Saturday, October 29, 2011


Photography Basics - Exposure / Aperture / Shutter Speed / ISO

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Getting the right exposure

Getting the right exposure for a picture is like filling up a cup of water. In this example, think of photography as filling a cup of water to the right level. We can adjust the tap opening, the time collecting water, and the size of the cup, to achieve the right level of water in the cup.

Aperture as a tap,
Shutter speed as the duration of time the cup is under the tap collecting water,
ISO as the cup, and light as water.

You want to fill your cup just right (right exposure), as too little water (underexposed), or too much water (overexposed) in your cup is not good.

.A smaller aperture has a small water flow, and a large aperture has a large water flow

The tap with the smaller aperture fills the cup slower as compared to the tap with a large aperture
 ISO is like the size of the cup. The smaller the cup, the faster it will fill up

What is aperture?
The definition of aperture is a opening in the lens, that light can travel through it. It is measure in f-number and we describe aperture by saying if it's large or small. A larger aperture will allow more light to enter the camera, and a smaller aperture will allow lesser light into the camera.

However, when being expressed as numbers and figures, a larger aperture would mean smaller f-number (e.g.: f/1.0, f/2.8) and a small aperture will mean a larger f-number (e.g.: f/20, f/22)

Aperture controls the amount of light that enters the camera and affects time taken to exposure the picture correctly, and depth of field (background blur).


To achieve the background blur (also known as Bokeh), I set the lens at a large aperture of f/2.0. The properties of such a photo are: A fast shutter speed (1/6 seconds), and a really nice background blur. A large aperture is normally used during portrait and macro photography to bring out the subject from the background.

In the second photo, the background blur is not as visible, because a small aperture of f/22 is being used. The properties of such a photo are: A much slower shutter speed (15 seconds!), and an overall sharp photo. A small aperture is normally used during landscape photography to capture all the details of the landscape.

What is shutter speed?

Shutter speed (or exposure time) determines the amount of time, measured in seconds, that the sensor is exposed to light. Most of us would relate the shutter speed to the brightness of the photo, which is not wrong, provided the aperture and ISO settings are kept the same.

1/60 Seconds, f/1.8, ISO 100
1/10 Seconds, f/1.8, ISO 100

The 2 photos above show the effect of exposure on the photo under the same settings and light condition. Typically, a faster shutter speed (1/250 seconds and below) is used to freeze moving objects such as sports and flowing water. A slower shutter speed (1/2 seconds and above) is used to create a sense of motion in moving objects, and make water look silky.

Always getting blur pictures when shooting handheld? A good rule of thumb to get sharp pictures when shooting without a tripod is to use the formula: Shutter speed = 1/focal length. (for example, if focal length is 50mm, then minimum shutter speed should be 1/50 seconds)*

*This rule generally applies to lenses/camera without Image Stabilizer (IS) or Vibration Reduction (VR). Lenses/Camera with IS or VR can shoot at much slower shutter speeds than the rule of thumb recommended.

What is ISO?

ISO is actually a system that is used to measure the light sensitivity of sensors. A lower ISO means the sensor is less sensitive to light (lowering shutter speed), and a higher ISO means the sensor is more sensitive to light (increasing shutter speed).

An increase in ISO will give you a faster shutter speed. For every fold increase in ISO, the shutter speed is reduced by half (e.g.: A photo is taken at ISO 100, 1/10 seconds, if taken at ISO 200 will only take 1/20 seconds). So why are we not using maximum ISO every time we take a photo? Isn't faster always better?

 ISO 100, 1/6 Seconds, f/2.0
ISO 12800, 1/800 Seconds, f/2.0

Not quite. Because an increase in ISO will also bring about an increase in the grains (noise) in the photo. In the 2 photos above, the photo taken at ISO 12800 is clearly more grainy than the photo taken at ISO 100. Nobody loves grainy photos. We all want to capture that professional clean and sharp photo, right? Try shooting at the lowest ISO setting possible unless the shutter speed is too slow and pictures start to have unwanted motion blur.

Sum it up!

I hope that sums up the 3 fundamentals of photography; Aperture, Shutter Speed, ISO, and how it all work together to bring you the right exposure.


  1. I was thinking about doing a tutorial similar to this for my webpage but you've summed it up beautifully!

  2. Thanks a lot.Love the post. May God bless you.