[pure-silver] Re: Densitometer for print exposure calibration

Thanks Jonathan.  I could have sworn I bought a copy of Phil Davis' BTZS
book years ago, but I can't seem to find it now.  I'll start there.

Skip.

mail1 wrote:
> 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 
>
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