Google| Subject | Re: ISO value names are becoming ridiculous |
| From | Sandman |
| Date | 01/07/2016 11:39 (01/07/2016 11:39) |
| Message-ID | <sandman-16c764f578f83d7514d092ec644a4483@individual.net> |
| Client | |
| Newsgroups | rec.photo.digital |
| Follows | nospam |
| Followups | nospam (6h & 8m) > Sandman |
In article <070120160402078938%nospam@nospam.invalid>, nospam wrote:
Sandmannospam
There's nothing inherently wrong with it. And since most people learn quickly that ISO is an arithmetic scale, they know the value doubles for each stop.
logarithmic, because each stop is double the previous versus an increase by a fixed amount, the very definition of a logarithmic scale.
<https://en.wikipedia.org/wiki/Logarithmic_scale>It is based on orders of magnitude, rather than a standard linear scale, so each mark on the scale is the previous mark multiplied by a value.
in this case, the value is 2.It would be, it the values were "ISO 1", "ISO 2", "ISO 3" and each value represented a doubling of what it describes. This is how the Ritcher scale works, or decibel. ISO is arithmetic.
That said, ISO *has* a logarithmic part, inherited from DIN, where each step is one third of a double in sensitivity. Hence the ISO 100/21, ISO 200/24 etc.
<https://en.wikipedia.org/wiki/Film_speed#Current_system:_ISO>
"The ISO system defines both an arithmetic and a logarithmic scale. The arithmetic ISO scale corresponds to the arithmetic ASA system, where a doubling of film sensitivity is represented by a doubling of the numerical film speed value. In the logarithmic ISO scale, which corresponds to the DIN scale, adding 3° to the numerical value constitutes a doubling of sensitivity. For example, a film rated ISO 200/24° is twice as sensitive as one rated ISO 100/21°"
That part is rarely used these days, however.
-- Sandman
01/06/2016-
