Ah, a few thoughts about ISO-less

Started Jul 10, 2013 | Discussions thread
Jeff
Veteran MemberPosts: 4,470
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Looking for the gain knob ...
In reply to bobn2, Jul 11, 2013

Bobn2 wrote:

Part 1, unlearning what you know about ISO and exposure.

The exposure index (EI) as defined by the International Organisation for Standardization (ISO) defines how the exposure at the sensor maps to the brightness of the output file. You can read about it here . ISO does not measure the sensitivity of the sensor, nor does it measure the gain applied to the sensor. All it says is if you shine so much light on the sensor, it results in an output image with given tone, and which amount of light produces which tone depends on the ISO setting. Thus, since it is about mapping an amount of light to an output shade it is fundamentally about how you (or the camera) process the captured latent image to produce your output image. If you are using in-camera processing, you need to per-select the ISO to one of a limited number of processing options and then match your exposure to that. If you process from raw files you can tailor the processing precisely to the captured exposure, and therefore do not need to preselect the ISO. One caveat about that is that some cameras have limited capture electronics, and require to be set up differently for different amounts of light. The manufacturers link that circuitry (which changes the analog gain in front of the analog to digital converter) to the ISO control, and on those cameras you do have to pre-select the ISO to match the exposure, within a broad range. You need to know how your camera operates to know how much leeway it will give you.So ISO doesn't measure sensitivity, nor does it measure gain. But it does specify how exposure is translated into a final image. I see the semantic difference, and understand the underlying mathematics and definitions.

Let's see. ISO doesn't measure sensitivity, nor does it measure gain. But it does specify how exposure is translated into a final image. I see the semantic difference, and understand the underlying definitions.

So in practice, what does the ISO knob on my camera do?

Or differently, can you tell me where to find the gain knob on my camera?

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Jeff
http://www.flickr.com/photos/jck_photos/sets/
You don't make a photograph just with a camera. You bring to the act of photography all the pictures you have seen, the books you have read, the music you have heard, the people you have loved.” -- Ansel Adams

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