[SI] Heat - my shot

(Might be multiple posted ... probs with server)


I did a few different sets of shot for heat and selected the
presented shot as the most appealing for several reasons...
http://www.pbase.com/image/33170478

Like Vic, I shot a lamp (a small one, very close with a macro
lens). http://www.aliasimages.com/images/Lamps_0001.JPG

I didn't like these shots very much, because even at the lowest
exposure, the "bleed" from the light was excessive. I think the
right way to shoot a lamp filament is to drive it with a much
lower than design voltage so that it glows rather than burns.
The second problem I had was that the glass had bubbles and stuff
on the inside that caused terrible highlights during the filament
on shots:
http://www.aliasimages.com/images/Lamps_0002.JPG

So the shot here is a storm candle shot with a 100mm f/2.8 macro
lens at near 1:1. What I wanted to bring out were the orange
"embers" of the tip of the wick and the blue (~3000 deg C) of the
parafin burn at the bottom.

Heat? I searched the web and found that candles output a range of
power depending on several factors, most important of which is
the wick size. Not content to just use a web reference, I
measured the heat output in a simple kitchen experiment. I used
the candle to heat 500ml of water over 15 minutes. The temp rise
was 12 C, (500ml * 12 * 4.1868 j/cal) = 25,121 joules (W-s) ...
over 900 seconds that comes to 28 Watts. I suppose that doesn't
account for the heat stored in the vessel floor and lower walls
(a 1 kg coffee can) so a few watts probably can be added to the
28 watt figure to account for that and other losses.

Cheers,
Alan


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