How does ISO work technically

Started Dec 5, 2005 | Discussions thread
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Yoddle Laheehoo
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How does ISO work technically
Dec 5, 2005

Disclaimer: if the answer is already on this forum somewhere, I apologize for not being able to find it. I did search, though.

I'm trying to understand the technical aspects of my E500 and hope someone can explain to me how ISO is handled, from a technical perspective. With my analogue camera's I used to buy film with different ISO-values. These films where physically different. I would adjust the camera's ISO setting according to the type of film. On some occasions I would "upgrade" the film by using a high ISO setting (e.g. 800) with a lower ISO film (e.g. 400). When developing the film, I would correct the development times accordingly. When pushing this too far, there would be a drawback with the granularity of the film becoming visible in the prints.

In the digital world, there's no such thing as different films, so I guess that the camera uses a mechanism similar to upgrading an analogue film and taking the ISO value into account when processing the image. The drawback here for high ISDO values would be the noise issue. However, it's not totally clear to me how the ISO is processed in the picture. Is it something that is done afterwards or is capturing the light already influenced by the ISO value (does the CCD "know" the ISO value)? As ISO cannot be altered for RAW images (like wb), it must already be "in" the RAW image somehow. I really would like to understand, since understanding the tech things of the E500 makes it easier for me to determine when to change what settings.

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