White Balance

White Balance is a very complicated and wide topic. In the old days, during the film era, people require color filters to adjust the white balance in films. But today, it becomes an Automatic feature in a digital camera. An expensive DSLR will be equipped with a more sophisticated algorithm (program codes) to identify ambient light to select a more accurate WB for it.

But take note, WB affects almost every little setting you tweak on your camera, especially those who love high ISO, slow shutter speed, wide aperture and flash. I will talk about this in the advanced flash topic.

White Balance are measured by Kelvin (read this on why it's called Kelvin), measuring from 2000k to 10k (not all cameras are capable to reach full scale though, some can only set from 2500K to 9900K)

2500K - very strong orange tungsten light
2800K - strong orange tungsten light
3200K - yellowish tungsten light
4500K M6 - flourescent light (most flourescent tubes are green even though our eyes don't see it)
5500K - flash (depending, some flash manufacturer is 5800k or 6000k)
6500K - daylight (or daylight-balanced flourescent light)
9900K - strong blue stage lighting or evening light

Pre-set White Balance

Let's talk about presete WB mode first, and AutoWB later, because it has indirect involvement with preset mode, so let's get the basics of preset mode first.

Commonly a DSLR will have 6 preset WB. (some has more, which i will not talk about it because all this info you can get from the camera manual book.)

The 'it' here refers to the camera.

• Daylight
where it reads more blue under the sun, and turn the Kelvin high to balance back (6500K-7000K)
• Shade
where it will ignore the skyblue (more blue tint) and use appropriate WB for under the shade (usually 6000K)
• Cloudy
where it will ignore the sky and use appropriate WB for under the shade (usually 5000K)
• Tungsten
under normal tungsten lighting condition, it's preset to 3200K. It won't go below to 2500K
• Fluorescent
as mentioned above, most fluorescent tubes are green even though our eyes don't see it (4500K M6)
• Flash
it will lock at 5500K because the flash light is at 5500K (or other temperature depending on the flash manufacturer, eg. Nikon)

Automatic White Balance AWB

Now, for the AWB. AWB does not automatically scale from 2500K to 9900K, it will not. The current technology/algorithm AWB will only allow to pick from the preset WB. (but correct me if i am wrong, because i dont own a professional body like the nikon D3s so i do not know if Pro body does automatically scale from 2000 to 10k)

So when it meets a tungsten lighting ambiance, it will only be able to select the preset tungsten WB. It also means that the lowest Kelvin it can go is 3200k. hence if you are in a very strong tungsten lighting, your photo will still turn out very tungsten-ish (orange-ish), its not a good or bad thing, because some people would love to show others how nice the ambiance light is. but for product shooter, or serious event shooter, it is still a wrong white balance. they will go custom and set it to 2500k if requireed to do so, or shoot in raw and PostProcess it later.

So when you pop up the flash, it will automatically switch to flash WB lock at 5500K. So even if you are in a tungsten lit room, the WB is lock at 5500k, it will not turn to tungsten WB at 3200K, because your 5500K flash will turn out blue. another key issue is that the area that is not lit by the flash, it will be in very deep tungsten orange color (eg. background will be very tungsten-ish). So many of you will surely captured photo in restaurant with clear subject and really tungsten background. it is normal.

Same goes with an external flash being mounted on the hotshoe. the AWB will lock at FlashWB 5500k.

I did mention that White Balance is a very wide topic, but this part seems short to read, well, i have not added the Flash and environmental issue yet, this will all be discussed in another advance topic.