Film density related to paper filter grades
Can anybody shed some light for me on the following question:
If I measure a density range in a negative from say .90, can one determine the filtration for the paper from this? I seem to remember an article where it was stated that every 0.3 density increment amounts to one step in filter grades, but I can't find it any more.
I use a Heiland Electronic TRD2 densitometer and an Opemus 6 with a Meograde variable contrast head for B&W printing. This head permits one to dial in filter grades from 5 to 0.
Thanks for any suggestions.
Have you seen the light..?
You cannot have a theoretical rule for this because different papers labelled with the same nominal grade accept negatives of varying density ranges. Worse, papers respond sometimes non-linearly to dichroic/VC heads, so the same increment of filtration might be applicable to both a jump from 1 to 3 and from 4.5 to 5.
If you have a reflection densitometer, your best bet is instead to measure your paper's density range, and work your way backward to your negatives. BTZS is more or less about that.
Using film since before it was hip.
"One of the most singular characters of the hyposulphites, is the property their solutions possess of dissolving muriate of silver and retaining it in considerable quantity in permanent solution" — Sir John Frederick William Herschel, "On the Hyposulphurous Acid and its Compounds." The Edinburgh Philosophical Journal
, Vol. 1 (8 Jan. 1819): 8-29. p. 11
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Find the ISO(R) of the paper from the manufacturer's data. ISO(R) is the density range required to give a full tonal range, to two significant figures, with no decimal points. Thus ISO(R) 90 is a density range of 0,90.
Do not forget the importance of enlarger + lens flare. To take an easy but not inconceivable case, if your enlarger + lens has a flare factor of 2 (1 stop, log = 0,3) then you need a log density of 1,20 on the neg to give a full brightness range.
Paper grades are NOT standardized, so one manufacturer's paper grades may have a different ISO(R) from others. There's a lot of overlap, but very roughly, grades go from under ISO(R) 40 (grade 5 graded) to ISO(R) 180+ (grade 00 VC). That's from memory after a big dinner and lots of wine so don't hold me to it...
R. (and you might find The Photo School at www.rogerandfrances.com interesting)
read Ilfords MG data sheet from thier web site.
One of the tables in the data sheet tells you the range in negative density that the paper goes from black to white from on explosure, for a given developer type, dilution, temperature and time.
In reality the denisty is only a guide. I do not always want all of my images to have a full tonal scale from whitest white to deepest black.
The density does give you a place to start from though. I typically take a typical looking neg from a roll, read its maximum density above film base and fog denisty baseline, That gives me the grade that I will contact print the plastic neg file sheet with film strips loaded into it at.
I try to get the images to print well at #2 grade. I do this by varying film developemnt. - See Barry Thornton's The Unzone System article on the web. Things do not always work that well if I am using a new to me film, or have screwed up and forgot about a filter factor, etc. hence the need to test the pre first full contact sheet exposure if the first test strip of the contact trial looks screwed up.
I try to keep contrast at 2, for most of my stuff, becuase that gives you options later on if you want to move on to flashing the paper, or doing unsharp masks. Both of these activities, which can be worthwhile, do require for you to increase the overal printing contrast.
If the original neg was developed to print well on its own at #4, then you don't have much head room left to play successfully with either of these techniques.
Obtain a transmission step wedge and calibrate your enlarger/paper/developer combination. You can create a chart of density range as a function of enlarger setting. You can then use the chart to get you in the ballpark. I did it years ago but gave it up as, for my taste, it was really no better than starting with a standard filtration and adjusting. Make sure your bulb isn't ready to die. I chased my tail on that one once. :>)
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Thanks for all replies
Thanks everybody for all the information. It is nice to know that there is no straightforward relationship between the two. It could take one some time looking for something that doesn't exist.
Have you seen the light..?