Exposing BW sheet film for film/developer testing

[sanking]

But it is a commitment because ideally one would have the Winplotter software and the ExpoDev for Palm software which some might find to be a clumsy extra step in the field. I have never figured out how to use the little slide rule card for exposure. As an aside, how do people use BTZS without a Palm or slide rule?

I generally don't use the Palm ExpoDev software in the field. If there are a number of complicating factors such as reciprocity effect, filter compensation, magnification compensation, etc. I will generally pull it out to test my own calculations, but for most scenes I just figure the SBR by taking a reading in the shade and in full light, expose for the shadows and then mark my film holder for the SBR condition noted.

For my personal use it is in the efficiency of the film testing that BTZS really shines. People who have limited their film testing to traditional zone system methods really don't know what they are missing.

Perhaps I should give the usual caveat. True, film testing and technical aspects do not replace or substitute for vision. But they allow one to control and shape his/her vision.

Sandy

[nolindan]

If you want to contact a standard 0-3OD step tablet on to film, using an enlarger as a light source, a starting exposure exposure might be:

• Meter the back of a sheet of photographic paper and adjust the lens aperture so the meter reads 1 second/f4.0/ASA 100 (or 4 on a Pentax digital spot);
• Expose for one second if exposing ASA 100 film;
• Adjust time and/or aperture for other ASA's;
• Stop down to increase time if you are using an analog timer.

This should give clear film on the darkest step of the tablet with a slight increase in density in the next step or two.

The above are for a tungsten light source and may need adjustment with a cold-light head. Any light source will work: load a photoflood reflector with a low wattage bulb and aim it at the ceiling.

As always: YMMV and advice worth price charged.

If you do contact a step tablet on to film please post the exposure you used for the best result.

[ic-racer]

Seems like people have different views as to what 'testing' involves.

The main reason I would make a step wedge contact is to answer the question "how long do I process this film"

That question needs to be answered by everyone and how you do it doesn't make any difference, as long as you are happy with your prints.

In my case I 'reverse engineer' a film and development time combination that produces good prints. I get the gamma of that combo and when I want (or am forced into it by limited availability) to use an 'unknown' film, I run a few strips to see how the unknown film responds. This gives me a good starting point.

[Bill Burk]

Steve Benskin and Sandy King pointed out a major flaw in my argument to avoid step wedge exposure on an enlarger. I concede that too many variables spoil the scientific process.

I was upset when my tests under Tungsten gave me a lower film speed rating than I would have gotten if I had done my tests outside.

I was also upset that my results with an uncoated Tessar and ancient Compur shutter were not as expected.

So I resolved to test my whole system.

Now as I concede my earlier major flaw, I would like to suggest that it is not total nonsense but recommend at least one sanity test of your whole system before you go into the field. If you have scientifically eliminated your other variables, this might give you a single "system factor" to apply.

I will try BTZS.

How do you account for the difference between enlarger light source and Daylight?

I don't think I am wrong about the validity of speed testing. You can't take the manufacturer's ISO into the Zone system.

I believe that once you start developing to exposure range, you are no longer developing to ISO. Your first departure is you take a different B+F target. Your next departure is you develop your highlights to a density of your own selection.

This does not invalidate the simplified "Zone System in a nutshell" method above. I believe it will work superbly. In that simple method you use the manufacturer's ISO and place shadow on Zone III. In a Zone system speed test by Picker/Adams/White etc, you would find your own EI. It is going to be lower than manufacturer's ISO. You would place your important shadow on Zone II. With a lower EI than manufacturer, placing the shadow on Zone II sounds to me like the same thing placing the shadow on Zone III with the manufacturer's ISO rating.

I still highly recommend the White pamphlet-sized book from 1963. With a two-tone target and tests that he describes in 3 pages, you can find your film speed without a densitometer. You don't have to read and understand the whole book. His esoteric comments about art can be set aside when you are doing the tests.

[Stephen Benskin]

[
How do you account for the difference between enlarger light source and Daylight?

That's a good question. This is one of the many variables I referred to earlier. The ISO standard specifies the color temperature for the light source for that very reason. Don't forget both enlarging and daylight have different color temperatures too. You have incandescent and cold light for enlargers, and open shade, sunlight, overcast, and variable clouds with exterior shooting. Most ZS photographers use open shade, which is only skylight, and that is rather blue. Not only can the different color temperatures affect the film's response but it can also affect the meter's.

I don't think I am wrong about the validity of speed testing. You can't take the manufacturer's ISO into the Zone system.

I believe that once you start developing to exposure range, you are no longer developing to ISO. Your first departure is you take a different B+F target. Your next departure is you develop your highlights to a density of your own selection.

This does not invalidate the simplified "Zone System in a nutshell" method above. I believe it will work superbly. In that simple method you use the manufacturer's ISO and place shadow on Zone III. In a Zone system speed test by Picker/Adams/White etc, you would find your own EI. It is going to be lower than manufacturer's ISO. You would place your important shadow on Zone II. With a lower EI than manufacturer, placing the shadow on Zone II sounds to me like the same thing placing the shadow on Zone III with the manufacturer's ISO rating.

To properly explain the strengths and weakness of both systems would be rather daunting to work through, but suffice it to say that what we have are two different approaches to testing and two different goals. You can't really compare reversal with B&W negative because the desired results and testing parameters are different. With reversal the midtone and highlight reproduction is paramount, and with negative film it is the shadows. Reversal film speed is determined in the midtones and negative film in the shadows. In a way, it's like that with ZS and ISO testing.

In 1960, the ASA film speed standard changed. The new standard eliminated part of a safety factor thus increasing film speeds by one stop. The idea was that better lenses and meters eliminated the need for such a safety factor. The increased use of smaller formats with the longer printing times and loss of sharpness and increased grain with denser negatives was also a deciding factor. According to earlier psychophysical testing, it was determined that excellent images are producible for a number of stops over the minimum exposure necessary to produce excellent images. In other words, there are in fact a few stops of overexposure latitude possible without image quality loss. So, the change in the standards couldn't have been based solely on improving the quality of the reproduction because there wouldn't have been much. Therefore, we can conclude there's really no practical difference between the quality produced when films were one stop slower and the quality produced with today's speeds.

Now, consider that the Zone System was developed before 1960. Adams had to have used the ASA speeds to compare his method to as he was developing the ZS testing method. As he tested different methods, he probably referred to the scientifically determined method of the ASA standard as the source to compare whether his current method's results would be in agreement. After all, he does use the fixed density of 0.10 over Fb+f as the speed point (the concept of a fixed speed point and whether the exposure is supposed to fall at the speed point or that the speed point is only the place to determine the film speed is a complex and interesting topic - for another time). When the ASA standard changed in 1960, the Zone System method didn't. That means for film testing today, the ISO and ZS testing methods are looking for two different speed values. As we know about the images produced with the old ASA and current ISO speeds, both systems produce quality results. So it is with ZS and ISO, two different systems that both produce quality results.

It's possible to extrapolate a very freeing concept from that those facts. Exposure is just about giving the film enough exposure to produce a quality print and negative densities aren't locked into specific print densities. There isn't an exact density for Zone III. As long as you have recorded the shadow detail, where Zone III falls on the curve, it will have approximately the same relationship to the other tones for any exposure above the minimal amount required. So, exposure doesn't have to be exact, you just need to record the range of scene luminances on a usable part of the film curve. Then you can adjust the printing exposure to place them where you want them. We can therefore conclude there isn't a rigidity to exposure that many seem to believe, and that is freeing.

Steve

[AJ Edmondson]

I have to agree with Sandy in that, in my experience, the BTZS "procedure" seems to provide very concise data and, compared to other test methods I have used, is the least "unwieldy." I really got "wrapped around the axle" in my desire to satisfy my OCD a few years back and bought the whole package - plotter/matcher software, Palm Pilot, etc. After working with the system for a while I simply evolved to using the data to determine my exposure and development, rather than using the Palm Pilot. In speaking with Fred Newman at "The View Camera Store" he once indicated to me that the "Zone System" approach was not the favored usage... the primary intent being centered around the incident light approach described in "Beyond the Zone System." Obviously there are less "interpretational issues" arising from assigning zone values which way be quite exaggerated.
At any rate I find the system (with the software which eliminates the time-consuming drawing of curves) works quite well with a minimum of testing.

[Maris Rusis]

The dark slide method sounds like it would have potentially many accuracy problems, not to mention intermittent exposure effects.

In practice the potential accuracy problems in "dark-slide" testing are negligible compared to uncontrollable variables in the field; changing light, uncooperative subject matter, non-linear light-meter, wind, cold, rain, that sort of thing.

Precise adjustments to the aperture and shutter speed are not really possible or repeatable, and small multiple exposures will have a different result than one complete exposure.

My shutter speeds run within a few milliseconds worth of repeatability every time I set them. And I know what they actually are as opposed to what is marked on the shutter speed dial.
The same with aperture settings. I set them as accurately in testing as I do in shooting. Any finer than that does not deliver a result I can translate into actual camera use.

Every time I check I find there is no significant intermittency effect with multiple exposures on film except at very high frequencies (thousands of exposures per second!) or at low light levels where reciprocity failure starts to bite.

There are advantages in testing actual cameras, lenses, and film in front of physical subject matter under the same lighting conditions as one will use for shooting. The biggest plus is the way mystery variables like "flare factor" get calibrated out of the system.

The down side of real-world testing, not BZTS, is that one ends with a highly personal set of numbers, odd shutter speeds, bent f-stops, effective EI values, quirky development shuffles, that work perfectly but are of no use to anyone else.

Sandy's suggestion of BTZS testing is the most accurate way to go for most.

I agree, if you want laboratory standard objective data that photographers can trade among themselves then BTZS is the way to go. But given a "bad" camera, "bad" lens, "bad" film, or "bad" subject matter, with the light sliding away at the end of a "bad" day neither practical testing or BTZS data is much salvation.

[Stephen Benskin]

There are advantages in testing actual cameras, lenses, and film in front of physical subject matter under the same lighting conditions as one will use for shooting. The biggest plus is the way mystery variables like "flare factor" get calibrated out of the system.

I'm going to have to disagree with you on that point. 80% of flare comes from the subject. Most testing via the camera use a single toned test subject which produces very little flare. Flare also varies from subject to subject. It tends to increase with higher subject luminance ranges and decrease with shorter luminance ranges. It also varies within the same luminance range depending on tonal distribution. Plus, it is incredibly hard to measure. By eliminating all flare through contacting a step tablet, you are able to deal exclusively with the film/developer combination. A flare factor is than reincorporated into any interpretation of the curve and when deciding any actions to be taken, such as in development determination, and speed determination.

I've attached a curve showing how differing amounts of flare affect the shadow placement. I make a flare box as described in BTZS and place different toned squares around the "black hole" opening of the box and photographed it using the same settings. If no flare existed within the camera system, the opening showing the inside of the box should be at film base plus fog. As you can see on the curve, that wasn't the case. The resulting density difference between a black surround and a white surround is 0.09 and a log-H difference of 0.39 or around 1 1/3 stops of exposure. When doing a speed test, how can anyone be certain the amount of flare influencing the test and consequently, the accuracy of their results?

Photographers can trade among themselves then BTZS is the way to go. But given a "bad" camera, "bad" lens, "bad" film, or "bad" subject matter, with the light sliding away at the end of a "bad" day neither practical testing or BTZS data is much salvation.

I don't see it that way. Earlier I suggested sensitometric testing of the materials and then field testing them. The personalize to one's own equipment argument is one that seems to make common sense until you begin to carefully analyze it. Even if it were the best way to factor in all the materials, to really accomplish that, you would have to do tests for all of the lenses at each shutter speed and f/stops and the f/stop should be adjusted to T/stops. Nobody does that. When I mentioned accuracy for apertures, I was mostly thinking about attempting to accurately place the settings. 35mm cameras don't have 1/3 increments. How accurate can testing be with that?

Sensitometric testing isn't isolated from the real world results. Far from it. Everything is based on carefully evaluated real world tests, then a mathematical model is made that reflects those findings. Yes, everything tends to be based on the average of the conditions studied, average lens flare, average scene luminance range, etc. Still, there is always a bell curve for each showing the range and frequency of variance. I can't remember who said it "The universe is only truly knowable through math." As is the technical aspects of photography.

There's also a greater amount of information obtainable from sensitometric testing and the data can be utilized in a number of ways not possible with other methods. I have to admit that you aren't utilizing the full potential of sensitometry when you only use the film curve or paper curve alone. Real insight into the process and greater control can be gained when you start combining the information. Ultimately, a four quadrant reproduction curve offers the entire photographic process from original subject to camera/flare image to negative curve to paper curve to reproduction curve in graphic form. This would be a truly daunting task if it weren't for computers. I've attached an example of a four quadrant reproduction curve. BTZS is like any "system", it tends to simplify and gloss over certain details and concepts, but it is clearly written and free of bad information and BS.

Steve

[Chuck P.]

I've attached a curve showing how differing amounts of flare affect the shadow placement. I make a flare box as described in BTZS and place different toned squares around the "black hole" opening of the box and photographed it using the same settings.

Stephen,
You say that you photographed them using the same exposure settings----what method of metering for the exposure did you use----spot, incident, wide area reflective? Just curious.

Chuck

[Andrew O'Neill]

BTZS method is a great way to learn a ton of info about your film and developer combination. And you can get there with minimal waste of film. I use BTZS (I don't use that palm pilot thingy), but do not expose under an enlarger. I use Gordon Hutchings' Zone Board. Testing is indoors under consistant lighting (daylight balanced bulb). I graph all my data by hand and a rubber, flexible ruler. I've been doing it this way for over ten years and have been quite happy...