[rollei_list] Re: OT Infared film and shooting with it.
- From: "Eric Goldstein" <egoldste@xxxxxxxxx>
- To: rollei_list@xxxxxxxxxxxxx
- Date: Wed, 26 Sep 2007 08:35:35 -0400
Thanks for this interesting and accurate post...
Speaking of dead nomenclature, we have yet to cover the Weston, GE and
GOST standards!
Eric Goldstein
--
On 9/26/07, Richard Knoppow <dickburk@xxxxxxxxxxxxx> wrote:
> I don't want to reiterate my rather long post about
> this. ASA is the American Standards Association. This was
> renamed the American National Standards Institute, probably
> because people can't stand simple names. The ISO is an
> international association of national standards groups and
> attempts to co-ordinate standards. An ISO standard is also
> an ANSI standard.
> The DIN, which is the German association for
> establishing industrial standards, is also a member of ISO.
> The original film speed standard adopted by the ASA in
> the United States, in 1943, was a modified version of a
> method which had been developed at Kodak and used internally
> there for several years. The method was devised by Loyd A.
> Jones after many years of research on determining the
> _practical_ exposure of film for pictorial use. Jones's
> method required measuring intercepts of a double slope and
> evidently was not very simple in practice. Jones idea was
> that the minimum exposure point should be at a high enough
> contrast (or gamma) point on the toe of the film curve to
> provide for some shadow detail. His research found that tone
> rendition of prints improved until the negative exposure
> reached this point but that there was little detectable
> change for greater exposure. He chose to determine minimum
> exposure because film tends to become more grainy with
> density and also to loose some sharpness.
> Unfortunately, the original ASA version of this included
> a two times safety factor so that negatives were inevitably
> too dense thus destroying the purpose of the standard.
> In 1958 the ASA reviewed the method for determining
> speed. It examined the method used by the DIN at that time.
> This was _not_ the original pre-WW-2 DIN method but one
> which measured a speed point determined by a minimum density
> above gross fog and support density. The ASA conducted tests
> of a great many emulsions and found that a fixed multiplier
> of this minimum density point would result in practical
> aggreement with the speeds determined by the Jones Mimimum
> Gradient method but was much easier to measure reliably. The
> ASA adopted this system with the fixed factor (about 1.25)
> and eliminated the two times safty factor previously applied
> to the Jones speeds. The practical result was the doubling
> of all published film speeds.
> Film speed is still given in both ISO and DIN even
> through the two are identical methods because ISO speeds are
> stated in an arithmetical series and DIN speeds in a
> logrithmetic method. This is to match existing light meter
> calculators.
> The ISO/DIN method specifies the exposure range and
> density range to result from it, thus it specifies the
> contrast or gamma of the negatives. The last change in the
> standard eliminated the specification of a standard
> developer, however the developer must be specified along
> with the resulting speed.
> If a film is developed using a different developer than
> that used for the measurement, or is exposed and developed
> to a different contrast index (or gamma) the ISO/DIN speed
> no longer applies. However, the ISO/DIN speeds still give at
> least a rough estimate of the differences among films.
>
> ---
> Richard Knoppow
> Los Angeles, CA, USA
> dickburk@xxxxxxxxxxxxx
>
> ---
> Rollei List
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