by Peter Irwin <pirwin@[EMAIL PROTECTED]
>
Oct 29, 2007 at 10:57 PM
Richard Knoppow <dickburk@[EMAIL PROTECTED]
> wrote:
> Assuming
> the minimum usable gradient is somwehere around log -2.5
I had been under the impression that the Jones
point for a 200 old ASA film was at log -2.9.
I'm not really reliable at math, so I'd be glad
if someone would show me if I've gone wrong.
If the old ASA speed definition is:
old ASA speed = 1/(4xE)
then E = 1/(4x old ASA)
E = 1/(4 x 200)
E = 1/800
Log (E) = -2.903
> the
> arithmetical range is around 1:400 or a bit less than nine
> stops.
The curve probably would continue as reasonably linear
a fair bit to the right of what is shown on the graph,
so the actual range of the film is pretty huge.
The slight bend at the right of the tri-x graph might
have some effect on tone reproduction, if you actually
gave the film that much exposure, but it hardly looks
like a major departure from linearity.
Peter.
--
pirwin@[EMAIL PROTECTED]
