Does changing film speed affect zone employment?

[Bill Burk]

I cringed when Mark posted that Kodak scanned all the negatives and sold them for scrap. I hope he meant all the Shirley pictures and not the historically significant Jones series

 

[138S]

The ISO Film Speed Diagram is used to determine film speed and not exposure placement. It is a graphical method of the Delta-X Criterion. Fractional Gradient speed point is derived by psychophysical testing and produces the most consistently accurate B&W film speed. When the ISO diagram's parameters are adhere to, the difference between 0.10 over Fb+f is always Δ0.296 log-H from the fractional gradient speed point.

Any point of density is not an adequate way to determine consistent print quality.

View attachment 269548

If you are interested in better understanding film speed, I suggest checking out these two papers. This forum has a number of ways you can obtain them.

Nelson, C.N., Safety Factors in Camera Exposures, Photographic Science and Engineering, Vol 4, No 1, Jan-Feb 1960.
Nelson, C.N. and Simonds, J.L., Simple Methods for Approximating the Fractional Gradient Speeds of Photographic Materials, JOSA, Vol, 46, No. 5, May 1956.

Of course the ISO method is not perfect... Probably the ISO method was designed to provide the greatest conceptual simplicity still offering the important information for most of the films. This Delta-X Criterion looks a more refined way, but the ISO method says the exposure that (in standard conditions) places -3.33 spots at 0.1D (over F+B) providing a very plain explanation, IMO that conceptual simplicity is the strong point of the ISO method. Also ISO method is the one.

My understanding is that the Delta-X Criterion can have an advantage if we want to understand what happens when pushing.

 

[Stephen Benskin]

One thing I find with discussions about film speed and exposure, and especially Zone System film speed and exposure, is that without a good understanding of the background photographic theory, it's hard to come to any consensus. What doesn't help is that any system, like the Zone System, tends to simplify of a process and is going to exclude parts that can shed light on concepts or caveats associated with the process. Conclusions can appear absolute and without caveats leading to or even presenting false assumptions.

Take for example some of the questions that are rarely discussed but I believe could help answer many of the zombie topics that never seem to die.

Why 0.10 over Fb+f? Is there anything intrinsic about that density value?

What is considered normal processing and why?

Why have B&W film speed determined in the lower part of the curve and reversal film speed in the middle?

What about all the variables not considered or incorrectly considered in Zone System testing? Such as flare or metered exposure being 18%?

The film's characteristic curve is a graphic representation of how a particular film responds to exposure under a particular processing regime. For all practical purposes, the curve doesn't change if processing conditions remain the same. Conceptually camera exposure can be thought of as being superimposed over the curve visually illustrating the placement and relationship of the photographed scene's luminance range on the film. Does the absence of curves in the Zone System cause unnecessary confusion and / or an unrealistic idea of exposure placement and precision? Is this one of the results of simplification for the sake of a system?

Film is just one part of the photographic process. Why doesn't the Zone System deal more with the relationship between film and paper? Yes, Phil Davis does, but it's also a system and more people know Adams'.

Stephen

 

[Stephen Benskin]

Bill, what is clear is that today the ZS table is inconsistent with box speeds... in nominal terms. (if we use a personal speed then we simply do what we want)

Z-I was stated (by Ansel Adams himself) to have 0.1D (over FB), if we use Box Speed and we meter for Z-V (stated to be a 18% grey card) then our Z-I won't be at 0.1D as it will be pure black, a -4 underexposure is lower than the the Speed Point exposure by a fair amount, you in particular are proficient in film calibration, so no need to insist in that...

Even if metering/exposing very accurately, even if performing a lab grade ISO calibration... we won't get the Z-I detail if we use the perfectly calibrated ISO speed for ZS, we have to shift a zone or to use half the EI!

IMO that speed change generated an incredible amount of confusion for the ZS, as ZS table was not changed we have 3 choices:

1> Using (Nominally) half of the Box Speed.

2> Exposure compensation +1

3> Shifting a zone, so expecting start having detail in Z-2 instead Z-1 which will be pure black.

Nominally:

With 1 and 2 we expose like Pre 1960, we overexpose the neutral 18% grey by +1 (in modern terms) and we have 4.33 stops shadow latitude.

With 3 we have 3.3 stops shadow latitude, and our 18% mid gray is exposed 0+/-. Our Z-1 is in the speed point so staring to have detail.

The question is: Do we aim a 3.33 or a 4.33 shadow latitude ?

These two graphs might help visualizing the situation. The graph on the left shows the relationship between the metered exposure point and the 0.10 over Fb+f, but mostly where the Zone System's four stops down from that point will fall. The graph on the right show what needs to happen to bring up the Zone System Zone I, four stops under the metered exposure, in order for the exposure to fall on 0.10 over Fb+f. Everything shifts to the right. As 0.10 doesn't necessarily represent the ideal shadow exposure and in truth there really isn't one. Notice flare isn't factored in. Interesting enough, Zone System in camera testing with a single toned target in effect doesn't incorporate flare either, but while one does eventually factor it in (with ISO film speed, it is part of the underlying determination), Zone System never does.

Perception of quality in a B&W photograph has to do with the shadow detail. Determine the minimum useful point and anything to the right of that point will produce a good image. That's one of the purposes of the First Excellent Print test. The other is to determine how to determine this point sensitometrically (and not have to repeat the arduous psychophysical test of the First Excellent Print). As it turned out, a single point of density wasn't a sufficient method. A point where the gradient of the curve in the shadow area was at a certain fraction of the overall gradient of the film was. Anything below this point, quality quickly fell off. Interestingly, for about a stop over this point, quality continued to increase and then leveled off. Sp. exposure to the right of the Fractional Speed Point is fine up to the point where other undesirable aspects being to appear.

Why 0.10? Germany used 0.10 with DIN, but Russia used 0.20 for GOST. Basically, it's usually in the shadow area and it's easy to find. Finding the fractional gradient speed point was difficult. You had to pick a point on the curve and then do calculations to determine if it's at the 0.3x of the average gradient. If not, a new point was chosen and tested. Accuracy in camera exposure, exposure meters, and film process had improved over the years. This allowed for a number of changes to speed testing. What Kodak discovered was that the fractional gradient speed point could be determined mathematically if you knew your processing. Because of the increased use of smaller format cameras and increased accuracy of exposure meters, the safety factor could be decreased. Other countries were willing to accept it as a universal standard to determine B&W film speed.

I generally like to think of film speed and camera exposure as being two separate things. Good testing reduces the number of unwelcome variables so that the test results only represent what is being tested. Than the other variables can be incorporated later. How else can you be certain the value represents the film / developer combination or whether it's your shutter, aperture, or meter?

 

[Stephen Benskin]

Consensus suggests that average results from Zone System testing appear to fall between ½ to 1 stop below ISO speeds. As the metered exposure point and the speed point between the two mythologies creates a 2/3 stop difference, the general range of results is considerably small. Surprisingly so considering all the variables that the Zone System testing “purposely” and unknowingly includes.

For instance, according to Safety Factors in Camera Exposures, the current speed equation would have been 1/Hm except that there was a proposed change in the color temperature of sensitiometers from simulated sunlight to simulated daylight (sunlight plus skylight). The adjustment from 1.0 to 0.80 compensated for the increased amount of blue light which would have increased the apparent film speed.

As far as I know, The Zone System never defines the type of light for the test. Some shot outside in the shade, some in the sun, and some indoors with incandescent light.

Another is the use of a meter. Adams had a conspiracy theory that the meter manufactures nefariously incorporated a K factor into their meters. Whereas the K factor is a variable in the meter’s exposure equation to compensate for light loss inherent in the system and introduced by the physicality of the exposure meter. The camera exposure equation uses a variable (q) that factors in assumed average conditions. If the conditions differ, so does the test results. This doesn’t generally matter in actual shooting conditions, but testing needs to eliminate as many variables as possible.

Through the lens metering doesn’t require the same type of K-factor because it measures the actual light passing through the lens. All meters use some material that has a photo-voltaic response to light. None consistently respond the same to all wavelengths.



Testing with a camera introduces a number of issues. The movie industry uses t-stops instead of f-stops to film with. This makes their exposures consistent from shot to shot no matter what camera or lens used. F-stops are a mathematical determination whereas t-stops are bench tested. Camera shutter speeds can also be bench tested. In many cases the errors between the aperture and shutter speed can offset each other. Although the effects can also be additive.

The number of elements in a lens contributes to the amount of flare that lens will produce. As 35mm lenses tend to have more elements, they tend to have more flare. Kodak changed their average flare value from about 0.30 to 0.40 sometime in the 80s. While the reasoning was never given, I believe it was to account for the dominance of 35mm. This changed the CI for their normal process from 0.56 to 0.58.

The degree of flare in any given situation is determined by the luminance range how it is distributed. Flare from a scene with the same luminance range can vary wildly depending on the degree of dark to light values within and just outside the frame. Here’s where The Zone System testing might come as a good surprise.

While Adams claims Zone System testing will incorporate flare as it uses an optical system, it really doesn’t. Sensitometric testing eliminates flare from the film test. Flare can then can be applied back during tone reproduction calculations. This is how ISO film speed testing works. The test itself is without flare, but flare is part of speed determination and exposure theory.

Flare is basically non-imaging forming light scattered by the various lens / camera elements. The scattered light mostly from the highlights is distributed across the film. Proportionally, the extra exposure affects the shadow exposure more than the highlight. A one stop flare factor means the shadow exposure is doubled.

Since Zone System testing uses a target with a single tone, there isn’t any highlights to bounce around or any shadows to add to. Metering a middle gray target and stopping down means there is no shadow values. So there is almost zero flare from the subject, and no shadow for flare to influence. This is actually good for the test, but the results obtained when shooting will be different from what would be expected based on the testing.

And finally, there is hold time. Film speed will tend to drop off in the period between when the film is exposed and when it is processed. Most of this occurs in the first few seconds, but it will continue at a reduced rate and then plateau. The ISO standard prior to 1993 had a hold time of 2 hours, but the currently ISO standard has a hold time for professional film of between 4 hours and 7 days and 5 to 10 days for amateur film. Zone System testing never mentions a hold time.

Considering all the factors, how can Zone System speed testing conclusively determine a "true" or personal film speed?

The tendency for Zone System testing to falling within a third of a stop from its methodology indicates is incredible, and that it’s only around half a stop to a stop from the ISO speed isn’t too bad either. Being that part of the purpose of B&W film speed is to define the usable range of film, that speed and exposure are two separate concepts, and that personal metering techniques tend to have the greatest overall influence on exposure placement. It’s probably best to skip personal speed testing for general purpose films and developers. Use the ISO speed as a base and determine through actual shooting if any adjustments need to be made.

 

[Doremus Scudder]

Stephen,

I love reading your contributions here. They are both informative and sobering. As a ZS user, I find it enlightening and helpful to know the limitations and pitfalls of ZS testing. Additionally, I feel somewhat validated in using field tests and notes from exposures of real-world subjects to refine my personal E.I. and development times (I'm about to enter another round of "refinements," since I've been having a run of not-quite-contrasty-enough negatives lately... could be my developer or...). It's nice to be reminded of the hold-time issue going into more testing.

Since the ZS was intended to be a simplified practical application of the sciences of sensitometry and tone reproduction, I see no real conflict here. People need to realize that the ZS was never intended to do anything but help make printable negatives and, more importantly, to help visualize the final results. Too many try to turn it into a science and make it perform more accurately and quantifiably than it is designed to do.

I'm happy to have adequately exposed negatives that I can make fine prints from without a lot of lab work, measuring and graphing. The ZS works fine for that; make negatives, print, adjust E.I. and development times till you like your prints. Use your meter to help you understand what your final result might look like. That works for me, but I don't pretend that it's science

Best,

Doremus

 

[ChristopherCoy]

I'm really sorry I ever asked this question... or even began to think about the ZS.

 

[Bill Burk]

@ChristopherCoy I just pick little bits here and there.

For example hold time... I knew there was a hold time but hadn’t seen how many minutes or hours it’s supposed to be.

 

[mrosenlof]

I haven't read every word in this thread, but it's the internet, so somebody has probably gotten something wrong.

I suggest taking a look at this workbook for anybody who wants to get into some of the science and measurement behind the zone system.

https://www.kodak.com/content/products-brochures/Film/Basic-Photographic-Sensitometry-Workbook.pdf

I don't think I've seen it mentioned here, but then again, I could be wrong.

 

[Bill Burk]

I haven't read every word in this thread, but it's the internet, so somebody has probably gotten something wrong.

I may have but usually I fix it. Stephen gives the most correct answers like Donald Knuth . If you find an error in anything he wrote I will send you two dollars.

 

[Stephen Benskin]

@ChristopherCoy I just pick little bits here and there.

For example hold time... I knew there was a hold time but hadn’t seen how many minutes or hours it’s supposed to be.

Bill,

I did a latent image keeping test years ago. Sheets of T-Max 100 4x5 were sensitometrically exposed using a calibrated sensitometer at the intervals listed below, and stored at room temperature. All the film from test 1 was run together, as was test 2. They were processed in a Refrema dip and dunk using seasoned T-Max developer.

Stephen

 

[MattKing]

I'm really sorry I ever asked this question... or even began to think about the ZS.

Why?
If nothing else, it showed you that there were a couple of things you understood one way, that might actually be different.
So there was at least something useful that came from it.
And there may be even more benefit, if others got something as well.

 

[Stephen Benskin]

I doubt latent image keeping has anything to do with test problems, ZS etc.

The issue I have with the Zone System is that other than it perhaps being a visualization tool of some use, it adds no real value from the perspective of print quality,

Hi Michael,

Not alone, although it is in the standard. My point is with all the variables that have an affect on the determination of accurate film speed. Just trying to help dismantle the misconception that ZS speed testing is a practical methodology. Remember all those years of "True" film speed claims?

Stephen

 

[wiltw]

I'm really sorry I ever asked this question... or even began to think about the ZS.

Do you recall reading the story about Pandora's box? In this case it let out some Gorgons.

 

[Stephen Benskin]

Hi Stephen,

Indeed, true speed conspiracies persist. I just meant given all the slop (including poor dip/dunk uniformity but that's another story...), LIK is probably a relatively minor consideration. On the other hand you are of course correct in pointing out all the potential variables.

Michael

Michael,

True. Could we be discussing testing vs application? Controlling the process and eliminating the variables for testing compared to understanding acceptable variance within real world usage. Debating the pros and cons of Gamma vs Average Gradient vs Contrast Index on one hand and on the other hand knowing that because of the normal distribution of most scene luminance ranges, Normal processing can produce negatives that will produce a quality print using different graded paper for the majority of situations. Or even better, that the LER of paper doesn't necessarily correlate precisely with the DR of film in every situation. My favorite Jones quote (paraphrase), "but what else can you do?"

Stephen

 

[Bill Burk]

I wonder Stephen. If TMAX-100 has an effective speed of 64, (assuming a typical hold time for my film) why wouldn’t I just shoot it at 64?

Or was that just the 0.10 speed? Maybe Delta-X speed remains 100?

 

[Stephen Benskin]

I wonder Stephen. If TMAX-100 has an effective speed of 64, (assuming a typical hold time for my film) why wouldn’t I just shoot it at 64?

Or was that just the 0.10 speed? Maybe Delta-X speed remains 100?

I wasn't using Delta-X Criterion at the time. The results wouldn't have been as dramatic if I had. I was never very happy with speeds in seasoned T-Max. Eventually I began using additives. Switched to Xtol as soon as it came on the scene.

Actually, in seasoned Xtol, TMX usually fell at or close to 100 with a a minimum two hour hold time. Personally, I tend to look at the latent image test as the rate and degree speed falls off over time than the actual film speed of the test. I'm pretty sure that for a film to have an ISO of 100, it would have to be higher than that directly after exposure.

 

[Stephen Benskin]

I haven't read every word in this thread, but it's the internet, so somebody has probably gotten something wrong.

I suggest taking a look at this workbook for anybody who wants to get into some of the science and measurement behind the zone system.

https://www.kodak.com/content/products-brochures/Film/Basic-Photographic-Sensitometry-Workbook.pdf

I don't think I've seen it mentioned here, but then again, I could be wrong.

That is an excellent sensitometry primer. I also recommend it, and as a bonus, it's free. My bible starting out was Photographic Materials and Processes by Stroebel, Compton, Current, and Zakia. I knew it so well, I could almost open the almost 600 page book to the exact page I wanted. Used it so much the pages fell out of the binding.

I cannot emphasis enough the importance of getting your hands dirty plotting your own curves. That's when theory begins to make sense. It also where your realize a film curve doesn't exist in a vacuum. It's part of the photographic process. This is where everything comes together with Tone Reproduction. How the subject luminance range becomes the illuminance range of the camera image and how it falls on the film curve and how the film curve works in conjunction with the photographic paper and finally, how the end results compare to the original subject. Sadly, I believe this is where Adams really failed to take the Zone System to it's full potential.

The drawback is how labor intensive drawing four interrelated curves can be. Phil Davis created a plotter program for BTZS which works relatively well even though he only used the film and paper curves. It didn't exactly fit my needs, so I learned Visual Basic well enough and wrote my own set of programs. Making sure they were working properly and being able to play with different scenarios answered may questions that had persisted for years.

Stephen