ISO setting

[tro]

Hi,

As encouraged, I did register for the forums after lurking for a while. :)

So, I have an idea for podcast topic. What does ISO value in digital photography denote? And actually what does it denote in traditional film too? Does it make a difference to set the ISO value at all if shooting raw images?

Although I probably could just search the answers from the web, I was just wondering maybe this might be something other listeners would be interested learning also.

[Marko]

Hi tro - This is too basic for a podcast imo so I'll just answer it here.

ISO just refers to film speed for film and the sensitivity of the camera's sensor for digital.

When you increase the ISO you need LESS light for a proper exposure.

But there is no free lunch.

When you increase the ISO, at a certain point the shot will be more grainy/'pixelly'/noisy. MOST photographers hate this stuff. SOME photographers use it to their advantage when shooting certain types of subjects.

As a general rule most photographers choose the lowest ISO for any given situation...but depending on the available light level that usually is NOT possible except when you are shooting in bright sunlight.

Hope that helps and PLEASE let me know if you have additional questions - Marko

[tro]

Oh, I was not after this level of basic answer. Sure, I know how it goes, more ISO, less light needed but more noise. What I was after was pretty much the geeky tech stuff that goes into ISO values.

In traditional film, ISO 100 means something, how is it defined? And how was this mapped to digital photography? Does ISO 100 mean something like x lux of light produces full white pic or something (here I have no clue what it might be, as I did not google it yet)?

The one question I had was does it make a difference if shooting RAW images. So from this I'd think it does, so the setting actually does affect the recorded RAW pixel values, so under/overexposed images due to inappropriate ISO value just cannot be later recovered.

[Marko]

Hi tro,

Indeed it DOES make a difference when shooting Raw, Jpeg or any other format. If you shoot a frame of RAW at ISO 1600 it always stays 1600 (AFAIK).