ISO?

It is the film speed or sensitivity to light, i think typical values are 100, 200,400,800,1600,3200 and 6400. The higher the ISO number is the faster the film reacts with the light, and so you can get the same exposure with less light if you use ISO 1600 compared to ISO 100. This can be an advantage in low light situations or where you want a high shutter speed to freeze the action. The disadvantage to this however is that as it is more reactive to light, there is more noise picked up and images can often apear grainy whn using films with a higher ISO speed.

In digital cameras there is settings you can use to change the ISO speed, rather than having to change a roll of film in a camera.

Thats my understanding, I'm sure if i'm wrong or missed anything out someone else will correct me. Hope that helps :)
 
ISO rating on a digital camera is essentially an indication of how much the signal on the sensor is being amplified, so that the exposure would be the same as it would have been on a film camera with the same ISO rated film.

In the film days, ISO was an indication of film sensitivity, with higher sensitivity as the number went up. The numbers went something like ISO50, ISO100, ISO200, ISO400, 800, 1600, etc (some intermediate steps too, like ISO640). Twice the ISO number means the film was twice as sensitive, requiring either only half the shutter time or half of the aperture size to have the same brightness (exposure).

In the context of digital cameras, the ISO number indicates how much the sensor has to amplify the amount of light actually hitting the sensor surface. Higher ISO means the sensors are amplifying the signal more (in order to provide a brighter picture with less light actually hitting the sensor), which generally tends to result in "noise" as a result of the poorer S/N ratio.

On a D-SLR, you can generally expect acceptable or even good results up to ISO1600, but on a compact digital, you are unlikely to get decent results with anything higher than ISO400 (although some of the newer models seem to make a point of emphasizing "ISO1600 capable" etc, and some models are definitely better at higher ISOs than others).
 
Evil-Penguin said:
It is the film speed or sensitivity to light, i think typical values are 100, 200,400,800,1600,3200 and 6400. The higher the ISO number is the faster the film reacts with the light, and so you can get the same exposure with less light if you use ISO 1600 compared to ISO 100. This can be an advantage in low light situations or where you want a high shutter speed to freeze the action. The disadvantage to this however is that as it is more reactive to light, there is more noise picked up and images can often apear grainy whn using films with a higher ISO speed.

In digital cameras there is settings you can use to change the ISO speed, rather than having to change a roll of film in a camera.

Thats my understanding, I'm sure if i'm wrong or missed anything out someone else will correct me. Hope that helps :)

Yep thats correct, the only thing u might wanner know is the reason the film picks up noise, is the silver grains on the film become larger the higher the iso. So the grainyness is visible silver grain, and the large gaps inbetween these grains.

I never understood why this occured on digital though, maybe noise produces a similar effect.
 
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