Steve
Before I labor through your long note, could you please paraphrase, in a sentence or two, what you are trying to get across? I cannot get rid of the feeling that we are in violent agreement, and just prefer to expose and process our films differently. Keep in mind, nobody questions ISO. We are just trying to clarify what EI means to different people.
Jack Dunn's book is missing in my otherwise pretty extensive library, so I ordered a used copy on the web. (Actually, I accidentally ordered two, so, if somebody is interested?) Interestingly enough, it is published by the same company as mine, and I still have never heard of it. I'll never seize to learn.
Even within this thread there has been rejections of the fractional gradient point as the minimal useful density point and the information presented in the exposure chart.
Stephen,
Yes, I, for one, reject it, for now. But I do so under the advisement of "myself". To my understanding, the basic fractional gradient at point #1 (what is it's log exposure value by the way?) on the graph you presented basically "looks" to be a base+fog level on any other graph as far as I can tell. I can't print that on my paper with any degree of satisfaction. So, it then becomes irrelevant to me. If I can't print it, it is non-essential information.
Since we know what #4 is on the zone scale, zone I 2/3, correct? Then another 2/3 of a zone to the left would be zone I, or log exposure value 0.0. Help me with the positions on the zone scale of #1, #2, and #3? The x-axis units are confusing me. Please be brief.
People can explain how to do Zone System testing, but does anyone ever wonder if it is correct?
No.
Like I and others have tried to explain, negative density below 0.1, perhaps to .09 are valueless---this has been confirmed in practical usage. So questioning the basic concept in the ZS that a neg density of 0.1 really is the "useful threshhold" is not warranted when that assertion can be clearly verified on the surface of the print.
Chuck
As I look through the Gallery and see the the film used and the ISO rating I see that many time people shot film at rating different than the box speed.
Can some one explain the basic reasons that this technique is used? If you rate a film slower, say a 100 ISO box, shot at 80 what is the reason? Is it more tone, more contrast????
...For example, you and I have talked previously about the Delta-X Criterion and I've had to present large amounts of documented information to support it. Tell you the truth, I still don't think you believe it...
Make sure you keep the fourth edition of Exposure Manual.
Steve
I don't question the delta-x criterion at all. It is a sound method to determine film speed. It's well published and accepted by image scientists. However, I question that the additional complexity of it is of any value to the practising photographer doing his or her own testing. Also, as others have already mentioned, theoretical discussions about density values below 0.10 are meaningless. Regardless of what theoretical image scientists will tell you, these values have no contrast to speak of and are not 'useful' to a printer trying to get some tonal information out of Zone 0. Minimum density testing works just fine with most modern emulsions.
I call it Nelson's Objective Tonal Reproduction Cycle.
PE -I have said before that the final EI is derived from working backwards from the print.
Ralph, your plot is entirely correct with one omission. W. T. Hanson of EK has shown that the color of silver images is not black or gray but rather varies across the spectrum, and therefore the adjust for flare must also be adjusted for each photo film and paper to account for spectral sensitivities of them both to give accurate results.
...
I did many of these plots as we adjusted the spectral sensitivity of the paper and the dye set in color films. It was a very time consuming effort to do this and to balance the EI...
PE
A question for PE and or Ralph,
Stephen, I'm aware of your thoughts on this but please be brief if you respond, thanks.
If I had an older uncoated lens that introduced significant noticeable flare, thereby adding density to the negative, let's consider it unwanted density. Is that density effectively neutralized by the calibration process as is commonly done under ZS principles? Meaning, controlling the speed point at zone I and calibrating normal development at zone VIII, or IX for that matter, either way. Does this "act" of calibrating account for such a variable as lens flare? In other words, is the added density caused by the flare effectively neutralized by a negative density range that one consistently develops for? In my case, a range of 1.2 between zone I and zone VIII. In The Negative we are led to believe this, but I thought I would get your thoughts.
I believe it is probably not an issue worth being concerned about with modern day multi-coated lenses but maybe not, IDK.
Chuck
...
If I had an older uncoated lens that introduced significant noticeable flare, thereby adding density to the negative, let's consider it unwanted density. Is that density effectively neutralized by the calibration process as is commonly done under ZS principles? Meaning, controlling the speed point at zone I and calibrating normal development at zone VIII, or IX for that matter, either way. Does this "act" of calibrating account for such a variable as lens flare? In other words, is the added density caused by the flare effectively neutralized by a negative density range that one consistently develops for? In my case, a range of 1.2 between zone I and zone VIII. In The Negative we are led to believe this, but I thought I would get your thoughts...
As flare goes up, apparent contrast goes down. However, if you compensate in development, you can "adjust" for flare in terms of its effect on contrast.
...So, all I have are the spectral sensitivities on a sheet of graph paper that I would have to scan in. Not very interesting IMHO...
...The Delta-X Criterion might be more complex, but it is more accurate and it is part of the current ISO standard. I also think that if someone is advanced enough to plot curves, they should have a calculator to do an additional math problem...
...Notice how at the Δ 0.80, which is the ISO standard, there is complete agreement between the two methods. Beyond that, the speed differences aren't dramatic, but it questions the affect of developmental differences on film speed...
...It also questions whether people really getting the film speeds and exposures they think they are getting?...
...I'm curious to hear what you think about the metering/speed point discrepancy with the Zone System or to put it another way, the 3 1/3 stop relationship between the meter calibration point and the speed point...
Ralph,
My only concern is using film curves to show flare. The film curve doesn't really change...
Steve
Have you looked at my graph in post #113? Did the characteristic curve not change with additional non-image exposure?
There is a metering standard but unfortunately, it is not followed by exposure meter manufacturers.
See, it is not worth it. Plus, the fixed density method gives me more exposure, which, for a Zone System advocate like me, can never hurt.
It moves the shadow points a bit more up the curve, just where I like them!
I'm not convinced. Since flare affects toe, midtones and shoulder differently, I don't see how development can correct for it. It can, of course, correct and bring back the total negative density range, but the shape of the characteristic curve is distorted by flare. I don't believe a change in development can correct that.
I was more interested in seeing how this was graphically handled throughout the tonal reproduction cycle (more than four quadrants?).
The curve itself actually doesn't change with flare...
...Really? Do you have any proof of that? It's another urban myth IMO. Just like Adams' K factor conspiracy theory or that meters read 18%...
...Actually, fixed density gives you less..
...But simply knowing that the film speed doesn't really change much with development, according to the Delta-X Criterion principles, eliminates the need to do endless testing and worrying about how speed changes with processing. When I'm shooting a scene and intend on doing extended processing, I know I don't need to change my EI. And that is worth it even if you don't go to the trouble of using the criterion...
Ralph;
Yes, I agree that the curve is not affected uniformly, but you can approximate the result by increasing contrast. This is why Consumer films are higher in contrast than Professional films. It is assumed that consumers cheaper cameras have higher flare. (read point and shoot plastic lenses as an example) But, this is, as you point out, a simplistic answer. (among other things, the average consumer prefers higher contrast and this is why there are professional papers and photofinisher papers for B&W and color both)...
Steve
If you don't see that curve changing with flare, in the graph attached to post #113, I don't know what else to say, really.
Read the standard and check the calibration factors for Gossen, Minolta, Sekonic and Pentax meters. You'll see. All different. No myth.
Yes, less speed, more exposure.
Steve
No, it is not. You can repeat this as often as you like. It's still wrong.
Film speed does change with development!
PE - This is why Consumer films are higher in contrast than Professional films.
Actual lightmeter calibrations are typically to a lower value, assuming the average scene to reflect less, which means more exposure if you visualize the measurement at 18% or Zone V.
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