I will try to respond at length later, but there is one
quick thing I would like to point out.
Richard Knoppow <dickburk@[EMAIL PROTECTED]
> wrote:
>
> The point at log 0.1 density is called log10 Hm and
> arithmetric speed is S=0.8/Hm (note that the arithmetric
> value rather than the log value is used). For log speeds the
> formula is S (in degrees)=1+10log10 0.80/Hm
s = 1 + 10log10 0.8/Hm
Is a convoluted way of very very nearly saying:
s = 10log10 1/Hm.
For proof of this look at the table from below
and notice that all you have to do to convert
DIN speed to the 0.1 density point is to divide
by minus 10.
> ISO speed Log exposure at 0.1 density point
> 25 -1.5
> 50 -1.8
> 100 -2.1
> 200 -2.4
> 400 -2.7
> 800 -3.0
DIN speed
or ISO Log
15 -1.5
18 -1.8
21 -2.1
24 -2.4
27 -2.7
30 -3.0
>
> Note that the exposure equivalent to the Jones point would
> be about 1.25 times these values, i.e., about -2.63 for ISO
> 100 film.
I don't understand how you got that number.
When I use the OLD ASA formula for a speed
of 50, I get -2.3. Your number looks closer
to OLD ASA 100.
>
> Thanks for asking about this, its been educational to
> figure out the answer.
Thanks very much also,
Peter.
--
pirwin@[EMAIL PROTECTED]
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