film speed

[sanking]

Stephen;

I'm afraid that your arguments avoid the point that the human eye integrates the data in the image. In that case, due to having a toe and shoulder in the photographic image, the toe and shoulder are 'soft' and the mid scale is higher in contrast than the 1:1 slope we would otherwise expect. Therefore, it is unavoidable that the 'contrast' of a print would be about 1.5 in the mid-scale to compensate for the toe and shoulder. This is what we designed for.


PE

This brings up another question. How useful are speed point designations based on the FG method in the age of digital? For example, using Mark Nelson's Precision Digital Negative system for establishing correlation between negative and print densities it is possible to effectively use virtually every bit of density on the negative, from densities of as low as 0.02 to almost 99% of Dmax.

Sandy

 

[Photo Engineer]

Sandy, I agree. What you say is possible with a totally linear D Log E curve generated digitally. It is also possible in analog photography using appropriate chemical means to generate the same end result.

Stephen, I disagree. Just for example, a negative film has an average mid scale gradient of about 0.6 and an average grade 2 paper has a mid scale gradient of about 2.5. The optimum print from this combination yields a gradient of about 2.5 x 0.6 or a mid scale gradient of about 1.5. This is what I was referring to.

As for the Munsel scale, it is mainly only used for color, however another useful scale is the CIE Chromaticity Scale. Neither of these is used strictly for the design of B&W materials. Only the H&D curves and 'print through' scales are used in design of B&W AFAIK. Print through scales, are H&D curves of film printed onto paper and then compared with H&D curves of the paper, using mathematics to determine the effect of printing.

I did all of the above during the design phase of Ektacolor 30/37 paper and Kodacolor 400 film. I used both B&W and color print through, undercut and double undercut imaging methods almost daily. I also used the 'silver criterion' for obtaining exact results from both B&W and color materials. This takes into account any deviation in color of the original negative image from the spectral sensitivity of the print material. This latter factor is significant, particularly with todays MG papers, when the silver image is not perfectly neutral.

PE

 

[Mark Layne]

Stephen;

I'm afraid that your arguments avoid the point that the human eye integrates the data in the image. In that case, due to having a toe and shoulder in the photographic image, the toe and shoulder are 'soft' and the mid scale is higher in contrast than the 1:1 slope we would otherwise expect. Therefore, it is unavoidable that the 'contrast' of a print would be about 1.5 in the mid-scale to compensate for the toe and shoulder. This is what we designed for.

This 1.5 mid-scale contrast compensates for the loss in contrast in toe and shoulder and gives the human eye the overall impression of a curve with a slope of 1. It is, in effect, an optical 'delusion'.

As for the Munsel chart, well, it can be used as a B&W tool, but we never did. To use an analogy, you can remove an appendix via the mouth! Why bother when other methods are so much more convenient and less difficult. So, we just used the H&D curve for both B&W and color. We used the Munsel chart only for color space.

I'm afraid that our methods differ, but I am familiar with what you refer to. I'll defer to the experts that I know, and rely on the work of DeMarsh, Zwick and others that I worked with personally and who taught me the methodology one on one in the lab. I have no doubt that what you say will work, but it seems rather round about to get to simpler solutions to the problem.

PE

Ah yes, 'the human eye integrates data in the image.' When a friend who is an optical and acoustic research scientist made a similar statement and said something to the effect that the most theoretically perfect lens may not give the best image the debate became hostile and heated.
Mark

 

[Stephen Benskin]

Sandy, I agree. What you say is possible with a totally linear D Log E curve generated digitally. It is also possible in analog photography using appropriate chemical means to generate the same end result.

Stephen, I disagree. Just for example, a negative film has an average mid scale gradient of about 0.6 and an average grade 2 paper has a mid scale gradient of about 2.5. The optimum print from this combination yields a gradient of about 2.5 x 0.6 or a mid scale gradient of about 1.5. This is what I was referring to.

As for the Munsel scale, it is mainly only used for color, however another useful scale is the CIE Chromaticity Scale. Neither of these is used strictly for the design of B&W materials. Only the H&D curves and 'print through' scales are used in design of B&W AFAIK. Print through scales, are H&D curves of film printed onto paper and then compared with H&D curves of the paper, using mathematics to determine the effect of printing.

I did all of the above during the design phase of Ektacolor 30/37 paper and Kodacolor 400 film. I used both B&W and color print through, undercut and double undercut imaging methods almost daily. I also used the 'silver criterion' for obtaining exact results from both B&W and color materials. This takes into account any deviation in color of the original negative image from the spectral sensitivity of the print material. This latter factor is significant, particularly with todays MG papers, when the silver image is not perfectly neutral.


PE

We're just talking about different things. It's just a misunderstanding. You were talking about paper contrast. I was talking about the reproduction curve. In a four quadrant Tone Reproduction Graph, you are talking about quadrant 3 and I am talking about quadrant 4. You are right about the negative/print match. It can be expressed as unity equals neg contrast times print contrast.

I never said the Munsell system was used extensively for b&w. I was talking about the concept of the psychological scale which is about perceptually equal reflection density steps from black to white. I used as an example of a psychologically based scale which could give Zone shooters the impression there are target reflection density values for the print Zones. I also used it as an example because I believe Ansel Adams was inspired by the Munsell scale to use a print Zone scale of ten steps. I also believe this has cause much confusion for people attempting to learn the ZS (such as the original poster).

Did I happen to mention the adaption of and the revision of the CIE Chromaticity Scale through the work of the JOSA Committee of Colorimetry chaired by Loyd Jones, and it's relation to the testing of the Munsell system and particulally the neutral scale? It's hard to believe there was a fight between the different scientific disciplines as to what color was. It took over ten years for them to define it.

I agree with Sandy that there really is little left of any great importance concerning traditional photography in todays reality of digital. I do believe; however, that there is value understanding FG in a digital world. The parameters of the FG method are directly tied to camera exposure, understanding FG and its relationship with the ISO speed method helps in the understanding of camera exposure. Of course, a large portion of the population won't care and just let the camera do it for them, but I figure those who frequent this forum aren't part of that mindset.

Thanks Sandy for the Mark Nelson reference. I'll check him out.

For those interested in the Munsell N/ values. Notice how N/5 is now 19.77% and not 18% and N/10 is 102%.

Munsell Values
Column A - Reflectance from 1929 Book of Color
Column B - OSA 1943 Renotation recommendations

N/ A B
1 1.12 1.210
2 2.90 3.126
3 5.95 6.555
4 11.05 12.001
5 18.00 19.770
6 27.3 30.050
7 38.9 43.060
8 53.6 59.100
9 72.8 78.660
10 100.00 102.570

 

[sanking]

Stephen,

Here is the site. http://www.precisiondigitalnegatives.com/

In my opinion his system for making digital negtives is simply outstanding. Guess that is why he calls it "precision." But there are some other excellent methods out there as well.

Best

Sandy

Thanks Sandy for the Mark Nelson reference. I'll check him out.

 

[sanking]

I agree with Sandy that there really is little left of any great importance concerning traditional photography in todays reality of digital. I do believe; however, that there is value understanding FG in a digital world. The parameters of the FG method are directly tied to camera exposure, understanding FG and its relationship with the ISO speed method helps in the understanding of camera exposure. Of course, a large portion of the population won't care and just let the camera do it for them, but I figure those who frequent this forum aren't part of that mindset.

Stephen,

I would assume that you have a graphing program for testing the FG method. If so, is this something you might make available to others? Since I work in several processes with different exposure scales I would be very interested in carrying out some experiments of my own to compare the FG to the current ISO method for these kind of applications.

Sandy

 

[Kirk Keyes]

Sandy - Check for the Photo Techniques article that Stephen mentioned earlier in the thread. I think he covers it in there. I think the title as something like "Black & White Film Speed: An Analysis". I think it was Mar/Apr or May/Jun 2005. (I can't find my copy of it for some reason so I'm not sure of the date.)

Or if you have a copy of the SPSE (Society of Photographic Scientists and Engineers) Handbook of Photographic Science and Engineering laying around - look in there, p. 811 of the 1973 edition. I found one really cheap online - sadly it has a label in the front that says "Library of Polaroid Corporation"...

Anyway, as it uses a graphical method I'll refrain from trying to put it into words...

 

[Kirk Keyes]

SPSE (Society of Photographic Scientists and Engineers) Handbook of Photographic Science and Engineering

Oh yeah - I meant to mention that this book is a really neat resource with a lot of info about photography and related issues. Well worth having if you are really interested in the fine details of photography.

 

[sanking]

Kirk,

I have most of the literature mentioned, including the Dunn and Wakefield book, edition of 1972, and a 1973 edition of the Handbook of Photograpic Science and Engineering.

What I want to know is if Stephen, or you perhaps (?), has a computer graphing program that allows one to enter sensitoimetry data and evaluate the differences between FG and contemporary ISO standard for different ESs.

I will check his article in Darkroom and Techniques to see if there is anything about graphing programs.

Best,

Sandy

Sandy - Check for the Photo Techniques article that Stephen mentioned earlier in the thread. I think he covers it in there. I think the title as something like "Black & White Film Speed: An Analysis". I think it was Mar/Apr or May/Jun 2005. (I can't find my copy of it for some reason so I'm not sure of the date.)

Or if you have a copy of the SPSE (Society of Photographic Scientists and Engineers) Handbook of Photographic Science and Engineering laying around - look in there, p. 811 of the 1973 edition. I found one really cheap online - sadly it has a label in the front that says "Library of Polaroid Corporation"...

Anyway, as it uses a graphical method I'll refrain from trying to put it into words...

 

[Stephen Benskin]

Kirk,

I have most of the literature mentioned, including the Dunn and Wakefield book, edition of 1972, and a 1973 edition of the Handbook of Photograpic Science and Engineering.

What I want to know is if Stephen, or you perhaps (?), has a computer graphing program that allows one to enter sensitoimetry data and evaluate the differences between FG and contemporary ISO standard for different ESs.

I will check his article in Darkroom and Techniques to see if there is anything about graphing programs.

Best,

Sandy

Sandy,

I've tried to write something that works, but being the world's worst programmer, I have been unsuccessful finding a way to find the .3x point. Having said that, by using the Delta X equation, you can determine just as accurately the FG speed point. Although without a calibrated sensitometric strip, the results will only relate to relative speed, but if you're looking to compare the differences between two techniques using the same test strip, it should work just fine.

I'll have to look it up and get you all the pertinent information. I only have time at the moment just to make this quick post to let you know.

 

[Photo Engineer]

Since the H&D curve is a standard cubic spline, I would think that there was a program out there for it.

But, you may want to look at the work by DeMarsh et al. Or, Kriss et al. Well, provided they published.

PE

 

[Stephen Benskin]

PE,

It's not about plotting the curve, it's about reading the curve. I've written a number of plotting programs including a 4 quadrant tone reproduction graph.

Sandy,

Delta X eq.

DeltaX = 0.83 - (.086 * DeltaD) + (0.24 * DeltaD^2)

Example: based on the ISO contrast Parameters

DeltaD = 0.80

0.83 - (.086 * 0.80) + ((0.24 * 0.80^2) = 0.296

DeltaX = 0.296

I've attached a word document of a Delta X Criterion table.

Steve

 

[Stephen Benskin]

Sandy,

I only gave you how to calculate Delta X and not about calculating FG. Sorry, it was late.

To compare ISO with FG I use two equations.

1. Finding FG exposure using DeltaX and ISO Hm

Hfg = Hm / antilog(DeltaX) or Hfg = Hm / 10^DeltaX

example for a film with an ISO speed of 125:

DeltaD for ISO standard is = 0.80 which equals a DeltaX of 0.296

0.0064 / 10^0.296 = 0.0032



2. FG speed calculation

Sfg = 0.4 / Hfg

where Hfg = exposure in meter candle seconds at fractional gradient speed point

example for FG speed

0.40 / 0.0032 = 125

As you can see, they are the same when DeltaD = 0.80, but they begin to diverge when DeltaD changes. Also, please be aware that the FG speed calculation is not the same as the original FG equation. They modified it to work with the adjustment to flare in the 1960 ISO speed version.

Above and beyond the concept of FG as being the most consistently precise speed method, it helps explain exposure theory. The DeltaX for the ISO standard also happens explain the difference between the log-H range from the mid-exposure / meter calibration point and the where the shadows fall (log-H 1.28) and the difference between the meter calibration point and the ISO speed point (log-H 1.0). In other words shadow exposure for a statistically average luminance range, 2.2 (in which exposure is based), will fall at the FG speed point. Average flare will bring it back up to around the ISO standard. It will not fall exactly on the ISO speed point because 0.80 in the speed equation gives a slight safety factor since average flare is considered 0.34 in the calculation of speed. This is what I meant when I said the ISO speed point is a point to determine speed and not where shadow exposure falls. With the dominance of 35mm, average flare is approx. 0.40. It only makes for a slightly higher safety factor. Of course, flare isn't consistent, which means actual shadow exposure placement will differ depending on flare.

To me, knowing about the variance of exposure is beneficial. Knowing about the lack of rigidity can save many from worry and obsessive speed tests.

Steve

 

[sanking]

Stephen,

Thanks for the additional information. Once I get all of this sorted out I am going to compare the speed point with this method and the approximate contrast method in Davis' plotting program using different parameters for exposure scale.

Sandy

Sandy,

I only gave you how to calculate Delta X and not about calculating FG. Sorry, it was late.

To compare ISO with FG I use two equations.

1. Finding FG exposure using DeltaX and ISO Hm

Hfg = Hm / antilog(DeltaX) or Hfg = Hm / 10^DeltaX

example for a film with an ISO speed of 125:

DeltaD for ISO standard is = 0.80 which equals a DeltaX of 0.296

0.0064 / 10^0.296 = 0.0032



2. FG speed calculation

Sfg = 0.4 / Hfg

where Hfg = exposure in meter candle seconds at fractional gradient speed point

example for FG speed

0.40 / 0.0032 = 125

As you can see, they are the same when DeltaD = 0.80, but they begin to diverge when DeltaD changes. Also, please be aware that the FG speed calculation is not the same as the original FG equation. They modified it to work with the adjustment to flare in the 1960 ISO speed version.

Above and beyond the concept of FG as being the most consistently precise speed method, it helps explain exposure theory. The DeltaX for the ISO standard also happens explain the difference between the log-H range from the mid-exposure / meter calibration point and the where the shadows fall (log-H 1.28) and the difference between the meter calibration point and the ISO speed point (log-H 1.0). In other words shadow exposure for a statistically average luminance range, 2.2 (in which exposure is based), will fall at the FG speed point. Average flare will bring it back up to around the ISO standard. It will not fall exactly on the ISO speed point because 0.80 in the speed equation gives a slight safety factor since average flare is considered 0.34 in the calculation of speed. This is what I meant when I said the ISO speed point is a point to determine speed and not where shadow exposure falls. With the dominance of 35mm, average flare is approx. 0.40. It only makes for a slightly higher safety factor. Of course, flare isn't consistent, which means actual shadow exposure placement will differ depending on flare.

To me, knowing about the variance of exposure is beneficial. Knowing about the lack of rigidity can save many from worry and obsessive speed tests.

Steve

 

[Claire Senft]

Mr Beskin I am happy to see you posting again. I missed you.

 

[sanking]

BTW, I asked Phil Davis what method he used to calculate approximate CI in the WinPlotter program. Phil said that he did not remember the exact factors but that he used the fractional gradient method. Since the plotter programs allows use to choose either approximate CI or fixed density of 0.1 over B+F to calculate curves it looks like I may already have a graphing program that can be used to show speed point with the two systems. Well, I already knew that I had two methods but did not know that one of them was based on the fractional gradient method.



Sandy

 

[Stephen Benskin]

Sandy,

That's right. Now, that you mention it, I remember he had that choice. It's been years since I last saw it. I seem to remember the FG method in his program had more to do with calculating gradient than speed. Is that correct? Either way, the one thing I never liked about Davis' program is that the speeds were all relative and it didn't allow for a calibrated exposure approach.

Anyway, I hope the Delta X equations and Davis' programs will give you what you need. Please let me know what you come up with.

Steve

 

[sanking]

Steve,

I have no idea how the calculations are actually done in the program, and Davis may not remember some of the specifics since he wrote the program over 20-25 years ago and the current version was ported to PC from Mac by someone else so he probably has not looked at the code for a very, very long time. However, I am fairly certain that the FG method in Plotter calculates speed as well as gradient. For sure, if you run the program with all of the parameters except choice of approximate CI or fixed density you get different speed values with other than N values.

Perhaps you might like to share some plotting data with me for a specific film and devleopment and I will run it in Plotter to see how it corresponds to your figures for speed point?

Plotter does have provisions for calibrating to a personal speed point. This was added to Plotter just a few years ago. However, the exposure axis is still express in terms of Relative log E.

My major complaint about the Plotter program is that it will not accept direct readings from my densitometers, whereas an Excel spread sheet would. This means that I have to make density reading manually and then key them into Plotter one by one, which can be a royal pain in the rear if you do a lot of testing. Unfortunately, I have never found an Excel program for curve graphing that will do all of the things that Plotter is capable of. From time to time I hear of people who plan to make one, but it never seems to happen.

Sandy

Sandy,

That's right. Now, that you mention it, I remember he had that choice. It's been years since I last saw it. I seem to remember the FG method in his program had more to do with calculating gradient than speed. Is that correct? Either way, the one thing I never liked about Davis' program is that the speeds were all relative and it didn't allow for a calibrated exposure approach.

Anyway, I hope the Delta X equations and Davis' programs will give you what you need. Please let me know what you come up with.

Steve

 

[Stephen Benskin]

Sandy,

It's good to hear Davis has updated the program, and I know what you mean about manually entering data. That was a major goal in writing my own. Maybe someone who knows much more about programming than I could always write an plug-in to the Davis program. I guess there's not too much motivation now a days with the advent of digital.

About the data, I'll see about e-mailing you something. The work I did on the Delta X Criterion was over a year ago. Since I already have the results of those tests, out of pure laziness, I wish to send you those numbers. I just have to see if I can remember which curves I used. Something should be coming in the next few days.

Claire,

Thanks. And it's Steve, please.

Steve