Local Gamma and the workings of VC paper

[Nicholas Lindan]

There is a new application note on the Darkroom Automation web site that introduces the concept of local gamma in printing papers and explains the workings of variable contrast papers.

http://www.darkroomautomation.com/support/appnotevcworkings.pdf

The note is of general interest and not limited to users of Darkroom Automation products.

 

[ic-racer]

Well worth reading.

Do you have an experimental sample of 00 or 0 Ilford MG showing the the flat spots on the first derivative curve?

 

[df cardwell]

cool beans

 

[ic-racer]

I recall the last time we looked at prints, I had some printed with 00 or 0 filtration. After we spoke I spent some time analyzing them based on a premise that the paper curve at 00 and 0 is 'much less than ideal.'

I concluded:
I still liked the prints
B&W is all about distortions in tonal scale, somehow the quite distorted scale either did not matter or added to the print's presentation
Perhaps the areas of zone convergence (adjacent zones printing the same density) were not so easy to detect because the flat areas only contained portions of a single zone (less than one stop in length) or, because there were more than 8 zones of negative density in the print, the effects of a complete adjacent zone convergence were more difficult to detect.

On a little different tangent, I would paraphrase that whole pdf as indicating that high-contrast negative development and low contrast MG printing is NOT the same as low contrast negative development and high contrast MG printing. Perhaps we are at the level that with the darkroom tools available, one could specify a low neg/high paper contrast or visa-versa at the time of negative exposure, based on an intended interpretation of the scene.

 

[dpurdy]

Wow, I hope we aren't being tested on that! I am certifiably confused. I did note a typo where toe is spelled tow.
Dennis

 

[Nicholas Lindan]

Well worth reading.

Do you have an experimental sample of 00 or 0 Ilford MG showing the the flat spots on the first derivative curve?

Ilford warm-tone has the worst example:
http://www.darkroomautomation.com/support/mgivfbwtd72hd.jpg

Actually, all it means is the 00 filter is beyond this paper's capabilities and shouldn't be used. Grade 1 is probably the lowest usable grade with MGWT, grades 0 and 1/2 are very close to 1 and only exhibit anomalies to set themselves apart.

But all the MG papers exhibit roller-coaster curves at the lowest contrast grade:

http://www.darkroomautomation.com/support/mgivrchd.jpg

 

[Larry Bullis]

Well worth reading.

Do you have an experimental sample of 00 or 0 Ilford MG showing the the flat spots on the first derivative curve?

I'm missing something. Was there an attachment or link that I'm not seeing?

 

[Nicholas Lindan]

I recall the last time we looked at prints, I had some printed with 00 or 0 filtration.

I remember them. They look perfectly normal until the print reaches a certain dark grey tone and then all the detail disappears in the area - like a local fog cloud obstructing the view - and as things get darker again the detail reappears. Could you post/link to the prints? I think they are a great example of the phenomena.

I concluded: I still liked the prints

That's what makes photography an art. The flat spot in the curve isn't really a defect if you want to take advantage of it. If all the tone reproduction was perfect there wouldn't be any fun in it - it would be like it was, er, digital.

Perhaps we are at the level that with the darkroom tools available, one could specify a low neg/high paper contrast or vice-versa at the time of negative exposure, based on an intended interpretation of the scene.

One could. It would be interesting to see a scene rendered both ways.

Me, I just mostly just muck about when making pictures.

There is nothing - absolutely nothing - half so much worth doing as simply messing about in boats.
- Ratty, Wind in the Willows, K. Grahame

 

[Lee L]

I'm missing something. Was there an attachment or link that I'm not seeing?

I think that ic-racer may be talking about the 'flat spots' on a print represented by the two low contrast areas in the 'local gamma three emulsion model' at the top of page 6 of the .pdf. They are the low points (not flat on the graph, but flat as in low contrast on the print) on the yellow line in that graph near 0.475 and 1.2. print density on the x-axis.

I could be wrong.

Nicholas has several typical VC paper H&D curves for varying contrasts on his web site, and you can see the characteristic transitions between VC paper emulsion layers in those. They would be valuable for anyone using these papers, not just folks who have his enlarging meter. But I do really like his enlarging meter, which I've been using for about a year now.

Lee

 

[Larry Bullis]

Lee,

I see no pdf. Pdf? Am I going nuts AGAIN?

 

[Lee L]

Lee,

I see no pdf. Pdf? Am I going nuts AGAIN?

In the first post. I'll email it in case it's not showing for you for some odd reason.

Lee

 

[Larry Bullis]

In the first post. I'll email it in case it's not showing for you for some odd reason.

Lee

I'm sure that there is no first post, if that's the problem. The first one I got must have been the second, and there was no going back. In front of the first post I saw was a solid wall.

Weird, but I'm getting sort of accustomed to weird. How did we get addicted to these monstrous electronic things anyway?

Anyway, Lee, I got your email and I can see it now. I find the topic quite interesting because I think it may refer to something (at least analogically) I became aware of about forty years ago. I'm not sure, though, because where I noticed the flattening was with #1 Agfa Brovira. It was a bit strange, and I've never quite understood why. Maybe this will help.

Larry

 

[Bob Carnie]

Nicholas
I am following this thread with interest, I am not sure I understand all of this but in simple layman terms , could this be part of the reason that when I first starded doing split printing I used the 0 /00 grade and 5 grade method I was not happy with the the prints and after a while I started using a 1, 1 1/2 grade and 5 grade method , and only using the 0 for occasional flash into hot zones.
The only paper I have really used since its birth to the market place is Ilford Warmtone , as I have always felt it met my needs.
Could you describe or post images that show the problem areas of using 0 or 00 with Ilford Warmtone.
I have always felt that for split printing, or at least for 10 years now that starting off with 0 was not such a good idea for my work.

thanks
Bob

Ilford warm-tone has the worst example:
http://www.darkroomautomation.com/support/mgivfbwtd72hd.jpg

Actually, all it means is the 00 filter is beyond this paper's capabilities and shouldn't be used. Grade 1 is probably the lowest usable grade with MGWT, grades 0 and 1/2 are very close to 1 and only exhibit anomalies to set themselves apart.

But all the MG papers exhibit roller-coaster curves at the lowest contrast grade:

http://www.darkroomautomation.com/support/mgivrchd.jpg

 

[ic-racer]

Ilford warm-tone has the worst example:

Thanks for showing those. I don't have a reflection densitometer so I don't know the curve shapes for my papers. I did run some 21 step contacts for visual analysis using "max Yellow" on my new Dichroic head and there were no mergers between any two steps with Ilford MG Fiber. To the naked eye, there looked to be a good progression between each step. I did not get a chance to compare it with the Ilford "00" filter yet, as my "max Yellow" may just be a "0" and not "00." I'm using Dektol at the usual dilution. Not sure if that makes any difference.

So, I agree with all your comments. That is, not all papers are as bad, and the worst ones are still OK if you don't go down to "00."

 

[ic-racer]

Nicholas
I am following this thread with interest, I am not sure I understand all of this but in simple layman terms , could this be part of the reason that when I first starded doing split printing I used the 0 /00 grade and 5 grade method I was not happy with the the prints and after a while I started using a 1, 1 1/2 grade and 5 grade method , and only using the 0 for occasional flash into hot zones.

Seems at first like what Nicholas has shown with the poor "00" performance of could explain that, howerver, as Nicholas will probably detail, once you add ANY magenta or blue exposure to the paper you no longer are on the "00" curve. The paper curve does not change if it gets the blue at the same time as the green or later or earlier.

 

[Bob Carnie]

I guess that in my case sometimes the bulk of the exposure was G-00 then a slight 5 to set the black. When I worked with 0 and 5 this way I never really liked my results on different papers, when I started with a 1 or 1 1/2 then five I always liked the result better.
Today I do not use 0 and then 5, I only use the 0 to flash in some tone by burning after the main and 5 is complete.

Seems at first like what Nicholas has shown with the poor "00" performance of could explain that, howerver, as Nicholas will probably detail, once you add ANY magenta or blue exposure to the paper you no longer are on the "00" curve. The paper curve does not change if it gets the blue at the same time as the green or later or earlier.

 

[Ken N]

Nicholas shows with math why our common thinking about paper grades is so wrong. Boy, is it so wrong. I've been in the darkroom since the age of two or three and I never realized (although, I should have) that the emulsion layers all have the same intrinsic contrast and it is dependent upon the additive nature of the layers working together to achieve maximum contrast. I'm having heartburn on a few things about it, though, as I "know" what I've experienced in the darkroom seems contrary to his conclusions but a wee bit of experimentation will most likely take care of those doubts.

What is most fascinating about looking at these graphs is that it totally explains why split-grade printing works.

Ken

 

[Kirk Keyes]

I did run some 21 step contacts for visual analysis using "max Yellow" on my new Dichroic head and there were no mergers between any two steps with Ilford MG Fiber.

If you did contacts with the actual Stouffer with it's 0.15 OD steps, you probably would be pressed to see any two steps the same. I'd try a using a neg made from contacting with the Stouffer tablet so the difference in steps is less than 0.15 OD - maybe make one with a 21 steps going from 0 - 1.2 in the new neg. And then see how if the darker Zones start to merge.

 

[ic-racer]

If you did contacts with the actual Stouffer with it's 0.15 OD steps, you probably would be pressed to see any two steps the same. I'd try a using a neg made from contacting with the Stouffer tablet so the difference in steps is less than 0.15 OD - maybe make one with a 21 steps going from 0 - 1.2 in the new neg. And then see how if the darker Zones start to merge.

Yes, a 'standard' wedge with 0.15 steps. But I was just going back the an earlier post on the possibility of a hypothetical "Total Zone Merge" which I did not demonstrate. Smaller increments may not matter as much. But this is all quite open to differing opinions.

I, am not yet convinced one way or the other that the tonal range of platinum paper offers an advantage over low contrast MG paper. Nicholas' graphs seem to be the first step in an argument FOR platinum printing. What I don't know is how the MG paper curve at 00 responds to different developers or even to flashing.


Anyway, here is a real example from my darkroom:
Ilford MG IV FB
Dektol
Durst Dichroic Filter (Max Yellow)
0.15 step wedge

The two slices under the bar are somewhat similar, confirming that the tonal scale is less steep there as Nicholas has suggested and predicted. But, I suspect those tonal steps spaced that close can still make a fine print.

 

[Nicholas Lindan]

I think this is the step tablet print that generated the above graph, if not then it is close.

Ilford MGIV WT FB, D-72 1:2 3 minutes, #00 Ilford under lens filter, condenser/PH212 lamp, Stouffer 31-step 4x5 tablet projected to 5x7.

You can see where the delineation between the steps goes flat in the dark greys in the middle of the strip. The contrast then picks up again just before the shoulder.

The effect in the print is like a veil has been drawn over parts of the print - the parts that are the same tone as the flat spot on the HD graph.

 

[ic-racer]

Yes that is pretty bad. Is that the Ilford Warmtone with 00 filtration?

 

[L Gebhardt]

Nicholas, I have never seen any of my step wedge prints do that to that extreme. What paper and printing conditions were you using?

In fact I have plotted the curves of several papers using my Ilford 500 head and I get nice smooth curves on most papers. Most of my tests have been on Forte Polywarmtone, Ilford MGIV, and Ilford WT.

I have attached my curves for MG IV and a scan of the step wedge contacts. These were from the Analyser 500 calibration, so they are not quite standard. The low curve (0) is using only the green light. The high curve (150) is using only blue light. In this case the paper shows a contrast range of ISO 55 (~ grade 4.5) to 173 (< grade -1). The first two curves show conditions that turned out to be outside the calibration range so were not used.

 

[Nicholas Lindan]

I added notes to the step tablet post. Yes, the paper is MGIV WT FB in D-72 with 00 filtration.

It isn't that the paper is defective ... the effect is due to exposing the paper to more filtration than the paper can handle.

Warm-tone simply doesn't go down to 00 with acceptable performance. No big deal, the paper has lots of redeeming properties.

 

[genk]

Hi
My name is Genk, I have been told that there is a powder that removes black carbon from photographic paper. Do you know the name or the process that can be applied. Underneath the carbon is a printed image. I have seen the powder being applied and then a brown liquid chemical wash applied and then another clear liquid chemical dissolving the carbon away, leaving the print intact. Please let me know if you can offer me any advice.

Genk

 

[ic-racer]

It isn't that the paper is defective ... the effect is due to exposing the paper to more filtration than the paper can handle.

I agree that is the important point here.