In order to judge “white” the camera needs:
- a white object in frame
- white light
Humans do a pretty good job of interpreting white. We have knowledge that cameras don’t. We recognise the objects for what they are and this gives us hints about the colour we expect them to be. But even we struggle sometimes; the colour of cars under sodium street lighting for example.
I’ve found that it’s often best to set white balance manually, though this needs care too. I have on occasion set the camera to daylight when I should have chosen cloudy, resulting in a blue cast across images. Auto generally seems to work well when flash is being used.
The PRE setting
The D300 has an excellent tool in helping set white balance. By setting white balance to PRE and then d0 you can take a measurement of “white”. Upto 5 white balance measurements can be stored and named. This is a really handy feature. I have measurements for rooms around the house so that they can be quickly recalled.
The K setting
Sometimes you won’t have a white object to measure off. By setting the camera to “K” you can force the white balance to anything you like. The default value is 5000k, which is sunlight. I used this setting to take the photo above. I wanted to capture the true colour of the light without the camera trying to correct it.