Samsung SLRS manual White balance, Metering, Typical auto white balance settings

METERING, SENSITIVITY AND WHITE BALANCE

Metering, sensitivity and white balance are three key aspects of the way your image looks once you press the shutter button, irrespective of the focus, sharpness or number of pixels you throw at it. Here we will look at key components of the DSLR that make an image look right in terms of colour, image noise and exposure

Sensitivity

A camera’s ISO setting defi nes its sensitivity to light. The higher the ISO, the more sensitive it becomes and vice versa. But

a downside of higher sensitivities is the introduction of image noise (analogous to grain in fi lm) that can adversely affect a shot. Think of noise as interference, just like the ‘snow’ in a badly tuned TV picture. It appears because increasing sensitivity is actually turning up the gain on the sensor. Things that can affect noise include internal electrical interference from camera components, heat and the amount of light. The light is the good signal, everything else is noise, and hence a

good signal to noise ratio is important: the HIGH ISO more light the less noise. This is why noise

becomes more evident in low-light shots. To reduce the effects of noise within your

images, try to use the lowest possible setting for the shot at hand. Set it to ISO 100 or its lowest setting for best overall results. Set your camera’s noise reduction (it’ll be there in the set-up menus) to ‘On’ when shooting above ISO 400. Bear in mind however, the extra image processing required might slow the speed at which the camera can handle the images and may affect detail in the shots, since it tries to ‘smooth’ away the tiny speckles of blue, red or grey that denote noise in a digital image.

Here is a ready reckoner for the use of a particular ISO (sensitivity) and why, based upon typical DSLR sensitivity settings...

LOW ISO	MATRIX OR EVALUATIVE
	These are many small (in some cases over
	200) metering ‘zones’ around the frame that
	are used to intelligently assess and measure
	light from all locations within the frame (based
	on pre-programmed algorithms) to get a
	balanced exposure. This mode is ideal for
	general photography or broader subjects
	such as landscapes or subjects where there
	are no tricky high-contrast areas.
	CENTRE WEIGHTED
	A central portion of the frame (the size of this
	zone can be adjusted on some DSLRs) is
	‘weighted’ to simply measure the average of
	light non-judgmentally, without trying to apply
	any adjustments. Ideal for where you want
	to bias the exposure to the central area, in
	backlit subjects for example. It’s also useful
	in that you can predict how it will react to a
	scene and when it will be fooled, so you can
	more easily compensate for it.
	SPOT
	A very small area of the frame (1%-8% of the
	frame, depending on the camera) that is ideal
	for measuring light from a very specifi c area
	in a scene. Ideal for macro (close-up) work,
	or for portraits (metering from a skin tone) or
	for high-contrast scenes, so you can exclude
	bright highlights/deep shadows (or meter
	from both and apply an average).

White balance

Your DSLR offers a variety of White Balance (WB) or colour temperature settings to combat colour casts from differing light sources. Whether in menus or accessed via an external control it is not always a good idea to leave your camera set to its ‘Auto WB’ setting. The colours may not be rendered as accurately in a shot as needed. To help get the most from any shot, use the correct WB setting for the job at hand: daylight setting for daylight and so on. Moreover, if you are not sure, use the custom setting; DSLRs enable you to tailor the WB quickly and simply to any lighting type.

The typical settings available will include all or some of those set out in the box below, indicated using small icons, text or both. Some DSLRs have

ISO 100

Bright daylight, sunny conditions, hand-held shooting where clean images are a priority.

ISO 200

Where faster shutter speeds are required or slightly longer lenses, or where you need extra fl exibility with apertures/shutter speeds.

ISO 400

For indoor or overcast conditions; or if you want to avoid using fl ash, or need a fast shutter speed/aperture to shoot hand-held.

ISO 800

For overcast or dark indoor shooting, sports or action photography where you need to freeze the motion and some noise is okay.

ISO 1600

Night time, low-light shooting, very long lens shooting; noise will almost certainly become quite noticeable in the shot.

ISO 3200

For hand-held night time or low-light shooting or where high shutter speeds are required. Noise will be very evident in shots.

Metering

DSLRs come with a light-measuring system
or ‘metering’ to ensure your shots are
properly exposed; not too light, and not too
dark, for example. The system is designed
to measure light refl ected from your subject
from either the entire frame (Matrix or Evalu-
ative metering) a central-biased average
of the scene (Centre Weighted), or from a
small spot, usually in the middle of the frame
(Spot metering). You can set the camera to
use whatever metering method you require
to achieve a well-balanced exposure for the
task, but its effect can be altered to suit the
subject (or your preference) by controlling the
aperture and shutter speeds in the manual
modes, for example.
Importantly, many DSLRs have their
focusing zones linked directly to the metering
system, thus providing a very accurate
bias in the metering to whichever AF point
(or points) are in use. This makes accurate
metering from specifi c (often tiny) areas in
a scene possible and provides a great level
of extra control should it be required, if, say,
the camera’s main metering systems are not
cutting the mustard.	Above: One stop over

Typical auto white balance settings

•Auto: General scenes/mixed lighting but colours may not be accurate in some lighting.

•Direct Sunlight: Ideal for bright, sunlit daylight.

•Shade: Best for shade or shots in deeper shadow.

•Cloud: Use for overcast daylight shots.

•Flash: Use with fl ash photos including fi ll-in fl ash.

•Incandescent: Use for atmospheric candlelit images.

•Fluorescent: Use when shooting photos using light from kitchen- style strip lights.

•Tungsten: Ideal for household bulb/lamplight shots and shots taken indoors.

•Custom: User set (see text above) to whatever ambient light is present in any conditions for most accurate colour rendition.

a Kelvin scale for even fi ner tuning as well as the custom mode. The latter allows you to set WB specifi cally for the current ambient light; typically this involves taking a shot (in the custom WB set- up screen) of something plain, fi lling the frame and you know to be white: paper, anything. It does not even have to be in focus. Using the custom method of WB control means no matter what the ambient light, you will always have white whites!

Here is a quick guide to colour temperature using the Kelvin scale and the corresponding (typical) light source. The lower the Kelvin

figure, the warmer (or redder) the colour is going to be. The higher the Kelvin fi gure, the hotter the light source is and bluer the colour.

1,700-1,800k = Match fl ame

2,000-3,000k= Sun: sunrise and sunset

2,500-2,900k= Household tungsten bulbs

3,200-7,500k= Fluorescent lights

5,000-5,400k= Sun: direct sun at noon

5,500-6,500k= Daylight (bright sun in clear sky) 6,000-7,500k= Overcast (cloudy) sky 7,000-8,000k= Outdoor shade

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