Phil Davis's "Beyond the Zone system" is the definitive work on this subject. http://www.btzs.org/ is the web site for articles and info on the book, and software http://www.btzs.org/Software/Plotter.htm This windows base software plots both film and paper curves and the matcher feature graphically compares the film and paper relationship. I have seen some really good buys on eBay for densitometers that have the ability to measure both film, and paper densities. http://www.btzs.org/Software/ExpoDevPalm.htm I have used a Palm Pilot loaded with info from Plotter software to determine exposure and film development times. The Palm creates a log that saves some time with note taking. I will admit it took some effort to get up to speed on all this. This system has provided me with a method to use Subject Brightness Ratios and metered EV values to determine film exposure and development that yield negative density ranges to match the papers I use. "The Book of Pyro" by Gordon Hutchings "Edge of Darkness" by Barry Thornton Both of these authors write about there experience with staining developers and VC papers. Barry Thornton wrote about the effects of stain color and there effects on VC papers. He also formulated different developers that optimized the stain for VC papers Now available from, http://www.photoformulary.com/DesktopDefault.aspx?tabindex=0&tabid=1 The BTZS Plotter software will graph projected or contact prints from step tables. The density values from the stained negative can bet entered in the step table column and the corresponding reflective print densities enter to complete the plotting. Unfortunately the negative density values are not linear like a step table; therefore I suspect this would skew the curves. I have used transmission densitometers, reflection densitometers, and on easel photometers to determine negative density range, paper log-exposure range, and paper exposure, only to find the local gradation causes me to change exposure, and paper grades (paper log-exposure range). To make an analogy all this testing gets me in the ball park for sure, I see fewer balls, and strikes, and some times I get a home run. Remember negative exposure and development are finalized upon completion of development, and all this effort is to make fine negatives that are a delight to print. Jonathan Ayers [mail1&redwoodhorses.com] -----Original Message----- From: pure-silver-bounce@xxxxxxxxxxxxx [mailto:pure-silver-bounce@xxxxxxxxxxxxx] On Behalf Of Richard Knoppow Sent: Saturday, November 10, 2007 12:16 PM To: pure-silver@xxxxxxxxxxxxx Subject: [pure-silver] Re: Densitometer for print exposure calibration ----- Original Message ----- From: "vellum" <vellum@xxxxxxxxxxxx> To: <pure-silver@xxxxxxxxxxxxx> Sent: Saturday, November 10, 2007 6:02 AM Subject: [pure-silver] Densitometer for print exposure calibration > Shannon's interesting thread about multigrade paper has > made me want to > test my enlarger and paper to better understand it and > calibrate my > system. It's something I've never done before. I'm fuzzy > on some of > the concepts and what they really mean, like Log Exposure > Range, but > I'll figure it out as I go. > > I have a Jobo Colorstar 3000, but I don't have the B&W > density probe for > it. I just have the standard color probe. > > What densitometers might be the best candidates for B&W > print exposure > densitometry if I were shopping used on ebay? I'd rather > buy a new one > but I suspect new ones may be costly. Ease of use on the > enlarging > easel and accuracy (or consistency) would be priority. An > exposure > timer function would be nice, but not essential. > > Ability to use it to measure density of negatives would be > nice too. I > develop using both MQ and pyro developers. Having one > densitometer that > "does it all" would be cool, but probably there may be > none that do > everything well. In that case, it is the printing > densitometry that > matters most to me. > > Skip. > I think the key here is understanding that there are two media to be measured: negative and print. A transmission densitometer will allow you to measure the densities, but more important, the contrast, of the negative (with some qualifications). The resulting range of densities on the paper will also depend on the characteristics of the enlarger. Nearly all transmission densitometers measure diffuse visual density. Some enlargers use semi-specular (condenser) light sources which produce different effective densities than a diffuse source. This is called Callier effect and varies with the film. It is nearly absent for color film and greatest for coarse grain silver film. To measure the print one needs a reflection densitometer. A number of these have been made and are available. Both types of densitometers are made for either white light or standardized colors. The effective density of a negative with a stain image such as produced by Pyro is dependent on the color sensitivity of the printing material. If its printed to a panchromatic material the effect is nearly absent. For blue sensitive material the effect is to increase the contrast but not the shape of the film curve. For variable contrast materials the stain image may look like a masked filter causing the contrast to vary with the negative density. Since the filtering effect is strongest in the dense regions the effect is greatest on the print highlights. Since VC paper prints lower contrst for blue exposure than for green the effect will be to lower highlight contrast in about the same way a shoulder in the film characteristic would do. The amount of this effect willd depend on the relative density of the stain versus the silver density, the spectral characteristics of the paper, and the light source. Beacause the paper characteristics affect the resulting curve it is difficult to measure using a densitometer. You would have to have filters at the correct colors to match the two components of the printing paper. I don't think the blue and green filters used for color work are at the right wavelength. One could presumably print a step tablet onto the film, process it, and make prints from which a reflection densitometer could measure the resulting density curve. I am pretty sure I have seen published results of such tests but can't cite a source. --- Richard Knoppow Los Angeles, CA, USA dickburk@xxxxxxxxxxxxx ============================================================================ ================================= To unsubscribe from this list, go to www.freelists.org and logon to your account (the same e-mail address and password you set-up when you subscribed,) and unsubscribe from there. No virus found in this incoming message. Checked by AVG Free Edition. Version: 7.5.503 / Virus Database: 269.15.28/1123 - Release Date: 11/10/2007 3:47 PM No virus found in this outgoing message. Checked by AVG Free Edition. 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