how to read graph : LUSENET : B&W Photo - Film & Processing : One Thread

please advise how best to read the graphs printed with developers and films . sounds silly i know but i have no understanding of them what-so-ever. what area on the graph should a beginner be aiming at thanks and regards peter

-- PETER (, March 31, 2002


It appears that the graphs contain information useful to those who apply densitometry to their negatives. I've always used trial and error to find workable exposure and development for b&w film and have never referred to the graphs.

-- Keith Nichols (, March 31, 2002.

I presume you mean characteristic curves, such as 363ac.gif

I'm not the best person to answer this, but the cc shows what is generally possible with a given film. You can compare curves for different films and see why one might give better highlight seperation, and why one might be higher contrast, why one might respond to development changes more, etc etc. A steeper section of the curve means more density buildup per exposure units, which translates into more contrast. The "toe" is the gently sloping area to the left, where a lot of exposure is required to get increase in density. There is lower contrast here because of the gentle slope. Think about it and it makes sense. Compare this to the mid section, where an increase in expsoure causes a correspnding increase in density. Most modern films are pretty straight lined past the toe, allowing better highlight rendition. many older films would "shoulder" (slope decrease) to the right and you'd get less contrast again, meaning blocked highlights.

Looking at the effect of developer, you can see that increasing development time causes a greater increase in density (and a steeper curve overall) in the highlights, while the toe is virtually unchanged. This will be true for just about any film, hence the rule, expose for the shadows and develop for the highlights, because developing time wont affect the shadows (toe) much. Hopefully I got most of that right, I'm no curve expert and replied mostly to try to organize my thoughts on curves. for some insane reason I decided to go back to school a couple months ago and take a mid-life calculus course, and i've become pretty fascinated with curves (though I still hate word problems). Curves are pretty darned useful. Ansel Adams discusses them in The Negative, and hopefully someone else will come along and explain them further.

-- Wayne (, April 01, 2002.

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