[pure-silver] Re: Densitometer for print exposure calibration
- From: vellum <vellum@xxxxxxxxxxxx>
- To: pure-silver@xxxxxxxxxxxxx
- Date: Sun, 11 Nov 2007 15:24:48 +0000
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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