High ISO = Less Card Space?

[Daniel Browning]

You never said whether these two bulleted examples were of
the same subject matter.

It doesn't have to be. I used the word exposure to make such disclaimers unnecessary. If the subject is two stops brighter, and one adds a two stop ND, then exposure stays the same. Exposure relates to the total amount of light per area.

You only said this was two different
images/files. You said both shots have the exact same exposure, which
we could see plainly by reading the text.

No, what you can see plainly by reading the text is that they have the same f-number and shutter speed. If flash was used on one, or ND filter on the other, or different scene luminance on one, then exposure would be different. I specifically stated that exposure was the same, therefore all those other factors (flash, ND filters, scene luminance) are the same.

Based on your previous posts, you define 'exposure' to be shutter and aperture.

No, I define exposure the same way as the dictionary and photography textbooks (e.g. "Photography", by London and Upton): total amount of light per area.

I consider that to be data (it's expressed in 1s and 0s, and varies picture-by-picture), and it happens to be data about the exposure, so I called it 'exposure data'.

It appears that we differ on the definition of "exposure".

And the same "exposure" in no way signifies that it's the exact same amount of light. I can set my camera to manual exposure, f/4 and 1/500, and shoot all
day long. There's no inherent likelihood that any two pictures would
have the same amount of light.

A change in the amount of light *is* a change in exposure.

Chances are, the second example shot (i.e. f/4 1/500th with an ISO selection of 25,600) was taken in 1/16th the light (within the parameters of the metering mode selected) as the first example shot (i.e. f/4 1/500th with an ISO selection of 1600). But guess what? They've got the same exposure (and you'll find the same exposure data in each image file).

That's incorrect. They may have the same brightness, and the same raw data values, but they have very different exposures.