# ISO speed determination constants - question for Stephen, Bill etc

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• 03-04-2013, 05:55 PM
Stephen Benskin
Inertia Speed = 34 / i where i is the the point where an extended line from the film's characteristic curve intersects at film based plus fog density.
• 03-04-2013, 08:56 PM
Bill Burk
Quote:

Originally Posted by AndreasT
I have been trying to make a mental picture about the Delta-X Criterion.

My mental picture of Delta-X Criterion is that when the curve is flatter (less development), you would print on a contrasty paper. The salvage grades of paper would amplify the shadow detail that would otherwise be inadequate on a normal paper. So you can get more out of the thin shadows.

The converse happens when you develop the heck out of film. Once you decide to print on a flat paper, that paper needs more shadow separation, so you need to provide more shadow exposure.

The end result is that the speed doesn't change that much with development changes.
• 03-05-2013, 01:31 PM
Stephen Benskin
Quote:

Originally Posted by AndreasT
I have been trying to make a mental picture about the Delta-X Criterion. Where I agree is that when pushing to expand contrast keeping the speed near the normal EI one moves up on the curve which results in a steeper gradient (one could shorten the development as a result) and one gets away from the toe.
What bothers me is when pulling. Looking at curves left of the 0.1 speed point the curve has largely the same shape as right of the speed point. So shortining the exposure would work out mathematically.
But in my point of view in the shadows we have dark places next to light places, in the dark places we have even more dark places which I feel may have too thin a density.

Andreas, you are drawing conclusions based only on assumptions. Jones' tests proved that quality isn't defined by a set minimum shadow gradient, but that the minimum shadow gradient is linked to the average gradient. It's a question of perception. While the shadows might be flatter, their appearance is related to the average gradient. Of course, personal taste will play a factor.

Don't forget that with extended development while the shadow gradient is increased, so is the overall gradient and with the Delta-X Criterion, the relationship remains the same. Also, the fractional gradient speed point defines the minimum useful gradient, not where to place the exposure.

The Delta-X Criterion will produce identical film speeds for a delta D = 0.80 as will the ISO method even though the speed point is approximately a stop below the ISO's 0.10 fixed density.
• 03-05-2013, 06:37 PM
AndreasT
I understand what you are getting at. I actually came to similar results in the past, but for other reasons. Or by other means, by thinking about curves, overall contrast as well as local.
One when pushing keeping the speed constant to get a quicker contrast increase and to get a bit more off the toe as stated. I agree also about when pulling a film.
However for me, my taste I prefer a bit more dense shadow detail when pulling. Makes me feel more secure and if my shadows are a bit more dense I can manipulate them a bit afterwards
Basically meaning a selenium toning to strengthen the negative just in case something goes wrong.
I like to keep a backdoor open.
Certainly I will try this out the next time I am in the field.
This is all a very interesting thought.
• 03-05-2013, 07:30 PM
Stephen Benskin
Quote:

Originally Posted by AndreasT
However for me, my taste I prefer a bit more dense shadow detail when pulling. Makes me feel more secure and if my shadows are a bit more dense I can manipulate them a bit afterwards.

I do the same thing, but preferring a little bit of a safety factor shouldn't be confused with film speed. Actually, accurately defining the lower limits of exposure can only be a benefit when considering exposure adjustments.
• 03-06-2013, 08:21 AM
AndreasT
I agree Stephen

Quote:

Originally Posted by Bill Burk
My mental picture of Delta-X Criterion is that when the curve is flatter (less development), you would print on a contrasty paper. The salvage grades of paper would amplify the shadow detail that would otherwise be inadequate on a normal paper. So you can get more out of the thin shadows.

The converse happens when you develop the heck out of film. Once you decide to print on a flat paper, that paper needs more shadow separation, so you need to provide more shadow exposure.

The end result is that the speed doesn't change that much with development changes.

This sometimes make me wonder why all the effort. When the scene is contrasty we compensate developement and need a harder grade to get the contrast back into the picture otherwise the brilliance suffers. It fits on the paper sure.
What if we always expose and develop normal.
• 03-06-2013, 08:48 AM
Michael R 1974
This is a topic I've tried to get people to think about (usually in the B&W processing and Enlarging forums as it is not strictly an exposure issue). My view, particularly when dealing with long subject luminance ranges, is that relatively mild ZS contractions are helpful, but that more extreme contractions and compensating procedures can result in more loss than gain. I still think that beyond a reasonable range, the goal of "fitting the negative to the paper" is flawed when it comes to the use of applied densitometry methods (ZS, BTZS etc). One must consider the printing process when making a negative exposure/development decision in the field. Developing printing skill and techniques allows one to view the negative slightly differently - as an information source. The goal in exposure and development of the negative then becomes more about recording the most information, not about trying to match the negative density range to a grade of paper.

I'm still working through some thoughts on the Nelson/Simonds paper, Delta-X and print judgement speeds so apologies to Stephen for the delay in posting more. I haven't had enough time yet. Please bear with me.
• 03-06-2013, 09:32 AM
Stephen Benskin
Michael, no worries. I still have about two more parts to do.

Just like with the ISO speed standard, there is much about film and paper matching that isn't readily accessible. Jones wrote a paper in the late 1940s, plus there's a basic tone reproduction concept that print quality requires the mid-tone reproduction gradient to exceed the mid-tone contrast of the original scene.
• 03-06-2013, 09:41 AM
Michael R 1974
This is actually an interesting lead-in to some of my questions about print judgement and fractional gradient speeds. How were these print evaluation studies actually carried out? What was the subject matter? Who made the prints? Were there experimental limitations places on the printers? Who were the people looking at the prints? What specific feedback was solicited? Etc Etc.

I guess the thing I keep coming back to here is, we seem to have a situation in which we are asked to accept the evaluation of some group of people. What are their standards? Etc...
• 03-06-2013, 10:43 AM
AndreasT
Quote:

Originally Posted by Stephen Benskin
..... that print quality requires the mid-tone reproduction gradient to exceed the mid-tone contrast of the original scene.

What does this mean?
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