Subject | Re: ISO value names are becoming ridiculous |
From | Sandman |
Date | 01/08/2016 16:31 (01/08/2016 16:31) |
Message-ID | <sandman-452242993369c375b8198929c57627b8@individual.net> |
Client | |
Newsgroups | rec.photo.digital |
Follows | nospam |
Followups | nospam (14h & 44m) > Sandman |
Nope.Sandman
<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.nospam
it's misuse of terminology.
f/stops are also a logarithmic scale, with each step 1.4x the previous one (f/1.4, 2, 2.8, 4, 5.6...), versus 2x for iso (100, 200, 400, 800, 1600...).
if you're going to call iso an arithmetic scale, then you must also call f/stops an arithmetic scale.http://www.merriam-webster.com/dictionary/arithmetic%20scale "a scale on which the value of a point corresponds to the number of graduations the point is from the scale's zero"