Smart_Photography_-_January_2016_

change the WB settings? Putting it

another way, how does the camera

change the WB?

To understand how the camera

manages to get you accurate colours

in spite of the light being coloured, try

this out. Take a white LED torchlight

and cover the front with a blue gel. If

you put the switch ‘on’, the emitted

light will be blue. Focus the light on a

white paper and take a photo of that

spot light. The spot will be blue. Now

repeat the shot but this time place a

yellow coloured filter on your camera

lens. What happens? The blue and

yellow light cancel out each other

and the spot will no longer be blue

(assuming that the correct density of

the yellow filter is used).

A similar thing happens in a digital

camera. Let’s say that you are

photographing in a room lit by

household bulbs (incandescent light).

These bulbs emit yellow light and so

your photos will have a yellow colour

cast. When you set the camera’s WB

to ‘incandescent’, the camera places a

virtual blue filter on the lens (virtual,

not physical) to counteract the yellow

light of the bulbs, thus giving you a

neutral image without any colour cast.

Important note: If you set the WB

to ‘incandescent’ for example, the

camera assumes that the light is

yellow. But if the light is not really

yellow, the camera has no way of

knowing that. It will assume that it

is yellow and will place a virtual blue

filter in the light path, thus making

your picture blue. This little trick

could be used to your advantage if

you want to create a moonlight effect

during the day time.

Is there anything else that I need to

know about the WB settings on my

camera?

Yes. And this is very important.

Generally, low Kelvin temperatures

indicate ‘warm’ colours, while high

Kelvin temperatures mean ‘cool’

colours. But on the camera, things

are reversed. If you set your camera

to a low Kelvin setting (say, 3000K),

images will turn out ‘colder’ (blue-

ish); setting the camera to a high

Kelvin setting (say,7000K), images

will turn out ‘warmer’.

and/or very narrow aperture set when

starting the procedure. This is why I

suggested the exposure mentioned

earlier.

Note 3: If the lighting conditions

change during your shoot, repeat the

procedure for a new CWB, which can

also be stored separately from the

earlier CWB.

Note 4: If you do not store the CWB,

the earlier CWB will be overridden by

the new CWB.

About Mixed Lighting

Under mixed lighting, it can be

a nightmare to achieve perfect

colours. If the area in which you are

photographing has varying coloured

light sources, it is impossible to achieve

correct WB for all the light sources at

the same time. In such cases, decide on

the most prominent light source, or the

source that is covering the largest area

of the room in question and proceed

to acquire the correct WB for that

source. Obviously, the areas lit with the

remaining coloured lights will exhibit

colour casts.

Is there any other way to set the

WB?

Yes. If you know the Kelvin temperature

of the light that is illuminating

your subject, you can set the Kelvin

temperature directly on your camera,

if the camera has this feature. Light

meters that read in degrees Kelvin are

available, if needed.

You could also use a White Balance

filter (like the ExpoDisc) to set accurate

WB on your camera. After setting the

camera for a Custom White Balance,

hold the filter in front of the lens and

point the lens to the light source and

take a shot. The image will not be

recorded, but the colour of the light will

store the reading.

Note: Under strong sun, it is desirable

not to point the lens at the sun. Take

the reading nearest to the sun but

without including the sun.

What exactly is Kelvin temperature?

Just as we have Celsius and Fahrenheit

scales that measure temperature, the

Kelvin temperature scale is used to

measure the colour of light.

I don’t get it. How can you measure

‘colour’ of light?

Yes, this calls for some explanation

(which I shall try to over-simplify).

Let’s say that you have a cube of iron

(which, in physics, is referred to as a

‘black body’) which you want to heat.

As the iron heats, we see different

colours in the heated iron. First it

glows red, then orange, then yellow

and then blue before it melts. The

Kelvin scale provides a numerical

value to each of those colours so that

when you mention a particular Kelvin

temperature, you know what the

colour of the heated black body would

be.

At 1500K, the colour emitted by the

heated black body would be yellowish,

which is compared to the yellow of

a candle flame. At 5500K, the colour

emitted by the heated black body

would be similar to the colour we

see at around noon. Between 9000

• 10,000K, the colour emitted by the
  black body would be similar to the
  colour of north blue sky.

So, the Kelvin scale allows us to

compare the colours we see on a

daily basis, to the colours that would

be emitted by a heated black body at

different temperatures.

I am curious to know what changes

take place within the camera as you

Expodisc White

Balance filter

LEARNING

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Smart Photography January 2016