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Let me try to explain this in layman’s terms.
Let’s turn our attention to gravity, for a moment. Gravity is what our life is based on, from how we measure our weight to how far a car will stop within a given speed, from air travel to sea travel, from the tides to the weather. Without gravity we wouldn’t exist.
In the same, (but much smaller), way, white balance is calculated to provide the basis for the camera to work from regarding exposure. Once this base is established, then we are able, using the camera’s controls, to either over or under expose to suit the lighting conditions to get a well exposed image.
Similarly, once experience is gained, manipulating the exposure for artistic effect is possible.
May I ask the question. How many times have you taken a photograph only to find it has a red/green/blue cast to it? Do you know what’s caused it?
The answer is incorrect white balance for the given light at the time of shooting.
In simple terms, light is made up of the seven primary colours seen in the rainbow.
Your camera only deals in red, green and blue. These colours are present in different proportions in all light sources. For example, tungsten lights have more red in them than fluorescent lights, which are greener. This proportion of colours is measured as the colour temperature.
Our eyes and brain make a wonderful combination. When we look at a white object our eyes will automatically adjust to the lighting conditions, so that the object appears perfectly white to us whether we are indoors under a tungsten bulb, a fluorescent tube or out in the bright sunlight. Not so with a camera. Fluorescent light has a deficit in the blue range of visible colour in the spectrum returning a green hue to the image. Tungsten will return a red hue to the image.
White balance is the process of giving the camera a helping hand, so that it can reproduce the whites in the photo as they should be. Once it gets the white right, all the other colours in the scene fall into place, and we're left with an image that perfectly reproduces what our eyes saw.
Camera manufacturers know that their Automatic White Balance (AWB) setting doesn't always get it right, so they also include several white balance presets for us to choose from.
Typical white balance presets include Daylight, Shade, Cloudy, Tungsten, Fluorescent, and Flash. These work exactly as you'd expect -
For situations where the white balance presets won't do, most cameras also come with a Custom White Balance setting. In this mode you begin by taking a photo of a white object (a sheet of white paper or a professional white balance card) under the lighting conditions of your scene.
Then you just tell your camera to use that image as its white balance reference, by going into the menu and selecting White Balance Preset Manual, from the shooting menu, (Nikon). The options given will be ‘Measure’ and ‘Use Photo’. If you select ‘Measure’, you will need to take a shot of the white card. If you select ‘use photo’, use the shot of the white card taken previously. The shot must be taken under the lighting conditions you’re shooting in.
Then all photos taken under those conditions will come out correctly balanced. Remember, you have to reset the white balance when you start shooting in daylight again. That said, follow the section regarding the Grey Card, below.
Paradoxically, you can achieve exactly the same with a professional grey card.
A grey card is designed to help photographers to adjust their exposure and white balance settings consistently by providing a reference point. This reference point will set a white balance, or colour balance, point for a particular image set and all images captured thereafter. We aren’t talking about the colour from the scene that has been reflected through the lens, rather than the actual colour of the light you are shooting in.
Essentially, the grey card works because of its lack of colour. Grey is a neutral tone, and even though there are many different shades of grey, the grey used on a grey card is considered to be a “middle grey” (18%),. The middle grey hue makes it easy for the camera to understand a given lighting situation and prescribe the best solution.
In exactly the same way as the white card. You photograph the grey card under outdoor daylight conditions, then follow the same instructions as above.
In Auto shooting mode, the camera automatically, and tonally, searches for this medium grey hue in a scene in order to determine the right exposure and white balance.
This is also how the camera determines the correct white balance when you set the white balance to Auto.
Incidentally, if you are shooting in RAW, the white balance isn’t quite so necessary as you will be capturing exactly what’s in front of the camera. The white balance adjustments are made in post processing.
The quality of daylight, for the purposes of photography, changes as the day progresses. The more atmosphere the light has to travel through, the softer the light is. So the hour after dawn and the hour before sunset are known as the golden hours, as the light is at its softest.
As the day progresses the light becomes harsher producing very strong shadows, to the point where taking a photograph in direct sunlight between the hours of 11.am and 3.pm will result in a harsh flat image, especially in the tropics.
This needs to be recognised when out with the camera. Wait until there is a cloud covering the sun before taking the shot, or get somebody to stand so the subject is shaded. Taking a before and after photo will really show the value of what I’m saying.
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