Sunday, January 24, 2010

Project 51

The hardest part of this project was finding some old Tungsten lights and replacing the new low energy bulbs in my office.  I have also noticed looking around for examples of Tungsten lighting that it is becoming very much less common.  My office is normally lit by 7 small spotlights, a mix of LED's and 7W low voltage bulbs.

Now just 5 minutes after sunset, as I moved my eyes from the scene out side the window to the inside of my room I can see a very definite yellow caste that diminishes as I spend more time looking at the the white walls of my room.  Looking back outside the light looks colder and has a slightly blue caste, although this is very much less evident than the yellow caste from the Tungsten lighting. As the light goes down the blue caste is starting to become more prominent.

I have three Tungsten lights in a fitting with 3 spots shining from more or less the center of the room.  The lights are 40W each, so a total of 120W in a room of about 10 square meters.

Using a hand held meter with ISO 100 and f/8 I get the following shutter speeds.

Directly under the lights: 1.6s
Middle of the room: 4s
Darkest Corner: 15s

Even taking the meter right up to the light gives a shutter speed of only 1/25, so a very low light level.

With my widest aperture lens, f/1.2 the best speed at ISO 100 would 1/10s.  As the lens is a 50mm this is far below the level at which I could hand hold the camera.  At higher ISO's I would be able to hand hold and with image stabilization I could do a little better.  My widest full frame IS lens is an f/4 24-105mm.  It claims to have 3 stops of IS, so the lowest practical shutter speed should be around 1/(24/8) = 1/4s.  With a predicted 100 ISO exposure of 4s at f/8, I would need 1s at f/4.  In order to hand hold the lens I would need to push the ISO to 400 and would probably go to 800 for security.

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