CI of Blank Film
Sorry to all concerned if this thread brings up sad memories of another recent thread, but there was a big conceptual issue in that thread that went unresolved. As many of you know, I am big on finding analogies to help better our (my?) understanding of complicated concepts, and I thought of one that may have helped in that other thread. For some reason, that thread has been closed, so I am posting it here.
The opinion was stated several times in the other thread that a sheet of blank film cannot have a CI. In defending this opinion, it was said that the film must have at least two areas of exposure in order for the film to have recieved a development of a certain CI. I disagree with the opinion - CI is not dependant on exposure, and therefore a blank sheet can and will have whatever CI (or gradient or gamma or...) that it was processed to.
Here's my proof:
So let's take a sheet of film that has been exposed by contact printing it with a step tablet. Sufficient exposure was given to create a suitable range of film densities that will allow us to measure and calculate a CI. Let's say it has a CI of 0.60, just to give it a value.
I hope everyone will agree that this sheet, has a CI of 0.60 - we determined this by making measurements of all the wedge steps that were exposed onto the precessed film.
OK - and I think we will all agree that this sheet - the entire sheet of film - has a CI of 0.60. So now let's get our scissors out, and start cutting this sheet of film into smaller pieces. Let's cut it in half. We all agree that both halfs of our film have a CI of 0.60 still - the act of cutting the film will not change the contrast index of that peice of film.
So let's make a few more cuts. Say we separate out a few of the steps, one has a density of say 1.50, and another one a density of 0.74, and a third has a density of say 0.31. All of these steps still have a CI of 0.60. Cutting the film does not change the CI of our film.
OK, so now, let's cut out that step that has not recieved sufficient exposure to have gained any density at all - it is at the base+fog level of density. It is a "blank" piece of film. I hope that no one will argue that this film has a CI of 0.00, because it does not - it cannot. It has the same CI as the rest of that sheet of film. And therefore a peice of film does not have to have at least two different exposures to have a CI. It does to actually measure the CI, and they need to be the right exposures, but a films CI is purely dependant on the processing conditions.
So lets take this info and extend it to a second sheet of the same film as the one we just exposed with the step wedge and processed. That first precessed sheet of film had a CI of 0.60, the entire sheet did. And in the same processing batch, we had also run this second sheet. If the first sheet that we processed had a CI of 0.60, then we can be pretty certain that the second sheet does as well. (At least to the extent of our ability to measure CI when we consider sheet to sheet variability and the experimental error of measurement.)
Now if we had made an identical exposure of a step wedge on this second sheet, we could actually verify that it did receive the proper development to achieve a CI of 0.60 by measureing it and doing the calculations. And it should be very close, if not identical (remember the experimental error of the density readings as well as sheet to sheet variations.) If we had not used a step wedge, but had given enough of a fogging exposure to create a density on the sheet of 1.00, that's fine - as this film still has a CI of 0.60. If we had given a much larger exposure, then the density may well be 1.8, that's fine as well, as the film still has a CI of 0.60. If we had given no exposure to this second sheet, all's still fine - it also is processed to a CI of 0.60. CI is dependant on development, and not exposure.
Think about all the people that do roll film zone testing. They are using a series of exposures, each on an individual frame. They process the roll, measure densities, and calculate a CI. I hope no one will argue that each frame on that roll has been processed to a CI of 0.00 - although that is actually what has been argued here. While you can't calculate the CI of that roll using just one frame, each frame has been processed to some CI and it can be measured.
Let's stick some more sheets or rolls of the same film in the development batch and process them simultaneously, say in a drum or tank. Each roll in that run will have the same CI. If we did not make a proper set of exposures on some of those films, we cannot determine the actual CI the run was processed to. But, thanks to the science of process control, we don't need to actually have prepared a set of exposures to make the measurement of CI on each and every run. (This of course assumes that you do have control of your processing!!)
So I hope you all can see, it is very easy to give no exposure to a peice of film and process it so some CI value.
And I think the issue that was being pointed out about Davis' phrase "SBR", is that it should probably called "Subject Illumination Range - SIR", as an incident meter can only measure the light that falls on it - the amount of illumination, not "brightness".
Kirk - www.keyesphoto.com
How many angels can dance on the head of a pin? Does the pin exist if no one recognizes it for a pin? Does the pin exist outside of objective awareness? Is an angel and angel if someone sees it and mistakes it for a pixie? What if an angel is not seen, is it still dancing on the head of a pin?
Originally Posted by Kirk Keyes
Attached from Kodak. "It is a measure of the degree of development." Kodak replaced gamma with CI a number of years ago. Gamma used only the straight-line portion of the curve, but good negatives make use of the toe, below the straight-line portion. CI includes the toe, whereas gamma did not.
Originally Posted by Kirk Keyes
I left out the content of your message because it belongs in a category I label as "masturbation intellectuel, inutile et sans plaisir" as we might say in French. You fellows who continue to annoy the rest of us with this nonesense would most likely be a much happier lot if you lost the mental and just used your hands.
With all due respect,
Sandy, I didn't know you had it in you! Well said, chap!
"EVERY film and paper is good .......... for something"
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The CI is the slope of a line. Said line has a slope in every single point of the line, so even the "0" point has a slope - and an unexposed film can be developed to a given CI - just like one exposed to a uniform "zone V".
What's so difficult to understand about that, and why do so many otherwise intelligent people feel so upset by it?
-- Ole Tjugen, Luddite Elitist
yeah but it requires at least 2 point to first determine that slope. If this is not true, then here is a set of coordinates on an x,y frame. 2, 5 please tell me the slope......
Originally Posted by Ole
I now understand that saying that if you cannot dazzle them with your brilliance.....(fill in the blank)
Processing two things that appear to be the same but are not does not yield the same results. if I put water in one cup, and I put water and a bag of tea in another cup and then put both of them in a microwave oven to heat, I did not make two cups of tea, I made one cup of tea and one cup of warm water. The glaring error in this page long example is that after all the cutting, in essence the blank part of the film has a significant difference from the other parts..it did not receive any exposure, a essential part in determining CI. I hate to admit it but King is right, this is mental masturbation to the highest degree, but I think Don Miller said it best.....if you want to know, read his response on the SBR thread.
Jorge, the correct CI can only be determined by developing a standard test negative. When using any other negative you are assuming that they will be developed to the same CI by the same processing. It doesn't matter what scene, SBR or whatever you have captured on that negative - or even whether it has been exposed at all.
It takes 2 points to determine a slope, but any one exposure will correspond to one density.
-- Ole Tjugen, Luddite Elitist
Originally Posted by Ole
Gradient -- degree of inclination, inclined surface, rising or descending by regular degrees of inclination, and other similar.
Slope -- inclination from the horizontal, deviation from the horizontal, and other similar
Definitions of gamma, CI, and C-Bar always include the use of one of these two words, either slope or gradient. At least all that I have seen, and I have looked at about ten sources this evening, include one of these terms.
Fact. A sheet of unexposed film that has been developed for n period of time will graph on a horizontal line, i.e. at right angle to the vertical or parallel with the horizon. Get the point? No slope, no gradient!!! And no CI.
This discussion shows considerable ignorance of language on the part of some people who in other respects appear to be perfectly intelligent.
Originally Posted by sanking
Kodak said: "It is a measure of the degree of development." Where is your question? The H&D curves in the scan above show gamma values based on development time. In essence, the gamma (or CI/G-bar) values represent those times for reference purposes.