help me out pls - ISO


TPF Noob!
Jan 11, 2008
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Hi, what does ISO do and stand for?

I know the higher the ISO the sharper your shots are... I think? and theres something about theres extra noise when you turn your ISO up? How exactly does this work and when would you recommend using high ISO instead of AUTO mode?

"What does ISO ... stand for?"

Freedom, equality, fraternity?

ISO stands for the International Standards Organization, also known as the International Organization for Standardization. The committee responsible for photographic standards is led by ANSI, the American National Standards Institute, which used to be called the ASA, American Standards Association. Many older photographers will be familiar with ASA speed designations, now known as ISO designations.

That tutorial has a few minor errors, two of which might be worth mentioning.

ISO speeds for still photography are defined in ISO standards for colour negative film, colour reversal film (“slide film”), monochrome negative film and digital cameras, not just for colour negative film. The ISO speed setting on a digital camera should be a true ISO speed, not just an ‘effective’ one.

The ISO could be called the 'sensitivity' of the film (or digital sensor). The higher the ISO, the more sensitive it is to light (the higher the ISO, the less light you need to make an exposure).

Exposure is controlled by three main things. Shutter speed, aperture and sensitivity (ISO). So if you change one, you can change one (or both) of the others or else it will alter the exposure.
In practical terms, it means that if you want a faster shutter speed, you can turn up the ISO.

A slow shutter speed is often a cause of blurry in this case, turning up the ISO can give you a faster shutter speed...which may give you sharper images.

However...there is a trade off. The higher the ISO, the more grain or noise you will get. With film, it was because of larger bits in the film, which would show up as film grain. With digital, a higher ISO means that the signal is amplified, which causes distortion and this distortion is manifested as digital noise.

So the rule of thumb is that you want to use the lowest ISO possible...unless it becomes necessary to raise it, in compensation for a faster shutter speed or a smaller aperture.

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