Done correctly, what is known as a proper proof contact sheet will give us all the information we need, within the passage of a few films through the camera, to turn out delicious negatives virtually to the standards of the most obsessed zone system freak. Print quality will be transformed for many people.

So how does the contact sheet do this? We start from the simple basic fact that an area of any negative that is clear film base should print as black on paper. In other words, a part of a negative which received so little light through the lens during the exposure of the picture on this frame that, after film development, it shows no silver image at all we expect to be a black area in the resulting print. Note that we don't say it had no exposure to light, just so little that it did not result in any developed silver density at that point.

Even with no such silver density, the film base will have some small density - nothing is perfectly clear (even, or especially, when a politician claims to make it so!), and the process of film development additionally puts a very thin layer of fog unavoidably over the whole film surface. Therefore even the 'clear' area of a negative will have some density i.e. it will slightly reduce the intensity of a beam of light projected through it. That density is not surprisingly known as film base plus fog, and it varies between films and with different developers.

It's a big thing for zone system workers because, whatever that density turns out to be with a film/developer combination, a figure of 0.1 log density more than film base plus fog is deemed in the zone system to equate to zone 1. Now, don't get turned off because we have mentioned a number and the word 'log', because we don't need to use these with our contact sheet system. Let's just understand the importance of zone 1.

The literal foundation to a deep rich satisfying monochrome print with a sense of three dimensional depth, except one intentionally composed of high key light greys, is that it should have the mythical shadow detail. Note that it does not depend on having a 'good black' if that black is an unremitting area of unbroken smooth black - this destroys a three dimensional impression. The human eye finds it very difficult to discriminate differences between very dark greys compared to mid and light greys.

When we talk of shadow detail, what this means in a print is that areas in the shadow areas of the original scene that our eyes can see as different shades should be represented in the print as different very dark greys just discernibly different from black. For zone system workers, the first dark area of a scene to be visible in the print as a grey discernible from black is zone 1.

For such an area to print as a grey slightly but discernibly off black, it must have enough silver density in that part of the negative after development. How much is 'enough' density? The zone system, as I have said, arbitrarily sets this at a log figure of 0.1. But this is arbitrary. The actual figure will actually vary from user to user according to their camera and enlarging equipment, and their eyes' sensitivity to subtle changes of near-black greys.

In any case, when we are making a print, and produce a test strip, we don't read the blacks and greys with a densitometer. We eyeball it. Where it looks right, that's the exposure we give. And that's exactly how we use a proper proof contact sheet as practical tool. In fact, while it may seem less 'scientific' than densitometer readings, it is actually more so because the densitometer lulls us into a false sense of security that such precise numbers are correct, when we later ignore that numerical basis by making prints by simple eyeballing.

So here's what we do. If we give just enough exposure through the film base plus fog in contact with the actual make and grade of paper which we plan to use as standard that the paper, after a standard development time in our standard print developer, looks black to our eye, then we have given the 'minimum time for maximum black'. In other words, if we give any less exposure, the blacks in the print will look visibly grey to our eye.

Note that though the phrase talks of 'maximum black', it will in fact be nowhere near any paper's true maximum black. To achieve the absolute maximum black requires such overexposure that any negative would have its mid and light tones unacceptably darkened, and would have to be developed for so long - perhaps 8 minutes - that fog would begin to lower contrast and quality. No, when we use 'maximum black' in this catch phrase, we actually mean the first dark shade that your eyes accept as black.

If we give the whole of a roll of negatives in contact with our standard paper this minimum time for maximum black, then theoretically, in any picture on the roll, any area that we wanted to show as the very first hint of shadow detail should show as a dark grey that your eyes can see is different from the black. If you can't see it as different, then the negative had too little exposure to give that dark area of the subject enough density after development to print as different from black. Most people are surprised at just how much density it takes in the negative before it will print as non-black. Just because you can see the image in the shadow parts of a negative on the light box, don't just assume that it will print!

How do we find the minimum time for maximum black for our set up? Set up the contact frame on the enlarger base board, and adjust the enlarger head and focussing bellows so that the pool of projected light covers about four times the area of the frame. Put the frame in the centre of this pool of light. Stop down a couple of stops to get the most even lighting you can over the frame area.

Insert the film and paper in the frame, and make a test strip on your standard grade of paper. (That might be grade 2 for graded or 2½ for VC. Some people find thinner negatives and grade 3 better for 35mm). But don't make a test strip of the images themselves, use the clear film base plus fog of the film rebates. With 120, it is usually easy to place your test strip across the divisions between frames. With 35mm, use the sprocketed edge. Sheet film users can use the edge too. Be careful with the ubiquitous and excellent Paterson contact frames - the transparent plastic overlay on the glass that grips the film edges has density and will result in a false test strip reading if you don't move one strip of 35mm film out from under this plastic overlay so that it lies on the paper under clear glass only. Once the correct exposure is found, you will slot it back under the plastic for making the full contact sheet.

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