Newsletter - 2002 Archive

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An experiment

Harold Bridge


Some 6V3W halogen bulbs arrived from CTC yesterday, Friday, June 28. I wondered what improvement in illumination they would give over the normal 2.4W. I also wondered if a camera light meter would pick up the difference. But that required a light tight cone that would fit both the 9cm dia Union headlamp and the 6 cm camera lens. At the second go I allowed a bit more paper and glued the black plastic to the lay out before cutting out and rolling the paper into a cone.

The 85 mm lens was no good, the light was too bright for f16 at 1/1000th sec. Put the 28 mm lens on as it has an f22 setting. Something weird there, it required f22 at 1/30th. I then changed the bulb and the light meter needle was up toward the "+", but not enough for one whole stop. At 1/60th it was toward the "-". So, the difference between the 2.4W and the 3.0W bulbs would appear to be about half a stop.

Possible inaccuracies due to briefly shorting out the battery while dicking about with the connections. Other than that only a finer graduation of light meter would improve upon the experiment.

Now, who's clever enough to convert this info into real-on-the-road terms?