Yeah, unless you have a boatload of Tri-x you will be working with at long exposures, Tmax 100 is a better film for this, as it requires no correction up to several minutes. In a sense it's faster; 16s indicated will need 16s, instead of an hour plus 56m. Yikes.
Yeah, unless you have a boatload of Tri-x you will be working with at long exposures, Tmax 100 is a better film for this, as it requires no correction up to several minutes. In a sense it's faster; 16s indicated will need 16s, instead of an hour plus 56m. Yikes.
16" 1'56"
means 16 seconds to 1 minute 56 seconds, just under 2 minutes.
Howard Bond had a good set of complete and careful tests for several films in the July/Aug 2003 issue of Photo Techniques magazine, including TMX and Tri-X (not TXP 320). He found the manufacturers suggestions to be very different from his results. I'd go with the Brooks tests that Peter posted as a starting point for TXP.
I reckon the general converging function for non-integral order chemical reactions such as film/reciprocity response is like:
Tc = Ka+Kb(Tm)^1+Kc(Tm)^2+Kd(Tm)^3+.....
where:
Tc is corrected time
Ka, Kb, Kc, Kd, ...are diminishing system characteristic coefficients
Tm is the measured time and
^n is the exponent.
The function goes on forever but successive terms get smaller and smaller and cease to be worth chasing.
Flauvius, I used to have a mathematical background so I eyeballed Kodak's numbers, conjectured a few coefficients, tested the outcome, and collapsed the long formula into a short one.
Dr.Louie's approach is far saner.
__________________ Photography, the word itself, invented and defined by its author Sir John.F.W.Herschel, 14 March 1839 at the Royal Society, Somerset House, London. Quote "...Photography or the application of the Chemical rays of light to the purpose of pictorial representation,..". unquote.
The proposed empirical formulas and manufacturers' reciprocity charts fail to address the influence of film developers, personal development techniques, the actinic qualities of the light in which film is exposed, and goals of extended exposure as functions of reciprocity. As such, I submit that we need "target" film densities to determine the reciprocity characteristics of any film we use and process.
In this regard, does anyone know what are principles and goals Kodak used to determine their reciprocity chart for Tri-X 320? While TMX whose minimal need for exposure correction is well suited for grainless applications, Tri-X 320's grain structure is well suited for many out-of-door scenes which required extended exposures. As such, I am attempting to develop a principle based exposure system for my use with Tri-X 320 in the bush.
Flauvius
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The proposed empirical formulas and manufacturers' reciprocity charts fail to address the influence of film developers, personal development techniques, the actinic qualities of the light in which film is exposed, and goals of extended exposure as functions of reciprocity. As such, I submit that we need "target" film densities to determine the reciprocity characteristics of any film we use and process.
In this regard, does anyone know what are principles and goals Kodak used to determine their reciprocity chart for Tri-X 320?
Flauvius
I've never seen Kodak methodology or goals published. One reason the Bond article I referenced is interesting is because he establishes both to a greater degree than most. He uses a Stouffer step wedge and blue photofloods with specific target densities. However, he doesn't mention developer or development times. His article was briefly available from the PhotoTechniques web site as a .pdf, but it's gone now.
I expect that the manufacturers don't see how they could reasonably replicate the variety of developers, shooting conditions, or techniques used by any particular photographer when working in the realm where reciprocity failure occurs, so they don't invest the time or effort to attempt it.
One method used by astrophotographers to establish a Schwarzschild exponent to describe a given film is outlined briefly here: http://www.robertreeves.com/filmtest.htm This method is one used by Michael Covington, Reeves, and others. It is covered more completely in their respective books on astrophotography, both still in print. Astrophotographers limit their exposure length, usually to 45 minutes or less, because of problems with scattered light in the atmosphere causing sky glow that obscures the background sky.
Yeah, unless you have a boatload of Tri-x you will be working with at long exposures, Tmax 100 is a better film for this, as it requires no correction up to several minutes. In a sense it's faster; 16s indicated will need 16s, instead of an hour plus 56m. Yikes.
Not according to Kodak, which recommends exposure adjustments for TMax 100 at 1s and longer exposures. It however has distinctly better reciprocity than Tri-X, at 100 seconds metered TMax 100 only needs 200 seconds of exposure.
Fuji Acros is the B&W Emulsion that doesn't require exposure adjustments for reciprocity until 120 seconds (or longer).
Linear Mode
