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10-15-2008, 03:58 PM   #16
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Lowell, if you try high speed burst with the K20D with fluorescent lighting, you will see different colors in the pictures due to the flickering of said fluorescent. Just try different shutter speed, and you will find some places where the white balance has sudden shift. It's been demonstrated many times before.

10-15-2008, 04:01 PM   #17
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interesting, as I said, never seen it myself and have done tons of shots under fluorescents with *istD and K10D
10-15-2008, 08:44 PM   #18
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the change of colour happened to me when shooting at high speeds even with my old Nikon D80. that's a reason why i almost always shoot with custom WB when in artificial lighting. another is mixed lighting can confuse the camera's AWB. and it's also so i don't need to adjust WB in post-processing (especially if i'm shooting jpeg)
10-16-2008, 12:30 AM   #19
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The lights over the ice surface are 1000 watt Metal Halide (clear, non coated). If you have ever watched an HID lamp first fire, and come up to temperature (it can take up to 4 min to reach full brightness and fall within proper colour temperature), and watch the lamp cool down when the fixture is de-energized you will see that internal arc tube has mass and does not react as quickly as one would think (but camera shutter speeds can be very fast and may be able to capture subtle differences). When the lamp is cold and first fired its resistance is at its lowest. As it reaches proper operating temperature its resistance is at its highest. You can measure the voltage and see the voltage drop across the lamp increase as it heats up. Somehow I do not think tha the arc tube could react to the changes in a big way and would tend to average the effects of frequency.
The arena does have a lot of florescent lamps (in all the signage and concession areas). I remember watching a program once that demonstrated what a florescent fixture would look like to a fly (the fly would see the light flash on and off 120 times a second). Other than preheat elements at the end of a florescent lamp, the tube does not rely on a heat tungsten filament to produce light.
This question about colour shift based on frequency (120 alternation / second) should be solved by the K20D in 20fps burst mode and a colour card illuminated by a HID fixture. I think I have just found something to try at work during my lunch break...... ya thats when it will happen.... at lunch I will also place an oscilloscope and view the wave form of the supply at the lamp (these fixtures place a capacitor in series with the lamp

Here is a snip of an article that I copied from the web (too lazy and late for me to have written it all out - thanks to the original author)

CWA - Constant Wattage Autotransformer ballast. This is a lead type circuit and is used in most modern HID lighting systems. This ballast type consists of a high reactance autotransformer and capacitor in series with the lamp. The capacitor forms an important ballasting function, and allows the lamp to operate with better stability under fluctuating voltage conditions. It is the most efficient circuit, and hence most popular.

Last edited by spyglass; 10-16-2008 at 08:45 AM.

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