ISO, ASA…it’s the sensitivity of your camera sensor or film
The birth of digital has really brought the ISO to life. In the days of film you could buy different sensitivity of film, usually 100ASA*, 200ASA or 400ASA with 400 being the most sensitive. If you wanted to change ISO sensitivity (or ASA) you had to change film. Now with digital is it done with the turn of a dial…great!
*ASA is the same as ISO for all intents and purposes, they are just different standards organisations.
A more light sensitive film or sensor means you can use faster shutter speeds in low light reducing camera shake. Good for floodlit sports, weddings or other situations where you cannot use flash.
However, this excellent functionality comes at a price…noise or grain. High ISO or ASA film of say 2500 and higher would give a more grainy effect to images and it is the same with digital.
When using high ISO’s, the extra light has to come from somewhere and when the sensor adds it, it also adds digital noise. This is the same in video as well as photography. Again, as an experiment try this…
When lying in bed at night with the lights off, allow your eyes to adjust to the darkness and look around concentrating on the darker areas. You should see “noise” even using your eyes which have had millions of year’s evolution to deal with this!
As time and technology progress, we are actually starting to beat nature at this game as modern DSLR’s are producing much “cleaner” images in low light. Also, you are able to reduce this noise using excellent software such as Neat Image which I personally use for weddings.
You can see a full review of Neat Image here.
So remember that a change in one setting (shutter/aperture/ISO) will require another change elsewhere to compensate for the difference in light hitting the film or sensor.
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