Bill thank you so much for spending your time on charting my data! it is very much appreciated!
What i don't get is why you gain so different results from the same data (the 30 density readings from the stouffer)?
what is it that makes the results of Ralph's excel sheets differ so much from your chart, considering filmspeed and dev. time...?
I think i will repeat the test giving both films 4 stops more exposure...
Best regards, christoph.
That's a fair question. Ralph Lambrecht posts here regularly and often answers directly.
I've seen and tried to reconcile this difference between his programmed results and my paper graphs before.
First and most important. You can make excellent negatives following the results of his spreadsheet.
Second (and only less important because I want to stress the first point), Flare is distorting the results.
Third (this is where it becomes a journey), I think we define Quality differently.
I make negatives in the "West Coast" tradition of full shadow detail targeted for "Grade 2" for a "Diffusion" enlarger. I try to obtain the Best Possible Negative - For Printing.
I think Ralph prefers High Resolution, Minimal Grain, obtaining the Best Possible Print.
Notice, there is a subtle difference between what I want (pleasure in the darkroom) compared to what Ralph wants (pleasure at the Gallery Opening).
I want to add more thoughts...
Ralph's spreadsheet times will not make negatives that are "hard" to print in the darkroom... It's just that ease in the darkroom wasn't necessarily his measure of "quality". The difference between a properly exposed negative developed for 8 minutes compared to 11 minutes is about one paper grade number. Well within what can be pleasantly printed.
A negative that is "hard" to print in the darkroom would be one that was underexposed and underdeveloped... And you wouldn't make that kind of mistake after going to this much testing. Obviously following Ralph or my guidelines you would never expose the film at EI 800 and develop for 4 minutes.
I stray from tradition by choosing a longer development time for N than Ansel Adams would have chosen. I keep forgetting to mention, I put N at the ASA triangle (that dashed-line triangle I drew on the graph). Ansel Adam's N is probably between 8 and 11 minutes.
Description to Ralph's test procedure says that it will print well on grade 2 paper. Do you think that difference can be caused by
Dmin = 0.17, Dmax=1.37 used in the spreadsheet (input data sheet)? Also normal gradient by default is 0.57 (summary sheet).
I think the difference is due to trying to calculate Average Gradient (and for me, the Contrast Index) with less than enough information...
I aim for 0.62 Contrast Index, which I believe comes at a time slightly greater than 11 minutes. My aim fits 7 stops of subject brightness on Grade 2. Ralph's 0.57 would be 7 1/3 stops subject brightness on Grade 2, a trivial difference.
Ralph's aim for 0.57 Average Gradient, is calculated by the spreadsheet at 8 minutes.
But at 8 minutes I compute 0.45 Contrast Index !
The difference between 0.62 and 0.57 would be trivial. But the difference from 0.62 to 0.45 is significant. Now we have different development times advice that could impact your negative quality.
You really want a density difference from B+F to 1.05 above B+F for a negative that prints on Grade 2. So look at the graph! Which curve will get you 1.05 over a range of 7 to 7 1/3 stops? ... The 11 Minutes time. The 8 minutes curve gives you 0.90 above B+F in that range... Suitable for Grade 3.
Unless you are talking about a Condenser enlarger compared to a Diffusion light source...
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thank you for the explanation. I'm not trying to question your method. I'm trying to learn and understand. I was reading regarding film test from WBM 2 and Phil Davis Beyond the Zone System (I use BTZS Plotter for Windows program) but I'm getting different results. That's the reason for those questions.
Do I understand it correctly that Ralph's spreadsheet aims for AG 0.57 and yours is based on the calculation?
in WBM 2 Ralph is referring to Diffusion light source
Thanks wiedzmin for clarifying.
Even in my notes 0.57 average gradient is good for Grade 2 for Diffusing enlarger for 7 1/3 stops subject brightness range (which is a well-recognized standard for "normal").
0.62 average gradient is good for Grade 2 for Diffusing enlarger for 7 stops subject brightness range.
And this difference is insignificant - either way works for me.
So the main discrepancy is the question of... how many minutes of developing time gives 0.57 average gradient?
It just doesn't look like 8 minutes to me.
so you think that short development time is because test was underexposed 4 stops? or spreadsheet is overoptimistic with using grade 2 paper?
Christoph, I hope that you do not mind that I'm using your thread.
if you will have a moment could you take a look on attached files? xls it is Ralph's spreadsheet with my test of acros 100 in hc110, pdfs are from BTZS Plotter program one is without flare density entered , the other one with flare density of 0.02
spreadsheet calculates N development 6 min, BTZS plotter `5:15 with flare 0.02 , and just below 5 min without flare
ISOs are also different
Do charts from BTZS program look ok?
I think curve-fitting is difficult when there isn't enough information, so yes having more data will help matters.
But flare really gets my goat. When you tape a Stouffer scale to a glass and photograph it, you just can't get any information for steps with density higher than 2.0. At that step, only 1% of the light should reach film. But due to scattering around in the optics and inside the camera, you can't reduce the light further, for example at 3.0 only 0.1% of the light should reach the film. But what I see looks like 1% of the light hits the film.
Is there any way you can contact print a step wedge?
wiltw, thank you for your answer!
when i exposed the hp5 and fp4, i sticked the stouffer TP120-31 to a window masked it with black cardboard and took an average reading with the prism finder's internal light meter (relying that it would give me a more or less accurate exposure and compensating for the 2 stops for the bellows i used).
i wasnt able too take a reading off of bar nr. 16 with my spotmeter, because one bar on the TP120-31 is 3,3 mm wide, that is too narrow to take a reding with my pentax off of that single bar.
to take a reading of one single bar with a spotmeter, i think you have to use a Stouffer 4x5 inch with 31 (or 21) bars.
saying that, the spotmeter should have a close up lens, so that you can get close enough with the spotmeter to that one bar (16 or 11) to take a reflective reading...
FYI, i asked at Souffers for bar widths of different step tablet sizes,...so here is what i got as a reply:
The step size of the TP120-21 is 4.9mm and the TP120-31 is 3.32mm.
The step size of the TP4x5-21 is 9.525mm and the TP4x5-31 is 6.4mm.
Last edited by qualsound; 12-15-2013 at 05:50 AM. Click to view previous post history.