Why is Zone System EI often about half rated ISO/ASA?

Stephen Benskin said:

The Zone System doesn't have one.

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So the Zone System defines its benchmark log-H point in terms of the EI which corresponds to the "desired" shadow density quality, which in early versions was a visual determination where you could just detect detail difference between Zone 0 and Zone I on the print.

So many of our variables and constants are not defined... but might be inferred if the components could be isolated somehow... Say by doing flare tests and film sensitometry and working backwards to the same meter settings.

MattKing said:

It would surprise me if the ISO standard speed was the same as the EI used by ZS practitioners.

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It surprised me too-----but I began using the results as is and I've been using them for quite a while now and have no reason to argue with them. I test precisely as described here, in short, it's an in-camera exposure of a step tablet contacted to a sheet of 4x5 film, yielding flare-free step data.

Tmax 100 & D76 1:1-------Tmax 100 & XTOL 1:1 tested with the same results:
N+2 EI 125
N+1 box speed
N box speed
N-1 box speed
N-2 EI 80


Tri-X 320 & HC-110(1:63)
N+2 EI 400
N+1 box speed
N box speed
N-1 EI 200
N-2 EI 160

CPorter said:

It surprised me too-----but I began using the results as is and I've been using them for quite a while now and have no reason to argue with them. I test precisely as described here, in short, it's an in-camera exposure of a step tablet contacted to a sheet of 4x5 film, yielding flare-free step data.

Tmax 100 & D76 1:1-------Tmax 100 & XTOL 1:1 tested with the same results:
N+2 EI 125
N+1 box speed
N box speed
N-1 box speed
N-2 EI 80


Tri-X 320 & HC-110(1:63)
N+2 EI 400
N+1 box speed
N box speed
N-1 EI 200
N-2 EI 160

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CPorter, if my post is getting posted, I found your latest post to be very interesting. For the 3 middle listings in your little chart, you are exposing without regard for the developing procedure you intend. That is, box speed for both under and overexposure. I also note you are using D-76, which is a metol-hydro developer, which is supposedly heresy for Zone System use. Yet you use it. I wonder if this is how I reconcile your identical film ratings to expand or contract the print scale. Somehow I like your discoveries better than all the other rocket science these other guy are talking, which has me wondering where in tarnation film speed REALLY is.
So my question, will you please post corresponding development times to complete the picture? Thank you.

MattKing said:

It would surprise me if the ISO standard speed was the same as the EI used by ZS practitioners.

Because I think that the vast majority of photographs are taken by people who would most likely choose prints that are different then the prints preferred by most ZS practitioners.

Most people prefer lighter prints with more contrast. People who like "fine" prints tend to have different tastes.

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The ISO standard allows the film speed to be test by either the ASA/BS system (which Kodak had relaxed) or the more practical DIN system used by Agfa.

So with Agfa films like APX100 where the speed was tested using the DIN standard my Zone system tests gave me an EI thge same as the ISO speed, and many others found the same. The opposite was true with Tmax100 where I needed to use50 EI instead of the box 100 ISO.

It's also worth remembering that the developer used for the ASA tests gave slightly better film speed and shadow detail than D76.

Ian

While I appreciate and understand all the sensitometry data involved here, I really believe the answer to Bill's original question can be expressed in less technical terms.

First, we haven't addressed one important factor in the ZS; that of adjusting development time to include a wide tonal range of 9 Zones (or 10, depending on how you're counting) for "Normal." This, I believe, is somewhat more range than the ISO tests result in. Therefore, a ZS N-development is usually less than the ISO standard development. This results in a skosh less effective film speed.

Secondly, we Zonies use our spot meters as arbitrary tools to place shadow values and see where other values fall. In practice, this ends up having very little or nothing at all to do with speed points or metering points (or middle grey for that matter). It is more an "I know what my shadows will look like when I place them in Zone III (or II or IV), because I've tested, and that's where I want them" thing. That coupled with "and now I have to adjust development a bit to get the highlight values where I want them" (many times callously disregarding the slight changes in effective film speed with shortened or lengthened development!) and we can consistently get negatives that are "in the ballpark" enough to be able to be printed well, even if we need to print a grade higher or lower than our target grade. For me, using the meter to help me visualize print values is paramount.

Furthermore, I think the Zone System emphasis on shadow detail and shadow metering, coupled with the relatively greater range of Zones and the resulting need to develop a bit less results in E.Is. that are slower than box speed for two reasons. First, is the slight bit of film speed loss with reduced development to accommodate more Zones together with the use of compensating developers/techniques, which also results in film speed loss. Then there is a tendency to place of the shadow values higher than might be done in the ISO standard in order to get "detail." Since no one takes up the Zone System without having a desire for richly-detailed shadows, and since most of them are shooting large-format film and aren't overly concerned about grain, there is a tendency in the entire process of determining a personal E.I. and then metering and placing shadows to err on the side of overexposure.

I know that when I test for E.I. and there is any doubt at all exactly where that Zone I density falls, I'll just rate the film a third-stop slower. What the heck, one third of a stop makes very little difference in the field. Similarly, if I'm not sure exactly where I want a shadow to go, I'll err on the side of overexposure.

In the end, a personal E.I. is not a film-speed determination, but an accommodation and adjustment of all elements of one's photo-making procedure in order to get repeatable and usable results in rendering of shadow detail. It only stands to reason that, consciously or unconsciously, we tend to err on the side of overexposing, thus building safety factors into our systems without even being aware of it.

FWIW, I shoot 320 Tri-X at E.I. 250 and TMY at E.I. 320, both only a third of a stop slower than box speed. This with PMK. So not all of us Zonies end up rating our film at half box speed. Even so, I'm aware that I've built maybe 2/3 of a stop cushion into my system. When the chips are down and I need a faster shutter speed to stop wind movement or the like, I won't hesitate to go ahead and "underexpose" my film by a stop (thus undercutting my safety factor). No one likes printing underexposed negs, but sometimes that's the only way to get a shot...

Best,

Doremus


www.DoremusScudder.com

Stephen Benskin said:

The Zone System doesn't have one.

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I assume you mean "no safety factor" and that makes sense.

Part of what I see running through ZS thought, discussion, and testing is that everybody's seems to be trying to balance the absolute minimum amount of exposure (so as to minimize grain, exposure time, etc...) against a loss of expected shadow detail. They want to know where the edge of the cliff is.

Many times though it seems that the generic "1/2 box speed" advice is a lot like a parent telling a child to "step back from the edge of that cliff" even though we know its not really a cliff, the slope is just changing; it's not an absolute point beyond which things are unworkable, it's just starting to require more work.

It seems to me that over the years also, lenses/coatings had improved and flare was less an issue, at least in part that allowed the switch to ISO from ASA on a technical basis.

markbarendt said:

I assume you mean "no safety factor" and that makes sense.

Part of what I see running through ZS thought, discussion, and testing is that everybody's seems to be trying to balance the absolute minimum amount of exposure (so as to minimize grain, exposure time, etc...) against a loss of expected shadow detail. They want to know where the edge of the cliff is.
Many times though it seems that the generic "1/2 box speed" advice is a lot like a parent telling a child to "step back from the edge of that cliff" even though we know its not really a cliff, the slope is just changing; it's not an absolute point beyond which things are unworkable, it's just starting to require more work.

It seems to me that over the years also, lenses/coatings had improved and flare was less an issue, at least in part that allowed the switch to ISO from ASA on a technical basis.

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No, it has no exposure constant.

The edge of the cliff is the fractional gradient point. That is why it was chosen as the speed point. Once again, just because speed is calculated from the speed point doesn't mean that the shadow exposure is designed to fall there. That's where the exposure constant comes in. Post #23 and #25 on the thread ISO Speed Determination Constants begins to discuss this issue. I've also offered to email Simple Method for Approximating the Fractional Gradient Speed of Photographic Materials to anyone interested. Plus in thread #80, I've uploaded a pdf copy of Safety Factors in Camera Exposure if anyone is interested on exposure placement in regards to film speed. Thread #81 has a copy of Calibration Levels for Film and Exposure Devices if you want to know about the actual relationship between the metered exposure and speed point.


Flare is less of an issue. The illuminance range of the camera image has increased from approximately 1.50 to 1.80. But it is still a factor and many discrepancies between methodologies or confusion over numbers not matching up is do to flare.

Film speed is based on the first excellent print test. It showed that additional exposure over the first excellent print point showed no significant change in quality over a number of stops (large format). Adding 1/3 to 1 stop, therefore, isn't a big deal. Remember, film speeds were a stop slower before 1960.

The Zone System doesn't have any great insight into the photographic process. It's just that many people aren't familiar with anything else. The Zone System is just a simplified version of tone reproduction theory. Under tone reproduction the statistically average scene luminance range is 2.20. This is based on diffused highlights and shadow with some detail. That doesn't mean it ignores accent black and specular highlights. These simply print outside the LER range of the paper. Adams isn't much different. Anyone remember the aim density range in the testing section? It's from Zone I to Zone VIII, seven stops.



And I'm sorry Ian, you really should support such claims.

markbarendt,

So Stephen meant there is no exposure constant (0.8 in the numerator of the speed formula). But you are also right, there is no safety factor.

Also there is no K. Flare is included. Many of the factors are merged into the procedure and cannot be broken out individually.

Doremus Scudder,

Now you're talking my language! We need the technical, but it also needs to be translated to non-technical.

I forgot to mention... If you test with Tungsten lighting, and your meter is overly sensitive to red wavelengths... While your film is "more or less" sensitive to near infrared... Then your "speed" will be lower than ISO [meter needle is higher than it should for the actinic light] and the Tungsten "speed" difference from Daylight may vary between different films of the same ISO rating. This is because meter spectral response may depart from film spectral response. The Zone VI modified spotmeters are intended to correlate well to Tri-X - so if you have one of those, then your tests may correlate better. But change film to a tabular grain type film and the correlation may not be the same. I've tested 400 TMAX and find it can take a very long exposure to a near infrared (visible to the eye) red LED with little fog.

This thread makes me wonder if the 18% grey card issue is really the source of the apparent problem.
We have heard many times about how midtone does not get truly exposed to be mid-tone unless adjusting up the 18% grey card reading per Kodak's instructions. Put in other terms, reading a 12% grey card probably puts midtone closer to middle of the range!

Michael R 1974 said:

It is worth noting many ZS testers just try to find a net D of 0.1 4 stops below metered without giving more thought to local contrast in the toe. 0.1 above B+F in the context of the ZS is a means to an end, the end being adequate shadow contrast, which is subjective to some extent. A target Zone I density in and of itself is meaningless.

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That's a very important fact. The 0.1 Density for Zone I came later. First it was a noticeable difference between blackest black and first detectable tone. Ralph Lambrecht pointed out in the Focal Encyclopedia that later papers were able to reach such a higher D-Max that even the earlier visual match test became unreliable.

wiltw said:

This thread makes me wonder if the 18% grey card issue is really the source of the apparent problem.
We have heard many times about how midtone does not get truly exposed to be mid-tone unless adjusting up the 18% grey card reading per Kodak's instructions. Put in other terms, reading a 12% grey card probably puts midtone closer to middle of the range!

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If you meter a gray card and attempt to make its tone appear 0.1 density on the negative (or visual match in shadows), then you aren't using it as anything but an arbitrary gray.

The 18% gray issue isn't really a big problem for Zone System tests, though it is an important issue relevant to other metering and exposure topics.

You customize film speed relative to your own specific development method and what you consider as
acceptable film performance relative to your own "normal" lighting conditions. There are no hard rules.

For ZS users film speed is very simple and I have always used it. Ansel said Z1 is .1 over base fog as you have noticed. Exposure and development for Z1 is the least flexible of all the tones. For some reason box speed usually won't allow you to achieve .1 over base fog. If Ansel had said that zone 1 density should be .05 above base fog then box speed would work and people would just place their tone desires at a higher zone.

Using the Zone system everything becomes relative to what you want your prints to look like. It all becomes subjective. Ansel could just as easily said that Z1 should be .2 above base fog and then everyone would have changed how they place their shadows. I was taught to use .1 over base fog and so I place my shadows up around Z3 depending on the situation. Once you have established your normal development for Z7 or 8 and have that contrast look fixed in your mind then out in the real world with your spot meter you are trying to visualize what you want for contrast. Where you want detail and where you don't.

Would it be fair to say the ZS target is the point where the first excellent print can be made?

markbarendt said:

Would it be fair to say the ZS target is the point where the first excellent print can be made?

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The fixed density 0.10 over Fb+f is about 0.29 log-H to the right of the first excellent print judgment speed with normal development.

Different combinations of film and developer have different curve configurations. Therefore it is impossible to apply a blanket model to all of them. Some black and white films will actually deliver about twelve stops of straight-line separation without resorting to "minus" or compensating development, and at the other extreme, some might only deliver six stops of range. Eight is more common. Then you have to match that to the printing paper. And I'm more concerned about the shape of the toe than the overall range per se. This isn't a religion!!! There is no one set of rules or any
silver bullet. Rather, it's a simple tool kit for acquiring negatives which are reasonably within target range to print well. One has to customize all the variablse to their own specific needs. And as an anecdotal aside issue, I once measured a whole stack of gray card from various manufacturers on a high quality full range spectrophotometer, and not one of them was even close to 18% reflectance, nor did any of them match the peak sensitivity of my light meters. So one more reason you need your own standardized reference.

I completely agree with Mr. Scudder above. For the extremely non-technical minded, half box speed for most films means overexposure of one stop. If we err on the side of overexposing in order to make sure we've placed generous shadow detail in Zone III (or even IV, as some would have it), then we've in effect overexposed by a stop, functionally the same as halving the box speed. Same end result.
That's the way my fragile brain sees it, anyway.

I see target points above fbf as largely meaningless. It all depends on the actual curve shape and how you want the shadows to separate, based on your personal expectations and printing values. One reason that folks often rate film lower than box speed is to push the shadow futher up toward the straight line section of the curve. And in this respect, so-called staraight line films will dig way further down than something with a long toe. I really visualize the curve when I shoot, and only use the Zone System as a shorthand labeling tool to assign which batch of development I want a particular neg to go into (N verus N+1 etc). With some films I can easily get shadow separation way down to Zone 0. Only
with something like Pan F would I use Zone III as the metered shadow value. I work with a lot of different kinds of film and almost never botch an exposure unless the lighting very suddenly changes.

To elaborate, the first thing you do when researching a new film is go to the tech sheet and look at the
characteristic curve. That will tell you a lot. For instance, most Ilford films have a moderate toe to them, so that would inform me that in harsh lighting, I might in fact want to begin testing at half box
speed and work my way up (depending on my developer, of course). But with T-Max films, the toe is
much steeper, so I might start at actual advertised speed. With a true old-school 200 speed color separation films (most of which are discontinued), the toe retains contrast way down. Some films just
dont like overexposure of you'll push yourself off the cliff at the top, and blow out the highlights (that
is, if you want to maintain good midtone gradation). Then if you look at the curve for something like
Pan F, you'll see you don't have much wiggle end at either end of the curve, so maybe not the best
choice for harsh lighting at all. Once having made these generic distinction, you just have to test and
actually print until you understand a particular film's specific personality and pros and cons. Small camera users tend to have less choice because the priority is often upon fine grain, at potential sacrifice to tonality.

Shadow gradient is crucial for the perception of quality. That's why the fractional gradient method, based off the results from the first excellent print test, uses a gradient of the shadow that is proportionate to the overall gradient. Film speed is arbitrary if it doesn't have a direct connection to the characteristics of the film. The ISO speed standard is linked to the fractional gradient method through the use of the Delta-X Criterion. When the contrast parameters of the ISO standard are followed, there is a known and consistent shadow gradient 0.29 log-H units from the 0.10 fixed density independent of curve shape. This is how we are able to make practical comparisons of speed between different film types and to assign film speeds with relevance. The ability for the film to reproduce luminance differences of the subject is what determines quality. A fixed point of density as Jones writes, "has no significance as an indication of the ability of the photographic material...except insofar as it may have some bearing on the exposure time required to make a print from the negative."

DREW WILEY said:

Different combinations of film and developer have different curve configurations. ... And I'm more concerned about the shape of the toe than the overall range per se.

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I just drew a set of curves for an APUG'r and the lowest contrast negs have beautiful smooth toes that I know I could just reach right into to print a negative shot at half box speed. If I took the 0.1 density to base EI, it would say quarter box speed. But half box speed is more appropriate.

This is one of the factors I believe leads to lower Zone System speed ratings. When you develop N-1 etc, you may not achieve full speed. Especially if you rely on 0.1 density as the point where you take your speed reference.

And when I know that more of the toe is usable, I am reluctant to use 0.1 density-based speed.

Just depends on what look you want. Minus development sacrifices midtone expansion and microtonality
to some degree. I'd rather have full development and use and accessory unsharp mask to bring the
highlights into control, provided the original neg holds all the relevant information. The whole Zone
System mentality tends to be taught on a generic basis. But even when Ansel put the last version of
this in print, there were radically different popular films available. Something like Pan-X was engineered
for high-key studio portrait and fashion work, with a very long sweeping toe, while Super-XX had a
deadpan straightline from the basement to the moon. Tri-X was somewhere inbetween. Then Minor
White basically made a nutty religious cult out of the whole concept. It really isn't all that complicated.

Ooops, made a typo. Meant to say, Plus X pan had a long toe. The nearest equivalent today would be Delta film.

Michael R 1974 said:

The caveat is you kind of have to assume a normal luminance range (as discussed in the other thread).

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Where does it say that? I made a post last night on the other thread on this topic.

Drew, the various toe shapes is one reason why fixed density film speeds like the Zone System method are inferior speed methods.