Hi Ballard, As John Farrias said, "There is no curve to apply to reciprocity." I couldn't find one single curve that worked for all the times on the chart I have. I really have no idea what "There is no curve to apply to reciprocity. It is a linear logarithmic function" means. If it is a function, then it has to have a curve, so that sounds like it contradicts itself. I've never heard of linear logarithmic functions either, so my last sentence could easily be wrong.
I played around for quite some time using adjusted times from an extensive reciprocity failure table for tmax 100, but couldn't find much. All the equations I found either matched short exposures or really long exposures. I can send the original chart I obtained these formulas from as soon as the author gives me permission. (i obtained it from a guy named Chris Cline through either rec.photo.darkroom or rec.photo.equipment.large-format) >From 4 sec. to 4 min, the points are pretty close to the equation: y=(.00312782828831x^2) + 1.912257105111x -3.2132290636125 Where X is the metered time, and Y is the corrected time. >From 4 minutes to one hour, the points are pretty close to: Y=((2.1721280231785 * 10 ^ -4) x^2) + 3.3843212260403x - 272.36563833739 Where X is the metered time, and Y is the corrected time. The leading coefficient is 2.172... times ten to the negative fourth power. it looks kinda confusing in the equation. Keep in mind this is for Tmax 100, not 400. The reciprocity failure for 400 is worse than 100. You really can't get much of an equation from three points. Hope this helps, John Yeo > --------- Forwarded message ---------- > From: Ballard Borich <ballardbor...@juno.com> > To: pinhole-discussion@p at ??????? > Date: Thu, 21 Jun 2001 10:28:53 -0400 > Subject: Re: [pinhole-discussion] Reciprocity Problem > Message-ID: <20010621.102857.-222441.0.ballardbor...@juno.com> > > Eric or John > I have zero math apptitude or ability. I have always wondered what the > actual curve for TMAX 400 film would be like. The guidelines from Kodak > are @1sec +1/3 = 1 1/3 sec, > @10sec + 1/2 = 15sec, and @100sec + 11/2 =300sec. > I like the film just fine. It works well with my 120 film size toy > cameras. I have just started using a 120 film size pinhole. I have a box > of 5x7 film frozen to use with pinhole on a view camera. I have no > darkroom and won't for a long time. I would like to cut down on the > commercially processed (read exspensive) mistakes. > I do understand that they are only guidelines. Thank you if you can help > with the math because I just don't get it. > Ballard > > On Tue, 19 Jun 2001 11:40:11 -0500 "Eric Lawton" <lawtone...@hotmail.com> > writes: > > Hi Jeff, > > > > www.curvefit.com goes into a bit of detail if you're interested in > > the math > > - or maybe try a google search on linear regression and non-linear > > regression. > > > > Otherwise, I have a bit of mathematical ability and if you provide > > me with > > your data I could construct an equation for a curve. You might need > > a > > pocket calculator to evaluate the equation though. > > > > If you're interested in the math start by learning linear regression > > - it's > > fairly simple. You should use non-linear regression for your > > reciprocity > > failure data though (since reciprocity failure is, of course, a > > non-linear > > behaviour). Feel free to ask more questions. If you can't tell - I > > like > > math. > > > > Eric > > > > >From: Jeff Dilcher <r...@hiddenworld.net> > > > > > >*** Warning *** > > >*** Technical Question Follows ** > > >** press delete key if technical questions bother you ** > > > > > > > > >I have a technical question, that, perhaps someone on > > >the list can help me with. Please respond > > >directly if you like. > > > > > >I am trying to develop a mathematical function which will > > >help determine reciprocity compensations. > > > > > >Initially, I would like to be able to submit a small set of > > >reference values (metered exposure times along with > > >exposure time compensation for reciprocity). Using these, > > >I would like be able to enter in any exposure value, and > > >get a corresponding compensated value on the reciprocity > > >"curve". > > > > > >I am trying to boil this down into an algebraic equation > > >as easily as is possible. I have quickly reached the > > >endpoint of my math abilities. Can anyone provide a clue > > >for me? > > > > > > > > _________________________________________________________________ > > Get your FREE download of MSN Explorer at http://explorer.msn.com > > > > > > _______________________________________________ > > Pinhole-Discussion mailing list > > Pinhole-Discussion@p at ??????? > > unsubscribe or change your account at > > http://www.???????/discussion/ >
