Help with exposure on a 7D

Started Jan 17, 2013 | Discussions thread
Matt
Senior MemberPosts: 1,899
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Re: Help with exposure on a 7D
In reply to Sailor Blue, Jan 18, 2013

Sailor Blue wrote:

bluestreakrem wrote:

TTMartin wrote:

I doubt a gymnasium was lit with tungsten lights.

Mercury vapor, florescent, or sodium are more likely.

You are correct...........My mistake.

They were the large Sodium Vapor bulbs. I remember looking up at them now. I was trying different white balances as I was trying to fiqure out what was causing the problem and Tungsten stuck in my head as the best looking balalnce so that's why I thought they were Tungsten.

I didn't realize S. Vapor lights could produce that problem. The white balance change does not occur EVERY other shot in a string but it does occur at some point in EVERY string of 5-6 shots. Sometimes twice in a string of 5-6 shots. The time frequency of the light temp change was random and erratic.

My sister was shooting her 3ti at the same time so I'm going to check with her to see if her camera produced the same white balance issue.

The lights were probably high pressure sodium lights. These light extinguish at the line frequency. As the lights turn on or off the color shifts. At your shutter speed you were occasionally catching the lights turning on or off.

http://en.wikipedia.org/wiki/Sodium-vapor_lamp

The only way to get consistent color with this type of light is to shoot at shutter speed equal to or longer than the reciprocal of the line frequency, i.e. at 1/60 sec or longer in the US.

yes or manual white balance

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