum focus distance” and you’ll find that the closest you can get to your subject is 2 feet (0.6m). This means that your rock may appear real small in the image, but at least it will be in focus.

Image Quality – most cameras have a choice of settings for image quality/size. If shooting RAW this will set the camera to the maximum image size, but when shooting jpeg you will have a range of choices.

I recommend using the highest (best) setting with maximum file size. This will allow you to take photos of small rocks from the camera’s minimum focal distance (see above) and have a picture that is focused.

With the large image setting, you will be able to crop the photo in an image editing software application such that the result is a reasonable size image which is in focus.  Also, Ebay recommends pictures that are a minimum of 1600 pixels wide; this usually means setting your camera to one of the highest image quality settings.

Composition – This goes hand-in-hand with the above two subjects – focal distance and image quality. Most mineral specimens will be small subjects – around 3” to 5”.

Most cameras must be positioned at least 2 feet from the specimen in order to be able to focus properly. The result is often an image with a small rock in the middle.

Shoot large size images at the highest quality and you will be able to crop the image to size and end up with a reasonable full-size image. Macro lenses improve this situation if your camera allows it, and zoom lenses will also help you zoom in on the specimen (with a corresponding increase in exposure time, lens shake, etc).

All kinds of tradeoffs….

Auto or Manual – I choose manual, always. This allows me to control the exposure time, the aperture settings, and the iso (the three critical settings).

Shooting in auto mode may seem a good choice, but remember that your camera is designed to take pictures of well-lit subjects.  It is not designed to take pics of glowing rocks.

Using manual you have full control of the time exposure, the iso, the aperture, and even the white balance. Invariably, photos taken using auto will have overexposed areas.

If you must shoot in auto mode, learn to use the exposure compensation setting (usually marked by a “+/-“ symbol). By decreasing this setting a few “stops” you can control the overexposures (or increase for under-exposures).

Other ways to decrease overexposure from bright minerals such as willemite, esperite, scheelite, powellite, hyalite opal, etc. is to move the UV light further away from the specimen.

When shooting in auto mode the camera will often automatically set the iso to a higher number because it “sees” a dark subject/field with only a few bright spots. It assumes you are shooting a night scene – perhaps by candlelight, or fireworks (that’s what camera designers target in low-light applications; they probably don’t even know fluorescent minerals exist).

If the camera lets you, set the iso to a low number manually even though the rest is in auto mode. Then you may have a chance of getting a relatively well-exposed shot (plus you will be much happier not having the noise/graininess so often caused by high iso settings).

AND – just because you are shooting in auto doesn’t mean you don’t need a tripod!

Auto mode will probably set the time exposure to a quarter-second or more. Any time-exposure requires a tripod.

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Time exposures – If your camera allows manual shooting you will be able to select the time the shutter is open. This time will vary depending on the brightness of your subject, the wattage of your UV lamp, and the distance of the lamp from the specimen.

Setting the iso will also affect the time-exposure. For my typical shot I set my iso to 100, my aperture to f11.

I use bright UV lamps positioned a moderate distance from my subject. My shots vary from 1 second (for very bright sodalite, willemite, esperite) to 8 seconds for most average minerals (calcite, fluorite, etc).

The color of the fluorescence will also affect this exposure time; greens and yellows appear much brighter to the camera than blues.  Reds tend to saturate more quickly, and blues are often very hard to capture.

ISO – I use iso100. The resulting pic has more detail and minimum graininess.

But of course my exposures are much longer (around 2 sec to 8 sec usually), thus requiring a tripod and some method of triggering the camera without shaking it (I use my computer to control the camera – called tethered shooting; Canon and Nikon DSLR cameras both allow this).

You can set your iso higher and take pics with much shorter exposures (if your camera allows it), sometimes even almost (but not quite) getting away without a tripod. But the resulting pic will usually be of poor quality.

I only use high iso’s when shooting phosphorescent pics.

Shutter control – A tripod is an absolute for blur-free photos when shooting long time-exposures, with minimal iso noise. Some cameras have an optional attachment allowing shutter release without touching the camera.

Most have the ability to trigger a shot and the shutter opens a few seconds later (used to allow you time to join the picture in a group shot) – a neat trick to take a fluorescent pic without the camera moving.

Most DSLRs have an option that allows the camera’s mirror to settle before the shutter is opened, reducing vibration from the mirror movement. If you shoot lots of fluorescent pics, tethered shooting is the only way to go.

Camera stability – Both the specimen being photographed and the camera must be on a vibration-free setting.

Often our UV lights will have fans and if mounted on the same table as the camera and rock, you might see a “softness” in you photos from the minute blur cause by the fan vibration. Of course same goes for vibrations from the floor, pets and people walking around.

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White Balance – I set mine to “auto”. I shoot in RAW format which allows me to adjust the picture (“develop it”) and compensate for the “blue bleed” caused by our UV lamps – often non-fluorescent white areas of the specimen (and other areas too) will appear blue/purple from visible light leaking out of our UV lamps.

If your camera doesn’t have RAW, then set your white balance to the highest setting (usually), or “cloudy” (but even better – get a camera that produces RAW files). The white balance is probably the best tool used to get rid of the dreaded “blue bleed” (other than adequate UV lighting).

F-Stop – If you can set this, play around with it. Each lens has a “sweet spot” – mine works best around f11.

I prefer to get the most depth of field I can so the whole rock is in focus. Remember, the smaller your aperture, the longer your exposure.

Filters – I use a high quality UV filter. Some camera lenses will fluoresce upon exposure to UV causing foggy/blue cast pictures.

A good UV filter prevents this (just make sure the UV filter does not fluoresce – some do).

UV Lighting – Take a look at a white light photographer’s studio; it’s filled with lighting. We need the same thing – the more lights, the brighter your subject.

Of course placement matters, and can be difficult. But I generally go for overkill in lighting.

I also find the brighter the UV light, the less “blue bleed”. Bright UV causes a bright fluorescence and the camera doesn’t have to leave its shutter open for very long – less visible blue gets in.

Today’s shortwave lights almost all have Hoya U-325c filters; the best in the industry. They transmit the maximum UV while minimizing the visible blue bleed.

Longwave lights are a different story – perhaps the most common is the blacklight BLB (the blue fluorescent lights used to light up psychedelic posters). These are not satisfactory for taking LW photos; they simply put out too much blue light.

I use 365nm LEDs from Nichia for my LW pics. Others use lighting with Hoya filters or wood’s glass filters.

Some people use a handheld UV lamp to “paint” the rock with light. Often a large rock cannot be illuminated sufficiently with a small hand lamp so the lamp is waved over the rock while the camera shutter is open, painting every nook and cranny with UV light, insuring a full exposure.

Obviously this takes a little experimentation and great care to not move/bump the specimen or the camera.

I have a light cabinet with UV lights surrounding the specimen, and enclosed on all sides. Thus I don’t have to seal myself inside a dark room.

Some folks commandeer bedrooms with darkout curtains, or even bathrooms with no windows. I know one person who uses the toilet seat cover as the base for his specimens; it produces a subtle dark blue background – very pleasing (but I bet he cleans it real good before each photo session).

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Shooting RAW – I mentioned this above, but it deserves its own bullet. RAW allows you to “develop” the picture in software by adjusting brightness, saturation, white balance, etc until the resulting image matches your specimen to the best of your ability.

Most cameras have special software that allows you to develop their RAW files. Photoshop and Photoshop Elements both support RAW files.

If you want total control over your image, and the most exacting match to reality, RAW is the way to go.

Monitor/display color Adjustment – Figure out some way to calibrate the brightness, contrast, and color on your monitor.

There are web sites that help you do this (http://www.lagom.nl/lcd-test/) to a degree (not the best way to do it, but better than nothing).  There are hardware solutions for perfect results (I use the Spyder line of products for screen calibration – http://spyder.datacolor.com/en/). 

If you take pics with a monitor that is adjusted too dim, the resulting pics will be overexposed, and vice versa for monitors set too bright. You have no control how your viewer will adjust his/her monitor, but you can at least make sure yours is adjusted properly.

If you intend to print/publish the images, color matching is critical and you should probably invest in some calibration hardware.

Windows – The built-in Display Color Calibration tool can improve your display color by allowing you to change certain color settings:

  • Open Display Color Calibration by clicking the Start button, and clicking Control Panel. In the search box, type calibrate display, then click Calibrate display color.‌
  • In Display Color Calibration, follow the onscreen instructions.

Cleanliness – dust and lint are our enemies. White light photographers don’t normally have to worry about tiny hairs and dust, but under UV light they glow bright blue and ruin a photo.

Wash your specimen, brush it, or blow it off – but clean it up for a more professional pic. And make sure you have a brush handy to brush away the crumbs from the previous specimen.

Crystallized pieces can present a huge problem with lint captured in the nooks and crannies. If you plan on taking professional pics consider an ultrasonic cleaner to loosen the fluorescent bastards.

In some cases it may be impossible to get rid of all of the offenders; careful use of Photoshop’s cloning tool can be helpful if you’re really picky. A recent tip posted in the FMS Fluorescent Mineral Group suggested using a MAP torch to burn the lint away.

I tried it – works like a charm (but don’t heat your rock up too much!).

Phosphorescent pics – capturing the phosphorescence of the Winnepeg selenite above wasn’t as hard as it seems. I set my f-stop to f3.5, my iso to 800, and work out the timing of clicking the shutter and turning off my UV lights.

The resulting pic is usually grainy, but gives a good representation of the phosphorescence. A DSLR usually has a delayed shutter/mirror lockup that allows you to adjust your timing based on the noises coming from the camera – play around with it; not really as hard as you might think.

Backgrounds – I prefer a black background. I have seen folks use bright fluorescent backgrounds (hate ‘em) and dimly fluorescent backgrounds (can be very nice).

Some black construction paper will have a dull fluorescence and can make an interesting background.

I have shot on brushed aluminum to get a reflection of the piece with interesting results.  But in the end, I always come back to the solid black background.

HDR – High Dynamic Range – Some newer cameras (and even phones) have HDR where the camera will take several images and average them together to even out the over-exposed spots and the dim spots.

Very helpful, but I prefer doing this manually for best results (I take several photos at different exposures and merge them together in Photoshop – the only way to accurately show esperite mixed with willemite/calcite). Obviously requires some Photoshop skills.

Photoshop – This bears mentioning. PS is a tool to help you match your picture to reality as best you can.

You must be very careful not to exaggerate or change the image. Just make sure it’s real.

Hard rocks – not the café!  Some specimens are a lot harder than others. The classic “hard piece” is calcite/willemite/esperite/hardystonite as already mentioned – but any piece that has a couple of bright minerals along with a dim one will be difficult.

Usually the best approach is to shoot a couple of images – one exposed for the bright minerals and the other exposed for the dim minerals (HDR or manual HDR). But you may not have photoshop, or a camera that takes HDR pics.

In that case your best bet is to expose the bright minerals properly and “explain” the dimmer minerals. Note that many of the newer smartphones have built in HDR and with a little work can be prodded into taking a half-way decent pic.

There are many more things to worry about with fluorescent mineral photography – beyond the scope of this quick and dirty “how to”. Thermal considerations for your camera, CCD noise, iso and highlight recovery, many different software packages that will make your job easier.

Dig in and do some Googling – you never know what you might learn!