Yes Clay, but look. Here are the densities for my stouffer step tablet:
Originally Posted by clay
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.
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.
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.
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.
Last edited by Kirk Keyes; 08-14-2004 at 05:02 PM. Click to view previous post history.
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.
Originally Posted by Kirk Keyes
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
Originally Posted by Kirk Keyes
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"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.
Last edited by sanking; 08-15-2004 at 04:22 PM. Click to view previous post history.
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?
"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.
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.
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.