ISO 100, OMD-EM1II and firmware 3.0?

Started 2 months ago | Questions thread
bobn2 Forum Pro • Posts: 61,730
Re: ISO 100 Compared to Overexposure

Architeuthis wrote:

bobn2 wrote:

Architeuthis wrote:

Cafe Racer wrote:


Thanks for that. Perhaps I should also open a new thread as what I'm trying to ascertain is not S/N ratio as base 200.

Hi Cafe Racer,

I am not sure whether I understand your question. But as I wrote above, no additional btightness is added to the histograms of the raw files - they look more or less as would be expected (-1eV (ISO100) and -1.6eV (ISO64)).

You're looking at the wrong quantity, both of you. What the histogram is measuring is exposure, though in camera and setting dependent units. The exposure will be the same, since the exposure settings (aperture, shutter) are the same and, presumably, the third exposure parameter, scene luminance (the light coming from the scene) is also the same. Therefore there is no way that it can be different. The setting-dependent units get scaled down by a factor of two each stop lower ISO that is set.

Here are screenshots of the histograms of the unprocessed exposures

'Unprocessed exposure' doesn't mean anything. 'Exposure' is sufficient, and is what is being shown. Processing a exposure delivers a lightness, not a different exposure.

I'm not trying to be critical or pedantic here. Using the correct terms makes it much easier to conceptualise all this. Especially, confusing what 'exposure' is makes it really, really hard to work out what's going on.

Hi Bobn2,

Sorry for using wording that can be mistaken.

Don't apologise, that wasn't the point. The point of using the terms correctly is to help conceptualisation. Each different word in a technical context has a distinct meaning, representing a distinct concept. Muddle the words and you muddle the concepts, or else, you're muddling the words because you're muddling the concepts. Clear terminology and clarity go together. I wasn't criticising, just trying to lend a hand for both of you to get the ideas straight.

With "same exposure" I meant the photos were taken at the same shutter speed/aperture detting and just the ISO was different...

Same exposure would be with the same EV (that is combination of aperture and shutter speed) and same scene luminance. You're correct in thinking that changing the ISO doesn't change the exposure if the EV stays the same.

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263, look deader.

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