black and white tone reproduction 3
We’re still with curves I’m afraid. Sorry!
You’ll have realized by now that trial and error is necessary with film exposure and development, experimentation to find the combination that you feel is right for you, the right 'look' about the image. So now we must look at the printing paper characteristics because the ultimate aim is to produce a negative that will transfer all of it’s information directly onto the print, in the way that we want it too, or have pre-visualized.
Here we are again, limited by our equipment and materials and in this case it’s photographic paper. A properly produced b/w photographic print will yield a maximum image brightness range of about 32:1 from the deepest black, all halides fully exposed and developed, to the brightest white which can only be the base colour of the paper itself with all it’s silver untouched by light, fixed out and washed away.
The subject we’ve photographed may display a brightness range ratio far exceeding the paper’s limit - 100:1 or even more, 250:1. Modern film emulsions, with correct exposure and development, can embrace this but obviously not the printing paper.
The production of the negative and then the print is therefore a process of overall tonal compression in order to match the image brightness range of the paper. Exposure and development then is critical, increasingly so, the more contrasty the subject. Conversely some subjects may have a lower ratio, perhaps 20:1 in which case tonal expansion should be our aim.
Considering that photographic paper is, on the one hand the end product, but on the other hand the least flexible in processing terms so most limiting material in the process, perhaps we should work backwards from the characteristic curve of the paper in order to find the illusive perfect negative.
Exposure values and speed ratings are based on the assumption that the average subject brightness range is 100:1 so, the average subject (a rare find indeed), given normal exposure and development will compress the overall tonal range to suit the paper’s characteristics. It follows then that a normally exposed high contrast subject at, say 250:1 should receive less development to further compress the brightness range to suit the paper whereas, a very low brightness range, say 20:1 will need longer development to raise contrast and expand the tonal range in the negative to correspond with the 32:1 paper brightness range.
We should now have a basic idea as to what’s going on between pressing the shutter and seeing that great shot you took materialise, as if magical, in the dev. tray. Next we can look at two other vital ingredients of the image - graininess (a creative effect or an annoyance) and sharpness (which may or may not be important).
Text & graphics C steve rostron 2007
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