Talking about ISO w/o using the word 'exposure' (reply to clengman)

Started Mar 19, 2013 | Discussions thread
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noirdesir
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Talking about ISO w/o using the word 'exposure' (reply to clengman)
Mar 19, 2013

It is often argued that using the concept of ISO is necessary for relative beginners and jpeg shooters, as just recently elaborated on in a maxed-out thread by clengman.
I would like to suggest that by using Auto-ISO one can de-emphasise the ISO setting or completely replace it with something potentionally more intuitive and improve image quality at the same time. This applies naturally to users that understand the effects of shutter speed and f-stop on motion blur and DOF and want to influence them.
When the user is setting ISO (but not going fully manual), a common procedure is to first set ISO, then the f-stop and then evaluate the resulting shutter speed and adjust ISO and/or f-stop until the shutter speed reaches a desired level (or range). With Auto-ISO, the equivalent would be to also set two parameters, shutter speed and f-stop, and evaluate the resulting ISO and adjust shutter speed and/or f-stop to achieve an acceptable ISO level.
Three practical advantages can be seen: (1) adjusting shutter speed and f-stop is usually easier than adjusting f-stop and ISO as the latter almost always requires an additional modifier button or switching to a different control panel using on-screen menus. (2) Setting a fairly well-defined shutter speed is usually more important than setting a pre-defined quality level via the ISO setting. Thus setting the shutter speed directly compared to indirectly via the ISO settings seems the simpler approach. (3) By using exactly the shutter speed desired by setting it directly, one is avoiding a shorter shutter speed than required which would go along with a higher ISO setting than required and thus lower IQ.
And this can be taken even further, instead of displaying the calculated ISO [in Auto-ISO mode], the camera could display a quality indicator, stepped in stops, with zero (ie, the best quality) corresponding to base ISO, and -1, -2, -3, etc. corresponding to higher ISOs. This should make the link between the amount of light (scene illumination modulated by shutter speed and f-stop) and the image quality more easily apparent and understandable without the detour of first linking the image quality to ISO and then linking ISO to the amount of light available (eg, via the famous triangle). It also makes the 'lightmeter' actually display the amount of light reaching the sensor (the scene brightness modulated with shutter speed and f-stop).

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