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

Thank you Shannon for the more detailed description. 

Shannon Stoney wrote:
> It was pretty simple really. Sorry if I made it seem complicated.
>
> I got a stouffer step tablet in the 4x5 size from The View Camera
> Store.  I printed it using six different filters:  00, 1, 2,3,4, and
> 5.  Then I looked at the results.  Each paper had a step tablet
> printed on it, but on the 00 one for example, more steps had a shade
> of grade on it.  Grade 5 would have relatively few steps with a color
> of gray.
>
>   So, I would mark on each paper the step that printed at near black
> (zone 3 in zone system terms) and the one that printed near white
> (zone 7).  Then I took the step tablet negative to the densitometer
> and measured the density of those steps, say step 5 and step 11.  Step
> five might have a density of 0.4, whereas step 11 would have a density
> of 1.4. The difference between them--1.0--is the paper scale.
>
> That's all.
>
> Alternatively, you could send the paper tests to The View Camera Store
> and then they would measure them for you.
>
> The way I use this information is:  when I have a negative I want to
> print, I could measure its shadow density on the densitometer, measure
> the highlight density, subtract, and know approximately what
> filtration the paper will need, or indeed if I can print the negative
> at all on that enlarger.
>
> (If you use the Beyond The Zone System method, you also use this
> information to carefully expose and develop your negative to fit the
> paper scale you want.  Most of the time this works, but with roll film
> obviously the results are chancier and more uneven because all the
> exposures get the same development.)
>
> --shannon
>
>
> On Nov 10, 2007, at 11:26 PM, vellum wrote:
>
>> Thanks Richard.  I saved your post to review in the future when I might
>> hope to have a better idea what it means.  What I really want to do is
>> whatever it was that Shannon did, so what I was asking for was advice on
>> acquiring equipment that could help me do that.  That's probably what I
>> should have said to start out with.  I'm no longer certain I understand
>> what what it was Shannon did though, so I'll shelve that idea while I
>> assess the matter further.
>>
>>
>>
>> Richard Knoppow wrote:
>>>
>>> ----- 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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>>>
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