It is all about exposure, not ISO setting - real world photos

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Magnar W
Magnar W Senior Member • Posts: 3,048
It is all about exposure, not ISO setting - real world photos
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There was another discussion where some of us went away from the topic, starting to discuss "exposure", which per definition is shutter speed and aperture value for the camera. For the scene, scene luminance is the criteria, and the factor for setting "proper exposure".

ISO is left outside, for good reasons, since adjusting the ISO value has no effect on the amount of light hitting the sensor whatsoever. When adjusting ISO value, photographers often compensate for decreased or increased gain. Altering ISO setting has no effect on the amount of light hitting the sensor, unless either shutter speed or aperture, or a combination of both, are adjusted! Unless the exposure is adjusted!

Here is a series of photographs showing that ISO setting has nothing to with exposure. Three frames of a house, taken with the A7rIII and GM 100-400 mm at 400 mm, exposure 1/8000 sec at f:11. The camera was set to ISO 100, 800 and 6400. The files were processed with Photoshop. No sharpening or noise reduction was applied to the files.

Actually, ISO 100 shows a tad more noise than ISO 800 and ISO 6400. This is exactly what is expected for those knowing how exposure affects the files, since this camera - and many other Sony cameras - has dual gain feature implemented.

A quick exposure test at ISO 100, ISO 800 and ISO 6400. Exposure is the same for all pictures, 1/8000 sec at f:11 - result as expected. All crops are 100% pixel size.

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