I didn't know these are called dates, couldn't figure out what the joke is. I learned something today.
I didn't know these are called dates, couldn't figure out what the joke is. I learned something today.Teenagers. Always trying to get a date!
Tim, he posted a picture of dates!!!
Stephen,I'm glad to see that our results match so closely.
Fellow members and subscribers, I doubt if there is another member here that has had to do this on a real basis for film or paper. I have had to do both. No single method is best, but the one that approaches best is one that works making good negatives (or slides) and prints. It does it over and over. Mees and Haist show it. I have done it and it really works.
You can use the zone system (a dumbed down system of 21 step sensitometry) and other methods, but use is what works. First acceptable print works. Whatever you use though, remember that what works for you is OK. It is just that it may not work for the rest of us due to your conditions.
PE
I hope you don't think the same about the speedometer in your car!Like buying a thermometer with the numbers already on it. I'm still free to use the thermometer however I want.
I didn't know these are called dates, couldn't figure out what the joke is. I learned something today.
No two people see the color green the same way, but statistically, the vast majority see it similarly enough for the word to have meaning. We all have different concepts of quality depending on our experience with the subject and what is possible for the time. A well typed paper in the 1970s would probably appear sloppy compared to today's computer print outs. A good color image that had blown out skies and heavy shadows is less acceptable today because of high dynamic range imaging. Special effects in movies are another good example as is movie editing.
For the first excellent print test, the judges were given instructions to pick the print that best represented what the original scene might have looked like if they where standing at the scene's location. Did the instructions influence their interpretations? Does this suggests any image where the photographer wants to interpret a scene differently would begin to fall outside the judged parameters. So the test results may not apply universally, nor can they. The test; however, establishes an understood frame of reference which the majority of people can relate to. As with most phenomena, everything else falls somewhere else on the bell curve.
Here is why the test yielded a lasting concept of film speed. The two film curves below are from a long and short toed film. The fixed densities of 0.10 and 0.20 are shown. As is the fractional gradient point, 03G. Notice the differences in log-H between the fixed density points and the fractional gradient point in the two examples? This isn't intuitive and could only be found through psychophysics.
View attachment 215104
Stephen, the curve with the sharper toe is much slower. This is why we tried to maximize the toe and also get the highest toe speed. The actual speed of an emulsion is the inflection point of the curve over fog. Anything else is meaningless due to variations in toe and contrast. One works with this value to optimize the curve that "follows".
PE
Late response, but what the hell... Yes, I've done such a test in the past with homebrew D76d and 400TX IIRC. I had followed Kodak's recommendation and indeed, the characteristic curve had two points where it met the ISO criteria, for whatever speed it was. It has been a while, but I used the same homebrew Xtol with some outdated (7-8 years) Agfa APX100. I followed Kodak's recommended time from an old Xtol datasheet. The film had quite a lot of fog (fb+f = 0,8!) as you can see at the following figure, but the curve meets the ISO criteria for a speed of 64 as it seems:You are really close to having the ISO parameters. But, since your developer is the variable you want to test, I'd do a control test with D-76 and try to hit the ISO parameters with that (a more standard developer). Later, when you hit the ISO parameters with your home-made developer, you can compare the x-axis differences between the standard developer and your developer.
From that you can determine whether your developer gives more or less speed. Chances are the speed difference will be negligible.
Nice find, thanks for posting it. No problem in using HC110 for a speed estimate though. IIRC the ISO standard doesn't require a specific developer for testing anyway. Any developer is ok and you actually get slightly different speed when using different developers.Interestingly enough, here are the developer formulas per the old ASA standard. This is out of Practical Photographic Chemistry by O’Hara & Osterburg.
View attachment 214844
Of course, I said f’ it and just base my dry plate speed estimate on developing in HC-110 dil B for 5 minutes.
Yes, that's true. I've tried the same film in different developers and it behaved differently, even plotted curves to make it clearer. One had a fairly normal toe, with a smooth transition to the straight line, the other had a pronounced toe that turned to a very steep straight line, followed by strong shoulder. Dmax was about the same and needless to say, the latter was pretty bad. Sometimes I really wonder how some people can claim that film X, developed in Y can give them a usable EI of Z.... All the calculations in the world won't help you if you don't understand this fundamental fact first, or really, how to interpret film curves with respect to toe, straight line, and shoulder. I personally consider the specific characteristics of the toe to line transition far more important than any ISO conventionality. And even this kind thing is affected by developer variables...
whew ! i was starting to think they were a large box of pencil erasers and the yoke was on meHaa, the photo was of dates.
.3G is the fractional gradient speed point which falls at a point 0.3 times the overall film gradient. It tends to fall further to the left in relation to the 0.10 fixed density with long toed films and when the film is developed to a lower overall gradient, Because of the changing relationship between the two points, the ISO standard needed to have stricter contrast conditions than the fractional gradient ASA standard pre-1960 which only suggested the film be processed over a minimum gradient. Please see all the references and examples that I've presented that support this.
BTW, the two examples from Jones also contain inertia speed points.
Drew: There is a film here that purport to show Super XX being coated. It was made in Rochester and probably other locations.
Stephen: They end up being one and the same.
PE
Film curve changes with choice of developer and development.One thing I like about characteristic curves is that they don’t change when you talk about them.
You can call the speed point anything you want, the curve is the same.
I think you might be confusing inflection with inertia.
H&D “inertia” is a projection of the straight line portion. It’s not what PE is talking about. He’s talking about identifying the place where you are first able to detect a density change above base plus fog.
There’s certainly nothing useful ‘to the left‘ of that point.
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