Tuesday, February 22, 2011


This article below was a casual writeup by me on Clubsnap forums, where it first appeared. I was writing a reply to (Sam Goh) my brother-in-law's post in his thread where he was asking for some guidance in using his Canon G12.

Higher ISO [ more sensitive to light, allow for bigger apertures (smaller F numbers) and shorter (faster) shutter speeds to achieve the correct exposure ]
However, as ISO goes higher, your picture will turn out less sharper.
Lower ISO will result in sharper images.

Higher F numbers (aka smaller apertures) will result in sharper pictures but will require shutter speeds to be longer to achieve the correct exposure.

Faster shutter speeds will prevent handshake blur and reduce subject motion blur but will require an decreasing F number [ larger apertures ] in order to achieve the correct exposure.

On the other hand, slower shutter speeds is sometimes preferred to capture the motion blur intentionally [ ie moving headlights on road at night ]

This formula served me well

Perfect exposure = (F number)/(Shutter speed)
ie Shutter speeds are inversely proportional to the aperture.

And if the metering system of the camera still shows that the pic is under or over-exposed when u have reached the limits of both the apertures and shutter speeds of the camera and still unable to achieve the correct exposure...

It's time to up the ISO.

My advice.
indoors during the day : ISO400
indoors at night with fluorescent lighting : ISO800 (ISO400 if using external flash)
outdoors during sunny day : ISO100
outdoors during overcast day : ISO200
outdoors during night : ISO800 and above depending on intended exposure time(shutter speed) and flash or non flash
For long night exposure outdoors, can try ISO100 for landscape with long exposures.

Last but not least,

Taking a photograph is like filling a bucket of water..[ aka achieving correct exposure ]

How long you wanna open the tap for [ shutter speed ] 
What is the diameter of the water pipe outlet [ aperture ]?

The 2 critical factors and have different values and will eventually fill up the bucket..

The only question left is how fast you wanna fill it up.

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