Film speed test in winter

Quote:

---

Originally Posted by Michael R 1974

Andreas - the point Stephen is making, further to Mark's earlier post, is that we should ask some questions about testing methodologies, sources of error/distortion etc. Otherwise we may not know how to interpret the results, or apply them in a meaningful way to different situations, in which case we can't be sure we're better or worse off than simply using the manufacturer's instructions.

For example, flare is a significant factor which is often overlooked in typical zone system testing methods.

---

That's the basic idea. Important elements can get lost when the necessary simplification occurs when creating a methodology and accompanying step-by-step approach. Ever notice how no method concerns itself with hold time? Now, I'm not just talking about how Simmons' shooting a wall example has no mention of the color temperature of the light, or color of the wall, or the choice of the material of the wall and how they reflect various wavelengths like infrared. Not only can this have differing effects on the film, but can influence the exposure meter which is the principle instrument toward measuring the testing conditions. The vague instruction of "take a meter ready of the wall" doesn't address whether the wall should be in specular or diffuse light, or the angle of the meter in relation to the camera potentially causing results very different from what is intended.

While scrutinizing each element of testing is an important part of any evaluation of a methodology, let's not overlook the more fundamental question of theory, and how the methodology addresses it. Like what is the difference between the metered exposure and the speed point, or what is the metered exposure, or even what is film speed?

Simmons' use of the just black printing method is a good example the need to question the theory behind the approach. What are the assumptions about proper exposure and film speed that the use of this method suggest and are those assumptions correct?

Another example which is a personal favorite of mine is about metering the object and stop down four stops. Ever wonder where's the theory to support this assumption? What if this assumption is wrong, how will using this approach influence the results?

Personally, I find it kind of peculiar that people are determined to put all that effort to come up with their own testing method when one already exists that has been standardized. All the fiddling around introduces too many potential errors, but as they will persist in doing so, we need to approach each methodology with the proper level of skepticism.

Where does it say 0.10 over Fb+f is the target shadow density, or the minimum useful density? Where does it say it is a universal speed point?

I always enjoy these mouse traps of yours... ;)

I don't know where/if anyone called it a universal speed point. As you know it is simply a common targetted net negative density called "Zone I" in most Zone System books/methods, used to determine a working EI that presmubaly will lead to "full" local contrast around the "Zone III" density.

michael,please read ssteven's multiple and highly-educational postings concerningspeed points and systems to measure film speed. most of themworkwith a toe densityor shadow contrastto determine film speed.at the end of the day, you have to pick a method that works for you.snsel's assumption about zone Ihaving a target density of 0.1works very well in my opinion.what assumption do you work with?

Ralph - I've participated in Stephen's threads - that's why I made the mouse trap comment. He challenges us to think critically about the "traditional" wisdom, rules, parameters, targets etc.

Quote:

---

Originally Posted by Michael R 1974

I don't know where/if anyone called it a universal speed point. As you know it is simply a common targetted net negative density called "Zone I" in most Zone System books/methods, used to determine a working EI that presmubaly will lead to "full" local contrast around the "Zone III" density.

---

But how legitimate is that? You are referring to a system/method and what it states. Does the theory support the premise and if so where is it? And the reason I used universal is that it is the speed point only in a specific situation and cannot be applied to all situations.

One of the questions I propose is what is film speed. And one of the conclusions is that there is a difference between film speed and exposure. This is a distinction not frequently made.

Not disagreeing with you. I was simply describing a common approach to exposure index determination. The legitimacy of it is another story. Further, even if 0.1 above Fb+f is "correct", depending on how you test for the exposure that produces that density, you can get all sorts of exposure index values. My approach to film speed is somewhat different (as we've discussed before), although it may or may not intersect with 0.1 above Fb+f depending on the case.

I'm not sure I'm following the dichotomy of film speed and exposure. Why wouldn't they be different?

Quote:

---

Originally Posted by Michael R 1974

Further, even if 0.1 above Fb+f is "correct", depending on how you test for the exposure that produces that density, you can get all sorts of exposure index values.

---

Exactly my point. Stuff everyone needs to be aware of when considering testing.

Quote:

---

I'm not sure I'm following the dichotomy of film speed and exposure. Why wouldn't they be different?

---

Many systems, including Zone System, considers the fix density speed point of 0.10 the same as the minimum exposure / shadow exposure point of exposure. In fact, the just black printing method is predicated on this concept. Film speed is a standardization for comparison between films and a guide for exposure. According to the standard model and not factoring in personal exposure preference, shadow exposure isn't intended to fall on the speed point.

I see now. I think my approach is more consistent with the standard model, at least in the sense I am concerned with comparisons. Ultimately for me the speed point is a means to an end, not a target in and of itself, the end being maximized local contrast. If a film/processing combination delivered a perfectly straight line from Fb+f onward (ie there existed no "toe"), my speed point would be nothing more than 0.01 above Fb+f.

Quote:

---

Originally Posted by Michael R 1974

Ultimately for me the speed point is a means to an end, not a target in and of itself, the end being maximized local contrast.

---

Another important point of theory generally missing in most methodologies. Film speed is about the shadow gradient and not a point of density. That's why the ISO standard has the contrast parameters. How many methods incorporate this concept?