Choose a suitable time, perhaps two seconds, to use as test strip steps, or you can use f stop fractional divisions for constant density changes if your timer has the facility. Make the test strip of the clear film base plus fog. Develop, stop, fix, and wash in a completely standardised way that matches your normal working routine. With RC papers, and working at the shadow end, dry down isn't an issue, but it is easier to view and judge a dry test strip, so you might want to do that for this exercise.

Now examine the test strip under the same viewing light you would use for assessing the test strips of actual prints (which should, incidentally, match the light under which they will be displayed). You are looking for the first step in the test strip which appears black i.e. you will not be able to discern the next step as different from it.

Now examine the test strip under the same viewing light you would use for assessing the test strips of actual prints (which should, incidentally, match the light under which they will be displayed). You are looking for the first step in the test strip which appears black i.e. you will not be able to discern the next step as different from it.

The first step which reaches black may not be easily apparent, especially if your test strip steps were fairly finely spaced in exposure time terms. You have to train yourself not to look at the pictures next to the clear film. The test strip step lines which run across the picture frames can be translated by the eye into a line across the edge black area which is not actually there. The ability to see or not see the sprocket holes helps with 35mm, but with all formats covering the picture areas with a couple of sheets of white paper helps to clarify the decision about the correct minimum time for maximum black. I also find it helps sometimes to view the test strip with transmitted light for a few moments on top of a light box, then switch off and decide under normal reflected light.. However, make your decision with your own eyes.

Once you have decided what this is, you have a standard time which you can apply with this film/developer/paper set up. Mark the enlarger column/ focusing bellows position so you can return to it. Note that if you ever change anything in this standard line-up (e.g. a new box of paper) you will need to do a new test strip.

Now using this minimum time for maximum black exposure, make your full contact sheet processed in the standard way. Be careful how you give the exposure. If, say, you found the time on the test strip to be 5 two second steps, do not give a ten second contact sheet exposure. This will give significantly greater exposure. Give the same 5 two second bursts of light. Process as standard. When the contact sheet is washed and dried, examine it under the same viewing light.

Let's first look at the overall sheet rather than individual pictures. What we are looking for first is the shadow detail i.e. are the darkest areas in the pictures generally where we wanted to see some detail just discernibly different from black? School yourself - ignore the middle and high tones at this stage.

If the shadows are mainly all black when there should be some detail, you have generally underexposed the negatives. This means the film speed is wrong for your technique and equipment. If the shadows are very dark you may be using a film speed double or even more what it should be i.e. 1 to 1½ stops out. This means that a film nominally of EI 400 should actually be re-rated at 200 or 160. If the shadow darkness is less marked, your true film speed may be only 50% = ½ stop out, say EI 250.

If generally the shadow detail is too light, you would need to make the opposite corrections. This would be extremely rare in my experience. Most people carrying out this test for the first time find they need to drop their film speed rating by about 1 stop.

If the shadow detail is generally OK, but there are just a few shots where it is low or missing, this means that your film speed rating is actually OK, but that your metering technique is letting you down in the particular circumstances of the defective pictures. Often this will be down to including a lot of sky in the metered area of the picture, or to a scene with an exceptionally high subject brightness range - that's one where the difference between the brightest part of the scene and darkest part of the scene pictured are especially great. This might be with harsh directional sunlight and deep shadows outside, or an interior scene with an external window in shot for instance. Just by looking at the 'failed' exposure pictures you very easily and quickly learn the type of scene where you will need to intervene and correct metered exposure, and by how much. Usually that means taking an exposure reading of the darkest area in which we want to see full textured detail - for instance the grass in the sharp-edged shadow cast obliquely by a rock or tree - then stopping down 2 stops from the reading given. Zone system aficionados would tell you that's the equivalent of placing that area of the scene on zone III.

Now let's ignore the shadows and look at the highlights. There's an old photographic catch phrase 'expose for the shadows and develop for the highlights'. Most people have heard it but many don't know what it actually means. The following is an over-simplification, but it will serve for the sake of clarity. The film density that was needed to show that shadow detail as just different from black is purely the function of the amount of exposure given to the negative, and is virtually unaffected by film development time. The highlight density of the negative, i.e. the darkest heaviest parts of the negative, are controlled almost solely by the development time.

Imagine that you were hanging a curtain on a rail. Getting the first hook on to the first fixed ring at the start of the rail is the equivalent of exposing enough to place the shadow detail just above black. Now all the other hooks are placed into the rings lined up next to the first fixed ring. These are all the other greys from dark, through mid, to light in sequence. This is what happens at the very start of development. As development proceeds, the curtain gets drawn along the rail gradually spreading out the rings until the furthest hook and ring, the equivalent of the negatives densest highlight, reaches the end of the rail.

This is the equivalent of the negative's brightest highlight becoming so dense that if it were given the same minimum time for maximum black exposure to paper on our contact sheet, it would print as pure paper base white - just. Any less development would allow it to pass just enough light to show on the print as a light grey only just discernible from white.

Of course if we were to continue drawing the curtain further, that is to continue developing the negatives, more and more of the hooks/rings would stack up at the white end of the rail. Effectively, this would mean that areas in the pictures that we expected to see as different light greys - clouds in a landscape for instance - would all get bunched up with the furthest white hook/ring, and thus simply print as the same blank white. We term this 'burned out' highlights.

If we try to rectify this by burning in the area in the subsequent print, or by switching to a lower contrast paper, the highlights will print, but the hooks/rings are still all pressed together resulting in a virtually flat light grey area with virtually no separation between the light grey tones as we saw them in the original scene. Additionally, such areas are inevitably mottled and over-grainy in comparison with a negative where the curtain was drawn - the negative was developed - just enough to place the very brightest highlight on white while leaving the other rings/hooks spaced out along the rail.

Continued...