TR
Hello everyone,
I am currently looking into the extent to which the contrast of the negative – increasing it – can also be controlled through exposure.
I’d like to start from the assumption that black (Zone I) always remains black, or rather that the completely transparent areas in the negative always remain transparent, regardless of how long the exposure or development lasts. This would then be the prerequisite for increasing the contrast – because all other zones ‘shift’ upwards both when the exposure time is extended and when the development time is extended.
At some point, however, a fog would have to form, which would also cover the transparent areas of the negative. I assume, however, that such a fog would only form after extreme overexposure or prolonged use of the developer, and that I can disregard fog formation here.
Now, it would of course be interesting to simply increase the contrast in scenes with a low contrast range – e.g. a landscape under overcast skies – by means of “overexposure”. I have deliberately put the word overexposure in quotation marks, because in such a low-contrast lighting situation, one is naturally still far from overexposing a standard black-and-white film rated at 100 ISO.
So I would meter in such a way that the shadows also gain definition and achieve an exposure two stops above my reading. What would happen? Black would remain black. Everything else would ‘shift upwards’. In addition, better shadow definition would be expected. Because nothing would have changed in Zone I, but all other zones would have ‘shifted upwards’ by two stops, I would have increased the contrast range by two stops. Now comes my actual key question:
Is this method of contrast enhancement identical to the one where the negative is developed for longer? Does anyone know more?
Or am I fundamentally mistaken in my theory of contrast enhancement via exposure?
Regards,
Thomas
MirkoBoeddecker
I’d say you’re wrong, even if I might not have quite grasped the crux of the matter.
You are shifting everything upwards, but this does not increase the contrast, only the density. The contrast would increase if the number of distinct grey levels on a grey scale (or zones represented as a grey scale) between pure black and pure white were to decrease.
Or, in terms of a curve, if the slope of the characteristic curve in the differentiation range (the ‘linear’ part) were to increase.
In the situation you describe, one would UNDEREXPOSE and OVERDEVELOP to increase the contrast, because extended development increases this slope of the curve and underexposure prevents the highlights from ‘clipping’.
Best regards,
Mirko
Wolfgg
Hello Thomas!
The key question is: where do the crucial parts of the image end up, i.e. at what point on the characteristic curve? With this approach – a low-contrast subject and overexposure – everything is clearly crammed right at the top of the highlights. There are no longer any transparent areas in such a shot; everything is quite dense. Nothing is gained by this. This was the approach taken by some many decades ago, following the motto ‘what’s on the film is on the film’, out of fear of underexposure, usually due to a lack of a light meter. The aim must be to distribute all the important parts of the image nicely along the characteristic curve between the lower and upper curves, thereby creating optimal ‘material’ for the enlarger. Then not only is ‘everything there’, but it also has printable contrast. And for this, you need a characteristic curve whose steepness matches the contrast of the subject, so that the darkest part of the subject on the film just causes a visible density (technically: 0.1D above the fog) and the brightest part of the subject causes the maximum density permitted for printing (technically: 1.6D above the fog). The film then renders the subject with a contrast of exactly 5 f-stops (=1:32), suitable for special paper gradation. And this adjustment of the characteristic curve to the subject is achieved through the film development time.
The film contrast is the product of the contrast built in by the manufacturer and the development process. Only these two factors determine the course of the characteristic curve. During exposure, the only decision is what part of the subject should lie where on the curve, which is usually S-shaped.
Regards, Wolfgang
TR
Hello and thank you for your replies!
Your explanations have already been a great help.
With this approach – a low-contrast subject and overexposure – everything is clearly crammed together right at the top in the highlights.
That actually sums up quite well what I’ve been able to observe so far – but: the deep blacks remain ‘down below’. The deep black isn’t rendered any lighter – in contrast to the rest of the image, of course (it doesn’t reflect any light onto the film – not even with a longer exposure). That’s what I mean by increasing the contrast.
However, in most scenes there is very little non-light-reflecting black, so I suspect that the increase in contrast caused by overexposure or the ‘compression’ of information in the highlights will look rather odd, tending towards ‘high-key’.
An example would be a room with white wallpaper. Everything would become brighter due to the extended exposure, or ‘shift upwards’ evenly. Only the black gaps between the drawers and cupboard doors in the interior would produce just as little density on the negative as with a shorter or ‘normal’ exposure. The floorboards, with their black joints, also display such characteristics. Nothing would change in these areas. The contrast would therefore be increased. One could thus enlarge this negative to be brighter and it would not be technically flawed, as the maximum black would indeed be present, for example, in the aforementioned ‘cupboard gaps’.
michael-kielgmxnet
There is no such thing as a black so deep that it reflects absolutely no light, unless you manage to photograph a black hole. All objects reflect some light, even if they appear completely black to the naked eye. As a result, during overexposure, even the deepest black shifts along the film’s characteristic curve.
TR
OK – that makes sense then. All right.
Morte
I also believe that the theory about blackness is untenable. In addition to the arguments already mentioned, even a hypothetical absolute black could not be captured on film – perhaps in space, but not here, because the light down here is never directional or polarised, but radiates in all possible directions and is refracted, reflected, scattered and so on; in other words, even the deepest black is fogged by the glare from neighbouring bright areas. Apart from that, the severe overexposure makes the negative unpleasantly granular and out of focus.
Wolfgg
Thomas, there’s another misconception here:
In many scenes, there’s a shade of black that’s best described as ‘ultra-black’. It is so deep that it makes no sense to measure it with the light meter (spot meter) and include it in determining the optimal exposure time. This is because the corresponding zone is always well below Zone 1, once you have tentatively distributed the important parts of the image across Zones 1–9.
Example: a landscape with a cave entrance. The rearmost wall in the cave is, for example, 20 stops darker than the rock next to the entrance. How, then, should one take the black in the cave into account in terms of exposure? If one were to place the black at Zone 1, one would need, for example, around 24 zones – in other words, a film capable of handling an exposure range of 24 stops! However, the main subject, the landscape, has a contrast of perhaps only 10 stops and, with your approach, would be squeezed into the upper part of the density curve, i.e. zones 14–24. The cave would then be in zone 1 and zones 2–13 would be unused! In the enlargement, the cave entrance would then be the only black area; everything else would be light grey to white, i.e. very low in contrast.
So: there are subjects where you have to consciously accept that extremely dark parts of the subject will be ignored during exposure and ‘slip off to the left’ on the density curve. The same applies to highlights, by the way. How are you supposed to incorporate sun reflections on water into the zones? They are often 8 stops above the brightest white. They simply end up in ‘ultra-white’, i.e. beyond the highest zone recorded by the meter.
Regards, Wolfgang
TR
Thanks again for your input! The point you made about ‘external light’ obscuring or causing fogging of non-reflective black is also very helpful to me.
Best regards,
Thomas
