Sandman
In article <f97cb4e5-840a-47c7-ab91-1e7853f6650c@googlegroups.com>, Whisky- dave wrote:

So with the D5, it can boost its ISO to ISO 3,280,000, and suddenly how ISO is named is becoming just stupid. We should use EV steps instead:

Whisky-dave
SO why start at -1 ?

Sandman
The base would be what is today called ISO 100, which corresponds to an expected brightness level of the resulting bitmap image.

Whisky-dave
Why limit it to bitmaps?

Sandman
Because ISO is film sensitivity and sensor amplification, ...

... so it's only a variable for the resulting image.

So ISO 50 is one step lower than that, naturally.

Whisky-dave
not a 'step' but half I'd say.

Sandman
No, going from ISO 50 to ISO 100 is one full stop. The scale is arithmetic, remember. Each stop is a doubling of the value. ISO 100 is one stop more sensitive than ISO 50, just as ISO 800 is one stop more sensitive than ISO 400.

Whisky-dave
are you sure about that as it makes NO sense or is it nonsense. Doubling the ISO effectively doubles or makes it twice as sensitive to light meaing you only need half the exposure.

Sandman
Which people understand when you talk about ISO 200 or ISO 6400 because those numbers are easier to understand.

Whisky-dave
I don;t remmeber having problems when I was exposing film at 10 ASA up to 6400 ASA

Sandman
Which is what I just said...

Whisky-dave
I doubt I'd have any trouble working out what 12,800

Sandman
Which is why it's only a problem now when we have ISO values of 3,200,000 and 4,000,000

Whisky-dave
would have meant either. which is why DIN or EV would be better than ISO as sensitivities increase as they do today.

Sandman
Which incidentally, is what I'm saying. In fact, the old arithmetic ASA standard had a logarithmic equivalent later called APEX which is very similar to what I am proposing, where APEX 5° = ASA 100 and APEX 6° = ASA 200 etc etc.

Only difference is that APEX 0° was equal to ISO 3, which no one used (or uses), so to reset the scale for ISO 100 seems more obvious today.

And the new D5 would have a max ISO value of "ISO EV+10" which can be pushed in-camera to "ISO EV+15", which would still be equally impressive.

Whisky-dave
EV values already have a meaning best not to change them.

Sandman
Yes, and ISO can be part of the EV. So when changing the EV by using the ISO setting, it would be "ISO EV+4" for instance. Meaning that with "ISO EV 0", ISO is no part of changing the EV.

Whisky-dave
EV is for sensitivity really as it was the measure of the light level inside the camera not of the subject brightness.

Sandman
???

EV stands for exposure value. It's the combination of shutter speed and aperture and that's it. So any given exposure has an exposure value. Using ISO, you can then amplify the signal by one or more stops to emulate a different EV.

So, shoot an image with 1/250 shutter speed at f4. That results in a bitmap with a given brightness.

Now, change the ISO to 200 and that result would be amplified to be an equivalent EV as if you had used 1/250 f4 or 1/250 f2.

Hence - ISO 200 == "ISO EV+1", you have increased the brightness of the image by one stop.

Some more math. A "native" EV of 0 is equivalent to a 1 second exposure with f1.0. So the "native" EV of the exposure of 1/250 f4 is EV 12, that's the setting in your camera. Now, adding ISO EV+1 to that resulting bitmap, means it is now equivalent to EV 13, easy.