0.6 -- standard contrast?

[Chris Livsey]

I do enjoy a happy ending

 

[RobC]

To answer the OP question directly, the manufacturers target the Film Speed ISO to determine what their film box speed is as in the graph below.

http://en.wikipedia.org/wiki/Film_speed#Determining_film_speed

taking figures from that graph and dividing 0.8 / 1.3 = 0.615 which is the contrast index you are talking about. So infact the 0.6 is a by product of the Film Speed ISO (or vica versa depending on which direction you're coming from).

 

[Photo Engineer]

Rob, that is not entirely true.

Film speed can be increased with no contrast increase and vice versa and that simple fact throws off your comment. Toe can be soft or sharp and that throws off the calculation.

BTDT.

PE

 

[Bill Burk]

One of the most important figures in Mees was overlooked in this "study".

His graph of usable latitude A' to B' in the figure, is right where it should be. On the straight line portion.

Just thought you might appreciate it.

PE

If I understand the chart, A' to B' on the straight line section and the illustrated gradient 1.1 is for a 4 2/3 stop subject brightness range.

That's nearly N+2 in Zone System nomenclature, coincidentally a scenario very similar to 7 sheets of film I just shot and developed today for the Negative Exchange.

You see, it was a rainy day and I could not find more than 5 stops of subject brightness range in the small scene I had chosen. Practically the same as this Mees graph. Perfect timing!

The chart I follow suggested in my case, negatives should be developed to 0.86 CI which I didn't feel was really needed. I looked across and down a column and row to see what contrast might be good for something close to what I had. (assuming a third stop more subject range and half grade higher paper)... The chart shows 0.73 CI in that cell. So I averaged and decided to aim for 0.80 CI...

I consulted my Time/CI chart (my own only went to 0.75 so I imagined a line extension to 0.80)... From that I decided to develop for 17 minutes 15 seconds in D-76 1:1 (I don't think the 15 seconds really mattered but I set the timer to 17:15 anyway).

I'm done and now the negatives are hanging to dry. I believe they will be good, printable negatives.

When I measure the sensitometry strip that I included in this run, I will mark a dot on my Time/CI chart at the Time and actual CI... effectively I turn my Time/CI chart into a scatter diagram.

 

[RobC]

I disagree. The standard specifies m, 1.3 and 0.8. anything else will be different and not to standard. The contrast range when using those two numbers will always be the same. Putting a long toe in won't change that without going outside of the standard. So whats your point.

I would like to make it obvious that the zone system starts out by breaking the film speed standard by trying to get 10 stops of range on film instead of the 7-8 that the ISO standard implies/uses. (even though you can't fit 10 stops onto paper).
Curiously Adams then says zone 8 should be density 1.3 or therabouts and my results show that 1.3 density is pure white. i.e. His zone 8 is my print tone 10 (white) which suggests to me that for all the zone system theory implies its actually an 8 zone system and not 10 so that it fits paper and if you have anything in zone 9 or 10 it'll be a real bugger to print if you follow Adams figures. But hey, that could just be me.

 

[Bill Burk]

I disagree. The standard specifies m, 1.3 and 0.8. anything else will be different and not to standard. The contrast range when using those two numbers will always be the same. Putting a long toe in won't change that without going outside of the standard. So whats your point.

0.6 is close to the contrast if you imagine a pure straight line from the ASA/ISO parameters continuing in both directions. But contrast index (and other measures of contrast) include different segments of the curve than the ASA/ISO parameters, including more or less of the toe for example. So by other measures it's not always 0.6

Also, I don't think the manufacturers have to specify the same time in their recommended development charts as the times they used to establish ISO speed. An obvious example is the push processing times.

 

[Photo Engineer]

I think that Bill has explained the caveats that reside in the standard.

Thus, some films need testing due to this deviation in fact from the standard.

PE

 

[RobC]

well once you start halving your film speed and giving less film development in the persuit of zone system values then it hardly matters since you're breaking the standard and if you do get 10 stops of subject brightness range to just fit the paper then you aren't likely to get to 0.6. You'll more likely get a very flat looking image and need to do somersaults to get it looking OK. Far better to just pick subjects that have good lighting in the first place.

 

[Bill Burk]

Curiously Adams then says zone 8 should be density 1.3 or therabouts and my results show that 1.3 density is pure white. i.e. His zone 8 is my print tone 8 which suggests to me that for all the zone system theory implies its actually an 8 zone system and not 10 so that it fits paper and if you have anything in zone 9 or 10 it'll be a real bugger to print if you follow Adams figures. But hey, that could just be me.

This is another whole discussion, if you place Zone VIII at a density 1.3 and your Zone II comes up to 0.4 density thanks to flare, then you neatly fit Grade 2 paper. I'm working with a young man who is baffled by Ansel Adam's suggested densities, and he tries too hard to hit them with camera tests. I'm trying to show him the contrast is what matters and that he is getting remarkably consistent results. I'd be happy to help you if you are getting baffled the same way.

 

[RobC]

I'm not baffled at all. I was, but I have now seen the light.

 

[Stephen Benskin]

This is another whole discussion, if you place Zone VIII at a density 1.3 and your Zone II comes up to 0.4 density thanks to flare, then you neatly fit Grade 2 paper. I'm working with a young man who is baffled by Ansel Adam's suggested densities, and he tries too hard to hit them with camera tests.

Bill, that's a major concern I have with "systems." By their very nature, they simplify the process which can lead to misunderstandings and in the case of the Zone System, dogma.

RobC, the ISO B&W speed standard contains instructions on how to determine B&W film speed for general use. The theory behind it is found in other sources, like Nelson's Safety Factors, Nelson's and Simonds' Simple Method's for Approximating the Fractional Gradient Speeds of Photographic Materials, and Jones' seminal papers. The first two can be found in APUG. What you noticed about the 10 Zones is a good example of problems with systems.

 

[Xmas]

I'm not baffled at all. I was, but I have now seen the light.

My LTM Canons (P & VI) have baffles my Leicas (M3 & M2) don't.

 

[Stephen Benskin]

One of the most important figures in Mees was overlooked in this "study".

His graph of usable latitude A' to B' in the figure, is right where it should be. On the straight line portion.

Just thought you might appreciate it.

PE

Ron, I found a reproduction of the example in The Theory of the Photographic Process, 3th Ed. p. 438 , but it only uses the curve as an example of "derivative of the characteristic curve." It doesn't explain what points O and P represent. Do you know the original source of the graph? As far as I can tell, the area between points A and B only represents the straight-line portion.

 

[BetterSense]

I consulted my Time/CI chart (my own only went to 0.75...)

When I measure the sensitometry strip that I included in this run, I will mark a dot on my Time/CI chart at the Time and actual CI... effectively I turn my Time/CI chart into a scatter diagram.

I am assuming your time/CI chart is homemade. Where do you get the sensitometry strips?

Ansel never claimed that his main goal was to generate easy-to-use negatives or ones that "fit" the paper. I seem to remember him being explicit about the fact that Zone system methodology was intended to optimally capture the desired information from the scene, which may or may not result in a negative that prints easily.

 

[Photo Engineer]

Ron, I found a reproduction of the example in The Theory of the Photographic Process, 3th Ed. p. 438 , but it only uses the curve as an example of "derivative of the characteristic curve." It doesn't explain what points O and P represent. Do you know the original source of the graph? As far as I can tell, the area between points A and B only represents the straight-line portion.

My graph comes from the revised edition. I'll have to look up the original.

PE

 

[Bill Burk]

My graph comes from the revised edition. I'll have to look up the original.

PE

A to B is definitely what Mees called Latitude, the region of direct proportionality (the straight line). For some purposes, like astrophotography, that's all the Latitude you get.

And that graph also illustrates a Gamma around 0.6 giving about Normal 7 stops Latitude.

The graph doesn't illustrate "Latitude" as commonly understood: Exposure error you can get away with.

My favorite "Latitude" graph in that sense, is the one that plots quality of prints against exposure. That graph shows a bell curve for enlargements (you have to expose more precisely if you enlarge) and a plateau for contact prints (you can overexpose lots more for contact printing).

 

[Photo Engineer]

Bill, I agree and I will stop searching now. I just wanted to be positive what Mees meant because of Stephen's post.

PE

 

[Stephen Benskin]

Bill, I agree and I will stop searching now. I just wanted to be positive what Mees meant because of Stephen's post.

I hope you don't stop looking because I'd like to read the paper, and I was hoping you knew where it was from.

 

[Photo Engineer]

This is from the work of Tupper and is D density / D log E as I have mentioned before. Multiplying this derivative of film x derivative of paper will give one the derivative of the print at any given point. I had not earmarked it because few people like calculus. It is in the revised edition of Mees, Fig 299 on P 870.

PE

 

[RobC]

So where can I see all the photographs from Mees and all the other scientists and theoreticians because I want to be able to judge for myself whether they actually knew anything about making a fine print.

 

[Photo Engineer]

Rob, take a look at my gallery, at photos I took. Some won awards and some were published in newspapers. And then consider that I once designed film too. Many of the members of Kodak Research were fine, award winning photographers. So, I think that most of us knew not only the theory but the practice.

PE

 

[Stephen Benskin]

So where can I see all the photographs from Mees and all the other scientists and theoreticians because I want to be able to judge for myself whether they actually knew anything about making a fine print.

It's not about whether Jones et al had an eye. It's about psychophysics. Each image to be judged was photographed over a range of exposures. These negatives were printed on a number of different grades, papers, and exposures. A group of people then judged which print looked the best. The characteristics of the negatives that produced the prints with the highest judged quality where evaluated and a methodology was determined that would most consistently produce results like the judged prints.

 

[Bill Burk]

I am assuming your time/CI chart is homemade. Where do you get the sensitometry strips?

Ansel never claimed that his main goal was to generate easy-to-use negatives or ones that "fit" the paper. I seem to remember him being explicit about the fact that Zone system methodology was intended to optimally capture the desired information from the scene, which may or may not result in a negative that prints easily.

Yes it's home-made. I am fortunate to have an EG&G sensitometer which makes the work easy.

I have a new data point for the Time/CI chart too. I got Contrast Index 0.92 (when I aimed for 0.80 — a 15% miss, overdeveloped). But since I aimed low and hit high, this actually turned out well - the negatives look very printable.

 

[Stephen Benskin]

FYI, a free ebook of The Theory of the Photographic Process, 1st ed is available online Here.

 

[Photo Engineer]

There are several revised editions following this first edition.

PE