BTZS Testing on negatives developed in Pyrocat-HD

[sanking]

I'm glad that we agree on many of these things! You say you disagree with how the initial readings of the step tablet should be made. I've given my logic as to why they should be read as I've stated above, but I've lost track of your reasoning (it's been a long thread). Could you please state it again? I understand that you appear to be tiring of this thread, but I am truly interested in what the flaw you believe is in my reasoning. I wish we could discuss this face-to-face instead of through a forum, but that is our avenue...

Thanks for all your replies!

Kirk

OK, once again. I am going to post two actual curves from the same test film. All of the data used to plot these curves is the same except for one thing, and that is the step tablet values that are used to calculate the curves. In the curve called StepTableVisual the step tablet values were based on UV reading, and they ranged from a low of log 0.05 at Step 1 to log 3.05 at Step 21. In the curve called StepTablet UV the values were based on a UV reading and they ranged from a low of 0.10 to a high of 2.85. So let me state all the important things you need to know, in addition to the above.

Here is all data.

1. Film = Efke PL 100
2. Step Wedge = Souffer TP 45
3. Exposure = 0.5 seconds at f11
4. Exposing light = tungsten with 80A filter
5. Development = Pyrocat=HD 2:2:100
6. Time of Development = 12 minutes
7. Test film densities read in UV mode
8. Paper ES 1.70 for palladium printing


The other values result from the use of either StepTabletUV or StepTabletVisual. I will comment more about this later, but for now please observe that the results are different in terms of CI, SBR and EFS depending on which values were used.

Okay, assuming that you have now looked at the curve graphs, you will have noticed that values on the X axis are calibrated in LogE units, not meter-candle-seconds. They are in fact relative LogE units since their values are being determined relative to something else. The something else is the units of density on the y axis. If the units on the two axis are not determined by a measuring system with the same spectral response they may be different.

Now, assume that you have developed the test negatives ( made by exposure to the calibration step wedge). Now you measure them in UV mode because you plan to print in Pt./Pd. What is the unit of density? It is a relative unit of density determined by a specific measurment. It would be different by a whole lot (because of the stain) if we measured in Visual mode instead of in UV mode.

So we determine above that a given log density unit, say 0.3, will have a specific physical length on the Y axis. It follows that the units of density that correspond to a given length on the y axis must be of the same length on the X axis. If they are not, the slope of the curve will be distorted.

Now look at the curves again. Notice that the curve plotted from the Visual step wedge begins at LogE 3.05, as we would expect from the Visual reading at Step 21. Now look at the graph plotted from the step wedge values read in UV begins at LogE 2.85, again as we would expect from the UV reading at Step 21. So which one should we use? Obviously we need to use the one that represents a log density of 0.3 with the same physical length on the x axis as it is represented on the y axis. That is only possible if we use the step tablet values read in UV. If you use the step tablet made in Visual mode you will expand what would be 2.85 units of density on the y axis into 3.05 units on the x axis, which makes any unit of a given value of different length on the x and y axis. As one would predict, and can prove by examination of the two graphs, this will reduce the slope of the curve and it will also have an impact on other values such as SBR and EFS.



Sandy

 

[Kirk Keyes]

Ed Sukach wrote: "My comment was directed at the initial in-camera EXPOSURE spectral sensitivity of the film. Whether it is IR, or "Extended red" or a blue filter was used in exposure, it would have minimal - to say the least -effect on the densitometer reading integrity. Developer "staining" WOULD - most certainly."

Ed, you are right. Once the film has been prcess all information about the light that was used to make the exposure is lost.

"and the processed film, acting as a dichroic filter."

A Filter yes, but probably not dichroic unless perhaps if you did not adequately stop development before fixing and then some dichroic effects may be observed in the film. But in general, the film simply acts as a filter.

Donald - what we are talking about here don't really become murky with staining developers - the film still acts as a filter, just something that is a bit more complicated than a neutral density filter that most people consider their step wedges or non-stained develped film to be.

 

[Kirk Keyes]

Sandy - That's for the graphs and data!

However, I'm looking over your data and it looks like you have an error with this sentence, "In the curve called StepTablet UV the values were based on a UV reading and they ranged from a low of 0.10 to a high of 3.05."

You really mean the the UV density of Step 21 is 2.87 and not 3.05 as you have listed here. (I got the 2.87 value from yor post on page 2 of this thread.)

Please confirm this typo.

I'll continue with reading your post!

 

[sanking]

However, I'm looking over your data and it looks like you have an error with this sentence, "In the curve called StepTablet UV the values were based on a UV reading and they ranged from a low of 0.10 to a high of 3.05."

You are correct. The actual value should be 2.85. I adjusted the value from the actual value of 2.87 so that the difference in log units between Visual and UV mode would be exactly log 0.2, or two of the log 0.1 units on the graph.

I have corrected the error in the message.

Sandy

 

[Donald Miller]

Kirk Keyes said:

"Donald - what we are talking about here don't really become murky with staining developers - the film still acts as a filter, just something that is a bit more complicated than a neutral density filter that most people consider their step wedges or non-stained develped film to be."

Kirk,

I intended to indicate that different proportional stain color (different developer formulations) would render the density as being different dependent on the light source and the characteristics of the process or printing material. I thought that this explanation was important to those who have very little or no experience with proportional staining developers. It may very well be that there are some here that may be following this thread that may fit into the novice catagory insofar as these types of developers.

 

[Kirk Keyes]

Sandy, thanks for your post. You have very clearly layed out you thoughts on this! I really appreciate it.

I agree with the all calculations used to make your two graphs. The math is really striaghtforward. And you are right that the slope (gradient) of the curve will change based on the numbers that we use for the x-axis. It is a simple rise over run calculation. And you are right that if we change the values on the x-axis, all of our derived data (SBR, EFS) will change as well. I completely agree with this observation. It's simple mathamatics.

So what we need to figure out now is which set of data is the correct one!

"you will have noticed that values on the X axis are calibrated in LogE units, not meter-candle-seconds. They are in fact relative LogE units since their values are being determined relative to something else."

It does not matter if we have relative logE for our x-axis or absolute logE. The only difference is that you have not accounted for the actual amount of light that was used in the exposure. You could have easily used a light meter to measure the light, in say Lux and then multiply that by your exposure time for Lux-seconds (which are the preferred units). It does not really matter - it is actually a non-issue, but using relative logE is simpler but it works.

"If the units on the two axis are not determined by a measuring system with the same spectral response they may be different."

Well, it is not that the units are different. They are still exposure units to which the logarithm has been taken. We have not changed units. We may have had to change the color content of those units to match the material we are exposing, but we have NOT changed units.

"Now, assume that you have developed the test negatives ( made by exposure to the calibration step wedge). Now you measure them in UV mode because you plan to print in Pt./Pd. What is the unit of density? It is a relative unit of density determined by a specific measurment."

This is correct - to be more explicit, we have density units for our y-axis that are logE as measured with UV light.

"It would be different (because of the stain) if we measured in Visual mode."

Correct again, we would then have density units for our y-axis that are logE as measured with Visual light. But we do not want that for our y-axis data because the NEXT STEP in our process is to print on Platinum.

You are completely correct that the y-axis units when printing on Pt paper should be density units that are logE as measured with UV light. Correct.

"So we determine above that a given log density unit, say 0.3, will have a specific physical length on the Y axis."

Correct.

"It follows that the units of density that correspond to a given lenth on the y axis must be of the same length on the X axis. If they are not, the slope of the curve will be distorted."

Correct. If the actual spacing of the lines on the paper or computer screen are not equal, there will be a streching of one axis of the graph.


"Now look at the curves again. Notice that the curve plotted from the Visual step wedge begins at LogE 3.05, as we would expect from the Visual reading at Step 21. Now look at the graph plotted from the step wedge values read in UV begins at LogE 2.85, again as we would expect from the UV reading at Step 21. So which one should we use?"

Yes, now we are getting to our quesion.

"Obviously we need to use the one that represent a log density of 0.3 with the same physical density on the x axis as it is represented on the y axis."

This is where you are getting confused. There is no such thing as "physical density", unless you are talking about the actual spacing of the lines on our graph. And we have endured that - Our log units on the x-axis are exactly the same spacing as the log units on our y-axis. This is because we were diligent and precise in the spacing of our lines. The graph paper is not changing size here.

"That is only possible if we use the step tablet values read in UV."

No. Not correct. This is where you are incorrect.

LogE units are logE units the world around. LogE units do not change size because of the color of light that we used to generate them. As I said above, we should really be labelling our x- and y-axis with units like "density units = logE as measured with UV light" or "density units = logE as measured with Visual light" or "density units = logE as measured with IR light". The logE units are all the same size, and they do not "distort" the curve. They are quite simply the units with which our exposure was made.

"If you use the step tablet made in Visual mode you will expand what would be 2.85 units of density on the y axis into 3.05 units on the x axis, which makes any unit of a given value of different length on the x and y axis."

And this is incorrect as well, for the reason given in my paragraph above. You are not "expanding" units. Units are units. They do not expand, they cannot expand. You simply want to apply one set of data points for the x-axis (the value of the exposure that was given to the step tablet) to your measured y-axis data points (the values measured from the developed test film). They can be made with different channels on the densitometer (as long as they match the conditions that match the material).

Keep in mind, when graphing data like this, the x-axis contains what is called the "independant" data, the y-axis contains the "dependant" data. The values of y are dependant on x, not the other way around. In your system, you have the x dependant on the y which is incorrect.

This actually comes into play here - the exposure being made through the steps in our wedge are the independant data. We could expose for 1/10th, 1, or 100 seconds if we want. The f/stop on the enlarger can be anything we like, as can the enlarger head height. The color quality of our light source can be anything we want - blue light, IR light or UV light. It is completely up to us as to what we do here, the x-values are independant. There are many combinations that will not make any density on the test neg or it will be completely overexposed, but we are completely free to use those combinations if we want (which could waste a lot of film in the process). The x-values are independant.

The density that results on the film for which we will use on the y-axis are completely dependant on what we did to the value at the x-axis. Nothing in the y-axis results has any effect on our x-axis data. It doesn't work that way. That's what my esoteric information theory discussion above was all about. It does not matter if we measure the values on the y-axis with UV, visual, IR, blue...

But we should measure the the y-axis data based on our intended goal for the negative. And you are right with that - if you are going to be Pt printing, measure y-values in UV, if silver printing use blue or visual. It should be based on your intended use of the neg.

But let me say it again, the x-axis data is completely independant of the y-axis data. So your claim that we should use UV for measuring the step wedge if we are going to be Pt printing is completely without any basis. What we must do is measure the x-axis data based on the sensitometric properties of that initial piece of film and the light conditions under which we will be exposing it.

"As one would predict, and can prove by examination of the two graphs, this will reduce the slope of the curve and it will also have an impact on other values such as SBR and EFS."

What your two graphs prove is that since we know that both of them can not be correct, then one of them must be wrong. But that actually does not prove that the other one is correct by default, it may be wrong as well... If the data used to prepare the graphs is not appropriate for what we are trying to prove, then that does not help us make our proof.

Here's another conundrum for you. Let's look at your Pyrocat graphs over at unblinkingeye.com http://unblinkingeye.com/Articles/PCat/pcat.html Your very first graph in your article, "Figure 1. A JandC 200 negative developed in Pyrocat 2:2:100", shows the densities measured from one neg in visual, blue, and UV channels. I suspect you measured all the values for the x-axis of this graph with the visual channel, right? Well, this is in contradiction to the advice you are giving above. What you are saying is that we will have to use a separate graph for the UV channel since we have to measure the x-axis data from the step wedge with UV light. Otherwise there will be distortion of our chart and data as you claim. If that is true, then all your graphs in this article are prepared incorrectly if you have both UV and visual data on it, because we know your step tablet has different values in UV vs. Visual. That is the conlusion that we must make from your claims above.

Well, I do not beleive that conclusion. Your graphs ARE prepared correctly (assumung you used the visual channel data for your x-axis). This is BECAUSE you were exposing a panchromatic film, and because of that, you selected a daylight source for the exposure. That's the reason that you should have used the visual channel for the x-axis. And you did (I think).

Sandy, if you are not convinced yet, could you take a look at the IR film/ Pt print scenario above? Could you tell me where my reasoning is incorrect on that? Would you use the UV channel to measure the step wedge in this situation even though the film is only going to be exposed to and pass IR light?

Thanks again for better stating your position.
Kirk

 

[Kirk Keyes]

Donald, thanks for the clarification. I agree with you, especially when threads get this long and detailed.

 

[gainer]

If you are plotting an H&D curve for pan film, you should measure the density steps of the original step wedge with a broad band sensor. Do not use a filter that simulates visual response. Panchromatic film has a much flatter spectral response than the human eye. It must be that way in order to capture faithfully all the shades of gray that the normal human eye can see. This sounds wrong, but there is an analogy with audio systems. Once upon a time, it was supposed that a high fidelity audio system need only have an output bandwidth and MTF that matched the human response MTF. Later it was realized that this reasoning caused a doubling of the high and low frequency loss. The audio output from the speakers was being preconditioned to provide the losses so the ear wouldn't have to, but they didn't tell the ear about it.

 

[Kirk Keyes]

On reviewing this thread some more, I came across this claim:

Sandy wrote, "The color of the light used to expose the film is of course important in that films have different response in both sensitivity and contrast to different color light, but in my opinion the color of the light used to expose the film is absolutely irrelevant to the plotting."

Sandy, this is incorrect too. Photographic materials are subject to what is called the "gamma/lambda" effect. Gamma and Gradient can be affected by the predominant color of the light used in the exposure. Of course this effect depends on the emulsion type, but in general for panchromatic films, blue and ultraviolet light will produce a lower gamma than white light, and red light will produce a higher gamma. This is also known, understandably, as the "gradient/wavelength" effect.

This effect is typically small, but the book I'm looking at shows a graph of this and at exposures made with blue light (400 nm) the gamma is 0.59 and with red light (650 nm) the gamma is 0.72. That's a bit of change there!

If anyone is interested, a really good book on all of this is "Sensitometry for Photographers" by Jack Eggleston. It was first published in 1984 and it is an excellent resource for this subject.

Kirk

 

[gainer]

Kirk,
The logarithm is not a unit of measure. It is a transformation of units of measure. The log of average anual income is not the same unit as the log of annual rainfall. The log of illumination to which platinum paper is sensitive is not the same as the log of illumination which the normal eye sees or the log of the illumination to which pan film is sensitive.

 

[Kirk Keyes]

Patrick wrote, "The logarithm is not a unit of measure. It is a transformation of units of measure. The log of average anual income is not the same unit as the log of annual rainfall. The log of illumination to which platinum paper is sensitive is not the same as the log of illumination which the normal eye sees or the log of the illumination to which pan film is sensitive."

Patrick, yes, a logarithm is not a unit of measurement. An LogE is a unit of measure.

Thanks for the catch - I'll fix my comment above to reflect this.

 

[Kirk Keyes]

Patrick - I just looked it over, and I did not change anything above.

I agree, a log is not a unit of measure. But a logE is a unit of measure of light.

"The log of average anual income is not the same unit as the log of annual rainfall."

Sure, but are you saying we can't graph two items against each other? You know that is not true. We can even graph items where the units do not match - take a look at most any graph out there. Salery($) vs. Age (Time), Concentration (mg/L) vs. Absorbance (Abs.), Development Time (Time) vs. Temp (Temp). The combinations of differing units is nearly endless. We can very most certainly graph LogE in UV vs LogE in Visual. There is no problem there.

"The log of illumination to which platinum paper is sensitive is not the same as the log of illumination which the normal eye sees or the log of the illumination to which pan film is sensitive."

YES - this is exapctly my point. The data on the x-axis only relates to the exposure that was given to the piece of panchromatic film. It does not and cannot relate to the exposure that was given to the platinum paper. They are unrelated exposures. And because of that we can use logE of visual light for our x-axis and plot it against our logE of UV light for our platinum print.

We are simply measuring and graphing "input" vs. "response".

Our step wedge controls the exposure on the film and then the processed film with steps on it controls the exposure on our platinum paper. Each expsoure is completely unrelated and that is exactly why we need to carefully consider the conditions and the sensitivity of our materials in each of these two steps. The UV light is not shining through our step wedge and then onto our Pt paper. There is another step invloved there and that is the creation of our negative. The UV light shines through the negative that we made, not the original step wedge. That's why the original step wedge MUST be measured with the visual channel on the densitometer.

Patrick, do you have any thoughts on my IR film/Pt paper example above? I would be interested in hearing it.

 

[sanking]

Here's another conundrum for you. Let's look at your Pyrocat graphs over at unblinkingeye.com http://unblinkingeye.com/Articles/PCat/pcat.html Your very first graph in your article, "Figure 1. A JandC 200 negative developed in Pyrocat 2:2:100", shows the densities measured from one neg in visual, blue, and UV channels. I suspect you measured all the values for the x-axis of this graph with the visual channel, right? Well, this is in contradiction to the advice you are giving above.

Sandy, if you are not convinced yet, could you take a look at the IR film/ Pt print scenario above? Could you tell me where my reasoning is incorrect on that? Would you use the UV channel to measure the step wedge in this situation even though the film is only going to be exposed to and pass IR light?


Kirk

Once again, the logE units on the x and y axis are relative, not absolute and the thing that links them for the purpose of graphing is the measuring instrument that is used to measure the step tablet and the tests strips produced from it. Nothing else. If you mix values (i.e. different measuring system) you will get apple to oranges units of measurement, assuming that the step tablet is not absolutely neutral in color. If you measure the step tablet in Blue mode and the test strips in Blue mode each unit of density will occupy the same physical distance on the graph. If you measure the step tablet in UV mode and the test strips in UV mode each unit of density will occupy the same physical space on the x and y axis. If you do anything else the units of distance will be of different length on the x and y axis.

About the charts, this is no conundrum. Since, as you correctly surmise, the same step tablet values were used for the Visual, Blue and UV curves, the UV curve is not correct. Assuming a step tablet with different Visual and UV values was used for the plotting of those, as I think was the case, the UV curve should have a steeper slope. When I prepared those curves I assumed that that the Stouffer step tablet used to expose the film was of neutral color and almost certainly measured it in Visual mode. I now realize that it is not.

I have considered the IR film/Pt/Pd scenario you describe. It is not relevant to my point because you are not using IR light to expose the Pt/Pd. print. You can expose the film with any light to which it has sensitivity and will get an exposure. You could do this with red, green, blue, ultraviolet or infrared, either by using light of that spectrum or using appropriate cut-off filters. This will no doubt result in negatives of different contrast and density but it will have little if any affect on graphing. In other words, whatever light you use to expose the film the densities could potentially read differently if the film is not neutral in color according to the spectral sensitivity of the measuring instrument.

This discussion has been interesting. I had been vaguely aware of the issue for some time but when the discussions began there were some questions in my own mind as to what would be the correct procedure when dealing with a step tablet that did not measure the same in Visual, Blue and UV mode. Having now worked through the situation more thoroughly, and having heard everything that has been said by many people whose opinions and knowledge I respect, I am convinced that I am right, not about everything of course but yes with regard to how the step tablet should be measured.

I would not preclude revisiting the issue at some point in the future but for now I am satisfied that I have nothing more to add. Folks will just have to read the messages for themselves and come to their own conclusion. But my position is that if you don’t agree with me we will just have to agree to disagree.



Sandy

 

[Ed Sukach]

I've used logarithms a LOT, having been in the "pre-PC" era. Heavens to Betsy, I have memories of Pickett Slide Rules, constructed with the basic idea of logarithmic scales ... and I've made more than a few pencil-and paper calculations (slide rule-less) with them.

Now ... I know how to use them ... how the squat do I describe what they are? ... try: (cheating), "The power to which a fixed number, called the base, must be raised in order to produce a given number, the antilogarithm."

In use, to mulitply 2 X 3: one would determine the log of 2; (determining both mantissa and characteristic) and the log of 3; add them together; and determine the antilog of the sum - which would be something like 5.9999999999999999.

The "base" could be ... commonly 2, 10 ... or "e" (small "e" = 2.7182818284+) - not to be confused with capital "E" ... which represents "Exposure".

"LogE" indicate the use of a logarithmically drawn graph, to plot the value of the exposure - whatever that was - in logarithmic terms.

Wow... what a memory exercise this has been. This is equal to trying to remember how to calculate square .. or cube roots - by hand!!

 

[gainer]

I've used logarithms a LOT, having been in the "pre-PC" era. Heavens to Betsy, I have memories of Pickett Slide Rules, constructed with the basic idea of logarithmic scales ... and I've made more than a few pencil-and paper calculations (slide rule-less) with them. "

I still have a 7" circular slide rule I called a slip disk. It is equivalent to about a 25" straight one and has all the log, trig square root and even cube root scales. I remember using 10 place log and trig tables to do calculations for topographic computing. The only desk calculators we had were adding machines. Later, Marchant and Friden made electromechanical desk calculators. Try inverting a 10X10 matrix on one of those. When I retired from NASA, we still did not have desk top PC's and the main frame that did much of the data reduction was limited. A fellow doing theoretical analysis of loads on helicopter rotors came to me one day saying he had to invert a 250 X250 matrix and the main frame couldn't do it. The computing time for the solution was over 80 hours, and that was greater than the mean time between failures of the IBM 7094 we had. When I left, we had graduated to an early Cray super computer, and last time I visited all the engineers had desk terminals.

Ain't life grand?

 

[PJC]

Greetings,

Interesting thread and I’m quite pleased to see it unfold unemotionally as seems to happen on other forums.

I don’t practice BTZS, nor am I very familiar with WinPlotter though I do have the software.

When I first started reading this I was thinking that Sandy’s logic was correct, but after reading Kirk’s replies and thinking about this, I’m in agreement with Kirk.

Here why: Forget WinPlotter for a moment. If we were charting an H-D curve we would place LogE (exposure) on the X axis and LogD (density) on the Y. Instead of using a step tablet, let’s say we actually made 21 separate exposures on 21 sheets of film. We would then have 21 unique exposures to plot on the X axis along with 21 densities to plot on Y. Now we’re not using individual exposures, but simulating exposures using a step tablet, hence the reason WinPlotter need to know the densities of the step wedge used to expose the test film – so it can calculate the exposures. For this reason Kirk’s explanation sounds most logical: the step wedge needs to be read with the same light that’s used to make the initial exposure on film.

Regards, Pete

 

[Kirk Keyes]

Patrick wrote: "I still have a 7" circular slide rule I called a slip disk."

Patrick, could you leave that to me in your will? :^) I love those things too. Who would have thought that scratching a bunch of lines based on logarithms would make such powerful calculating device. I have an aluminum Pickett and a Ivory and Mahogany K&E. But I haven't gotten a nice circular slide rule yet...

Ed, thanks for the refresher on logarithms for those that are not familiar with them. I was trying myself to remember what the number in front of the decimal was called earlier today and you have it here - the characteristic!

 

[Kirk Keyes]

Pete,

Thanks for adding to the thread! I'm glad that people are finding this subject interesting as this really covers a very fundamental issue and I'm kind of suprised that there is so much confusion on this.

You have made a very important point here, one that I overlooked. As I have been trying to point out from the beginning, the two axis on an H&D graph do not diplay the same information, and therefore there is no need that the units need to actually match. I believe that everyone is getting confused because at first glance, it seems like the units are exactly the same, and therefore that is why everyone is wanting to use the same units. But you are right, what we are really graphing on one of these charts are Exposure vs. Density. Nothing more, nothing less. We actually use the log of the Exposure and the log of the Density, and perhaps that is adding an extra layer of confusion to the issue, but the log part really does not matter as we only do that to make the graphs look nicer (and to make our doublings of numbers produce straight lines). But the log part does not matter, we could make these graphs without using logs.

Even the letters of the name of these types of graphs should have pointed this out to us - they are H&D graphs. H represents the Exposure given to the film, and D is the Density of that processed film. So we are not plotting the same units on the graph - we need to recognize this.

Pete, your example makes an excellent case and it does prove the point I'm making, in yet one more way.

 

[Ed Sukach]

... And, lest we forget ... Tables of Involutes. I did a lot of work with gearing .. calibrating Master Gears, and working with "Special" tooth forms.
We worked a LOT with Space Optics .. and sundry other "parts" that went up, never to come down again - and come to think of it .. some that went down, and HOPEFULLY did come up again (DSRV - Deep Sumbergenge R... (reasearch???) Vehicle....

My "Axe" was a Fifteen-Place Curta Calculator ... a much refined, hand-held Babbage Engine. Made at Vaduz, Lichtenstein. Never failed ... completely mechanical.

You know .. compared to the "Wimp" Engineers of today (sit there and push a few buttons)... we did truly *marvelous* work..

 

[Ed Sukach]

Even the letters of the name of these types of graphs should have pointed this out to us - they are H&D graphs. H represents the Exposure given to the film, and D is the Density of that processed film. So we are not plotting the same units on the graph - we need to recognize this.

You described it *VERY* well, Kirk.

Only ... The letters stand for (H)urter and (D)riffield, two guys who did a bunch of work in trying to determine a standard way for expressing film speed.
There was a H&D film speed; a Weston speed. and finally ASA, which morphed to ISO.

 

[gainer]

Greetings,

Interesting thread and I’m quite pleased to see it unfold unemotionally as seems to happen on other forums.

I don’t practice BTZS, nor am I very familiar with WinPlotter though I do have the software.

When I first started reading this I was thinking that Sandy’s logic was correct, but after reading Kirk’s replies and thinking about this, I’m in agreement with Kirk.

Here why: Forget WinPlotter for a moment. If we were charting an H-D curve we would place LogE (exposure) on the X axis and LogD (density) on the Y. Instead of using a step tablet, let’s say we actually made 21 separate exposures on 21 sheets of film. We would then have 21 unique exposures to plot on the X axis along with 21 densities to plot on Y. Now we’re not using individual exposures, but simulating exposures using a step tablet, hence the reason WinPlotter need to know the densities of the step wedge used to expose the test film – so it can calculate the exposures. For this reason Kirk’s explanation sounds most logical: the step wedge needs to be read with the same light that’s used to make the initial exposure on film.

Regards, Pete

But how do you know that the instrumant you use to measure the step wedge is responding in such a way as to tell you the true relationship between the steps of the wedge and your individual exposures? If you time those exposures, you run into possible reciprocity problems that vary from frame to frame. If you control them by f-stop holding time consyant, you need a ratio of max to min diameter of about 40. Your best bet for accuracy would be Waterhouse stops.

I know we are comparing thought experiments. My premise from the start of this thread was that the measurements we contemplate and sometimes do are more nitpickingly accurate than the accuracy of the materials and chemicals we test warrants. Sandy does measurements that let him get a pretty good idea how his customary materials will respond at various stages so that he knows if he will be able to get a good print in the end. If we were engaged in testing some theory of the photographic process, we would be using specially prepared emulsions and chemicals of the utmost purity, not to mention special processing equipment.

Considering what we need to know to be assured of being able to make a print that satisfies our wants, we are worrying too much about whether we are doing it exactly right. At every step of the way, we have controls that let us correct errors in the previous step. These steps are "closed loop" in the sense that they can be repeated with corrections. The initial exposure is often open loop, in the sense that it cannot be repeated because the subject is changing, but it has the greatest leeway for error. What are we woried about?

 

[Jorge]

Kirk, I agree with you and Pete with respect to the H&D curves, but in the case of the BTZS plotter program, it is important that the units in the y axis be similar to those of the x axis, as we are using that same density to provide the exposures. Since the program produces film speeds by calculating the average Gamma or Contrast Index, if the units are not uniform, the slope of the curve can change greatly and thus the film speeds. Of course if one chooses the b+f option of calculating film speeds then the "error" is reduced, but using CI is a more accurate way to estimate film speeds and the relation with development.

Which brings us back to what I imagine is the original question. How should the step tablet be read for the density units (or what we are calling y axis)? IMO and in my work I use the readings given by the Vis mode since in effect these densities are what are providing the exposure to the film and are blocking or letting the light the film "sees" pass through. I suppose one could input into the program evenly divided numbers for the density and choose the b+f option to make curves that are more similar to the H&D curves.

 

[Kirk Keyes]

Sandy, I hope you happen to make it back here and take another look, as I have another example for you to consider.

Let's go back and look at your chart on the unblinkingeye.com. Your chart IS prepared correctly even though you have convinced yourself that it is not. Please allow me to convince you that you did prepare them correctly.

Your chart shows what happens when we expose a piece of film to light, process it, and then measure the resulting densities on our densitometer. I know that you have been very diligent in the preparations for making this film test. You have adjusted the height of your enlarger to give an even exposure, you have picked an exposure time that is typical of those you use in the camera, you have adjusted the f/stop of your enlarger lens to give an exposure on the film that will not severely underexpose or overexpose your film, and you have adjusted the color temperature of your enlarger light source to be similar to daylight, which is what you will be using when out photographing in the real world. That's great, all very good things to do.

So now you place your unexposed test film under the enlarger, you overlay it with your step wedge, you push a button, and light pours onto your film. As the light is exposing the film, the light which starts out daylight balanced, is filtered only slightly as it goes through our step wedge. We know this because we have measured our step wedge with our densitometer which is in good operationg condition because we have calibrated it. If we are lucky, we actually have a step wedge that has been calibrated by the manufacturer with VRGB densities. That is not necessary, because we can make these measurements ourselves with our own densitometer, but it would add some extra confidence to our procedure.

So now our step wedge has slightly modified our daylight, it is perhaps a little more blue or red than it was before it hit the step wedge, but it is still very close to daylight as we know our step wedge is well made and fairly neutral because of our testing it.

The photons in the light strike the sensitized silver particles in our film. We now have a latent image on the film. We remove it from the enlarger baseboard and go off and process it. We can use any developer we want. It does not matter. We fix, wash and then dry our test film.

Ok, so now we have made a test film that has an image of our step wedge on it. I'm sure you'll agree with the methodology of all the steps above.

Here's the really important question -

At what point did the UV density of our step wedge come into effect in this process? No significant amount of UV light in our light source that we used to expose the film. We used panchromatic film in our test - that's why we chose to make our exposure with light that was similar to standard daylight.

As was pointed out by a previous poster - the data that we need to collect to place on our x-axis is data about the exposure that was given to our test film. Well, the amount of exposure we have given our test film has been determined by the amount of daylight that has passed through our step wedge. Since we used daylight to make the exposure on panchromatic film, we MUST make our logH measurements using the visual channel on our densitometer.

The UV density of our step wedge does not come into play anywhere here. Sandy, this is where you are getting confused.

The only time the UV density of our step wedge comes into play is when we are placing the step wedge itself onto our platinum paper in order to characterize the sensitometric properties of our paper (because we are going to be exposing our paper with UV light that has passed through the step wedge). That's it. Not when we are making exposures to panchromatic films with daylight.

So taking this all back to Sandy's chart on unblinkingeye.com, it is correct to plot the Visual, Blue, and UV measurements of that test negative all on the same chart. This is because we have given the one piece of film a single exposure. The exposure was made with our enlarger, and with the light quality as close to daylight as we could make it. Remember only one exposure was made - one exposure using daylight. No exposure was made with UV light. This means that all the data that we can generate by measuring the test film density can be plotted together on the same graph. The UV, blue and visual density measurements can all co-exist on the same graph. They all share a common exposure. And since that exposure was made with daylight on a panchromatic film, that exposure is calculated by measuring our step wedge with the visual channel only, not the UV channel.

So I now ask everyone, what am I getting wrong? What scientific principle am I forgetting in this assessment? If I am missing something, I really would like to know. I do believe that I am not missing anything here though.

Kirk

 

[Kirk Keyes]

Sandy, as to your reply above my last post, here are my comments on them:

"Once again, the logE units on the x and y axis are relative, not absolute and the thing that links them for the purpose of graphing is the measuring instrument that is used to measure the step tablet and the tests strips produced from it. Nothing else."

It does not matter if we use relative or absolute values for our log values. We can use either one if we like. Does not matter.

"If you mix values (i.e. different measuring system) you will get apple to oranges units of measurement, assuming that the step tablet is not absolutely neutral in color."

We are graphing two different types of data against each other. We have exposure data on the x-axis, and density data on the y-axis. As I pointed out above, there is no problem with plotting different types of data, and data made using completely different measuring systems. I could plot the position of a snail using fortnights for my x-axis (time) and furlongs for my for my y-axis. We could then figure out the speed of our snail in the units furlongs per fortnight. I can tell you right now the values will be quite small, be we can do it if we like.

When we make and H&D graph, we are plotting Exposure vs. Density. I think you will agree that this are two different types of data. They are apples and oranges. You can do it. (We should remember that "H&D" used to stand for Hurter & Driffield, but now the "H" is the international symbol for Exposure and the "D" is the symbol for Density.)

"If you measure the step tablet in Blue mode and the test strips in Blue mode each unit of density will occupy the same physical distance on the graph. If you measure the step tablet in UV mode and the test strips in UV mode each unit of density will occupy the same physical space on the x and y axis. If you do anything else the units of distance will be of different length on the x and y axis."

This is based on a false premise. See above.

"About the charts, this is no conundrum. Since, as you correctly surmise, the same step tablet values were used for the Visual, Blue and UV curves, the UV curve is not correct. [...] When I prepared those curves I assumed that that the Stouffer step tablet used to expose the film was of neutral color and almost certainly measured it in Visual mode. I now realize that it is not."

It does not matter what the UV transmission of the step wedge was - no UV light was utilized when exposing the test film.

"I have considered the IR film/Pt/Pd scenario you describe."

Thank you for finally addressing it. I have put a lot of thought and research into my posts here and I appreciate it.

"It is not relevant to my point because you are not using IR light to expose the Pt/Pd. print."

Using UV measurements of the film in determining the film exposure is not relavent as you are making it by measuring your step wedge with UV light. My description of the film exposing process should prove to you why.

"You can expose the film with any light to which it has sensitivity and will get an exposure. You could do this with red, green, blue, ultraviolet or infrared, either by using light of that spectrum or using appropriate cut-off filters. This will no doubt result in negatives of different contrast and density but it will have little if any affect on graphing. In other words, whatever light you use to expose the film the densities could potentially read differently if the film is not neutral in color according to the spectral sensitivity of the measuring instrument."

Yes, that is why the spectral sensitivity of our measuring instrument needs to match the spectral sensitivity and the quality of light that we are using to make the exposure. And that is why if we are exposing a piece of IR film we need to make sure our measurements measure the amount of IR light that exposure our film. Not the amount of UV light like you propose. It does not matter if we are printing on Pt/Pd, silver or some IR-sensitive paper, the data we are collecting to measure the exposure of the film needs to accurately portray the amount of light to which the film was exposured.

"This discussion has been interesting. I had been vaguely aware of the issue for some time but when the discussions began there were some questions in my own mind as to what would be the correct procedure when dealing with a step tablet that did not measure the same in Visual, Blue and UV mode. Having now worked through the situation more thoroughly, and having heard everything that has been said by many people whose opinions and knowledge I respect, I am convinced that I am right, not about everything of course but yes with regard to how the step tablet should be measured."

"I would not preclude revisiting the issue at some point in the future but for now I am satisfied that I have nothing more to add. Folks will just have to read the messages for themselves and come to their own conclusion. But my position is that if you don’t agree with me we will just have to agree to disagree."

Well, I agree that this has been a very good discussion. And I am sorry if you do not see the principles that I have present you with.

If you have some more ideas on this subject later, I would certainly be interested in hearing them. As I said above, if you find any errors in my reasoning, ones that can be backed up with scientific principles, please let me know. And that request goes for anyone else...

Kirk

 

[Kirk Keyes]

Ed wrote, "Only ... The letters stand for (H)urter and (D)riffield, two guys who did a bunch of work in trying to determine a standard way for expressing film speed."

Ed, Jdef - check in some of your modern photography texts, and you will see that H&D did originally stand for Hurter & Driffield. Later, the letters we commandered to stand for H=Exposure and D=Density as I said.