you may have heard the term 'ISO-9001 certified' before in some boring business conversation or seen it stamped on a big business ad somewhere. ISO stands for international standards organization. they set guidelines and absolute measurement scales for things so everybody can be on the same page. one day, long ago, cameras used to have this thing called "film". it was a thin plastic-like material that you shoved inside the back and the picture was saved onto it. this so-called "film" had speed ratings, which were measured in ISO numbers. the speed of the film was actually referring to how sensitive it was to light. the higher the number, the more sensitive the film, the quicker it could get enough light to expose properly which would allow you to shoot in low-light with faster shutter speeds. remember shutter speed? conversely, a low ISO number like 100 would be pretty insensitive to light. this would be the stuff you'd load into your camera if you were shooting outdoors on a bright sunny day.
ok, who cares, no one uses film anymore, right? that's pretty much true for 99% of people. we still care because digital cameras also have an ISO setting. in our fancy shmancy digital cameras there is a "sensor" that captures the image rather than using a roll of film. the sensor gets blasted with photons of light when the shutter opens and it records the intensities of the photons on each tiny subsection (these subsections of the sensor are called pixels - more on this in the future post about resolution). the ISO parameter controls the sensitivity of the sensor, the parallel of the film speed in analog world.
still wondering why you should care? i've talked to a few people who say their pictures keep coming out "grainy" or "blotchy". this is referred to as "noise". i will spare you the origin of the term or else i'll start talking about least significant bits and resistive ladders and delta-sigma modulators. generally the higher the ISO, the more noise will be introduced into your photo. noise most typically shows up as pixels being blown out completely. in addition, at very high ISO levels there can be severe color degredation and other negative effects. if your photos look real bad, check to see if your ISO is manually set high. keep in mind that the better the camera, the more capable it is to produce clean photos at higher ISOs. if you're shooting with an entry level dslr, you probably will start seeing degredation once you pass ISO800. with a point and shoot you'd want to have it set to auto and let the camera calculate what it needs. the exception to this rule is if the camera keeps producing poor quality photos because the flash is off, there's not enough light, and the only option it has is to jack up the ISO so it has a prayer of exposing the picture properly. in this case you'd probably want to enable flash so the ISO can be reduced.
here's an example of a clean image shot with ISO200
here's an example of a noisy image shot with ISO6400
the easiest place to see the difference is on the hardwood floor and the back wall. coloration varies between the photos and most textures appear pixelated. the differences are easier to see when the photos are larger.
now you know about shutter speed, aperture, and ISO. these are the big three for cameras. go mess around with your camera - the only way to learn is to try. good luck, and let me know if you've got any questions...
unrelated useless info: the bench cushion and the pillow in the forefront in these pictures was handmade by my lovely wife tara and the bench itself was built by yours truly. maybe i'll start bluefurniture if i find enough spare time.
next up: white balance