BTZS Testing on negatives developed in Pyrocat-HD

[sanking]

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


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,

I am going to address this issue one last time in a short message.

For one thing I do not want to give the impression that I have either ignored your reasoning or found any fundamental mistakes in it. That is not the case. I have read each of your messages carefully and largely agree with you as it involves typical H&D plotting.

However, all of my messages in this particular thread have been in relationship to using the WinPlotter program in BTZS plotting and with this system there is very little doubt in my mind but that the units of density on the two axis need to be alike in the way they are graphed. Yes, you can use other values but the program has a number of features that do not appear to give reliable results if the densities are not equivalent on the two axis. As you saw from the graphs I posted yesterday a change in step tablet densities results in a change in CI, EFS and SBR on the plot. In my case the difference in reading between Visual and UV values was not all that great and the results still had considerable validity. However, for some time I have noticed that my negatives when developed to a given CI appeared to be giving more than expected contrast in actual printing, which I can now understand in light of the fact that I was using mis-matched densities on the two axis and the step tablet values were higher than they should have been. Of course we have controls in alternative printing that can compensate for minor differences in CI but my goal is to make the best negative possible for the job.

So the bottom line is that I still firmly believe that when working with the WinPlotter program the step tablet densities and the test strip densities should be read with the same light to assure that we are working with equivalent densities on the two axis. And I believe Phil Davis had this in mind when he wrote on the btzs forum, "If you really want to optimize the conditions you probably should buy or make a stained step tablet and use it for all of your calibrations."

Sandy

 

[Kirk Keyes]

Patrick wrote, "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."

Interesting question - that's why we usually have to do a little pre-testing or actually measure the light that is exposing our materials before we can do a proper test. As to knowing the response of our densitometers, we have to trust that the manufactuer has done their job and come up with a design that follows some standards in design and used materials that are comparable from instrument to instrument, like using the appropriate kind of filters like Status A or M filters.

I think people have found that using a step wedge is a much more precise and desirable way than Waterhouse stops - Waterhouse stops will require multiple exposures whereas a step wedge requires only one.

"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."

We are not being nit-picky here. The questions asked here have been in regards to some basic and fundimental principles of sensitometry, not some abstract theory of the photographic process, and therefore these questions apply directly to our daily photography.

Sandy has clearly demonstrated that with the data he presented above with his two graphs, he can get the Average G of his test film to vary from 0.96 to 1.08. That's quite a big difference, and he is right in trying to determine which set of results are true. Using the wrong set of results could make all of his testing for naught - as well as make his prints more difficult to make.

"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?"

Remember that some processes will have less controls than others, and we may need to use more difficult techniques to correct any errors that we have in processing. Processing our film to a significantly less than optimal Ave. G will have an undesireable effect that ripples all the way down the process.

 

[Kirk Keyes]

Sandy wrote, "For one thing I do not want to give the impression that I have either ignored your reasoning or found any fundamental mistakes in it. That is not the case. I have read each of your messages carefully and largely agree with you as it involves typical H&D plotting."

I appeciate that. Thanks.

"However, all of my messages in this particular thread have been in relationship to using the WinPlotter program in BTZS plotting... "

Well there's a disconnect between us right there! I thought we were discussing general principles of sensitometry/densitometry and photography. I thought you were trying to use the BZTS software as proof of your side of the discussion! After all, You did say on page 5, "I can agree with many of the things you are writing but not with the issue of how the step wedge should be measured." Anyway... let's go on.

Sandy wrote, "... and with this system [BZTS software] there is very little doubt in my mind but that the units of density on the two axis need to be alike in the way they are graphed. Yes, you can use other values but the program has a number of features that do not appear to give reliable results if the densities are not equivalent on the two axis."

Even in regards to the BZTS software (I've read Phil's book and looked at the examples of the software so I'm not completely unfamiliar with it), I'm still confused by what you mean by "the units of density on the two axis need to be alike" - The units of the x-axis can only be units of exposure, and the units of the y-axis can only be units of optical density. These units are "alike" in the sense that we have taken the log of each of these values, and since we generate them by measuring a step wedge and our test film, and we can measuring each of them by using the same densitometer, they appear to be the same units. But they are not the same units.

If you mean that we can't plot a two curves on the same graph if they have different sets of x-axis values, I understand that. It is a limitation of the software. But since we are talking about plotting sets of the same film which have been exposed through the one step wedge using the identical conditions, then we will not have two different sets of exposure data values. Only one set of data - one exposure, one set of data. It does not matter is we are reading the UV, B, or Vis of that exposed sheet of film, it only had one exposure given to it. So we can plot UV, B and Vis all on the same graph, even if using the BZTS software.

Sandy wrote, "As you saw from the graphs I posted yesterday a change in step tablet densities results in a change in CI, EFS and SBR on the plot. In my case the difference in reading between Visual and UV values was not all that great and the results still had considerable validity [variability?]."

Yes, it is simple mathematics that causes this as I've said before.

Phil Davis in response to your question posed on the BZTS site even says, "Incidentally, the only reason why the x and y axes have to be marked off in equal increments is because that's what the Plotter expects. This is not necessarily a problem if you hand-calibrate."

So he does admit that you have some limitations that are imposed on you as a user of his software. This is a special case and it is not really too unexpected, it does makes sense for a software designer to force you to enter your data in only one format as it makes their job of processing that data much easier. As he said, if you plot data by hand there is no conflict here.

Davis also says, "First, I suspect you can get good results with any reasonable test methods if you use them consistently and refrain from comparing specific numbers with those from other test methods. In other words, it probably doesn''t matter a whole lot whether you arrive at a nominal SBR of 8.3 or 7.5 as long as you adapt your working habits to match the number of your choice..."

He is certainly right about this - you could use either set of CI, EFS, and SBR vaules you've calculated. One set of results may work with no modification while the other may need an offset added to the results or some other sort of correction factor. But that kind of takes away some of the value obtained by using a good film testing method. We both want our testing to give results that are directly usable.

Let's go back to the data in your example above:
Sandy wrote, "However, for some time I have noticed that my negatives when developed to a given CI appeared to be giving more than expected contrast in actual printing, which I can now understand in light of the fact that I was using mis-matched densities on the two axis and the step tablet values were higher than they should have been. Of course we have controls in alternative printing that can compensate for minor differences in CI but my goal is to make the best negative possible for the job."

Yes, that's why it would be good to get to the bottom of this - is it a procedural/conceptual error or a calibration error that is causing this discrepance?

(Continued in the following post.)

 

[Kirk Keyes]

(Continued from the previous post.)
Since you are convinced that you have no conceptual error in your proposed procedure, lets look at your calibration procedure -

Back near the top of page 3 of this thread, Jorge and Helen both discuss the UV vs. Visible light readings that they get when reading their step wedges. As Jorge correctly points out, the acetate base of the wedge will should have a higher UV absorbance than Visual, you found this yourself - 0.05 Vis versus 0.10 UV. Helen finds this as well - that's 3 people in agreement! Helen replied, "I've also noticed that the base adds a uniform level of difference between the UV and visual readings (UV density being higher than visual, as Jorge's readings) - but this does not, of course, alter the relative exposure values."

Helen and Jorge are on to something here. Unless the steps in the commercially prepared step wedge have some sort of staining going on or we have something going on with the shape of the processed silver grains in our step wedge that is causing them to vary absorbance as the optical density changes, the UV measurements should be very directly proportional to the visual readings. We do know that there is some variation in measurements between UV, V, R, G, and B channels, but these are usually pretty small (<0.05D). Your step wedge measures low at the high end by more than 2/3 stop (when you take into account the +0.05 bias that the wedge has when measuring the base in the UV.) That's pretty big and you are right to be conerned about it. By comparison, Jorge's says, "... in my densitometer the readings are uniformly higher by about 0.09 units." Since Jorge's densitometer is uniform in it's measurements (a slightly higher bias) his step wedge mesurements will only slightly affect (1/3 stop) his EFS calculations. Your densitometer not only has a bias with the film base, which is expected and perfectly normal, but your densitometer appears to have a proplem with it's linearity, which will most certainly have an effect on Ave G, EFS, and SBR.

So this kind of indicates that your densitometer, despite being calibrated, may have issues with either the calibration or with it's linear response. I suggest that you look into this issue more, as it may resolve the problem with your aforementioned conclusions.

As I beleive Patrick pointed out above, most densitometers are calibrated (for transmission measurements) by measuring a "Zero Point" by taking a measurement with no film or standard in the densitometer and then a "High" calibration point is measured to set the slope of our densitometer's response. The zero point is the intercept and the High point sets the slope that Patrick mentions.

It is the linear response of your densitometer that may be changing as you change channels that may be causing errors in your step wedge measurements. This could be an isue with the response of your densitometer's response or an issue with your calibration standard.

As I mentioned earlier, a friend and I were comparing film density results and we realized that one of our densitometers had linearity issues. It probably means that the problem densitometer either needs some adjustment to its electronics or it needs to have its internal channel filters replaced. We determined this by comparing the linearity of the response of our two densitometers.

I don't believe that you mentioned what kind of standards you are using to calibrate your densitometers. Could you describe your calibration procedure and the type of standards you use? Do you have any standards that you can use to check the linearity of your calibration, i.e. one with other steps on it? If so, could you describe them as well? Also, are your standards new enough that we can be reasonably certain that they have not changed significantly with time?

You say you have a Gretage D-200 and the X-Rite 810. I have not used either of them but I have looked at some info on them found on their manufactuers web sites. The Xrite 810 is designed to do Status M transmission RGB filters. These are designed for use with internegatives that will be printed on color neg paper. This is not the right kind of densitometer for measuring the materials under discussion here. Ideally, you should find a densitometer that uses Status A filters, e.g. the Xrite 811, 820 or 310. Your 810 does not do UV measurements I see.

The Gretag D-200 looks like a very nice machine! It looks like you have to swap out measuring tubes to switch between UV and RGB, right? Looking at the manual for the D-200 II, it looks like to calibrate it you make a reading on the "zero field" of the calibration film and then make a second reading with a high point of about 3.0D and adjust that reading to a value that Gretag has specified for that standard. Do they give individual calibration values for RGB/UV, or just one?

They then say to perform a calibration check by reading the standard again to verify the results. This only confirms that your densitometer can accurately read those two values. But it does not prove that there are not any linearity issues - we can draw many different curves that both pass through two points and they can all hit completely different points both in between those two points as well as beyond that high point. So we need to verify the linearity of your densitmeter.

What I'm wondering is does Gretag give you a standard for each measuring tube, or do they give one standard with a calibration value to be used for each measuring tube. If you only have one value and are applying it to all measuring tubes, that may cause the error that you may be seeing in your calibration as your calibration film is probably not completely neutral across the range of R, G, B, and UV.

This method of calibration also does not allow us to check the linearity of our densitometer either. As I mentioned on page 4, I have a calibration wedge made by X-rite that has 4 calibrated steps on it, and each step has calibratin values in R,G, B, and Visual channels. Originally I had a single piece of what looked like litho film that someone had marked 3.19 onto a piece of tape and affixed it to the film. Now that I have the X-rite calibration standard, and I have demonstrated that my 3.19 film was off by quite a bit. I had to reread all my step wedges because of that error.

As I said, the X-rite film has 4 steps - you calibrate the densitometer with no film for zero, and then use step 3 on the X-rite film for a Hi Cal point, it's around 3.0D. So I calibrate in exactly the same way as you do. But then the film also has 3 other steps, about 0.25D, 1.50, and 3.75 with which I can check the linearity with. One reason I'm interested in how you are calibrating is that each step on the X-rite cal standard has a slightly different value for Visible, R, G, and B channels. For example, on the Hi Cal step:
V=3.01
R=3.04
G=2.99
B=3.01

I have no idea what the UV value of this step is, but I have no reason to beleive that it is equal to any one of the RGBV values (although I suspect that is would be close, but it may be off a fair bit - who can say?).

Note that the R and G channel readings are different by 0.05D. Not far off, but not the same. And these are not based on measurements that I have made with my densitometer, these are the calibration values that the calibration technician at X-rite has hand-written on my standard. So I would expect that unless someone got a really neutral step wedge (which is probably not very likely), we should see a difference between readings in different channels.

So did Gretag supply a standard specifically for the UV channel, and do they have any linearity check standards that you can get to verify the performance of your densitometer?

I strongly suggest that you get one of these calibration standards for your RGBV work. The X-rite transmission standard part nr. 810-68 costs around $40. The reflection plate they offer also has a mid-point spot with which you can check reflection linearity. Check out this page, it lists both reflection and transmission standards suitable for what we are talking about here: http://www.xrite.com/product_accessories.aspx?Line=17 )

I hope this discussion has given you more things to think about for this subject. Remember that if we have an issue with our calibration, then that will affect all of our results. And it may be key in solving the issue about what channel to use in calibration - BZTS or not.

I understand that you are a professor of language arts and you probably do not have much background in instrumentation. I am an analytical chemist and it have been studying, using, and trouble shooting many different kinds of analytical intrumentation (including densitometers and closely related spectrophotometer) for over 20 years, so I hope you'll take my suggestions seriously.

Kirk

 

[clay]

Well there's a disconnect between us right there! I thought we were discussing general principles of sensitometry/densitometry and photography.
Even in regards to the BZTS software (I've read Phil's book and looked at the examples of the software so I'm not completely unfamiliar with it), I'm still confused by what you mean by "the units of density on the two axis need to be alike" - The units of the x-axis can only be units of exposure, and the units of the y-axis can only be units of optical density. These units are "alike" in the sense that we have taken the log of each of these values, and since we generate them by measuring a step wedge and our test film, and we can measuring each of them by using the same densitometer, they appear to be the same units. But they are not the same units.

Kirk, I think the reason it matters is that the data is entered into the BTZS plotter program into pre-set numerical 'buckets' for each step on the test wedge. It makes the assumption in the program that these 'buckets' are 0.15 Dlog units apart. If they aren't, then the gradient calculations will not be correct. Fortunately there is a provision in the program for entering what is called a 'custom' step wedge and that feature will allow you to put the actual units from the particular step wedge you are using. Does this make sense? I believe that you and Sandy are in violent agreement, only the BTZS program has it's own peculiarities in that it will make assumptions about the X values on the plot unless you tell it differently.

 

[Jorge]

Kirk, I think the reason it matters is that the data is entered into the BTZS plotter program into pre-set numerical 'buckets' for each step on the test wedge. It makes the assumption in the program that these 'buckets' are 0.15 Dlog units apart. If they aren't, then the gradient calculations will not be correct. Fortunately there is a provision in the program for entering what is called a 'custom' step wedge and that feature will allow you to put the actual units from the particular step wedge you are using. Does this make sense? I believe that you and Sandy are in violent agreement, only the BTZS program has it's own peculiarities in that it will make assumptions about the X values on the plot unless you tell it differently.

Yes Clay, but look. Here are the densities for my stouffer step tablet:

UV Vis
.07 .04
.22 .19
.38 .35
.52 .50
.67 .64
.82 .79
.96 .93
1.11 1.08
1.26 1.23
1.41 1.36
1.57 1.53
1.72 1.68
1.88 1.83
2.04 1.99
2.18 2.13
2.33 2.27
2.48 2.42
2.62 2.56
2.78 2.72
2.93 2.86
3.09 3.02

As you can see, the UV are consistenly higher and they increase with greater densities. If Sandy is saying that he sees a drop in response in the UV channel at higher densities, then there is a problem. Since I lost my data due to a virus, I am recalibrating the BTZS and I just made some curves with Tmx 400 in HC110. Look at the response for the 21 min curve.
UV Vis
0 0
.01 .01
.02 .02
.04 .04
.08 .08
.17 .17
.28 .28
.41 .41
.57 .57
.72 .71
.85 .83
1.03 1.00
1.13 1.1
1.24 1.21
1.37 1.33
1.52 1.48
1.69 1.65
1.87 1.82
2.05 2.00
2.25 2.20
2.43 2.37

I think Kirk has a valid point, that if we are going to talk the same language and calibrate so that we can discuss the merits or lack there of, of stainning developers, we should at least agree in the basic calibration procedures.

IMO if Sandy is looking at variations in his densitimeter and the UV values, then there is a problem either with his calibration standard, or his densitomer. You know in science we worry mainly about two things when using measurement equipment. Accuracy and prescicion. I think Sandy has a problem with his instrumentation.

 

[Kirk Keyes]

Clay, I understand what you have written, and I understand about the way the BZTS software want you to enter data.

But the point I'm trying to make is that there is not going to be two sets of data for the log(exposure) when only one exposure has been made through the step tablet. It's not that one expsure on the test film is being made to the film in the UV and one exposure is made in Visible - only one exposure is made. That's why you don't have to take readings of the step wedge in two different spectrums. It's just one exposure.

Just enter your values in to the "Custom" step wedge so you have numbers that represent your step wedge. And measure the values using the channel that represents the film and light source that you used to make that exposure.

I have no issue with how BZTS wants you to enter data, I have issue with the way that Sandy says to measure that info.

Kirk

 

[Kirk Keyes]

Clay, you do see that there are two different measurments of the two different pieces of film - the one for the x-axis made on the step wedge to determine exposure, and the other one made for the y-axis on the test film to measure it's optical density?

I would not say that Sandy and I are having a "violent [dis]agreement" (I assume you meant disagreement) - I beleive we are actually have a quite civilized discussion.

Kirk

 

[Jorge]

Clay, I understand what you have written, and I understand about the way the BZTS software want you to enter data.

But the point I'm trying to make is that there is not going to be two sets of data for the log(exposure) when only one exposure has been made through the step tablet. It's not that one expsure on the test film is being made to the film in the UV and one exposure is made in Visible - only one exposure is made. That's why you don't have to take readings of the step wedge in two different spectrums. It's just one exposure.

Just enter your values in to the "Custom" step wedge so you have numbers that represent your step wedge. And measure the values using the channel that represents the film and light source that you used to make that exposure.

I have no issue with how BZTS wants you to enter data, I have issue with the way that Sandy says to measure that info.

Kirk

I would add that in the end this might be irrelevant if one is reading a "neutral" step tablet. A difference in reading of 0.05 would only shift the curve 1/6 of a stop. For testing purposes and the BTZS this might be even a smaller error than that of the lens speeds.

 

[clay]

I would not say that Sandy and I are having a "violent [dis]agreement" (I assume you meant disagreement) - I beleive we are actually have a quite civilized discussion.

Kirk

Actually, I did mean agreement. That is a tongue-in-cheek saying in my business that means that two parties are 99% in agreement, but are quibbling over the last 1% in a good-natured way. My opinion is that this has been VERY civilized, not to mention informative. Thanks

 

[sanking]

Kirk,

You wrote:

"I understand that you are a professor of language arts and you probably do not have much background in instrumentation. I am an analytical chemist and it have been studying, using, and trouble shooting many different kinds of analytical intrumentation (including densitometers and closely related spectrophotometer) for over 20 years, so I hope you'll take my suggestions seriously."

I have been working with densitomers for over 25 years and am very familiar with calibration procedures. So let’s get this out on the table. All of my densitometers are calibrated. I have the official Gretag Calibration wedge for the D-200-II as well as the 810-68 transmission wedge for the X-Rite 810. I told you this in an earler message so it makes no sense that you continue to insist there is a calibration issue.

The supposition on your part appears to be that if my reading of a Stouffer TP 45 step tablet is different in Visual and UV mode I must be doing something wrong, or there must be something wrong with my densitometer. This suggests to me that you don’t appear to be aware of the fact that there are considerable variations in step wedges and that very few, if any, are perfectly neutral.

Let’s consider, for example, calibration with the Gretag D-200-II. And BTW, I have two of these units so if there are any questions about whether one may or not be working correctly I can cross check the results. This does not appear to be the case, however, as they both read exactly the same when calibrated.

The official Gretag calibration wedge for the D-200 has three patches, 0.00, 2.04 and 3.05. Calibration is done in Visual mode with the 3mm aperture by entering calibration mode and setting the high value to 3.05. When this is done the Gretag reads the three values, 0.00, 2.04 and 3.05, exactly the same in both Visual and UV mode. This calibration wedge appears to be perfectly neutral.

But, compare readings by the D-200 of other step wedges.

1) Kodak Step Tablet #2
Visual, 0.05 to 3.22: UV, .05 to 3.26

2) X-Rite 810-68 calibration wedge
Visual, 3.76, 2.98, 1.54, and .29
UV, 3.67, 2.84, 1.55, .36

3) Stouffer TP 45 #1
Visual, 0.05 – 2.90
UV, .11- 2.76

4) Stouffer TP 45 #2
Visual, 0.05 – 2.91
UV, .10 –2.76

5) Stouffer TP 45 #3
Visual, 0.05 – 3.05
UV, .10 – 2.87

See any pattern? I do not. The densitometer reads higher in UV mode than in Visual with the Kodak Step #2 step wedge, lower in UV than Visual with the X-Rite transmission wedge and all three Stouffer TP-45 step wedges, and the same in UV and Visual with the Gretag calibration wedge.

I also read all of the above step tablets in Visual Mode with the X-Rite 810. The readings did not differ from the D-200 by more than log 0.01 on any given value. The 810 does not of course read in UV mode.

As you should immediately see from the above the difference in reading is not due to base filtration. If that were the case the difference between Visual and UV values would be a constant. It is not.


Sandy

 

[philsweeney]

Sandy,

knowing that you use BTZS for alt printing with great accuracy, I assume you have found that you have improved the accuracy of BTZS use by recalibrating the x axis using UV instead of visual readings of the step tablet?

 

[sanking]

Sandy,

"knowing that you use BTZS for alt printing with great accuracy, I assume you have found that you have improved the accuracy of BTZS use by recalibrating the x axis using UV instead of visual readings of the step tablet?"

Using the step tablet densities of the Stouffer TP 45 #3 test wedge provides better accuracy of the exact printing density of my pyro stained negatives than was the case with the default values of the WinPlotter, which are virtually identical to the Visual reading of this step wedge.

Exactly why this is the case is not entirely clear to me but the important thing to note is that calibration of the X axis to values other than default values or even to the Visual reading of the step wedge used to make the exposures results in different values for CI, EFS and SBR. In my case the new values suggest develoment times for normal ES values with my processes that give more accurate CI values.

Kirk has made the case that the use of UV values for the step tablet should not make any difference but the matter may be more complicated than he believes. For one thing film and papers have quite a bit of sensitivity to UV and even tungsten lights put out some UV radiation. There are after all filters called UV absorbing filters that are sold for use in enlargers, even with those with tungsten lights, to eliminate this source of light in printing. The Besler 23-CII enlarger that I use for exposing film in these tests originally had one of these filters but it was lost somewhere down the line so there is at this point no filtration of the UV light.

Sandy

 

[Kirk Keyes]

Jorge wrote, "I would add that in the end this might be irrelevant if one is reading a "neutral" step tablet. A difference in reading of 0.05 would only shift the curve 1/6 of a stop. For testing purposes and the BTZS this might be even a smaller error than that of the lens speeds."

Yes, Jorge, that's correct. The bias (shift left or right) of the curve you get on the UV readings of a step wedge would then only affect the speed rating slightly.

Thanks for posting the measurements of your step wedge. There is just a slight bias in your step wedge, and almost none in your HC100/TMax film. You do not have that definite slope difference that Sandy has in his step wedge. And Sandy's difference is in the opposite direction of yours.

It does seem to indicate there could be an issue with either his calibration or measurements of density.

 

[Jorge]

I have now taken UV vs Vis of 3 different transmission step tablets and they all give similar results. UV readings are consistently higher by a small amount than the Vis reading (which is a result that makes sense, a step table that at higher densities not only stops blocking UV, but actually starts facilitating UV transmission is a rather hard to grasp result). I too beleive King`s readings are faulty and actually all this discussion could have been avoided if we had agreeed on some basic results. A curve that is shifted 0.03 or 0.04 units right or left actually makes little difference what readings are used for the step tablet.

 

[gainer]

I do not have a comercially available densitometer, as I said before, so do not know what the various filters do in detail. What is the bandpass characteristic of the visual filter? Does it look like the average human visibility curve, or is it flat over the limits of human vision?

 

[Jorge]

I do not have a comercially available densitometer, as I said before, so do not know what the various filters do in detail. What is the bandpass characteristic of the visual filter? Does it look like the average human visibility curve, or is it flat over the limits of human vision?

I have tried and contact X rite about the spectra of their Vis and UV metering in the X rite 369, sadly they have not seen fit to answer me. It is not in their web site, nor is there any info for the Xrite 810 color densitometer. So in that respect I guess your guess is as good as mine. Some speculation, at least in the case of the 369 densitometer would suggest that it is a very narrow band response. The densitometer has a blue light and uses a filter for the UV mode. Either way I am sure it is not even close to the human eye visual range.

 

[sanking]

QUOTE=gainer]I do not have a commercially available densitometer, as I said before, so do not know what the various filters do in detail. What is the bandpass characteristic of the visual filter? Does it look like the average human visibility curve, or is it flat over the limits of human vision?[/QUOTE]


Pat,

The measuring geometry of the Gretag D-200-II is a specular/diffuse, ANSI-PH2, 19-1976. The color temperature of the measuring lamp is 3000º K.

I have measuring tubes for Visual, Blue and UV.

The center of the bandwith in Visual mode is 555 nm, and the bandwith is on average about 130 nm. The measuring range is 0.00 > 6.00D

The center of the bandwith in Blue is 458 nm, and the average bandwith is about 45 nm on average, with a measuring range of 0.00 > 4.00D.

The center of the bandwith in UV is 373 nm, and the bandwith is about 45 nm on average, and the measuring range is 0.00D >5.00D

The instrument will also measure IR, Ortho (500 nm), Green (543 nm) and Red (638 nm).

In the absence of measuring tubes of the correct type one could also use narrow band filters between the measuring light and the sample to simulate the filtration in the tubes. Using a 47b filter, for example, I get virtually the same readings with the D-200 as with the Blue measuring tube, and in turn these values are virtually identical to measurements with the X-Rite 810 in Blue mode.

Sandy

 

[Kirk Keyes]

Sandy, sorry for the couple of says absence.

Sandy wrote, "I have been working with densitomers for over 25 years and am very familiar with calibration procedures. So let’s get this out on the table."

Thanks for the in-depth info one your calibration procedures. I agree, it looks like you are doing all the manufacturer requires of you in that respect.

As a side note - I do have one issue though, and it's not an issue with you, but with Gretag. I may be wrong, and please correct me if I am, but it sounds like the calibration wedge that Gretag supplies has only one value on it for each step. Not separate values for red, green, blue, vis, UV channels. Is that correct? And the same wedge/value is used for calibration of all those channels?

If so, then if the calibration point varies in true density in different wavelenghts, as we really should expect it to, then this type of calibration procedure WILL cause differences in the slope of the densitometers response when changing channels. And that could easily account for errors in readings at higher densities when comapring different channels.

As you said, "This calibration wedge appears to be perfectly neutral." But if we could determine those fine details very well with our eyes, we would not need instruments like densitometers. Looking at your X-Rite 810-68 calibration wedge, you can see from the numbers on it that a wedge that appears to be "perfectly netrual" is not necessarily so. (See my last post at the bottom of page 8 where I list the RGBVis values for my 810-68 "Cal" step.)

So I am kind of concerned if Gretag is saying that the calibration wedge has exactly 3.05D in R, G, B, Vis, and UV from the same peice of film. Your measurements of your step tablets show that this is probably not a good assumption - none of them had identical measurements. But as I said, that is really an issue with Gretag's prescribed methods and you a fault of yours.

"The supposition on your part appears to be that if my reading of a Stouffer TP 45 step tablet is different in Visual and UV mode I must be doing something wrong, or there must be something wrong with my densitometer."

Not at all, but without a clearer understanding of your procedures one can not be certain.

Sandy wrote, "This suggests to me that you don’t appear to be aware of the fact that there are considerable variations in step wedges and that very few, if any, are perfectly neutral."

Not aware of the fact - if you go back through this thread I have been making that claim all along. I brought this up early on in this thread. From my second post in this thread on page 4, "It is quite difficult to make a step wedge for a wide range of the light spectrum that is neutral in color. And we have proved this to ourselves by measuring our step wedge with a calibrated densitometer." It is foolish to assume that a step wedge if completely neutral over a wide range of wavelengths.

Sandy wrote, "See any pattern? I do not. The densitometer reads higher in UV mode than in Visual with the Kodak Step #2 step wedge, lower in UV than Visual with the X-Rite transmission wedge and all three Stouffer TP-45 step wedges, and the same in UV and Visual with the Gretag calibration wedge."

The differences in the Kodak wedge are probably actually within the precision error of your densitometer so they can probably truly be considered neutral. You are right, your other step wedges to appear to actually have less absorbance in UV than Blue (Vis). Interesting because that is not what one may suspect a priori. But that's OK, because now we have precisely measured them with instruments that are making measurements of a known quality. That's great!

Sandy wrote, "As you should immediately see from the above the difference in reading is not due to base filtration. If that were the case the difference between Visual and UV values would be a constant. It is not."

DIfferences are not due to "only" base filtration. So that certainly means that there is some sort of "staining" or other factor that is going on that is contributing to the non-neutrality of our materials. There are many factors other than film base absorbances that can contribute, things such as the size and shape of the developed silver in the film that could cause this.

Well, great! I'm glad you've gone though that work and laid it out for us. I'm sorry that you feel like you are having to defend your practices when you know you are doing things as per the manufacturers methodologies, but until you fill us in on your procedures, we have every right to be suspicious of your data and methods.

 

[Kirk Keyes]

In response to Phil's excellent question, "knowing that you use BTZS for alt printing with great accuracy, I assume you have found that you have improved the accuracy of BTZS use by recalibrating the x axis using UV instead of visual readings of the step tablet?"

Sandy replied, "Using the [UV - right?] step tablet densities of the Stouffer TP 45 #3 test wedge provides better accuracy of the exact printing density of my pyro stained negatives than was the case with the default values of the WinPlotter, which are virtually identical to the Visual reading of this step wedge."

(Side note here - there is no reason to use the default values in the software, you should always use data derived from your own materials.)

"Exactly why this is the case is not entirely clear to me..."

Well, that's what we've been trying to determine here.

"...but the important thing to note is that calibration of the X axis to values other than default values or even to the Visual reading of the step wedge used to make the exposures results in different values for CI, EFS and SBR."

Yes, because of the simple math that is involved in the calculations.

"In my case the new values suggest develoment times for normal ES values with my processes that give more accurate CI values."

Using the UV values give you higher results for Ave. G than blue readings did. You did this by using the lower results you got by reading the UV spectrum of your step wedge. I would like to point out to you that you could have gotten the same Ave. G if you had gotten higher results for the y-axis data. Remember the math for the Ave. G is just one number devided by a second number. If your UV meaurements of the test neg had been proportionally higher, then you could have gotten the exact CI as your've gotten by using the UV results for the step wedge. (I hope that was clear - if not let me know.)

You've come to the conclusion that your visible readings of the step wedge are not valid because you've determined empirically that the UV readings work better. That's fine. But there's no scientific principle to support that conclusion, and many principles not to.

Have you stopped to think that it may be the readings of test neg that are suspect? Perhaps they need to be looked at?

I would like to suggest that perhaps the UV filter setting on your densitometer is not matching the "ideal" filtration we need to use for these measurements.

Sandy wrote, "Kirk has made the case that the use of UV values for the step tablet should not make any difference but the matter may be more complicated than he believes. For one thing film and papers have quite a bit of sensitivity to UV and even tungsten lights put out some UV radiation. There are after all filters called UV absorbing filters that are sold for use in enlargers, even with those with tungsten lights, to eliminate this source of light in printing. The Besler 23-CII enlarger that I use for exposing film in these tests originally had one of these filters but it was lost somewhere down the line so there is at this point no filtration of the UV light."

Interesting idea - my understanding is that modern enlargers are well designed and essentially have built in filtration. Perhaps if you have a cold light head that uses fluorescent bulbs which are rich in UV then this may be an issue, but not with a color enlarger. Also, the glass in our lenses do quite an effective job of filtering out UV. Most glass transmits about 92% of the visible wavelengths and around 380 nm it really starts to become a very efficient absorber of UV light. But combine this with the fact that a 3200K tungsten-halogen bulb produces virtually no UV light - especially when compared to the total output of all the visible wavelengths, I still believe that any UV contribution to the exposure of our panchromatic test film from our enlarger light source is negligible. If you have some data to suggest otherwise, I am certainly interested in seeing it.

As I have been saying all along, we MUST match the densitometer settings to match the exposure that we will be giving our material. So far, Sandy, other than your position that 1) it causes problems with Phil Davis' software if we have two sets of data for the exposure, and 2) you empirically have determined that the lower step wedge numbers "work" better, and now 3)your suggestion that UV filtration of the enlarger may be a key issue here, I haven't really heard any other reasons for your position.

After looking at the filter values you've listed for your densitometer, I see you have 373 nm listed as the center of the filter. Perhaps it is this filter that is not match your printing materials as well as you think for Pt/Pd printing. I believe that Jorge mantioned that according to Dick Arentz, Pt/Pd paper has a peak sensitivity at 290 nm. That is a bit off 373 nm. I don't know what type of light source you are using, I assume a Mercury lamp of some sort? Without knowing the emission spectra of the type of lamp you have, I can't make any suggestions there.

And we have yet to measure the UV filtration properties of your Pyrocat-HD processed films at wavelengths other than the 373 nm that your densitometer does. Perhaps a wavelength of 350, 320, or 290 nm would give you the extra density that it would take to make the simple math work. Looking at your pyrocat graphs on unblinkingeye.com, there is a trend towards greater density when we compare the blue and UV densities of your graphs. This suggests that a densitometer that could read shorter wavelengths may give better numbers, but there is really no way to predict the absorbance at different wavelengths simply by looking at two points of a spectrum. We'll have to try that and see what we get.

Again, from above, Sandy wrote, "Using the [UV - right?] step tablet densities of the Stouffer TP 45 #3 test wedge provides better accuracy..."

If your theory that the UV measurements of the step wedges was truely valid, then there should be no difference between any of the step wedges and we should be able to get predictable results from any step wedge as long as we measured them in the UV.

Have you asked yourself why Stouffer Step Wedge #3 works best? Is it simply because it has slightly higher numbers than Wedge #1 and 2 in the UV and not as high as any of them in the visible? Aren't you simply picking data sets that tweak the numbers to get results you like the best?

As I've been saying all along, there is no scientific reason to NOT use the visible density measurements of your step wedge for detemining exposure since you are using standard daylight with panchromatic film as this most closely matches. So now I suggest that instead of trying to rationalize the discrepancies between your calculated data and your empirically derived results, you should look at the measurements used to generate the data for the other side of your data set - we've looked at the x-axis data, so now let's look at the y-axis data. Does it best match the conditions that we will be exposing our materials?

 

[Kirk Keyes]

I'd like to correct a few things I said above:

I have been reminded that the density values used for the y-axis of our H&D graphs is the log(opacity). Not the log(density) that I beleive I said above.

Also, that an H&D curve should properly be called a D log-H curve.

Thanks, Kirk

 

[sanking]

Kirk,

In response to your remarks.

"I may be wrong, and please correct me if I am, but it sounds like the calibration wedge that Gretag supplies has only one value on it for each step. Not separate values for red, green, blue, vis, UV channels. Is that correct? And the same wedge/value is used for calibration of all those channels?"

I believe you are stating this correctly. The calibration itself is done based on only one density, 3.05, and in Visual mode.

"If so, then if the calibration point varies in true density in different wavelenghts, as we really should expect it to, then this type of calibration procedure WILL cause differences in the slope of the densitometers response when changing channels. And that could easily account for errors in readings at higher densities when comparing different channels."

That may be so, but there are in fact no errors at all in readings that I can see, and as I indicated, after calibration the calibration wedge reads identically at 0.00, 2.05 with the Visual and UV tubes, and also with the Blue tube that I checked after the last message.

"As you said, "This calibration wedge appears to be perfectly neutral." But if we could determine those fine details very well with our eyes, we would not need instruments like densitometers."

There may be a misunderstanding. I said that the calibration wedge appears to be perfectly neutral because I got identical readings of the low, mid and high densities with the D-200 in both Visual and UV mode. I did not mean that it appears to be neutral because I looked at it and it appeared neutral to my eye.


"So I am kind of concerned if Gretag is saying that the calibration wedge has exactly 3.05D in R, G, B, Vis, and UV from the same piece of film. Your measurements of your step tablets show that this is probably not a good assumption - none of them had identical measurements. But as I said, that is really an issue with Gretag's prescribed methods and you a fault of yours.

Again, there must be some kind of misunderstanding. The Gretag calibration wedge is different from all of the others because it actually measures identically in Visual, Blue and UV. All of the other step wedges are way off, except the Kodak #2 which measured very close to the same in Visual and UV mode.


"Not aware of the fact - if you go back through this thread I have been making that claim all along. I brought this up early on in this thread. From my second post in this thread on page 4, "It is quite difficult to make a step wedge for a wide range of the light spectrum that is neutral in color. "

OK, you did indeed make this point so I stand corrected.

BTW, I called Stouffer to discuss this situation and talked to one of their technicians. He told me that they neither test for nor attempt to control the UV absorption characteristics of their step wedges. He said that there was a UV densitometer on the premise and that they would pull it out and try figure out the reason for the discrepancy.

Sandy

 

[Kirk Keyes]

Patrick writes, "I do not have a comercially available densitometer, as I said before, so do not know what the various filters do in detail. What is the bandpass characteristic of the visual filter? Does it look like the average human visibility curve, or is it flat over the limits of human vision?"

Patrick, visible light ranges from 380 nm to 720 nm. Not everyone can see out to the full range of the spectrum, but we should all come close.

I'm sure you know about rods and cones. The reponse of our rods is from just above 400 to just over 600 nm, with peak sensitivity at 507 nm. But that's for our night vision.

Our cones come in 3 types, S, M, and L. S does blue response with a peak of 445 nm, M does green response with peak at 535nm, and L does red response with a peak at 575 nm. Your fovea contains the cones in the proportions of 64% L, 32% M, and 2% S. Despite this, your eyes are more sensitive to green than red.

Sandy's Gretag densitometer seems to be pretty "average" if I remember right - "visible" to our densitometers is usually centered in the green, and somewhat wide in bandpass. He lists 555 nm and a bandpass of 130 nm. 555 is at the upper end of green, and extends from just into the upper blue and into orange, but not quite red. This pretty much covers the middle wavelegths of our vision and near the range of greatest color sensitivity.

Note that his Gretag's green filter is actually pretty close to the center of the M cones' sensitivity, but because the bandpass of the filter is probably around 45 nm, it is not really suitable for replicating density response for human vision. (But fine for green!)

Kirk

 

[sanking]

Kirk,


“Interesting idea - my understanding is that modern enlargers are well designed and essentially have built in filtration. Perhaps if you have a cold light head that uses fluorescent bulbs which are rich in UV then this may be an issue, but not with a color enlarger. Also, the glass in our lenses do quite an effective job of filtering out UV. Most glass transmits about 92% of the visible wavelengths and around 380 nm it really starts to become a very efficient absorber of UV light. But combine this with the fact that a 3200K tungsten-halogen bulb produces virtually no UV light - especially when compared to the total output of all the visible wavelengths, I still believe that any UV contribution to the exposure of our panchromatic test film from our enlarger light source is negligible. If you have some data to suggest otherwise, I am certainly interested in seeing it.”

The enlarger that I use for testing is a Bes 23-C II and it uses a tungsten light source. The enlarger does not have any built in filtration, and as I mentioned, originally was equipped with a UV absorbing filter that was used in the filter drawer between the light and negative. How much UV light actually reaches the film, considering the absorption of the glass in our lenses and the radiation characteristics of a 3200K bulb, I don’t know. But it was apparently a serious enough issue for Beseler to include a UV absorbing filter as part of the original equipment of the 23 C II and I suspect that film has at least as much sensitivity to UV light as does paper. And it would only require a very small amount of effective UV radiation to skew the results in my plotting. In any event I plan in time to test this myself, but don’t have the necessary narrow band filters to do so right now.

"As I have been saying all along, we MUST match the densitometer settings to match the exposure that we will be giving our material. So far, Sandy, other than your position that 1) it causes problems with Phil Davis' software if we have two sets of data for the exposure, and 2) you empirically have determined that the lower step wedge numbers "work" better, and now 3)your suggestion that UV filtration of the enlarger may be a key issue here, I haven't really heard any other reasons for your position."

Three reasons gives me cause to think, especially empirical ones that result in better results.

“After looking at the filter values you've listed for your densitometer, I see you have 373 nm listed as the center of the filter. Perhaps it is this filter that is not match your printing materials as well as you think for Pt/Pd printing. I believe that Jorge mentioned that according to Dick Arentz, Pt/Pd paper has a peak sensitivity at 290 nm. That is a bit off 373 nm. I don't know what type of light source you are using, I assume a Mercury lamp of some sort? Without knowing the emission spectra of the type of lamp you have, I can't make any suggestions there.”

Well, I certainly have some thought about these issues.

As to what Jorge said, frankly I have no idea what he meant because it did not make any sense to me? Approximately 90% of the UV radiation below 330 nm is filtered by the ordinary float glass that is used in contact frames and vacuum easel, and when you get down to 290mm the figure is close to 99%. So even if it is true that the peak sensitivity of Pt./Pd processes are around 290 nm this information is essentially irrelevant for all practical purposes unless you find a way to contact print withouit using any glass.

By the way, I wrote the appendix on UV light sources for the new revision of Dick Arentz’s book on printing with palladium and platinum. Here is what I said, slightly abbreviated:

“Pt./Pd. printing requires a light source that emits much of its radiation in the UVA (320-400nm) range and in the violet and blue range up to about 420nm. Palladium and platinum are also very sensitive to UVB between 254nm and 313nm but sources of this type should be avoided because of the severe risk of skin cancer and cataracts. It should also be noted that approximately 95% of Ultraviolet B is absorbed by the glass of most contact printing frames and vacuum easels so in practice almost all UV B radiation is effectively useless to palladium and platinum printing. And above about 436nm the sensitivity of both palladium and platinum is extremely small.”

So, in essence the situation is this. Over 95% of the useful radiation in the Pt/Pd processes is in the 350 – 420 nm range, which happens to match fairly closely to the bandwith of the Gretag D-200 II densitometer.

“And we have yet to measure the UV filtration properties of your Pyrocat-HD processed films at wavelengths other than the 373 nm that your densitometer does. Perhaps a wavelength of 350, 320, or 290 nm would give you the extra density that it would take to make the simple math work. Looking at your pyrocat graphs on unblinkingeye.com, there is a trend towards greater density when we compare the blue and UV densities of your graphs. This suggests that a densitometer that could read shorter wavelengths may give better numbers, but there is really no way to predict the absorbance at different wavelengths simply by looking at two points of a spectrum. We'll have to try that and see what we get.

Again, a very valid question. But regardless of the exact absorption characteristics of a negative processed in Pyrocat-HD, shorter wavelengths, say of 290 – 320 nm, are virtually meaningless for all alternative processes.


“As I've been saying all along, there is no scientific reason to NOT use the visible density measurements of your step wedge for determining exposure since you are using standard daylight with panchromatic film as this most closely matches.”

I understand what you are saying, but I would modify it to include another possibility, i.e. that there is a scientific reason to not use the visible measurements but it has either not been discovered or fully documented.

“So now I suggest that instead of trying to rationalize the discrepancies between your calculated data and your empirically derived results, you should look at the measurements used to generate the data for the other side of your data set - we've looked at the x-axis data, so now let's look at the y-axis data. Does it best match the conditions that we will be exposing our materials?”

I am not trying to rationalize anything. To the contrary, I am trying to figure out how all of this comes together.

As for the question of the exposing unit, I expose Pt/Pd with a bank of BLB tubes that emits the great majority of its radiation in the 350 – 420 nm range, almost exactly in the center of the range of the most useful radiation to the Pt/Pd process, and very close to the center of the UV bandwith of the Gretag D-200 II. And my exposures are timed with an Olec light integrator with a photo sensor that almost exactly matches the bandwith of the light source. So I have at least tried to consider the importance of the Y axis.


Sandy

 

[Ed Sukach]

The enlarger that I use for testing is a Bes 23-C II and it uses a tungsten light source. The enlarger does not have any built in filtration, and as I mentioned, originally was equipped with a UV absorbing filter that was used in the filter drawer between the light and negative. How much UV light actually reaches the film, considering the absorption of the glass in our lenses and the radiation characteristics of a 3200K bulb, I don’t know. But it was apparently a serious enough issue for Beseler to include a UV absorbing filter as part of the original equipment of the 23 C II...

I think you'll find that filter wasn't for the absorption of Ultra Violet (very little of a tungsten source spectrum is UV) .. but for the other end; Infra Red ... there is quite a bit of that ... and its' alter ego - heat.
IR filters are very common in optical system .. they are commonly called "heat glass" or heat filters".