Tonal Range to Paper Grade Relationship Info?
I was just now looking for a chart that I recall seeing, either in print or on the web somewhere, that shows a general starting point for determining a good paper grade starting point relative to the tonal range of the negative. I was going to work out some baseline info for my materials and thought I could save some time and get some ideas from others before spending the time to get started on the wrong foot. I couldn't find any threads in APUG but perhaps I wasn't searching on the right criteria....
Be more descriptive. How do you determine the tonal range of your negatives?
There is a very clear relationship between the negative tonal range and the best paper grade for it. Most (if not all) darkroom meters rely on it. So you are on the right track, but I need more info to help you. Do you use a densitometer or just a visual inspection of your negatives?
I use 2 different densitometers.... An old Macbeth TD-902 and one that is part of my darkroom meter/timer/analyzer, a German unit... a Wallner-Labex System 500. I didn't include the Wallner info as I thought it might fog the issue as it is a bit unique in operation. Its intended function is based upon maximum black and whenever I've brought this up, it ends up being a distracting element that adds controversy to any discussions involving it (it seemed easier to remain mum on it for this inquiry). It is actually quite intuitive to use as intended (much more so than people tend to generalize). Lately, I use the blue channel primarily, as I am almost universally using Pyrocat style variants as primary film developers and don't have a UV tuneable rig.
My initial post was simply to see if anyone recalled the chart/table that I remember running into awhile back. I was embarking on some printing projects that would have me pulling negatives from the past 20 years (all manner of developers/film combos) and I was simply trying to streamline the project. My intention was to simply use the densitometer function to quickly determine the tonal range and paper/filter selection to speed up a lengthy printing project. I have no doubt that I'll quickly enough settle into some intuitive enough procedures but hoped to find some solid info on this.
Use the densitometer to measure the density of a significant highlight and a significant shadow; both where you still want some detail in the print. The difference between the two densities is your log exposure range (LER). Then use a spreadsheet and the following equation to determine the appropriate paper grade:
ISO Grade = 9.21 - 7.8(LER) + 0.421(LER)^2 + 0.486(LER)^3
If your LER is 1.05, this should return a grade 2 paper. You can use this to make a table for yourself. I derrived at this equation afew years back. Kodak used a slightly different version, but mine is more accurate at the extreme contrast grades.
This is what ISO(R) is about.
ISO(R) is an objective, transferable system of paper grading. Different manufacturers' paper grades correspond to quite a variety of ISO(R) figures. For example, most manufacturers' Grade 5 is nominally ISO(R) 40. But graded Grade 5 in (say) Dokulith is probably ISO(R) 35, while with VC paper, a VC head and an ordinary developer it may be closer to ISO(R) 50.
ISO (R) is the log brightness range you want to print, to 2 significant figures, minus the decimal point, so ISO(R) 40 is a density range of 0.40 (actually 0.35 to 0.44) and ISO (R) 160 is a density range of 1.60 (1.55 to 1.64).
Most manufacturers publish (somewhere) an ISO(R)/grade equivalent, but you may have to hunt for it.
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I don't agree entirely. As you, I also prefer the ISO(R) system. You are correct, it is easier and more adhered to by manufacturers. However, just as the ISO(R) system, paper grades are also defined in ranges. This was defined in an appendix to the standard to rectify the situation, you already outlined. Consequently, manufacturers don't need to publish 'their' ISO(R)/grade equivalent. It's in the standard.
From the papers I tested, most adhere to both standards. BTW, grade 5 ranges from 0.50 to 0.65, not 0.40. The confusion came with VC filters. Manufacturers labeled them from 00 - 5 (Ilford) or -1 to 5+ (Kodak). These numbers have litte to do with ISO paper grades. They are just numbers and differ, as you said, widely from manufacturer to manufacturer. That's why manufacturers need to publish ISO(R)/filter number equivalents. They are not a standard.
Your Dokulith example, on the other hand, might be explained with the fact that the standard call grade 5 the hardest grade, so a paper harder than 0.50 might be erroniously called grade 5 as well. That's why Kodak came up with the nomenclature '5+' for their filter numbers. The grade/filter number confusion also explains why so many people say that a color head doesn't reach a grade 5. In fact, they all do, but they don't reach a filter 5, since that is quite a bit harder with most manufacturers.
This sounds an is confusing. That's why I also propose to use the ISO(R) numbers where ever possible. Unfortunately, the old grade numbers are very common. Just keep them separate from the filter numbers, or it gets really confusing.
In my ignorance, I was not aware of the ISO(R) appendix defining grade ranges. Would you be kind enough to give me a reference (i.e. when it came out)?
My figures (from memory, which may be at fault) came from a conversation with an Ilford technical expert, no longer with the company (he was a casualty of the bankruptcy, not of ignorance), who was on the ISO standards committee. I can only imagine that I mis-recalled 40 for 50, in which case add 10 to the numbers I gave.
I was more than a little puzzled by the idea that filter numbers and grades might not, in fact, correspond, so, in the middle of drafting this, I called my old contact -- still a friend, though no longer on the ISO standards committee -- and his comments were illuminating.
First, my memory was indeed at fault: the highest ISO(R) for grade 5 that he recalled was 42, whiler Ilford's ISO(R) for 5 was 45. The only paper that regularly ventured into the 30s was Agfa's Extra Hard.
Second, he said, the correlation between grades and ISO(R) was in an obsolete standard, essentially a Kodak system that no longer obtained. The current standard does not (to his knowledge) contain the appendix you mentioned. As both you and he know more about this than I, I stand open to correction.
Third, Ilford's filtration for MG IV (and later papers) was indeed designed to correspond reasonably well to paper grades, so a grade 1 filter should be pretty close to grade 1 paper, and so forth up to grade 5. As he said, "It is hard to see why we should do otherwise."
Fourth, the ever-improving Dmax of paper made something of a mockery of the 1950s figures. Modern Dmax for VC papers is in the 2.2 - 2.3 range, well up on the Dmax available in the 50s.
As I say, you and he both know more than I, but as he was until a couple of years ago on the ISO standards committee, I would hesitate to dismiss his words.
You are probably taking about Mike Gristwood. Mike and I discussed this subject several times. He and Dave Valvo from Kodak have been a great support to me for years and both served on the ISO committe for their respective companies. Their are both great people, going out of their way to help folks. I respect Mike a lot and still work together occasionaly (watch the next edition of the Focal Enciclopedia of Photography for our contributions).
Mike didn't tell you anything wrong. The standard, I referred to is indeed outdated. I don't know when the appendix was dropped, but it appeared in the 1966 version first (ANSI PH 2.2 1966). A much needed standard at the time, because every manufacturer had their own but similar system. It was a mess. Later an attempt was made to add another grade (6), but that idea was dropped before it became official.
We are all better off using the new standard (ISO 6846, 1992) and getting used to the ISO(R) numbers as the grades are rather confusing and not linear, but as I said before, they are universially (mis)understood.
Ilford's attempt to match filter numbers with ISO grades is honrable, but actually impossible. Ilford has no control of the light sources or the chemicals used, nor do they know all the papers their filters might be used with. These are all significant variables. Nevertheless, according to their own technical information, MG-IV FB develops to grade 3.5 with their number 3 filter. The number 4 filter creates an ISO grade 5 with the same paper. Mind you, Kodak wasn't doing much better. Their number 3 filter made it just to ISO grade 2 on their very own Polymax II in their very own Dektol. Agfa was in a similar boat.
I see other folks posting things here but I can't figure out how yet. Otherwise, I would post a table comparing the Big Three filter values with the standard ISO grades and ISO(R). For people who have the book 'Way Beyond Monochrome', it's on page 67.
Again, I agree that we should drop ISO grades and use ISO(R), but as long as we use the grades, let's make sure that we don't confuse them with filter numbers. Ironically, I think it's because of the filter numbers that ISO grades are still used.
Allen Friday dropped me a note that directed me to the chart at the top of page 89 in Beyond the Zone System. When I looked it up just now, it is indeed the chart that I had in the dark recesses of my memory. I thought I'd post the info in case anyone else was scratching their head about where they had seen it. Thanks to all for the info....
Sorry Craig for digressing so much. The chart in Phil Davis' book is correct. If you want to use Excel to calculate the values yourself, the equation I mentioned before will return the same values.