Bennett Brown
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Ian:
I thought I had properly established my working EI by obtaining a good match between my zone V rendition and the 18' gray test card and relating the exposure value underlying this to the unadjusted film speed to determine my working EI.
Bennett
Bennett
Ian:
My times and temperatures are fine but do you really think that the time taken to fill and empty can cause such discernible darkening?
Bennett
So you usually get negatives like this when you do your Zone System tests then Ole
Ian
I'm not that unfamiliar with the zone system and don't really want to change developers and start all over again but...............developing at different times with my existing developer will likely adversely influence the proper rendering I have already achieved with zones 1 through V don't you think? My challenge is to change (lighten) zones V11 and V111 in partiular, without changing zones 1 through V.
Why in the world would anyone attempt to arrive at his optimal speed for a film based on Zone I? Zone I is on the non-linear portion of the density curve and yields no information whatsoever about the part of the curve that you care about, the straight line portion. That's where the tones live that you're going to print.
When testing a film for EI, I essentially follow Ole's procedure and expose until I get Zone 3 up off the toe and into the straight line portion of the curve. I know that I've got it when there's good detail in the Zone III shadows. I have no idea where that puts Zone I nor do I care. I think that people waste a prodigious amount of time and effort calibrating a "proper" Zone I simply because Ansel Adams said to do that in The Negative.
The subject you are touching at is the concept of "long-toe" vs. "short-toe", but at zone III that shouldn't really matter, as the curve should have straightend out by then, even if the film is extremly long-toed.
Ehh, every film manufacturer in the world does use zone I being at 0.10 above b+f.
That is fine if you will be placing things at zone V most of the time, like most people do with conventional exposure methods. This defeats the purpose of using the zone system. The problems are that this does not let you control your shadows very well, and that zone V is more variable with development than zone I, so is harder to keep consistent. You should find your EI by seeing what rating lets you consistently and predictably place a zone I. You need a handle on the foot of the film so you can swing the rest of it up and down around the foot, which is more or less nailed down where it lies no matter what you do with development.
In all the time you have put into this post, you could have read the applicable pages of The Negative and have known just as much as you need to know. Repeated Internet posting is a sure way to be led astray, and no way to learn every detail of this stuff.
The underlying problem here is that you have no idea why you want to use the zone system, and therefore the how of it is being made not only difficult, but entirely useless. You cannot understand the how if you do not have any idea why you even want to understand it in the first place. You need to go out and experience some practical problems. This means shooting, printing, analyzing, and coming to the realization that your printing is just too difficult and you aren't getting the results you want. You will not find your magic bullet on the Internet.
If, however, I am willing to sacrifice zI (just let it drop below the horizon) and allow zII to be the useful threshold, the whole curve snaps right into place.Bowzart, don't misunderstand the tone of this post, I'm just chatting with you.
I believe (I hope) that I understand enough about the sensitometry behind the ZS to say that this is misguided, I feel anxious as I'm about to make a bold assertion, potentially dangerous. First, let's agree on the definition of threshhold because that's at the heart of how EI's are determined in the ZS: the amount of exposure needed to yield the first useful density on the negative above the fb+f. So, the relative speed of one curve vs. another is determined by how close to zI the curve crosses the .1 density line. Ex: I have two tests where the original curve crossed the .1 line right at zI, which is great because then I get full box speed with my process for that film/dev combo. All my other tests, the curve crosses the .1 line forward of zI, indicating that with that combo, the speed is too slow to give me a neg density of .1 at zI. So, the amount that I shift the curve back toward zI is the same amount that I take off the box speed to become my EI.
I assume that you actually produced a curve to illlustrate your statement. Your statement says to me and sorry if I got it wrong, that the film/dev/time combo that you used to produce this curve showed that it crossed the 0.1 neg density line at zII. I say this because you said that zII would be the useful threshhold at the box speed of 400 with Edwal 12.
Forgive me while I try to explain myself
If indeed you assume to want zI to reflect a negative density of 0.1, like you say, then all it would require is that you shift that curve 0.3 log E units to the left on the horizontal axis from zII to zI so that the curve actually does cross the .1 density line at zI--------this is the same as rating the film one stop less at 200 instead of 400 (you asserted 125), with no need to redo the test, just shift the curve a known distance and then you know that if you had used an EI of 200, then your original curve would have crossed the .1 line at zI. That's a very common occurance in ZS testing as far as I can tell. BTW, a lot of this is discussed in John P. Schaefer's Book 2.
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Why 0.3? Because there are 0.3 log E units between each zone on the horizontal axis (this means that .1 log E unit is 1/3 of a stop). Paraphrasing and double checking my facts, I will say that what AA did was to redefine the horizontal axis of the curve by dividing it into zones that are separated by 0.3 log E units, which is an arithmetic factor of 2 as you progress up the scale between zones and one that cuts the values in half as you progress down the scale between zones. This is key because that's exactly what happens when you increase the exposure by one zone----it's a doubling of light intensity or a doubling of time. Or, when reducing by one zone, it's a reduction by half in the intensity of light or the amount of time with the shutter. And that's the beauty of the whole thing, it provides a very practical
"link between camera exposure and the exposure units of sensitometry" (AA, The Negative)
I tried to stop long ago but I could'nt. The crazy thing about all this BS, is that once a few ambiguous facts are totally understood (I think I've got them, perhaps someone like PE will cut me down ) it becomes crystal clear.
Chuck
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