Why don't we use Logarithmic ISO?

Started 7 months ago | Discussions thread
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tesilab
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Why don't we use Logarithmic ISO?
7 months ago

Today's crazy ISO numbers (going up to 409,600 and counting) are getting out of hand, from a user interface perspective. Why are camera manufacturers still using what is now--with values into the hundreds of thousands--the more unwieldy of the two official ISO numbers, the linear (corresponding to the old ASA) over the logarithmic value (originally the DIN numbering system)? The logarithm values would keep us in two digits for a long time, I think.  It makes for a cleaner UI, and it is starting to make sense. It allows for the the convenient 1/3 stop interim values, and it is easy to remember that multiples of 3 are the round ISO values.

http://en.wikipedia.org/wiki/Film_speed#Current_system:_ISO

Examples of some ISO values log, and linear:

12° = 12         (how many of you ever used ISO of 12?)
15° = 25
18° = 50
21° = 100
24° = 200
27° = 400
30° = 800
33° = 1,600
36° = 3,200
39° = 6,400
42° = 12,800    (actually, official ISO should be 12,500*)
45° = 25,600    (25,000)
48° = 51,200    (50,000)
51° = 102,400  (100,000)
54° = 204,800  (200,000)
57° = 409,600  (400,000)

Actually, these haven't all been officially "assigned", but this is the understood progression, with the exception of the fact that ISO actually recommends rounding the numbers similarly to the way we do with shutter speeds,

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