Many photographers setting out on the discovery of fine printing make the mistake of thinking that to be a fine print, the photograph should have strong black shadows of the maximum density the paper can yield. And not just beginners. I well remember listening to a lecturer at a Royal Photographic Society distinctions workshop for would-be Associates perpetuating the hoary myth that to get real print quality it is necessary to keep print developer temperature well up - say 24'C - and give a full 3 minutes development.

The only result of this is to give extra density across the tonal range and possibly to veil the highlights and give a muddy print. It also tends to inhibit toning and add to the chance of fog veiling, especially if toning is then prolonged. A richer print always results from the velvety subtleties of shadows away from maximum black, even if the absolute black is not as dense in objective measurement as flat maximum paper black shadows. In any case, I do not believe that the human eye can usually distinguish the difference between deep blacks, such as between print densities of 2.0 and 2.1, whereas it can far more readily discern this degree of difference in the highlight region.

The question, then, is how do we achieve the desired tonal rendition in the final print. Obviously a normal monochrome picture has a seamless range of shades from deepest black to paper base white - an analogue effect. If the paper white reflected almost 100% of light and the maximum black virtually 0%, then the ratio of the range of tone reflectance possible would be about 100:1. Obviously such perfect reflectance and absorption doesn't exist and the ratio is really far less - 80:1 would be reasonable. Yet the range of brightness of light reflected from the average scene will rarely match this. Occasionally it will be less, as in a scene with subject matter of similar tonal value when reduced to grey under flat shadowless lighting. Far more frequently it soars above it, and it's almost guaranteed in any landscape with sky.

It certainly was in the case of the Loch Arklett photograph here (Heat Haze, Loch Arklett 1991). The picture reduces the highlights into discrete areas. It depends on the subtle separation of the lighter tones and on their being free of the mottling produced by burning-in heavy negative densities - a different phenomenon from prominent grain, though I believe that grain would have spoiled this image. The original scene didn't 'feel' grainy. The only reliable way I know of realising in the print the picture I had visualised at the time is a method of exposure adjustment and development control known as the zone system.

I was using my beloved Rollei SL66 with its back loaded with Agfa APX25 rated at EI (Exposure Index) 12. (In another page on this site, I explain how to decide what film speed rating to use.) With the 250mm Sonnar mounted to compress the distant elements of the picture, I needed f/16 to give adequate depth of field. A spot reading of the sky above the mountains showed a light value of 17, which meant a shutter speed of 1/60 at this aperture.

However, the near shadows gave a spot reading of light value 8, i.e. 8 seconds at f/16. That's a nine stop difference between the shadows and the highlights in both of which substance was required to avoid a 'soot and whitewash' effect: shadows devoid of details and bald white high tones. Since each stop extra exposure gives twice as much light, it's easy to work out that the subject brightness range, increasing in the series 2, 4, 8, 16..., reaches 512:1 at nine stops. (Each stop difference for shutter speeds is calculated by halving (or doubling) the time. So starting at 8 seconds, one stop less is 4 seconds, two stops is 2 seconds, and so forth. Using conventional shutter speeds, the range for the Lock Arklett scene was 8, 4, 2, 1, 1/2, 1/4, 1/8, 1/15, 1/30, 1/60 - a difference of nine stops).

But this has to be shown on a paper with a reflectance range of perhaps 80:1, so something has to be squeezed. Significantly, if the range had been only six stops, that would have been 64:1 - somewhere around the reflectance range of the paper. Film manufacturers seem to assume an average scene brightness range of about five stops showing detail when they specify their film's speed and its normal developing time. Both would be wrong for this picture. If we split the 'analogue' continuous range of greys up into 'digital' steps for this picture, we could use the nine stops as the discrete steps. If, for simplicity, we say one stop less at the shadow end gives total black, and one stop more at the brightest end gives maximum paper white, we have a scale of 11 steps from black to white, with nine steps of grey in between where each is representing a step in the original scene twice as light as (i.e. one stop less than) the previous step.

These 11 steps are called 'zones' and, by convention, they are given Roman numerals, where 0 = featureless black and X = featureless white. Please note that these are the real brightness values of the scene, they are not the greys used to represent them on a paper print. These are obviously compressed to get within the reflectance range of the paper. By convention print greys are known as 'values' rather than zones. It is important to realise that, for all practical purposes, black is black in both scene and print, but not so white. Paper can only give its reflected white as the lightest value in a print, but the original scene may well have had radiant light sources, such as the sun, or specular reflections of the light source, such as water, snow crystals, glass, polished metal etc, which are very much brighter than paper white. Yet these all have to be convincingly depicted within the confines of the paper.

And what gives the maximum conviction is what fine photographs are all about. A blank paper white for all very bright zones, which can easily extend to XII or XIII, is not convincing or attractive, no matter how logical. On the zone scale, zone V is the standard 18% reflectance grey to which all exposure meters are nominally calibrated (actually, some meters aren't calibrated to 18% grey, but let's assume they are for this discussion). This means that if they are pointed at a scene they will assume that it is 'average', that a purée of all the tones in the scene will be this 18% grey.

Continued...