Densitometery and Contrast Index (CI)

[Ornello]

I'm going to have to look into the intention of Davis' use of the term, but I am not optimistic. I think you might just be too deeply immersed into BTZS to be able to judge it objectively. Still, I'll be open minded, after all, we are talking about the difficult and confusing subject of photometry. BTW, the Focal Encyclopdia of Photography partially defines Luminance as "the property of a source or surface that most closely correlates with the subjective percept of brightness, which, due to adaptation and contrast effects of the visual system, cannot be used as a reliable measure."

The person who initiated the tread said, "Can someone point me to a resource that might help explain how the CI is determined or perhaps offer a little Densitometery for Dummies..." So far, I have offered a number of reading suggestions including the original paper on the subject written by the people who invented Contrast Index. I've explained how flare should factor in. I've given the poster an equation to determine CI for different LSLRs, and I showed him graphically how it is supposed to work in relation to SLSR, the negative, and the print. I've corrected a long misused method of G-bar (there is no arc). I've given information on the origins and intentions for the different method parameters. In addition, I had a graph comparing CI, G-bar, and the Zone System approach. No offense, but I think I've written more to respond to the original poster than anyone else so far. Jorge, I think you might have been skimming over my posts.

Sandy,

If I misrepresented what you said, I apologize. I got "slope so it can't be developed to a given CI" stuck in my mind and went with it. As for finding a higher EFS when using a method of contrast determination...well that's not possible and has no relevance to contrast determination (as long as there is enough exposure to measure). They are two different methods. One method determines contrast and another speed. Perhaps there was confusion in the way it was written and the way I read it. Terming what you said was gibberish wasn't polite, I just got pissed off by your dismissive attitude from an earlier post. Maybe we should both practice more patience and understanding?

As for the CI / blank film discussion, it's over as far as I'm concerned. What was meant to be a little fun thought got blown way out of control. If it's OK with you, let's make a fresh start of things - mutual respect, civility and all.

Back to CI:

Kodak clearly uses the term to refer to degree of development:

http://www.kodak.com/global/en/professional/support/techPubs/f4016/f4016.pdf

It is much like saying that you develop your film to "N+1" or N-2", only with mathematical precision, as "N" can be quite different for different workers.

With CI, you're measuring the slope of the line connecting two defined points (strict definition) but it is also used to mean what affects that slope: the degree of development.

Kodak gives Contrast Index curves for various developers on its materials.

http://www.kodak.com/global/en/professional/support/techPubs/f4016/f009_0458ac.gif

Maybe Kodak is 'idiotic' for doing so?

See also:

http://www.kodak.com/global/en/service/tib/tib3115.shtml

 

[photomc]

Thanks to all who have added comments..most have been very usefull.

If anyone thinks I have ignored there reply's please forgive me, it was not intentional. Since some posters are at a different stage in their understanding and have attained a level of enlightenment beyond what my interest are, decided to filter this thread and read what was relevant to my level of understanding - My Thanks to you.

There are those that can teach, and those with a great deal of knowledge, but have a problem presenting that knowledge to others. This thread is a good example of that IMO.

At this time I am asking Sean to lock the thread before this becomes another catalyst for a flame war.

 

[Jorge]

BTW, the Focal Encyclopdia of Photography partially defines Luminance as "the property of a source or surface that most closely correlates with the subjective percept of brightness,

Exactly, luminance refers to the preceived brightness of the subject, Illuminance refers to the light falling on the object. This is clearly explained in Davis' book and the basis of what he calles subject brightnes range.

While you have given reading suggestions, they have been done in passing and were not specifically geared to explain in a simple way what is required for a beguinner. You have written all of this in an effort to defend an untenable position that blank film has a CI. All of this you have done it in such a complicated and convoluted manner that I would not be surprised anybody wanting to start learning sensitometry to acheive a better control would be put off and decided it was too much hassle. To what purpose does it serve to post graphics and curves to someone who is just strating and has no idea what they mean? Face it, you posted all this to show how much you knew, not in a sincere effort to help the original author of this thread.

 

[sanking]

As for the CI / blank film discussion, it's over as far as I'm concerned. What was meant to be a little fun thought got blown way out of control. If it's OK with you, let's make a fresh start of things - mutual respect, civility and all.

Stephen,

OK, sounds like an excellent idea. The present path clearly has no productive end. However, there are a couple of issues I would like to pursue with you in private communications and if you are willing I would be appreciative if you would send your email address to me at sanking@clemson.edu.

Sandy

 

[Sean]

thread owner has requested this thread to be closed.