# "N" Development and Negative Contrast Range

Discussion in 'Exposure Discussion' started by Photographica, Apr 23, 2006.

1. ### PhotographicaMember

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I have a question about the relationship of the negative's contrast range relative to the actual scene at the so-called "N" development.

It seems to me that one's "N" development process should yield a one-to-one relationship of contrast range between the actual scene and the density (or opacity) on the negative. For example, I find a zone III shadow at an EV 8 and a zone VII area at EV 12. shouldn't I expect my negative to (in theory) have a density of 0.7 in the zone III area and 1.9 in the zone VII area?

In other words, 4 stops of metered range yields 4 stops of density.

Thank you for any comments....

Bill

2. ### Donald MillerMember

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Pardon me for speaking frankly and honestly about this matter. This is one of the failings inherent in the Zone System. Four stops of metered luminance does not equate to four stops of negative density variation if we take .30 as the normally recognized density measurement of one stop of luminance. The reason is that this does not take into account the gradient or the shape of the film's characteristic curve.

A much more useable and accurate system is to determine the exposure scale of the paper or process that you are using and then targeting the camera negative density range (high density minus low density...not minus film base plus fog) to the printing requirements.

3. ### KinoMember

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The change (delta) in density is equal to the lux times the gamma;

.30 d x .65 gamma (assuming a perfect "normal" exposure") equals only a delta of 0.195 d

It would require a unity gamma of 1.0 to obtain a linear representation of density change and unity gamma looks like crap...

Of course, there is a bunch more to this, as this is lifted out of the totality of the gamma reproduction chain, but it illustrates the point well...

4. ### Stephen BenskinMember

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Don't forget the negative is just one step in the photographic process. The negative has a gradient half that of the original scene and paper has a gradient twice that of paper. Put these together and you get close to a 1:1 relationship. In fact, a frequently used equation to illustrate the relationship is:

Negative contrast x Print contrast = 1 (unity)

5. ### PhotographicaMember

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Thanks for the comments Donald. I failed to mention that I was refereing to only the linear portion of the film's curve and not considering the shoulder and toe. My experiments right now are only in that region.
I appreciate the comments about the zone system too.

Bill

6. ### PhotographicaMember

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Thanks Kino,
I'm playing around with the unity gamma and you're right it doesn't look all that good in some cases. your number of .65 gamma is what I'm finding to be more pleasing. Thanks for confirming that number for me!

Bill

7. ### PhotographicaMember

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You've given me a lot to think about Stephen. Neg Contrast * Print Contrast to equal 1.

I think a light bulb just went on!!!!

Thank you VERY much!

Bill

8. ### KinoMember

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Not to beat this to death, but in the motion picture industry, we strive for an end gamma of 1.5 to 1.7 for a film print upon projection (total systems gamma of a transparency) due to losses in light scatter from atmospherics and glass from the projection booth.

I don't know the actual end gamma should be for a still photograph (reflected); anyone have a typical end gamma figure?

Typically total systems gamma is calculated:

Scene is Unity (1) x negative processing end gamma (.65 for normal ASA rating) x gamma of projection printing system (unknown but generally assumed implicit in print gamma) x print gamma end result x environmental influences (presentation illumination expressed as gamma) = total systems gamma

Changes in desired density can be calculated in any part of the chain by multiplying the actual change in illumination (delta of lux) times the gamma (implicit gamma) to get the end result (actual delta/change).

So you can begin to see how when you point the gamma toward unity, the delta becomes linear and when you lower or raise the gamma above or below unity, you expand or compress your range of densities.

Took me a LONG time to understand that...

Frank W.

9. ### Gerald KochMember

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Although the actual value for gamma is a matter of personal preference the usual range quoted in books on printing is from 0.55 to 0.65, where the lower value is recommended for condensor enlargers.

10. ### KinoMember

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Yes, I could certainly see that for modern, hand-crafted still photographic images.

The "standard" I quoted is strictly for 1st generation, camera original, negative motion picture film printed to release print stock in a modern, commercial lab environment.

Go back to the silent era, when the sound track wasn't a factor, and you'd have a hard time telling still and motion picture labs apart; they even used Pyro soup and developed by inspection!

Another usless fact brought to you, courtesy of...

Frank W.