Saturday, November 19, 2011

Understanding Exposure

Understanding exposure and the factors that affect it, is key to obtaining beautiful photos that are properly lighted. The settings that will be talked about here can mean the difference between over exposed and under exposed photos.

Is the amount of light that falls on a light-sensitive material. An exposure is made when the shutter curtain opens and light-sensitive material (a film or image sensor) is exposed to light for a certain amount of time.

Circle Of Happy Friends With Their Heads Together Portrait
Portraiture: Group of friends - Image: photostock /
This is a sample of good exposure, even though the background is blown out. The faces of the people, which are the subject in the photo, are properly exposed.

Settings that affect exposure:
Shutter Speed
The amount of time the camera shutter curtain is exposed to light.

A fast shutter speed freezes motion, needs more light. 

Stacked checker pieces hand frozen - Image: graur codrin /
The movement of a hand climbing to the top of a stacked checker pieces is stopped by using fast shutter speed.

Slower shutter speed captures motion, may cause blurry images, needs less light.

Stacked checker pieces with motion - Image: graur codrin /

By using a slower shutter speed the movement of the hand climbing to the top of a stacked checker pieces is captured.

Shutter speed is measured in stops. Starting at 1 second to 1/2 of a second is one stop. 1/2 second to 1/4 of a second is one stop. To understand better, here is a shutter speed one stop chart.

Shutter speed one stop chart

Is the wideness or narrowness of the lens opening. This limits the amount of light that passes through the lens. Aperture affects depth of field, controls flash exposure and ambient light.

Wide aperture (Low aperture value) will give a shallower Depth of field this causes the main subject of focus to be sharp while the background to be blurred. Using a wide aperture produces the popular bokeh effect, needs less light.

Zen stone with bokeh background - Image: zirconicusso /

Girl With Sun Glasses, bokeh background - Image: Witthaya Phonsawat /

Wide apertures are used when you want to isolate the subject by blurring the background.

Narrow aperture (High aperture value) will give more depth of field this means that most part of the image will be more focused, needs more light.

Palm trees - Image: Arvind Balaraman /

Under the sun rays - Image: prozac1 /

Narrow apertures are used in scenes where you want most part or the whole photo to be in focus. This is usually used in landscape photography.

Aperture is measured in f-stops, from f1.0 moving to f1.4 is equivalent to one f-stop. Moving from f1.4 to f2.0 is also one stop. Look at the chart below to understand better.

Aperture one stop chart

Controls the light sensitivity of the imaging media. The higher the value, the more sensitive the media but this also makes the picture grainier.

Low (ISO value), less sensitive to light but more grainy
ISO 400 - Almost no noise at all

High (ISO value), more sensitive to light/needs less light but more grainy
ISO 1600 - Noise is fairly visible

Comparison of ISO noise
Noise comparison of ISO 400 to ISO 3200

Like shutter speed and aperture. ISO is also measured in stops. Starting from ISO 100 to ISO 200 is 1 stop. Moving from ISO 200 to ISO 400 is also equivalent to one stop. Use the chart below to understand better.

ISO one stop chart

Use the Exposure Meter
Exposure meter
Digital cameras have a built in exposure meter which works by evaluating the amount of light on the scene. The built in exposure meter can be seen in the camera viewfinder or LCD. Keeping the meter in the middle usually gives proper exposure. If you’re not getting the right exposure try playing with the exposure control settings: Shutter speed, aperture, and ISO.

The right combination of these three settings is the key to achieving perfect exposure. Good understanding of exposure and the basic settings allows us to know the right combination for various situations.

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