Digital Photography Underground

In response to several enquiries, here are my thoughts/experiences from a few years of underground digital photography, mainly for the production of this site!

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Cameras

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Should be easy to operate, not too fiddly ~ with cold wet fingers.
~ Solid grip ~ so you don't drop it into the void!
~ Manual focus (not hidden deep in the menu) ~ autofocus does not work well underground.
~ Manual exposure with full shutter speed and aperture control ~ some cameras only allow one or two aperture settings.
~ Wide angle zoom and a bright lens (equiv of 28 or 35 mm f2 or 2.8)
~ Hot shoe or sync socket (get flash away from camera) ~ don't use the camera's own flash.
~ Check that you can turn off any auto pre-flash or anti red-eye flash ~ otherwise any secondary (slave) flash guns will fire too early. (See below for slave units).
~ How many pixels ? 2 meg for web, 4 for 1/2 page, 6 or 8 for full page printing. You can print larger for a given size of pixel capture, but there is no increase of absolute detail.
~ What size of memory card ? ~ At least 512 mb, 1 gb is better. Set the quality to its highest jpg setting, and your pictures will be between 2 and 3 mb each, giving around 160 pictures from a 512 mb card.
~ I currently use a Canon G6 (though most shots on this site were taken with an Olympus 2500 or 5050, some others use the the 8080 (no we don't work for Olympus!). Nikon D70, Canon 10 or 20D or Canon G3 are also popular ~ check these out dependant on your budget.
~ For camera reviews, look at www.dpreview.com It has many digi cams reviewed with techie details for those that want them, as well as concise summaries.

Slave units

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Use good proven slave units like the Firefly or David Gibson's designs (he now has one that takes account of auto camera pre-flashes). These units work from the Infra-Red light that all flash guns emit, they work over long distances and even around corners, and are not easily triggered by caving lamps. Try to use the hot-shoe connection as this is more moisture-proof than the little pc socket connectors.

Flash Guns

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I use Vivitar 283 and 285 models. The 285 has a zoom head and variable power, which is useful, but these are hard to find now. Use the hot-shoe connector, via an adaptor, as this gives you more immunity from damp causing spurious flashing. These models seem to be fairly damp-proof. Some flash guns start to trigger spuriously in damp atmospheres. Occasionally I use Metz CL45s (these are bulky, but powerful - get the type that takes NiCad battery packs).

Underground photography tips:

~ Caves EAT light, get as powerful flashguns as you can.
~ Don't use the camera's own flash. Turn it off or cover it with a piece of unexposed, developed slide film. (This will only let infra-red light through, but this is enough to trigger most slave units). Watch out for the "pre-flash" when the camera is on auto (there may not be one on manual).
~ It's tempting to use the 400 asa setting on your camera, but these can give pictures that are too noisy (like film 'grain'). I stick to 100 or 200 asa and use a wide aperture, f4 or so. Cameras with larger image sensors (like dSLRs) don't have that problem, but they are more expensive and bulkier.
~ The replay screen will be your best friend and allow you to check your shots. However, as your eyes will be extra sensitive underground, the screen will look very bright and fool you into thinking that underexposed shots are ok. So from the menu, turn down the screen brightness to about 1/4. If your camera shows an exposure 'histogram' then all the better (but not essential). It's easy to underexpose.
~ Get lots of NiMH rechargeable batteries. These are now available at 2500 mAh, and you will need spare sets for your flashguns, as you will now be taking many more shots on every trip! Also a spare battery for your camera.
~ Before an important trip, give your equipment a trial run underground (or outdoors at night) to get used to it. Study the results carefully, especially focus, exposure and 'noise'.

Books:

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I can recommend Chris Howes' excellent book 'Images Below' ~ A manual of underground and flash photography'. A very complete reference with plenty of real examples explained.

Have fun! Let me know how you get on!

©Peter Collings-Wells
Oct 2004/5/6/7

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