The excellent 'Underground Reflections' and other photos on the aditnow site has prompted me to experiment with LED illumination rarther than flash. The advantages of LED lighting appear to be more controlled light and more 'natural' colurs than flash photography. The disadvantages appear to be the need to use a tripod, long exposure (people need to keep still and moving water gets a glassy effect).

A recent example of my experimentations are shwon below:

[photo]Personal-Album-242-Image-31725[/photo]
Flash illumination

[photo]Personal-Album-242-Image-31726[/photo]
LED illumination (F5.6, 15 secs, ISO 100, Fenix TK10 LED)

The two main questions that arise with LED illumination are the brightness of LED to use (EG TK10 type light with 200-250 lumens and a long exposure or a very bright super lamp such as this one on ebay:

http://cgi.ebay.co.uk/ws/eBayISAPI.dll?ViewItem&item=270364896979 

Has anyone got one of these?

So for the LED photographers out there; what sort of LED lights do you use and what are your recommendations on exposure times etc.

Martin

Yes I use one of these flashlights, I find it excellent for both smallish areas & huge stopes, as the torch has 3 settings, 2 leds,4 leds & all 6 leds. It's only a relatively small torch & easy to carry round & lasts about 2 hours in full use.

I use similar exposure times to your example, though in some large stopes will go for 1 minute , how ever a recent change in my camera from a nikon 5400 to a nikon 8400 has thrown up some issues with the dreaded purple fringe, as was recently discussed on here.

One point I have noticed is the white balance, if I leave my camera on auto, everything is a little blue, so have tended to use daylight now, I find the colours with my cameras more natural.

Still finding my feet a little with lightpainting though, like yourself was used to flash with the old film SLR's, but recent results are encouraging.

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I just use a Fenix T1 torch, I think its about 200 lumens, discontinued now but I think the TK10 is the same, combined with a Stenlight. Also I use cheapo Tesco led torches for positioning in tunnels for backlighting but the cheaper torches seem to have a bit of a blue cast.

Exposures for long tunnels tend to be f5.6 for 30 seconds, maybe 20 seconds depending on size of area, and always at ISO100. However I recently started taking a remote release and experimenting with shutter speeds over 30 seconds.

I mainly use a Fenix P3D (215 lumens) which is very small, robust, waterproof and reliable.
I use a Canon DSLR and usually leave it set on f8. Exposure times vary from a couple of seconds for close-up subjects to a couple of minutes for big stopes, but mostly in the 15-25 sec range for general pics in metal mines.

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The choice isn't only between flash and LEDs. In general I'm using a 50w xenon bulb, which seems to give a nice colour cast. (To my eye anyhow). The disadvantage is the 3+ kilo weight. However, it gives 1.5 hours of 1500 lumens.

Depending on the size of the place exposure times seem to be around 8 seconds or so.

The problem can be too MUCH light, especially if concentrated in a spot. The work around is to use a diffuser (baking parchment is good). Or to tone down the reflector by lining it with tin foil. The standard photographer's trick would be to smear the glass with Vaseline. Haven't tried that, as I think if you whipped out a pot of Vaseline underground, well, things might get a bit messy 😮

With regard to white balance there isn't a single good reason not to shoot everything in RAW, if available. If you're shooting jpegs, then most decisions about how your photos look are being made by a bunch of software engineers in Japan, not you. RAW also gives a good degree of latitude in the exposure. So that a good deal of under/over exposure can be brought back.

Hope I haven't diverted too far away from LEDs 😞

A good side by side example there mcrtchly.

Was the aperture the same on both? If it was it's interesting to see how foreshortened the flash example looks in comparison. I realise the angle is different and the flash example looks as if it was closer to the subject, but there's a lot more depth to the LED lit photo, probably further emphasised by the shadowing effect in the roof which the flash has lit uniformly.

On that point, I find if photographing a passageway you can get this shadow effect highlighting irregularities in the rock by shining the light down the floor, walls and roof, effectively tracing the outline of the passage rather than by random waggling.

Another interesting point is that the colour temperature of LED lights does vary quite a bit, anything with a Luxeon LED for example is whiter than P4/Q5 emitters and as BigLoada says the cheaper torches have a blue tint.

Avoid spot burnout by using a timed shutter release so the shutter opens a few seconds after you've pressed, that way it's not opening whilst your accidentally training the torch on a spot.

All that said, well positioned flash and particularly open flash can yield some stunning results and are some of the sharpest u/g shots I've seen. But nobody can stand the time taken to set it up on an exploring trip!

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