Flawed definition of grade?

When programming my LED-head controller, I discovered that if a paper has a low Dmax, its grade is higher than a paper having a normal Dmax and (importantly) the same contrast in the midtones. Same contrast; different grade. We have a problem.

This anomaly occurs because grade is based on LER, which is the log of exposure range corresponding to densities 0.09 and 0.9*Dmax. Because the paper's Dmax is low, its LER is lower, causing its computed grade to be higher.

This is a problem with a LED controller because if you specify grade 2 (for example) for your print, you'll get different contrasts for Ilford (Dmax=2.10) vs Foma (Dmax=1.87). In effect, the term 0.9*Dmax lets Foma cheat and claim higher contrast than it actually achieves.

In order for different papers to print at the same contrast (and thus look the same) for the same grade, it seems to me that grade should be based on the slope of the central portion of the paper's HD curve. I see two ways to do this:

* Determine LER between fixed densities of zones VII to III (i.e., densities of 0.19 and 1.61). This solution assumes 1.61 is off the shoulder for all papers. Grade can be determined by LER as in the past, but the thresholds for grades would change.
* Determine LER between variable densities computed as fractions involving Dmin and Dmax, and base grade on the slope, as illustrated below.


The constants 0.07 and 0.10 match zones VII and III when Dmax=2.1, but we can use 0.10 or somesuch for both -- I doubt it matters. Grade would be determined by slope and not by LER.

I believe this anomaly has not been a problem in the past because most people use tungsten lamps with filters, and as long as Foma yields the same visual contrast as Ilford with the same filters, users are happy. But when we apply the standard definitions to make LER (and thus grade) the same between papers via a microcontroller, the papers don't respond with the same contrast. I think this problem will become more serious as LEDs become more popular.

Your thoughts about this problem and my proposed solutions?

Before commenting, I assume you are referring to multigrade papers and have taken into account the spectral responses of the emulsions... Please confirm and clarify.

BCM said:

Before commenting, I assume you are referring to multigrade papers and have taken into account the spectral responses of the emulsions... Please confirm and clarify.

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Yes, although one must be careful about this when using LEDs. The contrast of each brand of paper is determined by the ratio of green and blue lumenance, but brands don't yield quite the same contrast for a given green/blue ratio. Thus, the ratio is not a universal function of grade (or vice versa). Just to complicate matters, wavelengths of green and (often) blue also affect contrast. The wavelengths and ratio combine to produce a LER, which, in the standard, determines grade. But as it's presently defined, LER is affected by Dmax, thus distorting grade. Hence my idea of using slope instead of LER to measure grade.

it seems to me that grade should be based on the slope of the central portion of the paper's HD curve.

Click to expand...

Seems like a reasonable solution. True test is to make some prints and look at them, comparing the two methods.

I (or my spreadsheet program) does something similar to look at the contrast of films. Rather than computing a true "contrast index" based on the plexiglas overlay.

I was hoping you'd graph the problem. Not really sure where you got the 0.07 from. LER is based on 0.04 over Paper base plus fog. Anyway, there's a paper by Jones from the mid-forties that evaluates how to determine matching a negative to paper. It's been an awful long time since I've read it, but Jones concluded, “because of the influence of the brightness distribution and subject matter in the scenes photographed, an accurate prediction cannot always be made of the exposure scale (Log Exposure Range) of the paper which will give a first-choice print from a negative of known density scale (Density Range)… But what other course is there to follow? Either we must make the best of a somewhat imperfect relationship or face the prospect of having no criterion whatever for choosing the paper contrast grade.”

Stephen Benskin said:

I was hoping you'd graph the problem. Not really sure where you got the 0.07 from. LER is based on 0.04 over Paper base plus fog. Anyway, there's a paper by Jones from the mid-forties that evaluates how to determine matching a negative to paper. It's been an awful long time since I've read it, but Jones concluded, “because of the influence of the brightness distribution and subject matter in the scenes photographed, an accurate prediction cannot always be made of the exposure scale (Log Exposure Range) of the paper which will give a first-choice print from a negative of known density scale (Density Range)… But what other course is there to follow? Either we must make the best of a somewhat imperfect relationship or face the prospect of having no criterion whatever for choosing the paper contrast grade.”

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Okay, here's a diagram showing HD curves of two papers having the same contrast, but different Dmax. We see that the differing Dmax values result in different LER values, resulting in different grades, though the contrast is the same.

The multiplier of 0.07 is the fractional distance along the density-range for zone VII, assuming Dmax=2.1, and was computed as follows:
frac = (Dmax-density)/(Dmax-Dmin) = (0.19-0.05)/(2.1-0.05) = 0.068

BTW, I goofed in my OP. The other multiplier of 0.10 (for zone III) should be 0.24.

ic-racer said:

True test is to make some prints and look at them, comparing the two methods.

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This. There's no replacing hard, empirical evidence. It will get you where you want to go. Plots and graphs are not the image, it's always about the image, only.

albada said:

Okay, here's a diagram showing HD curves of two papers having the same contrast, but different Dmax...

Click to expand...

The problem here is defining one point as 0.9 of Dmax. If the point was defined as 1.7OD then there wouldn't be much of a problem. Anything above 1.5OD is pretty much wasted when a print is viewed in normal room illumination.

Interesting graphs ensue if the Zones are plotted against relative exposure:

The lower the slope the higher the contrast. You can see the low contrast 'flattish spot' at highlight-skin for the lower contrast grades of MGIV. This has largely been taken care of with MGV papers.

albada said:

Okay, here's a diagram showing HD curves of two papers having the same contrast, but different Dmax. We see that the differing Dmax values result in different LER values, resulting in different grades, though the contrast is the same.
View attachment 322510
The multiplier of 0.07 is the fractional distance along the density-range for zone VII, assuming Dmax=2.1, and was computed as follows:
frac = (Dmax-density)/(Dmax-Dmin) = (0.19-0.05)/(2.1-0.05) = 0.068

BTW, I goofed in my OP. The other multiplier of 0.10 (for zone III) should be 0.24.

Click to expand...

There are many different directions to potentially take here. First, I might suggest using the standard methods when doing an evaluation. How can you make a conclusion something is flawed when the method being examined is not properly applied? Your LER method appears to be different from the ISO method. Second, I'm a bit confused as to what the fractional distance along the density-range for Zone VII is about and what it concludes. Also, you have two different values for Dmax in your equation. The variable "density" in the equation is referring to what? Clarifying this could help towards clearing things up. It would also be helpful if you provided all the results. What are the two paper's LERs and gradients? The graphs have no units of measurement so we cannot independently measure the results ourselves.

I'm not sure if I'm going to say this right. It's not the best idea to mix the Zone System with sensitometric testing. Do the sensitometry first and then add Zones as a reference.

I believe the answer to your problem has to do with objective vs subjective tone reproduction. For instance, if the reflection density of the print matches the original subject, it would appear to be too dark and somewhat flat. Photography is psychophysical and that is where may of the problems with defining aim and methodologies can be tranced. What makes precision harder is the expressive purpose and intent of a photograph. That's why any methodology or values within are less about absolutes and more about averages and how they tend to be. Perhaps an appropriate analogy is to aim for the bullseye in order to have a best chance of hitting the target.

With your concern, you have to determine how papers with different levels of DMax and having the same mid-tone gradients compare with matching the negative to the LER. Think about matte papers. They tend to have a maximum reflection density of around 1.60. How do they still work? What about alternative processes? They all have differing levels of DMax. What about the viewing conditions? Could the perception of the desirable print change under varying levels of illumination or surrounding environments? I believe we are looking at the concept of adaption. Subjective tone reproduction is a very complex subject of which I am very rusty at and never great at when I wasn't. It might be time to review the material and refresh what's left of my memory.

Gradient can be used to determine the choice of paper. Photographic Materials and Processes has the equation GI*GII*GIII = GIV. There should be a line over the "G"s for average gradient, but I don't know how to do that here. GI is the average gradient of the camera image, GII is the negative, GIII is the print, and GIV is the reproduction curve. The book's example has:

0.82 * 0.56 * 1.78 = 0.82 for



What could be the shortfalls of this approach?

In terms of considering which approach is applicable in most conditions, have you considered the differences between a condenser and diffusion enlarger on the range of the LER? The same same negative with the same paper gradient (questionable depending how it's measured) will have different aim LERs depending on the enlarger type. This is the same concept of which speed method to use. Most will work under average conditions with most films, but which one agrees closest under the greatest range of conditions?

One more thing to think about. The paper curve below is a grade two. The horizontal lines represents the density ranges of first choice prints and how they fall on the curve. First choice prints are the ones people have judged as being of excellent quality. There are no absolutes, only averages, caveats, and justifiers as "tend to" and "generally."

Stephen Benskin said:

I'm not sure if I'm going to say this right. It's not the best idea to mix the Zone System with sensitometric testing. Do the sensitometry first and then add Zones as a reference.

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Nicely done. This (above) is probably the largest error made when doing sensitometric evaluation of materials along with poor process (exposure, development, chemical exhaustion, etc) controls. As noted, the Zone System is really based on a visualization methodology which is taking a continuous analog function and dividing it into discrete steps. None of that applies in densitometry. Adams makes that pretty clear in his writings. That doesn't make it wrong, of course. Getting this to students in BTZS courses was one of the biggest difficulties we had. Art versus Science in some aspects.

There are multiple variables involved. The the specific developer, length of development, and dev temp can significantly affect how the respective low and high contrast curves interact in terms of final print characteristics. Toning afterwards too. Specific films and papers all vary between each other. So unless you want to make endless plots relative to each hypothetical case, there is simply no way to predictably pin it all down relative to Zone-this, Zone-that, especially when real graded paper now barely exists. There's nothing rigid and fixed about the Zone System itself anyway, You basically choose the length and elasticity of your own Bungee jumping cord, and hope it holds your weight.

Densitometer plots can certainly be useful. But one needs to realize that's just a starting point, and an optional one.

They don't even agree on a starting point. The standard Model or statistically average conditions model is the basic values in determining exposure. It starts with 100% Reflectance. Zone models key off of the metered exposure point. Based on the luminance value of the calibration point of a reflectance meter as stated in the standard and the stated illuminance for the average daylight scene, Zone V falls at 12%, and not 18% Reflectance. So any measurement is already not going to be in agreement. As the Zone scale is keyed off of Zone V, the Reflectance for each step will also be different. Whereas diffused highlights for the standard model falls at 100% Reflectance, Zone VIII falls at 95.5% with the 12% model and 144.5% with the 18% model. One more thing, Zone uses 7 stops and the average luminance range is 7 1/3 stops which is why the standard model has an extra stop of just log 0.10.

Stephen Benskin said:

It's not the best idea to mix the Zone System with sensitometric testing. Do the sensitometry first and then add Zones as a reference.

Click to expand...

Due to the crude technology of his day, Ansel Adam's zone system was implemented only halfway. Despite placing an element on a zone (density on the print), this system decided only the exposure and development of the negative. It failed to contribute to the other half of the process: printing.

With the advent of good easel meters, LEDs, and microcontrollers, the missing half of the zone system can now be implemented. Consequently, I have created some new capabilities:

1. Placing an element on the easel on a zone (= a specific print-density), thus determining exposure, but setting contrast separately.
2. Placing two elements on two zones, thus determining both exposure and contrast.
3. After deciding exposure+contrast above, one can determine dodge/burn time to place an element on a zone.

Capabilities 1 & 2 complete the zone system.

The print thus matches the original vision.
This system works well and saves me much time. Most of my work prints look good on the first try. I can fine tune them before making a final enlargement.

The problem is in capability #1: Contrast must be set separately, so I want a given contrast (grade) to look the same regardless of paper-type. With grade being dependent on 0.9*Dmax, two papers with the same overall contrast have different grades. Hence my question in this thread about how to improve the method of computing grade.

I suspect that our intuitive sense of contrast is based mostly on midtones and darker highlights. Darker shadows are difficult for us to distinguish, so they don't contribute to our perception of contrast, and thus should be excluded from the computation of contrast. Thus, I suspect that a function of the LER which corresponded to densities of around 0.2 through 1.3 would agree closely human perception of contrast. BTW, I'm assuming typical indoor lighting of EV 6 or 7 at ISO 100.

The proposed function above has no reference to zones, so let's leave them out. Now I'm sorry I mentioned them. The function is an idea based solely on my (probably poor) understanding of human perception of contrast. The long explanation above is to give you a broader view of what I'm doing -- implementing the missing darkroom-half of the zone system. And I love it; it's a big time-saver.

@albada I like your system. It lets you work out a practical way of getting optimal results. Please, allow me to share the system that's currently implemented in my program.Perhaps it will help figure out the apparent problem you mentioned in your opening post.

It's based on the Darkroom Automation system (by projection printing test samples and measuring iluminance levels with an an-easel exposure meter), but it's not identical. It's a system that allows practical assessment of paper's response to exposure and how it relates to both paper grades and Zone System zones, and of course, film performance. Yes, I know that it's, technically, not a good idea to mix the Zone System in, but a lot of photographers do use the Zone System on a daily basis, and it can, at least for my purposes, be useful to include it. It all depends on what one is after.

If one wants to work strictly within sensitometric theory, then the approach below is not ideal. However, if one wants to evaluate paper performance practically, then it works nicely, at least for me. I also want to point out that the goal here is to come up with paper grades empirically, rather than to comply with an a priori definition of paper grades. As far as I know, the ISO standard does not include paper grade definitions. Also, the 0.09 value comes from 0.04 over B+F, with the densitometer zeroed on the reflection plaque. You'll see that the Oriental Seagull VC FB Glossy does not have a perfectly linear response to Ilford's under the lens filters. This could be easily remedied by means of a dichroic enlarger head (or a modern LED-based system) and customized filtration, which my program helps figure out.

This system should work nicely with a precise, LED-based, enlarging system, like the one @albada has. It also works best with the f-stop timer method, but can be adapted to linear timers.

Currently, my program computes the relevant parameters and outputs an Excel spreadsheet with three sheets embedded in it: (1) paper speed table, (2) paper grades table, and (3) paper contrast table. Please, let me know if this could be useful to you, and if not, how you'd like it changed/adapted to your system. I will be glad to add whatever analysis type is required by darkroom practitioners.

It looks like Photrio won't let me attach an .xlsx file. If you'd like to look at it, please DM me. Sorry about that!
EDIT: I created 3 images from the xlsx file

aparat said:

@albada I like your system. It lets you work out a practical way of getting optimal results. Please, allow me to share the system that's currently implemented in my program.Perhaps it will help figure out the apparent problem you mentioned in your opening post.

It's based on the Darkroom Automation system (by projection printing test samples and measuring iluminance levels with an an-easel exposure meter), but it's not identical. It's a system that allows practical assessment of paper's response to exposure and how it relates to both paper grades and Zone System zones, and of course, film performance. Yes, I know that it's, technically, not a good idea to mix the Zone System in, but a lot of photographers do use the Zone System on a daily basis, and it can, at least for my purposes, be useful to include it. It all depends on what one is after.

If one wants to work strictly within sensitometric theory, then the approach below is not ideal. However, if one wants to evaluate paper performance practically, then it works nicely, at least for me. I also want to point out that the goal here is to come up with paper grades empirically, rather than to comply with an a priori definition of paper grades. As far as I know, the ISO standard does not include paper grade definitions. Also, the 0.09 value comes from 0.04 over B+F, with the densitometer zeroed on the reflection plaque. You'll see that the Oriental Seagull VC FB Glossy does not have a perfectly linear response to Ilford's under the lens filters. This could be easily remedied by means of a dichroic enlarger head (or a modern LED-based system) and customized filtration, which my program helps figure out.

This system should work nicely with a precise, LED-based, enlarging system, like the one @albada has. It also works best with the f-stop timer method, but can be adapted to linear timers.

Currently, my program computes the relevant parameters and outputs an Excel spreadsheet with three sheets embedded in it: (1) paper speed table, (2) paper grades table, and (3) paper contrast table. Please, let me know if this could be useful to you, and if not, how you'd like it changed/adapted to your system. I will be glad to add whatever analysis type is required by darkroom practitioners.

It looks like Photrio won't let me attach an .xlsx file. If you'd like to look at it, please DM me. Sorry about that!
EDIT: I created 3 images from the xlsx file
View attachment 322636View attachment 322637View attachment 322638

Click to expand...

I just looked over the files in the Darkroom Automation website, and I see the similarities. In both systems, you (1) measure the illuminance of an element on the easel, (2) look up an exposure on a graph based on desired grade and zone, and (3) subtract the two numbers to get the time (and/or f-stop adjustment). Or did I misunderstand?

With the LED/microcontroller system, software performs steps (2) and (3). In effect, I tell the controller, "An element measures 3.7; place it on zone 6." And it does so, using the current contrast and paper-type. And capability #2 is to place two elements on two zones, setting both exposure and contrast. I don't think anyone has done this before.

Like you, we want a system that's easy to use and practical. That means using zones because they provide us with an intuitive gauge of density, unlike log-densities or Munsell values. However, zones are not needed to calculate grades, which is the topic of this thread.

BTW, your middle graph has steep slopes at both ends. I guess those are a consequence of the zone-densities you're using. Could you post your zone-densities, and how you got them?
Your right graph is ISO grade. How are you computing those from log range? Are you using the cubic polynomials in Way Beyond Monochrome? Or something else?

albada said:

I just looked over the files in the Darkroom Automation website, and I see the similarities. In both systems, you (1) measure the illuminance of an element on the easel, (2) look up an exposure on a graph based on desired grade and zone, and (3) subtract the two numbers to get the time (and/or f-stop adjustment). Or did I misunderstand?

Click to expand...

It's a kind of hybrid method, which includes both existing standards, the Zone System, and personal/practical tools. Yes, it involves measuring illuminance levels on the easel and looking up the required contrast, exposure, base, dodging, burning, split-grade printing, etc. My program generates a spreadsheet that can be printed out pinned to a darkroom wall, along with a timer sequence to make "chips" that show the exact tone one's going to get by following the data. it looks kind of like that. There are three sheets inside the document with different looks at the same data, so to speak.

albada said:

With the LED/microcontroller system, software performs steps (2) and (3). In effect, I tell the controller, "An element measures 3.7; place it on zone 6." And it does so, using the current contrast and paper-type. And capability #2 is to place two elements on two zones, setting both exposure and contrast. I don't think anyone has done this before.

Click to expand...

Cool! With the DA timer, you can store more than one element in memory and program a sequence based on them, but it's not exactly what I think you're describing.

albada said:

Like you, we want a system that's easy to use and practical. That means using zones because they provide us with an intuitive gauge of density, unlike log-densities or Munsell values. However, zones are not needed to calculate grades, which is the topic of this thread.

Click to expand...

That's exactly my motivation, too. I want a tool that's based on cogent principles but is practical and easy to use.

albada said:

BTW, your middle graph has steep slopes at both ends. I guess those are a consequence of the zone-densities you're using. Could you post your zone-densities, and how you got them?
Your right graph is ISO grade. How are you computing those from log range? Are you using the cubic polynomials in Way Beyond Monochrome? Or something else?

Click to expand...

When I re-read my post, it seems to say that there's no ISO standard for paper grade. That's not exactly what I meant. I meant there's no ISO standard for paper grade filtration. So it's more useful to me to figure out what my paper grades are based on my hardware and materials, rather than trying to force my setup to conform to an ISO (or other) standard. It's just a personal preference. Nothing wrong with either approach.

I wasn't aware that they're using cubic polynomials for computing paper grades. For most of the things my program does, I use statistical models, if they can be made. For paper grades and for zones, I built a model based on existing standards and conventional "standards," including data from Darkroom Automation, Way Beyond Monochrome, BTZS, and other sources. I also implemented the very simple but very effective contrast model from Darkroom Automation based on Zone ratios. I find it very intuitive. To me, the Zone System is like a mnemonic device for getting a decent result very quickly.

May I ask if you built your own LED enlarger head and a timer/analyzer/controller? That would be beyond awesome. I was meaning to start a project to design an f-stop timer/analyzer when DA was going to stop making his, but now that they're available again, I don't feel motivated. It would be a pretty big undertaking.

@albada I went back and re-read the Way Beyond Monochrome paper calibration chapter. Their approach is solid, and is their data. If you implement their approach, I you're going to get good results. It's different from what I do and what DA does, but, in principle, the results should be very similar. It's a terrific resource.

albada said:

When programming my LED-head controller, I discovered that if a paper has a low Dmax, its grade is higher than a paper having a normal Dmax and (importantly) the same contrast in the midtones. Same contrast; different grade. We have a problem.

This anomaly occurs because grade is based on LER, which is the log of exposure range corresponding to densities 0.09 and 0.9*Dmax. Because the paper's Dmax is low, its LER is lower, causing its computed grade to be higher.

This is a problem with a LED controller because if you specify grade 2 (for example) for your print, you'll get different contrasts for Ilford (Dmax=2.10) vs Foma (Dmax=1.87). In effect, the term 0.9*Dmax lets Foma cheat and claim higher contrast than it actually achieves.

In order for different papers to print at the same contrast (and thus look the same) for the same grade, it seems to me that grade should be based on the slope of the central portion of the paper's HD curve. I see two ways to do this:

* Determine LER between fixed densities of zones VII to III (i.e., densities of 0.19 and 1.61). This solution assumes 1.61 is off the shoulder for all papers. Grade can be determined by LER as in the past, but the thresholds for grades would change.
* Determine LER between variable densities computed as fractions involving Dmin and Dmax, and base grade on the slope, as illustrated below.

View attachment 322502
The constants 0.07 and 0.10 match zones VII and III when Dmax=2.1, but we can use 0.10 or somesuch for both -- I doubt it matters. Grade would be determined by slope and not by LER.

I believe this anomaly has not been a problem in the past because most people use tungsten lamps with filters, and as long as Foma yields the same visual contrast as Ilford with the same filters, users are happy. But when we apply the standard definitions to make LER (and thus grade) the same between papers via a microcontroller, the papers don't respond with the same contrast. I think this problem will become more serious as LEDs become more popular.

Your thoughts about this problem and my proposed solutions?

Click to expand...

I'll stick to this standard:

aparat said:

@albada I went back and re-read the Way Beyond Monochrome paper calibration chapter. Their approach is solid, and is their data. If you implement their approach, I you're going to get good results. It's different from what I do and what DA does, but, in principle, the results should be very similar. It's a terrific resource.

Click to expand...

With all due respect to Ralph, while most of the chapter is correct, the Subject Zone Scale in fig 1a-1c for example do not incorporate camera flare and therefore aren't representing reality. Not a big deal if you are illustrating an idea, but if you are working with a tone reproduction diagram or program, your results will be skewed.

Stephen Benskin said:

With all due respect to Ralph, while most of the chapter is correct, the Subject Zone Scale in fig 1a-1c for example do not incorporate camera flare and therefore aren't representing reality. Not a big deal if you are illustrating an idea, but if you are working with a tone reproduction diagram or program, your results will be skewed.

Click to expand...

I was actually referring to a different chapter in the book. In my copy, it is on pp. 59-76. I only mention that to avoid confusion.

I hope this is not off topic, but I'd like to ask @Stephen Benskin if you change anything in your analysis when you add the Zone System display along the top. You showed a plot at some point showing the zone rectangles along the top of Q1 or in-between Q1 and Q4. Or is it just a "cosmetic" thing to include the zones in your tone reproduction cycle or are you adjusting your analysis to account for the zones?

aparat said:

I was actually referring to a different chapter in the book. In my copy, it is on pp. 59-76. I only mention that to avoid confusion.

I hope this is not off topic, but I'd like to ask @Stephen Benskin if you change anything in your analysis when you add the Zone System display along the top. You showed a plot at some point showing the zone rectangles along the top of Q1 or in-between Q1 and Q4. Or is it just a "cosmetic" thing to include the zones in your tone reproduction cycle or are you adjusting your analysis to account for the zones?

Click to expand...

It's just a reference. The Zone System basically applies different terms to established sensitometry. The underlying sensitometric principles don't change. Most errors occur attempting to use flawed Zone System interpretation of sensitometry.

As Zone V is the metered exposure point, I simply calculated the subject reflection density from there. And since the Zone System assigns Zone V as 18% (not the metered value), I did two, one with Zone V at 12% and one with Zone V at 18% Reflectance. In the camera image (Quad I) the RD of the Luminance range, along with the camera settings, determines the camera image. The Zone indication between Quad I & II illustrates the values striking the film. I'm able to key / align the exposure to certain points, like the metered exposure point to 1.0 log-H about 0.10 over film base plus fog, or the shadow exposure to 0.10, or to tweak the placement. Same with the print. So, Zone V can be keyed to 18% on the paper curve and how see how the other values fall and so forth.

aparat said:

May I ask if you built your own LED enlarger head and a timer/analyzer/controller? That would be beyond awesome. I was meaning to start a project to design an f-stop timer/analyzer when DA was going to stop making his, but now that they're available again, I don't feel motivated. It would be a pretty big undertaking.

Click to expand...

Yes, I built both a LED-lamp and a controller for it. Here's the controller:



Basic features include changing brightness of red, green, and blue LEDs (top row of display), and time, base/dodge/burn/untimed modes, and grade (bottom row of display).
Sophisticated features include various ways of setting exposure (ChgExp button), generating and analyzing test-strips (Strip button), a development-process timer with temperature-compensation (Process button), and misc. settings (Menu button).
More features include white-light for focusing, composing, and metering (White button), and red light for positioning a dodge/burn tool before starting exposure (Red button).

In any display, you can change a number by selecting it with the corresponding white button and turning the "Numeric" knob.

The "Grade" item in the display is what this thread is about. It would be nice if a given grade looked as similar as possible on different papers having different maximum/minimum densities.

albada said:

Yes, I built both a LED-lamp and a controller for it. Here's the controller:



Basic features include changing brightness of red, green, and blue LEDs (top row of display), and time, base/dodge/burn/untimed modes, and grade (bottom row of display).
Sophisticated features include various ways of setting exposure (ChgExp button), generating and analyzing test-strips (Strip button), a development-process timer with temperature-compensation (Process button), and misc. settings (Menu button).
More features include white-light for focusing, composing, and metering (White button), and red light for positioning a dodge/burn tool before starting exposure (Red button).

In any display, you can change a number by selecting it with the corresponding white button and turning the "Numeric" knob.

Click to expand...

This is beyond cool. My sincere congratulations. It looks like a very capable device.

albada said:

The "Grade" item in the display is what this thread is about. It would be nice if a given grade looked as similar as possible on different papers having different maximum/minimum densities.

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Okay, now I understand it better. The spreadsheet I showed earlier, along with the chips, is exactly what you're after. It doesn't have to be used that way, but you can calibrate it so that each paper produces roughly the same shade of gray with its unique filtration and exposure. Given the lack of standardization of filtration, it's something that one needs to build from the ground up. The difference, I think, is that it standardizes on the tone, not the grade. It's probably just a philosophical difference, such that the question is "It would be nice if a given tone looked as similar as possible on different papers, with a exposure and filtration automatically computed by the controller, " rather than the question you asked, if I am understanding it correctly.

For example, I print a lot of portraits, and so I have calibrated my papers (I use two or three different ones) to give me exactly the same skin tone values for a given combination of filters. All I have to do is pick a shade I want from the chips and look up its corresponding exposure and filtration. My program will also recalculate exposure for different size prints, so you can make small test prints and then scale up very easily without having to run test strips. But, as a working solution, is far inferior to having all the software built into the timer.

There's a professional printer, now retired, on YouTube. His name is Tim Hall, and he has come up with his own method of calibrating papers. It's a bit unorthodox, but it works very nicely. Have you seen his work? Maybe he will inspire you to try his ideas.

I believe we are hitting a wall here. Mark, you are only looking for an answer that fits your understanding of the situation which you are unwilling to consider is mistaken. Take some time and a step back and revaluate what the goal is. Do some research. Jones wrote two papers:

Jones, LA & Nelson, CN, The Control of Photographic Printing by Measured Characteristics of the Negative, J.O.S.A., Vol 32, October 1942.

Jones, LA & Nelson, CN, Control of Photographic Printing: Improvement in Terminology and Further Analysis of Results, J.O.S.A., Vol 38, 1948.

Grades cover a range of LERs. A range that falls at the lower end of Grade 2 will look different than an LER that falls close to the Grade 2/3 break. I keep suggesting LER. It defines the paper and can be determined from the negative. Matching gradients only works if you know the gradient the negative was process to and it doesn't hurt to know the luminance range of the original subject. It's possible to determine the paper gradient using the LER result and the the RD at 90% of the paper Dmax. The log exposure range is the run and the 90% of the paper Dmax minus 0.04 is the rise. You can take the LER range for a grade and break them down into tenths of a grade or something similar.

Just doing a quick flip through the second paper and your question and answer to your question appeared.



p. 912. "Consider first the case where the papers differ widely in maximum density, as shown in fig 10a. These curves are typical of the difference between glossy and matte surface papers having equal exposure scales. Careful tests have shown that these papers print the same negatives successfully. In fig 10b are shown curves for a glossy paper and matte paper which would be rated alike in terms of contrast. Tests show that these papers do not print the same negatives successfully. In practice, the user may, for instance, have made a print on the glossy paper in Fig 10a and decided that it was satisfactory in exposure and in exposure scale but that the subject matter was, for aesthetic reasons, especially suited to a matte surface paper. He should, we believe, be able to choose, for making another print, a matte surface paper having the same grade number as the glossy paper and obtain a satisfactory print. This will be the case if the sensitometric exposure scale is used as the basis for grading but it will not be the case if the case if the contrast of the paper is used as the basis. To obtain a matte paper having a contrast equal to that of the glossy paper, it is necessary to choose a grade of matte paper having a shorter exposure, as shown in Fig 10b. This matte paper must have a higher gradient and a shorter exposure scale to make up for the fact that its maximum density is less than that of the glossy paper."

"If these two curves in Fig 10b were assigned the same grade number, the user of the paper would be misled, for the matte paper is wholly unsuited for printing the negative which was satisfactory on the glossy paper. Its exposure scale is too short for the density scale of the negative. Much of the highlight detail and some of the middle-tone detail are reproduced as blank white paper; or, if the print exposure is increased to improve the highlights, the shadows are impaired by being pushed onto the shoulder of the curve. Tests have shown conclusively that the average user prefers the matte paper and glossy papers having the same exposure scale (and hence the same scale index) when the same negatives are to be printed on each."

Thanks for digging up the information above!
I think I understand your point now. Changing to a paper with a smaller LER (but same contrast) would cause elements in the highlights and/or shadows to be lost. Referring to Fig. 10, 2nd graph, I was proposing that B's print exposure and contrast be set such that its highlights and midtones are approximately equal to A's, thus losing elements only in the dark shadows. Your quote above addresses my proposal:


Assertion: Viewers prefer a small loss of contrast over a loss of dark elements.
Does the paper describe tests that verify this assertion? If you don't know, I'll be tempted to spend the $35 to buy the pdf of that article through their greedy paywall here, unless you know of a better way to obtain it.