Help with ISO

Started May 15, 2013 | Discussions thread
Deleted1929 Forum Pro • Posts: 13,050
Re: Help with ISO

To understand ISO you need to understand that an exposure setting is the combination of three parameters : ISO, aperture and shutter speed.

Aperture relates to the physical width of an opening in the lens that controls how much light is let through.  Aperture also controls another aspect of image formation called Depth of Field.

Shutter Speed is easy enough to understand.  The longer the exposure takes the more light is captured.  Shutter speed also affects how much motion ( and shake blur ) affects your shots.  Sometimes you want some motion blur, sometimes you want none,usually there's a balance that's acceptable.

ISO in film days related to the sensitivity of the film to light.  A sensor has only one sensitivity and ISO is an amplification setting that amplifies the values the sensor returns.  It also amplifies the noise ( as the sensor cannot distinguish between noise and valid data ).  Raising ISO means you need to light to capture the scene, but amplifies noise.

To understand the relation between these three things in an exposure setting I'd suggest you read these :

And to understand how aperture affects depth of field read this :

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