If this is your first visit, be sure to check out the FAQ by clicking the link above. You may have to register before you can post: click the register link above to proceed. To start viewing messages, select the forum that you want to visit from the selection below. |
|
|
Thread Tools | Display Modes |
#71
|
|||
|
|||
Improved T-Max 400
On Oct 31, 8:00 pm, Peter Irwin wrote:
UC wrote: It is my opinion, and that of many others, that the 'new' ASA speed sytem introduced in 1959 gives numbers that are too high, by about 2/3 stop. I think the primary reason for this is that the question you want the ISO rating to answer is a different question from the one it was designed to answer. The question the speed rating is designed to answer is "what is the minimum exposure required to produce a negative from which a print judged to be 'excellent' can be made?" The question you probably want answered may be something like "What exposure meter setting will consistently give negatives that are easy to print well?" The answer to the second question is going to generally be a lower exposure index than the ISO standard. Peter. -- Well, I don't think the shadow contrast is as good at ISO as it is at about 2/3 ISO. This is based on many thousands of negatives. |
#72
|
|||
|
|||
Improved T-Max 400
On Oct 31, 9:43 pm, "pico" pico.pico.net wrote:
"UC" wrote in message ps.com... On Oct 31, 8:05 am, "pico" pico.pico.net wrote: "UC" wrote in message What part of that line/curve is actually useful for making photographs? You never use the so-called shoulder - it is outside the useful exposure range. When you use the film, the differences appear. I develop much less than the longest time shown. The point is that you CAN easily see the differences. Kodak brought out Polymax paper specifically to combat the problem. Now that Kodak is out of the paper business, they may have adjusted the curve of TMY to work better with other papers. After all, Tri-X Pan does sell better. TMY is 20 years old! I use the film. And are you not aware that Tri-X has changed again? No, it has not changed, other than 'normal' manufacturing improvements. I got this from Kodak themselves a couple of years ago. |
#73
|
|||
|
|||
Improved T-Max 400
On Nov 1, 8:35 am, "pico" pico.pico.net wrote:
"Peter Irwin" wrote in message ... The important detail to remember is that the ISO speeds are intended to get you very near the minimum exposure that will work well with negative film. The maximum The optimum setting for your purposes is something you have to find for yourself. All film manufacturers including Kodak actually say this. Of course. So shoot short rolls or sheet film and custom expose and develop. That's not necessary or practical for 35mm users. Just set your meter at 2/3 ISO and usually you will have near-perfect negatives. |
#74
|
|||
|
|||
Improved T-Max 400
On Oct 31, 8:00 pm, Peter Irwin wrote:
UC wrote: It is my opinion, and that of many others, that the 'new' ASA speed sytem introduced in 1959 gives numbers that are too high, by about 2/3 stop. I think the primary reason for this is that the question you want the ISO rating to answer is a different question from the one it was designed to answer. The question the speed rating is designed to answer is "what is the minimum exposure required to produce a negative from which a print judged to be 'excellent' can be made?" No, I don't think so. It was "What index will produce the greatest number of correct exposures without losing definition through overexposure on automatic cameras". You have to remember that the late 50s saw the introduction of numerous compact, semi-automatic and meter-coupled 35mm cameras with primitive meters. The way these cameras metered resulted in overexposure errors more often than underexposure errors, if I recall correctly. It was felt that a reduction in exposure was warranted because of this. |
#75
|
|||
|
|||
Improved T-Max 400
In article .com,
UC wrote: Well, I don't think the shadow contrast is as good at ISO as it is at about 2/3 ISO. This is based on many thousands of negatives. Thousands of negatives with the _one film_ you've evidently decided is an acceptable film for anyone to use. How... tremendously persuasive. I don't suppose it might have occurred to you that you could probably get perfectly good results with almost any film you picked up from the store shelf if you were willing to adjust your own technique. Well, as materials disappear from the market faster and faster over the next few years, I don't think you're going to have much choice about it, unfortunately. -- Thor Lancelot Simon "The inconsistency is startling, though admittedly, if consistency is to be abandoned or transcended, there is no problem." - Noam Chomsky |
#76
|
|||
|
|||
Improved T-Max 400
On Nov 1, 12:50 pm, (Thor Lancelot Simon) wrote:
In article .com, UC wrote: Well, I don't think the shadow contrast is as good at ISO as it is at about 2/3 ISO. This is based on many thousands of negatives. Thousands of negatives with the _one film_ you've evidently decided is an acceptable film for anyone to use. How... tremendously persuasive. ??? What are you talking about? I use lots of different films. The point is that 2/3 ISO is better than ISO for almost every film I've tried. The exception was Ilford Pan-F, which works well right at 50. I don't suppose it might have occurred to you that you could probably get perfectly good results with almost any film you picked up from the store shelf if you were willing to adjust your own technique. Well, as materials disappear from the market faster and faster over the next few years, I don't think you're going to have much choice about it, unfortunately. -- Thor Lancelot Simon "The inconsistency is startling, though admittedly, if consistency is to be abandoned or transcended, there is no problem." - Noam Chomsky |
#77
|
|||
|
|||
Improved T-Max 400
"Peter Irwin" wrote in message ... Richard Knoppow wrote: For peter, the 0.8 factor is NOT the same as 1, it is 20% different which is quite different. The density value I stated is the value from the charts in the standard for the log exposure at the speed point multiplied by the reciprocal of 0.8, that is 1.25 and should be the log exposure at the point on the toe approximating the Jones minimum gradient point. The 0.8 factor is in the standard and it used to calculate the speed. I think this is getting a little confusing for me. I will state what I understand as clearly as possible, and you can tell me if I'm going wrong somewhere. Kodak Speed ----------- In 1939 Kodak introduced a new speed system based on the results of extensive psychophysical research. This research showed that the minimum useful exposure Required to yield an 'excellent' print was at a point where the gradient of the H&D curve was 0.3x times the average gradient of the slope over a range from the exposure point to log 1.5 above the exposure point. Finding this point called the "Jones Point" requires a recursive operation. One has to first guess the point to find the average gradient, and then refine your guess on the second try. Kodak speed is given by the formula: Kodak Speed = 1/E Where E is the Jones Point in Metre-Candle-Seconds. (Same as Lux Seconds). If you had such a thing as a exposure meter calibrated for Kodak speeds, there would be no safety factor. Kodak Speed didn't catch on because few if any people owned such meters. OLD ASA Speed 1943 ------------------ In 1943 the ASA adopted the Kodak speed system with one important change. The formula was now ASA Speed = 1/(4 x E) This was intended to give numbers usable with both Weston and GE meters. The new ASA standard meters were to be calibrated midway between the old Weston and GE calibrations. With an ASA meter, old ASA speed had a safety factor of 2.5 (1 1/3 stops). I don't think there was a particular level of negative contrast required by the old ASA standard, because the Jones point remains in the same place over a fairly wide range of development contrasts. Development contrast is supposed to be typical of photofinishing practice. DIN Speed --------- The original DIN speed system (1936) was very unsatisfactory. Sometimes it would even get the relative speeds of films in the wrong order. The reason for this was that the original DIN standard required films to be developed for maximum speed rather than according to normal use. Old DIN speeds are indicated by the presence of "/10" so 24/10 degrees DIN is an old DIN speed. In the 1957 DIN standard, the "optimal development" was replaced by a rigidly specified development more typical of real practice. People soon noticed that the new DIN numbers actually made sense. New ASA Speed ------------- Since the new DIN system was easier for film manufacturers in practice and actually worked pretty well, the ASA decided to adopt a new system based on DIN speeds. It was also decided to abandon the rather large safety factor and have speeds roughly twice that of the old while keeping meter calibration unchanged. The 2:1 relationship is typical, but is not exactly true of all films as the following table shows. Film OLD ASA NEW ASA ---- ------- ------- Plus-X 35mm 80 125 Verichrome Pan 80 125 Tri-X Pan Sheet 200 320 Tri-X Pan 35mm 200 400 ISO Speed --------- The current ISO standards for B&W film are essentially the same as the New DIN and New ASA standards. Where Hm = the 0.1 above base + fog point in lux seconds. Arithmetic speed S = 0.8/Hm Log speed S degrees = 1 + 10 x log10 0.8/Hm The Log ISO is in fact the same as the DIN speed. DIN Speed = 10 log10 1/Hm Because 10 log10 0.8 = -1 (at least very very nearly). So Log ISO and DIN are both equal to the log exposure of the 0.1 above base + fog point divided by minus 10. The 0.8 denominator in the arithmetic speed makes 1 ASA equal to 1 DIN and places the New ASA or ISO arithmetic speed where it was wanted. example: Tri-X pan 400 ISO 400/27 degrees New ASA 400 New DIN 27 OLD ASA probably still 200 0.1 above base fog point (Hm) is -2.7 log lux seconds This is true from all formulas. ISO Artith or New ASA = 0.8/Hm = 0.8/10^-2.7 = 0.8/0.002 = 400 ISO Log Degrees = 1 + 10 x log10 0.8/Hm = 1 + 10 x log10 0.8/10^-2.7 = 1 + 10 x log10 400 = 1 + 10 x 2.6 = 1 + 26 = 27 DIN Speed = 10 x log10 1/Hm = 10 x log10 1/10^-2.7 = 10 x log10 501 = 10 x 2.7 = 27 Same Answer! DIN Speed of 27 means Hm is -2.7 log lux seconds. - neat - all you have to do is divide by negative 10. If Old ASA 200 then Jones point E = - 2.9 log lux seconds ASA Speed = 1/(4 x E) = 1/(4 x 10^-2.9) = 1/(4 x 0.00126) = 1/0.00504 = 198.41 Close enough. Peter. -- This is getting long but I can't find anything to snip. I don't know when Kodak began using Jones' method internally but it did begin to publish Kodak speeds around 1939. Jones actually worked out his system much earlier. The ASA adopted the system in 1943 with a safety factor of 2. ASA speeds were 1/4 of Kodak speeds. The resulting number could be used with either Weston or General Elecric meters of the time with insignificant error. However, the safety factor increased the exposure by a stop over the Jones speed point. A film rated Kodak 400 would be an ASA 100 film by this standard. In its data sheets of this time Kodak stated that the exposure could be reduced a stop if work was carried out carefully. The second ASA standard changed the method of measurement from the Jones minimum usable gradient to a fixed minimum density method as adopted by the DIN in the early 1950's (don't have the exact date at hand). However, they wanted to accomplishe two things: first was to make the speeds compatible with earlier ASA speeds, and secondly, to maintain something like the Jones idea of the minimum gradient. The ASA conducted extensive surveys of films of the time and found that there was a nearly constant ratio between the fixed minimum density, that is log 0.1 above fog plus support density, and the Jones point as found using the Jones method. This obviated the difficult Jones measurement. The ratio turned out to be about 1.25 times the exposure required to reach the DIN density point. So, a factor of 0.8, the reciprocal of 1.25 is introduced into the calculation of the speed in the new ASA method. In effect the speeds were now double those measured by the old ASA method and half of the Kodak speed. I reiterate that the factor in the current speed method is NOT a safety factor but rather to bring measurements made by the method into agreement with the speed that would be measured by the Jones/Kodak method and reverts to Jones' original idea of finding the minimum exposure that results in good tone rendition. The original Kodak method does not seem to have had a fixed contrast, however, contrast does affect the speeds measured by either method. The Kodak method does specify a fixed exposure interval, much the same as the current method. Since the old ASA method and the new ISO method are compatible as to speed point even though measured by different techniques, its possible to translate old ASA (pre 1958) speeds to equivalent modern speeds by simply multiplying by 2. Keep in mind that the speeds in both systems are rounded off as were old Weston speeds so there may not be an exact agreement. Also, even though Kodak used the same trade names for decades the emulsions were changed many times. Current Plus-X is not the same as the product of, say, 1948 although its broad speed catagory is about the same and its intended use is about the same so speed comparisions must be made with some care. What is surprizing is how fast films of the mid 1940's were. The difference was, of course, grain. A 1940's film which would measure 400 on the ISO system would be extremely grainy compared to a modern film of that speed. -- --- Richard Knoppow Los Angeles, CA, USA |
#78
|
|||
|
|||
Improved T-Max 400
"pico" pico.pico.net wrote in message ... "Peter Irwin" wrote in message ... UC wrote: It is my opinion, and that of many others, that the 'new' ASA speed sytem introduced in 1959 gives numbers that are too high, by about 2/3 stop. I think the primary reason for this is that the question you want the ISO rating to answer is a different question from the one it was designed to answer. The question the speed rating is designed to answer is "what is the minimum exposure required to produce a negative from which a print judged to be 'excellent' can be made?" The question you probably want answered may be something like "What exposure meter setting will consistently give negatives that are easy to print well?" The answer to the second question is going to generally be a lower exposure index than the ISO standard. MOST EXCELLENT observation. Kodak set the metrics. Those are the same folks who conducted a hugely expensive and detailed survey of average customers (largely of automatic processing) and Kodak set their metrics to those standards, as abysymal and utterly tasteless as they were, they still represented the drug-store processing majority. (Imagine the Bell curve - who wants to live on top?) Oh, and what camera did Kodak come out with in response to that study? The wholly embarassing failure, the Disc Camera! But to add a contemporary data point - with so many people scanning negatives, a whole new scale must be developed (no pun). Me, I'm still scanning prints. So shoot me already. This is simply not true. The Kodak speed method was developed over a very long time by quite valid research all of which has been published in peer reviewed journals. Much of the work conducted under L.A.Jones leadership was published in the Journal of the Franklin Institute. There is a big difference between market surveys and scientific investigation and you are confusing the two. Kodak's main thrust has always been to make photography practical and easy for amateurs, that's what George Eastman's philosophy was and he built one of the most successful businesses in history on it. The influence is still there even though Kodak has moved from chemical to electronic photography. Actually, the ISO speeds are quite practical but many photographers do not understand how they are supposed to be used. The speed applies only whan the specified developer is used and when film is developed to the same contrast index as is used in the standard measurement. This is about the contrast for contact printing and diffusion enlarging. If film is devloped to a lower contrast the exposure must be increased. Also, Jones found that the quality of the prints changed little once the minimum exposure was reached. Minimising the exposure minimises the density of the negatives, which, in genera, is better for minimising grain and maximising sharpness, however, it is often the case that increasing exposure a bit improves tone rendition, perhaps because of errors in using an exposure meter. -- --- Richard Knoppow Los Angeles, CA, USA |
#79
|
|||
|
|||
Improved T-Max 400
Richard Knoppow wrote:
This is getting long but I can't find anything to snip. I hope that means that it was mostly ok. I don't know when Kodak began using Jones' method internally but it did begin to publish Kodak speeds around 1939. Jones actually worked out his system much earlier. I'm sure that's right, but published Kodak speeds from before 1939 are a different system. The Kodak speeds listed in the 1938 edition of "Eastman Professional Films" are not the Jones system. The pre-1939 Kodak system was based on inertia (Like Weston and H&D) and is equal to ten times the Weston speed. The ASA adopted the system in 1943 with a safety factor of 2. That's what you've said several times. But - In "Kodak Films" fifth edition 1951 from the Kodak Reference Handbook on page 16, it says "For the black-and-white continuous tone negative materials covered by the standard, a safety factor of 2.5 is used." In "Kodak Films" seventh edition 1956, it says the same thing on the top of page 21. ASA speeds were 1/4 of Kodak speeds. The resulting number could be used with either Weston or General Electric meters of the time with insignificant error. However, the safety factor increased the exposure by a stop over the Jones speed point. A film rated Kodak 400 would be an ASA 100 film by this standard. In its data sheets of this time Kodak stated that the exposure could be reduced a stop if work was carried out carefully. That's true, but I expect you have the same booklets I have where it says the safety factor is 2.5. The second ASA standard changed the method of measurement from the Jones minimum usable gradient to a fixed minimum density method as adopted by the DIN in the early 1950's (don't have the exact date at hand). The 1958 Ilford Manual by Horder has the date for revised DIN standard as 1957 (p. 284, 287). The older 1936 DIN system used the same minimum density requirement, but specified development for maximum speed, rather than a standard development representing something like normal use - as was used from 1957. I think the ASA Standard is ANSI PH2.5-1960, at least it is cited that way in Photographic Sensitometry by Todd and Zakia (1974 p.164). These would just be publication dates, the actual work would always be a bit earlier. However, they wanted to accomplish two things: first was to make the speeds compatible with earlier ASA speeds, That made a lot of sense given the number of meters already in use. and secondly, to maintain something like the Jones idea of the minimum gradient. It doesn't use the 0.3 times average gradient criterion though, it uses the 0.1 density above base + fog criterion. The ASA conducted extensive surveys of films of the time and found that there was a nearly constant ratio between the fixed minimum density, that is log 0.1 above fog plus support density, and the Jones point as found using the Jones method. It seems to hold good within a third of a stop based on the ratings of films just before and just after the change. Note that the inertia based Weston speed also tracked pretty well with the Jones Kodak Speed and Old ASA. The normal relationship would be that Weston 40 equaled Kodak 200 and Old ASA 50. Many films seem to have fit that relationship perfectly and I'm unaware of any that were more than 1/3 stop off. The key seems to be normal development. Weston, Old ASA, and ISO (New ASA/New DIN) use different criteria, but track quite well. They all use normal development. Old DIN (1936) tracked the other systems very badly. It used development for maximum speed. The same criterion, but with normal development, works very well. This obviated the difficult Jones measurement. The ratio turned out to be about 1.25 times the exposure required to reach the DIN density point. The math in my previous post showed that an ISO 400/27 film has a DIN density point at -2.7 log lux seconds and that an Old ASA 200 film had a Jones Point at -2.9. Unless someone shows that my formulas or math are wrong, I'm sticking to those figures. The Jones Point for a typical film is thus 0.2 log units to the left and represents 2/3 of a stop less exposure than the DIN point. So, a factor of 0.8, the reciprocal of 1.25 is introduced into the calculation of the speed in the new ASA method. That was to get the numbers they wanted, but the actual difference between the DIN point and the Jones point for films where New ASA is double Old ASA is 0.2 log units, 2/3 of a stop or a factor of around 1.6. In effect the speeds were now double those measured by the old ASA method and half of the Kodak speed. True for most films. I reiterate that the factor in the current speed method is NOT a safety factor but rather to bring measurements made by the method into agreement with the speed that would be measured by the Jones/Kodak method and reverts to Jones' original idea of finding the minimum exposure that results in good tone rendition. Yes but if the "Kodak Films" booklets are correct that Old ASA had a safety factor of 2.5, then the doubling of the speed ratings should have reduced this to 1.25. I agree that this has nothing to do with the 0.8 in the formula. The 0.8 in the formula just puts the scale where they wanted it. The original Kodak method does not seem to have had a fixed contrast, however, contrast does affect the speeds measured by either method. The Kodak method does specify a fixed exposure interval, much the same as the current method. Yes, but changes in development time tend to affect the contrast in the toe and the overall contrast at the same time. Since the Jones method depends on the ratio between the slope of the curve at the Jones point and the overall slope, changes in development will have less effect on the Jones point than on the DIN point. Since the old ASA method and the new ISO method are compatible as to speed point even though measured by different techniques, its possible to translate old ASA (pre 1958) speeds to equivalent modern speeds by simply multiplying by 2. Keep in mind that the speeds in both systems are rounded off as were old Weston speeds so there may not be an exact agreement. Also, even though Kodak used the same trade names for decades the emulsions were changed many times. Current Plus-X is not the same as the product of, say, 1948 although its broad speed category is about the same and its intended use is about the same so speed comparisons must be made with some care. Plus-X 35mm did vary in rated speed over the years. Kodak 200 in 1943 (Old ASA 50) ASA 50 in 1951 ASA 80 in 1956 But the speed of both Plus-X 35mm and Verichrome Pan just before the change was ASA 80 and both were ASA 125 just after the change and forever after. I'm aware that both systems round to the nearest 1/3 stop so that a 1/3 stop difference in reality may be hardly anything at all. My impression is that Plus-X 35mm, while now greatly improved from the film introduced in 1938, never underwent any rapid obvious change from year to year. Every now and then the new stuff would be just a little better. A bunch of minor changes over 69 years can add up a lot. Then again, it was always around 100 speed by today's standards. It was always a double coated film, always type B panchromatic, always had a high acutance, and was always fine grained for its time. What is surprizing is how fast films of the mid 1940's were. The difference was, of course, grain. A 1940's film which would measure 400 on the ISO system would be extremely grainy compared to a modern film of that speed. Medium speed films were actually pretty ok. I have some of my father's Verichrome negatives that he took with his Brownie in the 1940s. Even with department store processing, the negatives are still a bit finer grained than today's Tri-X in D-76 1:1. Peter. -- |
#80
|
|||
|
|||
Improved T-Max 400
"Richard Knoppow" wrote in message ... MOST EXCELLENT observation. Kodak set the metrics. Those are the same folks who conducted a hugely expensive and detailed survey of average customers (largely of automatic processing) and Kodak set their metrics to those standards, as abysymal and utterly tasteless as they were, they still represented the drug-store processing majority. (Imagine the Bell curve - who wants to live on top?) Oh, and what camera did Kodak come out with in response to that study? The wholly embarassing failure, the Disc Camera! This is simply not true. The Kodak speed method was developed over a very long time by quite valid research all of which has been published in peer reviewed journals. Much of the work conducted under L.A.Jones leadership was published in the Journal of the Franklin Institute. There is a big difference between market surveys and scientific investigation and you are confusing the two. The study I am familiar with was a market study; it strove to find the kind of print most people like so that they could recommend processing and materials to their mass processing clients. Market means the typical purchaser. |
Thread Tools | |
Display Modes | |
|
|
Similar Threads | ||||
Thread | Thread Starter | Forum | Replies | Last Post |
** Improved AGENT X SEARCH *** | Victorias Secrets | Digital Photography | 0 | November 11th 06 02:44 AM |
WTB Improved Seneca 5x7 | K.E. Carter | Large Format Equipment For Sale | 0 | October 7th 04 11:20 AM |
wtb improved seneca 8x10 | x | Large Format Equipment For Sale | 0 | September 29th 04 12:02 PM |
WTB: Improved Seneca 5x7 | Kirt E. Carter | Large Format Equipment For Sale | 0 | January 8th 04 05:03 PM |